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What Happens If You Destroy A Black Hole?

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The Last Light Before Eternal Darkness – White Dwarfs & Black Dwarfs

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The Most Dangerous Stuff in the Universe - Strange Stars Explained

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The Last Thing To Ever Happen In The Universe

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Black Hole Star – The Star That Shouldn't Exist

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The Black Hole That Kills Galaxies - Quasars

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Neutron Stars – The Most Extreme Things that are not Black Holes

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The Most Extreme Explosion in the Universe

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2024 Total Eclipse: Where & When - NASA Science

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The Monday, April 8, 2024, total solar eclipse will cross North America, passing over Mexico, the United States, and Canada.

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Britannica LaunchPacks allow teachers to personalize learning for K–12 classrooms through curriculum-aligned, multimedia content sets.

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Pourquoi les saisons changent ? - C'est pas sorcier

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JOURNEY TO THE EDGE OF THE (observable) UNIVERSE 1080p

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9:50-10:20; 18:38-18:56

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This phenomenon only happens in Hawaii . . . and Cuba & Nigeria & Indonesia & Peru & Sudan & Laos &…

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PlanetMaker - Create your own planet, real or imaginary

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La comète de Halley (1P/Halley) est la plus connue de toutes les comètes. Son demi grand axe est de 17,9 ua (soit environ 2,7 milliards de kilomètres), son excentricité est de 0,97 et sa période est de 76 ans. Sa distance au périhélie est de 0,59 ua et sa distance à l'aphélie est de 35,3 ua.

Elle est connue depuis plusieurs siècles. Elle aurait été aperçue en Chine sous le royaume des Yue en 467 av. J.-C., ce qui constituerait sa première apparition répertoriée. Elle fut décrite en 837 lors de son passage le plus spectaculaire durant les temps historiques (environ 3 millions de kilomètres), à la fois dans des textes chinois, japonais et européens, notamment par L'Astronome, auteur d'une chronique sur la vie de Louis le Pieux. Elle a pu également être observée en l'an 1066. Une comète attira en effet l'attention de l'armée de Guillaume le Conquérant et on la retrouve sur la célèbre tapisserie de Bayeux, qui illustre la conquête normande de l'Angleterre.

En 1705 Edmond Halley prédit, en utilisant les lois de la mécanique céleste de Newton, que la comète vue en 1531, 1607, et en 1682 était la même et qu'elle ré-illuminera le ciel en 1758. Après sa mort, la comète est en effet réapparue comme prévu et plus tard elle fut nommée en son honneur.

La période moyenne de l'orbite de la comète de Halley est de 76 ans, mais l'on ne peut pas calculer les dates de ses retours simplement en soustrayant des multiples de 76 ans à l'année 1986. Le champ gravitationel de certaines planètes peut changer sa période orbitale. Les effets nongravitationnels (comme la réaction au gaz évaporé pendant son passage près du Soleil) jouent également un rôle important, mais moindre, dans les variations de l'orbite. Entre les années 239 avant Jésus-Christ et 1986 après Jésus-Christ la période orbitale a changé de 76.0 années (en 1986) à 79.3 années (en l'an 451 et en l'an 1066).

L'orbite de Halley est rétrograde et inclinée de 18 degrés par rapport à l'écliptique. Et, comme celle de toutes les comètes, elle est fortement excentrique.

En 1986, cinq sondes russes, une japonaise, et une sonde européenne ont rendu visite à la comète de Halley ; la sonde Giotto de l'ESA a obtenu des photos en gros plan du noyau de Halley.

Le noyau de la comète Halley est approximativement de 16x8x8 kilomètres.

Contrairement à toutes les attentes, le noyau de Halley est très sombre: son albédo est d'environ seulement 0.03 le rendant plus foncé que le charbon et un des objets les plus foncés dans le système solaire.

La densité du noyau de Halley est très basse: environ 0.1 gm/cm3 indiquant qu'il est probablement poreux, il doit être composé en grande partie de poussière restante après que la glace se soit sublimée.

La comète de Halley reviendra à l'intérieur du système solaire en 2061.

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La comète de Halley (1P/Halley) est la plus connue de toutes les comètes. Son demi grand axe est de 17,9 ua (soit environ 2,7 milliards de kilomètres), son excentricité est de 0,97 et sa période est de 76 ans. Sa distance au périhélie est de 0,59 ua et sa distance à l'aphélie est de 35,3 ua.

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Comets | NASA Space Place – NASA Science for Kids

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NASA science games, articles and activities for kids

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Asteroids are small, rocky objects that orbit the sun. Although asteroids orbit the sun like planets, they are much smaller than planets.

There are lots of asteroids in our solar system. Most of them live in the main asteroid belt -a region between the orbits of Mars and Jupiter.

Asteroids hang out in other places, too. For example, some asteroids are found in the orbital path of planets. This means that the asteroid and the planet follow the same path around the sun. Earth and a few other planets have asteroids like this.

Where did asteroids come from?

Asteroids are left over from the formation of our solar system. Our solar system began about 4.6 billion years ago when a big cloud of gas and dust collapsed. When this happened, most of the material fell to the center of the cloud and formed the sun.

Some of the condensing dust in the cloud became planets. The objects in the asteroid belt never had the chance to be incorporated into planets. They are leftovers from that time long ago when planets formed.

Are all asteroids the same?

No way! Because asteroids formed in different locations at different distances from the sun, no two asteroids are alike. Here are a few ways that they differ:

Asteroids aren't all round like planets. They have jagged and irregular shapes.

Some asteroids are hundreds of miles in diameter, but many more are as small as pebbles.

Most asteroids are made of different kinds of rocks, but some have clays or metals, such as nickel and iron.

What can we learn from asteroids?

Since asteroids formed at the same time as other objects in our solar system, these space rocks can give scientists lots of information about the history of planets and the sun. Scientists can learn about asteroids by studying meteorites: tiny bits of asteroids that have flown through our atmosphere and landed on Earth's surface.

Several NASA space missions have also flown by and observed asteroids. The NEAR Shoemaker spacecraft landed on Eros, an asteroid near Earth, in 2001. Then, the Dawn spacecraft traveled to the asteroid belt in 2011. It orbited and studied the giant asteroid Vesta and the dwarf planet Ceres.

In 2016, NASA launched the OSIRIS-REx spacecraft to study an asteroid near Earth named Bennu. After studying Bennu for a few years, OSIRIS-REx scooped up a sample of dust and rocks from the asteroid's surface.

Now, OSIRIS-REx is headed back to Earth! Its sample container will land in the Utah desert in September 2023. Scientists will then collect the container and examine the dust and rocks for clues about how planets formed and life began.

Will an asteroid ever hit Earth?

There are no known impact threats, but tiny meteors burn up in Earth's atmosphere all the time! Watch this video to learn more from NASA asteroid expert Dr. Kelly Fast.

Related Resources for Educators

Asteroid Resources from NASA JPL Education

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And what can we learn from these space rocks in our solar system?

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If it's time for a meteor shower, you won't need a telescope, binoculars, or a high mountain to have a "star gazing" party. You might need a warm sleeping bag and an alarm clock to wake you in the middle of the night. But then just lying down in your own back yard will put you in the perfect spot to enjoy a great show.

A meteor is a space rock-or meteoroid-that enters Earth's atmosphere. As the space rock falls toward Earth, the resistance-or drag-of the air on the rock makes it extremely hot. What we see is a "shooting star." That bright streak is not actually the rock, but rather the glowing hot air as the hot rock zips through the atmosphere.

When Earth encounters many meteoroids at once, we call it a meteor shower.

Why would Earth encounter many meteoroids at once? Well, comets, like Earth and the other planets, also orbit the sun. Unlike the nearly circular orbits of the planets, the orbits of comets are usually quite lop-sided.

As a comet gets closer to the sun, some of its icy surface boils off, releasing lots of particles of dust and rock. This comet debris gets strewn out along the comet's path, especially in the inner solar system (where we live) as the sun's heat boils off more and more ice and debris. Then, several times each year as Earth makes its journey around the sun, its orbit crosses the orbit of a comet, which means Earth smacks into a bunch of comet debris.

The meteoroids are usually small, from dust particle to boulder size. They are almost always small enough to quickly burn up in our atmosphere, so there's little chance any of them will strike Earth's surface. But there is a good chance that you can see a beautiful shooting star show in the middle of the night!

In the case of a meteor shower, the glowing streaks may appear anywhere in the sky, but their "tails" all seem to point back to the same spot in the sky. That's because all the meteors are coming at us at the same angle, and as they get closer to Earth the effect of perspective makes them seem to get farther apart. It's like standing in the middle of railroad tracks and seeing how the two tracks come together in the distance.

Meteor showers are named for the constellation where the meteors appear to be coming from. So, for example, the Orionids Meteor Shower, which occurs in October each year, appear to be originating near the constellation Orion the Hunter.

Here are dates of major meteor showers. Peak viewing times will vary by a day or two each year. Keep in mind: If the moon is full or near full, you may not see many meteors. Some years are better than others for numbers of meteors per hour.

For more information, visit the NASA Solar System Exploration meteor and meteorite page.

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If it's time for a meteor shower, you won't need a telescope, binoculars, or a high mountain to have a "star gazing" party. You might need a warm sleeping bag and an alarm clock to wake you in the middle of the night.

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Less Than Five - What's the Difference Between Comets, Asteroids, Meteoroids, Meteors & Meteorites?

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Ancient scars

Whether they're the size of a molehill or a mountain, meteorite impacts are one of the most destructive forces in the solar system. Here on Earth, flying space debris triggered mass extinctions, but the same deadly asteroids might also have delivered the seeds of life soon after Earth was born. The effects of asteroid impacts linger for billions of years. Here are the 10 biggest impact craters known, from largest to smallest.

Vredefort crater

The oldest impact crater on Earth is also the largest. Vredefort crater in South Africa, also called the Vredefort Dome, was originally 185 miles (300 kilometers) across, scientists estimate. A meteorite or asteroid bigger than South Africa's Table Mountain blasted out the giant crater 2.02 billion years ago.

Sudbury crater

Sudbury crater in Ontario, Canada, clocks in at 81 miles (130 km) wide and 1.85 billion years old, close in age and size to Vredefort crater in South Africa. The original crater is believed to have sprawled 160 miles (260 km). Rock fragments from the impact have been found in Minnesota, over 500 miles (800 km) away.

Chicxulub crater

Chicxulub crater's discovery clinched what was once a wild theory: that a meteor impact wiped out the dinosaurs. A thin layer of exotic iridium metal from a meteor impact had been detected worldwide at Cretaceous mass extinction before Chicxulub was found. Now, the meteorite that carved the Chicxulub crater in Mexico's Yucatan Peninsula is widely thought to have caused or greatly contributed to the mass extinction at the end of the Cretaceous 65 million years ago, including the end of the dinosaurs. Some scientists think Chicxulub's original crater may have been bigger than Sudbury crater in Ontario. Estimates of its original diameter range up to 150 miles (240 km) in diameter, and its current size is 93 miles (150 km).

Popigai crater

A rare find is buried in Russia's Popigai crater: diamonds. Some 35 million years ago, a meteorite crashed into carbon-rich graphite rock deposits in Siberia, and the impact's immense pressures and temperatures converted the carbon into diamonds. The crater is 62 miles (100 km) wide and holds massive diamond reserves, according to the Russian government.

Manicouagan crater

Our first lake-filled crater, Manicouagan in Quebec is one the largest and best-preserved crater on the planet. The 62-mile-wide (100 km) crater is 214 million years old.

Acraman crater

Lake Acraman fills this round impact crater, excavated 580 million years ago in South Australia. The crater measures 56 miles (90 kilometers) in diameter. Impact ejecta from the crater can be found in the Flinders Range 185 miles (300 km) to the east, among rocks with fossils of the first complex life forms on Earth.

Chesapeake Bay crater

Buried under seafloor muds, Chesapeake Bay Crater offshore of Virginia is an estimated 35 million years old. The curving western shoreline of Chesapeake Bay takes its shape from the 53-mile-wide (85 km) marine crater. A drilling core revealed the first hints that a large impact crater was buried beneath the bay in 1983, when the core brought up an 8-inch-thick (20 centimeters) layer of impact ejecta.

Morokweng crater

Morokweng Crater is buried beneath South Africa's Kalahari Desert: Geologists discovered it through remote sensing surveys. But scientists got a surprise when they drilled into the crater looking for rock samples to confirm the impact. The remains of the meteorite that created this crater were still in its depth. The drill brought back a 10-inch (25 centimeter) fragment of the original meteorite from about 842 yards (770 meters) below the surface. Morokweng formed 145 million years ago and is 44 miles (70 km) wide.

Kara crater

Kara crater is a 70.3-million-year-old eroded crater exposed in Russia's Yugorsky Peninsula. Researchers think the 40-mile-wide (65 km) crater was once more than 75 miles (120 km) in diameter.

Beaverhead crater

This 600-million-year-old crater spans Montana and Idaho and is the second-largest impact crater in the United States. Little remains at the surface of the 37-mile-wide (60 km) crater, which wasn't discovered until the 1990s. That's when shatter cones - cone-shaped, violently-shocked rock - were found in Beaverhead in southwestern Montana. The crater is centered in Challis, Idaho.

Becky Oskin covers Earth science, climate change and space, as well as general science topics. Becky was a science reporter at Live Science and The Pasadena Star-News; she has freelanced for New Scientist and the American Institute of Physics. She earned a master's degree in geology from Caltech, a bachelor's degree from Washington State University, and a graduate certificate in science writing from the University of California, Santa Cruz.

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Crash! 10 Biggest Impact Craters on Earth

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Whether they're the size of a molehill or a mountain, meteorite impacts are one of the most destructive forces in the solar system. Here on Earth, flying space debris triggered mass extinctions, but the same deadly asteroids might also have delivered the seeds of life soon after Earth was born.

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C'est à partir d'un nuage de gaz et de poussière, il y a environ 4,5 milliards d'années, que se sont formés le Soleil et les planètes. Mais seule une partie de ces matières s'est retrouvée dans les planètes. En fait, ce qui n'a pas été utilisé se trouve encore dans tout le Système solaire. Certains de ces corps célestes sont assez gros pour qu'on les considère comme des planètes naines. Les petits objets, souvent de forme irrégulière, sont appelés comètes et astéroïdes.

Quelle différence y a-t-il entre une comète et un astéroïde?

Les comètes et les astéroïdes sont de taille semblable, mais leur composition est très différente. Ils sont situés aussi dans des parties très distinctes du Système solaire.

Les comètes sont un peu comme des boules de neige cosmiques sales : elles sont faites de glace, de gaz gelés, de roches et de poussière. Elles peuvent faire de quelques centaines de mètres à plusieurs dizaines de kilomètres de diamètre. Les comètes se trouvent le plus souvent aux confins du Système solaire, où elles restent gelées. Comme elles sont très loin du Soleil, elles sont difficiles à observer. Toutefois, en raison de leur orbite irrégulière, elles se rapprochent parfois du Soleil. De la glace et des gaz gelés se vaporisent et forment une queue derrière elles. Cette queue les rend bien plus faciles à détecter depuis la Terre.

Les astéroïdes, parfois appelés planètes mineures, contiennent en grande partie les mêmes éléments que les planètes telluriques du Système solaire, comme du carbone et des métaux. Leur taille varie : un grand nombre font moins de 10 mètres de large, mais le plus grand jamais détecté, Vesta, fait 530 kilomètres de large. La plupart gravitent dans la ceinture principale entre les orbites de Mars et de Jupiter. Cette ceinture contient des millions d'astéroïdes, mais leur masse totale serait beaucoup moindre que celle de la Lune.

Comme on vient de l'expliquer, les comètes et les astéroïdes sont bien différents. Toutefois, les scientifiques découvrent dans le Système solaire de plus en plus d'objets qui présentent des caractéristiques des deux. Par exemple, les comètes Manx (en anglais seulement) suivent une orbite de comète, mais n'ont pas de queue et sont composées de matières rocheuses, comme les astéroïdes.

Des astéroïdes et des comètes percutent toutes les planètes du Système solaire, y compris la Terre. Les gros impacts sont toutefois assez rares. Quand il y en a un, cela peut non seulement transformer le paysage de la planète, mais aussi provoquer des extinctions massives. (Source : Agence spatiale canadienne.)

Témoins du passé cosmique

Les comètes et les astéroïdes peuvent fournir des indices sur la naissance du Système solaire. Vu qu'ils n'ont jamais accumulé assez de matières pour grossir jusqu'à devenir des planètes, ils n'ont pas vraiment changé depuis leur formation.

Les scientifiques étudient la composition des comètes et des astéroïdes pour en savoir plus sur les molécules qui existaient il y a des milliards d'années. Certains croient même que les éléments de base de la vie sur Terre proviennent des comètes et des astéroïdes.

Plusieurs sondes spatiales ont été lancées pour scruter ces mondes de près, comme la mission OSIRIS-REx de la NASA, qui doit rapporter sur Terre un échantillon de l'astéroïde Bennu en . Les données de l'instrument canadien OLA ont servi à créer une carte 3D à haute résolution de la surface de Bennu, ce qui a permis aux scientifiques de sélectionner le site d'échantillonnage. Le Canada recevra une partie de l'échantillon, que les scientifiques canadiens pourront alors étudier.

Malgré leur nom, les étoiles filantes ne sont pas des étoiles. La lumière vive des étoiles filantes (appelées aussi météores) est produite par des matières de taille diverse. Ce peut être de minuscules grains de poussière jusqu'à des astéroïdes gros comme une balle de baseball. En entrant dans l'atmosphère terrestre, ces matières se consument et brillent avec éclat.

Des pluies de météores se produisent au même moment chaque année. C'est là qu'on peut le mieux voir des étoiles filantes - parfois des centaines! La raison est simple : l'orbite de la Terre croise régulièrement celle de certaines comètes ou de certains astéroïdes, qui laissent derrière eux des nuages de poussière concentrés. Par exemple, en août, la Terre passe à travers les débris de la comète Swift-Tuttle. On peut voir alors des dizaines d'étoiles filantes par heure dans le ciel nocturne : ce sont les Perséides.

Poursuivez l'exploration

Date de modification :

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Savez-vous faire la différence entre une comète et un astéroïde?

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Henry Lin: Ce que nous pouvons apprendre des galaxies très, très lointaines

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Dans cette présentation passionnante et amusante, l'adolescent Henry Lin regarde quelque chose d'inattendu dans le ciel: les groupes de galaxies éloignées. En étudiant les propriétés des plus grandes pièces de l'univers, nous dit le gagnant du trophée du Salon des Sciences Intel, nous pouvons apprendre beaucoup de choses sur les mystères scientifiques de notre monde et de notre galaxie.

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C'est pas sorcier -COMETES ET ASTEROIDES

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Instrument Status

Instrument

Voyager 1

Voyager 2

Cosmic Ray Subsystem (CRS)

ON

ON

Low-Energy Charged Particles (LECP)

ON

ON

Magnetometer (MAG)

ON

ON

Plasma Wave Subsystem (PWS)

ON

ON

Plasma Science (PLS)
OFF
ON

Where are the Voyagers now?

To learn more about Voyager, zoom in and give the spacecraft a spin. View the full interactive experience at Eyes on the Solar System. Credit: NASA/JPL-Caltech

Both Voyager 1 and Voyager 2 have reached "Interstellar space" and each continue their unique journey through the Universe. In the NASA Eyes on the Solar System app, you can see the real spacecraft trajectories of the Voyagers, which are updated every five minutes. Distance and velocities are updated in real-time. For a full 3D, immersive experience click on View Voyagers link below to launch the NASA Eyes on the Solar System app.
View Voyager

Space Flight Operations Schedule (SFOS)

SFOS files showing Voyager activity on Deep Space Network (DSN)

Select Year:

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Instrument Voyager 1 Voyager 2 Cosmic Ray Subsystem (CRS) ON ON Low-Energy Charged Particles (LECP) ON ON Magnetometer (MAG) ON ON Plasma Wave Subsystem (PWS) ON ON Plasma Science (PLS) OFF ON To learn more about Voyager, zoom in and give the spacecraft a spin.

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Where Does the Sun’s Energy Come From? | NASA Space Place – NASA Science for Kids

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Space Place in a Snap answers this important question!

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Une spectaculaire aurore boréale illumine le ciel de l'Antarctique

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NASA SDO - Spectacular Prominence Eruption, June 7, 2011

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Our Sun is a bright, hot ball of hydrogen and helium at the center of our solar system. It is 864,000 miles (1,392,000 km) in diameter, which makes it 109 times wider than Earth. It's 10,000 degrees Fahrenheit (5,500 degrees Celsius) at the surface, and 27 million degrees Fahrenheit (15,000,000 degrees Celsius) in the core. Yikes!

Our Sun is pretty impressive, but how does it compare to other stars? There are billions more stars in the Milky Way galaxy - the galaxy we call home. And there are many, many more in the rest of the universe. Is our Sun special?

The size of our sun

It turns out that our Sun is an average sized star. There are bigger stars, and there are smaller stars. We have found stars that are 100 times bigger in diameter than our sun. Truly, those stars are enormous. We have also seen stars that are just one tenth the size of our sun.

Suns with friends

Our Sun is a little unusual because it doesn't have any friends. It's just one Sun surrounded by planets, asteroids, comets, and dwarf planets. But solar systems can have more than one sun. In fact, that's often the case. More than half of all stars are in multiple star systems. That means the solar system has two or more suns in it.

Can you imagine having two suns in the sky at the same time? Well, there are plenty of planets throughout the universe where that is normal.

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How Does Our Sun Compare With Other Stars?

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The Sun is actually a pretty average star!

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1:30-6:10

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7:45-10:30

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Vue d'artiste d'une éclipse lunaire totale. (Source : ASC.)

Qu'est-ce qu'une éclipse lunaire?

Une éclipse lunaire a lieu lorsque la Terre se trouve entre le Soleil et la Lune et que celle-ci passe dans l'ombre projetée par la Terre. Ce phénomène ne peut se produire que lorsque la Lune est pleine et qu'elle se trouve du côté opposé au Soleil par rapport à la Terre. Contrairement aux éclipses solaires, il est possible de voir une éclipse lunaire dans presque tout un hémisphère. En d'autres mots, beaucoup plus de gens peuvent l'observer pendant une période plus longue.

Pendant une éclipse lunaire, l'ombre de la Terre se manifeste sous deux formes. Il y a l'ombre (partie qui ne reçoit aucune lumière du Soleil) et la pénombre (partie extérieure de l'ombre, faiblement éclairée par le Soleil). Selon la trajectoire de la Lune, il existe trois types d'éclipse lunaire :

l'éclipse pénombrale : la Lune passe seulement dans la pénombre;

l'éclipse partielle : la Lune passe partiellement dans l'ombre de la Terre;

l'éclipse totale : la Lune passe totalement dans l'ombre de la Terre.

Une éclipse lunaire totale passera par ces trois phases et durera habituellement entre 30 et 60 minutes. Même durant une éclipse lunaire totale, la Lune ne devient jamais complètement invisible. En effet, la lumière du Soleil est réfractée par l'atmosphère de la Terre, ce qui donne une teinte rougeâtre à la Lune. C'est de là que vient le nom " Lune de sang ".

L'éclipse lunaire se produit seulement au moment de la pleine lune. Selon l'heure de la journée et l'endroit où vous vous trouvez (et évidemment, la couverture nuageuse!), vous pourrez voir l'éclipse pendant toute sa durée ou seulement en partie. Si l'éclipse commence peu après le lever de la lune, vous verrez le phénomène du début à la fin. Si elle commence juste avant que la lune se couche, vous n'en verrez que le début.

Comment observer une éclipse lunaire?

Les éclipses lunaires sont un des phénomènes astronomiques les plus faciles à observer, car aucun équipement n'est nécessaire. Des jumelles ou un petit télescope permettront toutefois de voir plus de détails. Il est même possible de photographier une éclipse lunaire avec votre cellulaire dans les bonnes circonstances.

Contrairement aux éclipses solaires, on peut observer une éclipse lunaire à l'œil nu : nul besoin de se protéger les yeux.

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Eclipse lunaire : date de la prochaine eclipse au Canada

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Découvrez les causes des éclipses lunaires, comment les observer et quand elles se produisent.

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What is the Current Phase of the Moon?

What are Lunar Phases?

What Are Lunar Phases?

Our Moon doesn't shine, it reflects. Just like daytime here on Earth, sunlight illuminates the Moon.

Credit: NASA/Bill Dunford

We just can't always see it.

When sunlight hits off the Moon's far side - the side we can't see without from Earth the aid of a spacecraft - it is called a new Moon.

When sunlight reflects off the near side, we call it a full Moon.

The rest of the month we see parts of the daytime side of the Moon, or phases. These eight phases are, in order, new Moon, waxing crescent, first quarter, waxing gibbous, full Moon, waning gibbous, third quarter and waning crescent. The cycle repeats once a month (every 29.5 days).

What is a Lunar Eclipse?

What is a Lunar Eclipse?

During a lunar eclipse, Earth comes between the Sun and the Moon, blocking the sunlight falling on the Moon.

There are two kinds of lunar eclipses:

A total lunar eclipse occurs when the Moon and Sun are on opposite sides of Earth.

A partial lunar eclipse happens when only part of Earth's shadow covers the Moon.

During some stages of a lunar eclipse, the Moon can appear reddish. This is because the only remaining sunlight reaching the Moon at that point is from around the edges of the Earth, as seen from the Moon's surface. From there, an observer during an eclipse would see all Earth's sunrises and sunsets at once.

A composite of seven images shows the full Moon at perigee, or supermoon, during a total lunar eclipse on Sunday, Sept. 27, 2015, in Denver. Credit: NASA/Bill Ingalls

Understanding Lunar Eclipses

A lunar eclipse occurs when the Moon passes through the Earth's shadow, just as a solar eclipse occurs when part of the Earth passes through the Moon's shadow.

So why don't eclipses happen twice a month?

The reason is that the Moon's orbit around the Earth is tilted relative to the Earth's orbit around the Sun.

But if that's the case, why do eclipses happen at all?

Throughout the year, the Moon's orbital tilt remains fixed with respect to the stars, meaning that it changes with respect to the Sun. About twice a year, this puts the Moon in just the right position to pass through the Earth's shadow, causing a lunar eclipse.

As the Moon passes into the central part of the Earth's shadow, called the umbra, it darkens dramatically. Once it's entirely within the umbra, the Moon appears a dim red due to sunlight scattered through the Earth's atmosphere.

In fact, if you watched the eclipse from the surface of the Moon, you'd see the Sun set behind the entire Earth, bathing you in a warm red glow. Back home, you'll have to stay up late to watch a lunar eclipse, but if you do you'll see the Moon in rare form, and you'll catch a brief glimpse of our own planet's long shadow.

It's not often that we get a chance to see our planet's shadow, but a lunar eclipse gives us a fleeting glimpse. During these rare events, the full Moon rapidly darkens and then glows red as it enters the Earth's shadow. More details and download options ›
Photograph the Moon

Photograph the Moon

Capturing the Moon with a camera is one of the most satisfying-and challenging-projects available to an outdoor photographer. Here are 10 suggestions for making the most of a moonlit night with your camera.

How do Lunar Eclipses Affect Spacecraft?

How do Lunar Eclipses Affect Spacecraft?

Lunar eclipses can be a science boon and engineering challenge for orbiting spacecraft, such as NASA's Lunar Reconnaissance Orbiter. The solar-powered orbiter also falls in Earth's shadow, cutting it off from the source of its power. Mission controllers shut down most instruments to conserve energy.

The team leaves on one instrument-called Diviner-that can watch how the lunar surface responds to the rapid change in temperature caused by a lunar eclipse. The data helps scientists better understand the composition and properties of the surface.

Additional Resources

Eclipse Videos

Eclipse Activities

How to watch an eclipse and get students observing the Moon

Evaluating a Lunar Eclipse (Grades 3-12) - Students use the Danjon Scale of Lunar Eclipse Brightness to illustrate the range of colors and brightness the Moon can take on during a total lunar eclipse.

Observing the Moon (Grades K-6) - Students identify the Moon's location in the sky and record their observations in a journal over the course of the Moon-phase cycle.

Moon Phases (Grades 1-6) - Students learn about the phases of the Moon by acting them out. In 30 minutes, they will act out one complete, 30-day, Moon cycle.

Measuring the Supermoon (Grades 5-12) - Students take measurements of the Moon during its full phase over multiple Moon cycles to compare and contrast results.

Modeling the Earth-Moon System (Grades 6-8) - Students learn about scale models and distance by creating a classroom-size Earth-Moon system.

Make a Moon Phases Calendar and Calculator - Like a decoder wheel for the Moon, this calendar will show you where and when to see the Moon and every Moon phase throughout the year!

Explore More

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Lunar Phases and Eclipses | Earth's Moon - NASA Solar System Exploration

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What is the Current Phase of the Moon? What are Lunar Phases? Our Moon doesn't shine, it reflects. Just like daytime here on Earth, sunlight illuminates the Moon. We just can't always see it. When sunlight hits off the Moon's far side - the side we can't see without from Earth the aid of a spacecraft - it is called a new Moon.

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Explaining the science behind, "What time is it?"

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Our solar system has one star, eight planets, five officially recognized dwarf planets, at least 290 moons, more than 1.3 million asteroids, and about 3,900 comets.

It is located in an outer spiral arm of the Milky Way galaxy called the Orion Arm, or Orion Spur. Our solar system orbits the center of the galaxy at about 515,000 mph (828,000 kph). It takes about 230 million years to complete one orbit around the galactic center.

We call it the solar system because it is made up of our star, the Sun, and everything bound to it by gravity - the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune; dwarf planets Pluto, Ceres, Makemake, Haumea, and Eris - along with hundreds of moons; and millions of asteroids, comets, and meteoroids.

Our solar system is the only one we know of that has a planet that supports life. So far, we only know of life on Earth, but we're looking for life on other worlds.

NASA's Europa Clipper

Send Your Name to Jupiter

You're invited to #SendYourName to Jupiter's moon Europa by signing a poem by U.S. Poet Laureate Ada Limón that will travel aboard NASA's Europa Clipper spacecraft.

Saying Farewell: Which Spacecraft are Leaving Our Solar System?

Only two spacecraft have reached interstellar space, the space between stars. Three other spacecraft have achieved enough velocity to eventually travel beyond the boundaries of our solar system.

Voyager 1 went interstellar in 2012 and Voyager 2 joined it in 2018. Both spacecraft, launched in 1977, are still in communication with Earth.

NASA's New Horizons spacecraft is currently exploring an icy region beyond Neptune called the Kuiper Belt. It eventually will leave our solar system.

Pioneer 10 and Pioneer 11 also will ultimately travel silently among the stars toward the galactic core. The spacecraft used up their power supplies decades ago.

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Solar System Overview Our solar system has one star, eight planets, five officially recognized dwarf planets, at least 290 moons, more than 1.3 million asteroids, and about 3,900 comets. It is located in an outer spiral arm of the Milky Way galaxy called the Orion Arm, or Orion Spur.

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A lot of moons or no moons at all?

We on Earth have just one moon, but some planets have dozens of them. Others don't have any. Which planets have moons, and which don't?

Let's go in order from the Sun.

Mercury and Venus

Up first are Mercury and Venus. Neither of them has a moon.

Because Mercury is so close to the Sun and its gravity, it wouldn't be able to hold on to its own moon. Any moon would most likely crash into Mercury or maybe go into orbit around the Sun and eventually get pulled into it.

Why Venus doesn't have a moon is a mystery for scientists to solve.

Earth (That's us!)

Up next is Earth, and of course we have one moon.

Mars

Mars has two moons. Their names are Phobos and Deimos. Don't you wish our moon had a cool name like that?

Jupiter

Next are the giant outer planets. They have lots of moons. Jupiter, for instance, has 79 known moons!

The most well-known of Jupiter's moons are Io (pronounced eye-oh), Europa, and Callisto. Jupiter also has the biggest moon in our solar system, Ganymede.

These moons are so big you can see them with just a pair of binoculars.

Saturn

Saturn has 53 moons that have been named. Saturn also has 29 moons awaiting confirmation. They're unconfirmed because we're waiting to get more information about them. If all of these moons get confirmed, Saturn will have 82 moons. And that's not counting Saturn's beautiful rings.

Saturn's moons have great names like Mimas, Enceladus, and Tethys. One of these moons, named Titan, even has its own atmosphere, which is very unusual for a moon.

Uranus and Neptune

Uranus has 27 moons that we know of. Some of them are half made of ice.

Lastly, Neptune has 14 named moons. One of Neptune's moons, Triton, is as big as dwarf planet Pluto.

To learn more about the moons in our solar system, visit the NASA Solar System Exploration moons page.

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We on Earth have just one moon, but some planets have dozens of them. Others don't have any. Which planets have moons, and which don't? Let's go in order from the Sun. Up first are Mercury and Venus. Neither of them has a moon.

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Les phases (4:52-6:18)
Les éclipses (6:57-10:52)

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C'est pas Sorcier(l'Essentiel) La Lune, Les Éclipses.

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The Farthest Watch online full movie - Documentary Mania

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Is it humankind's greatest achievement? 12 billion miles away a tiny spaceship is leaving our Solar...

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What are sunspots and solar flares?

The surface of the Sun is a very busy place. It has electrically charged gases that generate areas of powerful magnetic forces. These areas are called magnetic fields. The Sun's gases are constantly moving, which tangles, stretches and twists the magnetic fields. This motion creates a lot of activity on the Sun's surface, called solar activity.

Sometimes the Sun's surface is very active. Other times, things are a bit quieter. The amount of solar activity changes with the stages in the solar cycle. Solar activity can have effects here on Earth, so scientists closely monitor solar activity every day.

Sunspots

Sunspots are areas that appear dark on the surface of the Sun. They appear dark because they are cooler than other parts of the Sun's surface. The temperature of a sunspot is still very hot though-around 6,500 degrees Fahrenheit!

Why are sunspots relatively cool? It's because they form at areas where magnetic fields are particularly strong. These magnetic fields are so strong that they keep some of the heat within the Sun from reaching the surface.

Solar Flares

The magnetic field lines near sunspots often tangle, cross, and reorganize. This can cause a sudden explosion of energy called a solar flare. Solar flares release a lot of radiation into space. If a solar flare is very intense, the radiation it releases can interfere with our radio communications here on Earth.

Solar flares are sometimes accompanied by a coronal mass ejection (CME for short). CMEs are huge bubbles of radiation and particles from the Sun. They explode into space at very high speed when the Sun's magnetic field lines suddenly reorganize.

Effects of Solar Activity on Earth

When charged particles from a CME reach areas near Earth, they can trigger intense lights in the sky, called auroras. When particularly strong, a CME can also interfere in power utility grids, which at their worst can cause electricity shortages and power outages. Solar flares and CMEs are the most powerful explosions in our solar system.

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What are sunspots and solar flares? The surface of the Sun is a very busy place. It has electrically charged gases that generate areas of powerful magnetic forces. These areas are called magnetic fields. The Sun's gases are constantly moving, which tangles, stretches and twists the magnetic fields.

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Alors que les taches solaires ont quasiment déserté la surface du Soleil depuis le début de 2017, voici qu'a surgi un archipel, début juillet, qui est rapidement devenu imposant. Le satellite SDO, de la Nasa, a pu observer ces régions actives, qui ressemblent à des tournesols, s'épanouir alors qu'elles transitaient sur la face de notre étoile tournée vers la Terre.

Le satellite ( Solar Dynamics Observatory) qui, depuis 2010, ne quitte pas des notre , a observé entre le 5 et le 11 juillet 2017 le développement d'un imposant groupe de taches sombres sur la surface de notre orientée vers la .

Bien sûr, ce n'est pas la première fois que le satellite de la aperçoit de semblables régions actives mais le début de 2017, elles se faisaient rares, et même très rares. Il s'est en effet écoulé plusieurs jours de suite sans qu'aucune ne soit apparue sur la photosphère . Signe d'une activité solaire très basse. D'ailleurs, pour des spécialistes de la Nasa, le minimum solaire est imminent .

Des taches solaires plus grandes que la Terre

Mais que l'on se rassure, le n'est pas malade et ne va pas s'éteindre. Cette baisse significative d'activité à sa surface est normale et récurrente : tous les 11 ans, en moyenne. C'est donc le creux de la .

Une fois le minimum passé, ces taches qui ressemblent à des tournesols -- ces régions moins chaudes que l'environnement qui les entoure apparaissent plus sombres par -- et peuvent avoir plusieurs fois la taille de la Terre, vont se multiplier de nouveau, témoignant de la reprise d' activité de notre étoile . Puis viendra ensuite le maximum solaire, comme tous les 11 ans (en moyenne), lorsque le nombre de ces points noirs sera au plus haut.

© Nasa

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D'immenses taches solaires observées par le satellite SDO

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Alors que les taches solaires ont quasiment déserté la surface du Soleil depuis le début de 2017, voici qu'a surgi un archipel, début juillet, qui est rapidement devenu imposant. Le satellite SDO, de la Nasa, a pu observer ces régions actives, qui ressemblent à des tournesols, s'épanouir alors qu'elles transitaient sur la face de notre étoile tournée vers la Terre.

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Lunar Eclipse 2011  Amazing!  Next Lunar Eclipse Video Will turn moon BLOOD RED like this!!

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The Solar Eclipse In Varanasi - Wonders of the Solar System - Series 1 Episode 1 Preview - BBC Two

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If the Moon were replaced with some of our planets

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Les astronautes, l’astronomie, l’exploration de la Lune et de Mars, les satellites, la science, la technologie, la robotique.

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Le télescope spatial James Webb , dont le lancement est prévu pour , est le télescope spatial le plus puissant jamais construit. Le Canada fournit au télescope un instrument scientifique et un détecteur de guidage. Des scientifiques canadiens auront la chance de participer à cette passionnante mission scientifique qui promet de changer notre compréhension de l'Univers.

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Le télescope spatial James Webb , dont le lancement est prévu pour , est le télescope spatial le plus puissant jamais construit. Le Canada fournit au télescope un instrument scientifique et un détecteur de guidage. Des scientifiques canadiens auront la chance de participer à cette passionnante mission scientifique qui promet de changer notre compréhension de l'Univers.

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, in full Encyclopédie, Ou Dictionnaire Raisonné Des Sciences, Des Arts Et Des Métiers, (French: "Encyclopaedia, or Classified Dictionary of Sciences, Arts, and Trades"), the 18th-century French encyclopaedia that was one of the chief works of the Philosophes, men dedicated to the advancement of science and secular thought and the new tolerance and open-mindedness of the Enlightenment. The Encyclopédie was a literary and philosophical enterprise with profound political, social, and intellectual repercussions in France just prior to the Revolution. Its contributors were called Encyclopédistes.

The Encyclopédie was inspired by the success of Ephraim Chambers' Cyclopaedia; or An Universal Dictionary of Arts and Sciences (London, 1728). Indeed, the work originated in an abortive attempt to put out a five-volume French translation of Chambers' Cyclopaedia. When this project collapsed in 1745, its intended publisher, André Le Breton, immediately embarked on plans for an expanded Encyclopédie. He secured the services of the mathematician Jean d'Alembert in 1745 and of the translator and philosopher Denis Diderot in 1746 to assist in the project. In 1747 Diderot undertook the general direction of work on the Encyclopédie, except for its mathematical parts, which were edited by d'Alembert. (D'Alembert resigned in 1758.) Seventeen volumes of the Encyclopédie's text were published between 1751 and 1765; 11 volumes of plates were also published between the years 1762 and 1772, making a total of 28 volumes. These were supplemented in 1776-77 by five more volumes-four of text and one of illustration plates-and by two volumes of index in 1780, all compiled under other editors, since Diderot had refused to edit the supplementary materials. These seven volumes, plus the 28 prepared by Diderot, constituted the first edition of the Encyclopédie in 35 folio volumes.

The Encyclopédie was a showcase for representatives of the new schools of thought in all branches of intellectual activity. The work was notable for its attitude of tolerance and liberalism and also for its innovative coverage of the trades and mechanical arts. In its skepticism, its emphasis on scientific determinism, and its criticism of the abuses perpetrated by contemporary legal, judicial, and clerical institutions, the Encyclopédie had widespread influence as an expression of progressive thought and served in effect as an intellectual prologue to the French Revolution.

The Encyclopédie's publication was opposed by conservative ecclesiastics and government officials almost from the start. The work was subjected to Jesuit censorship and the suppression of several volumes by the French Council of State (1752), and it was formally condemned and denied permission for publication in 1759 and for several years thereafter. At this point Diderot's friends urged him to abandon the project, but he persuaded the publishers to secure permission to bring out the relatively uncontroversial volumes of illustration plates, while the remaining volumes of text were edited and printed. Diderot also discovered in 1764 that Le Breton and a compositor had secretly removed about 300 pages of liberal or controversial material from the proof sheets of about 10 folio volumes.

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The group of writers that Diderot and d'Alembert assembled for the production of the Encyclopédie were at first relatively unknown, with the exception of Jean-Jacques Rousseau and Baron d'Holbach. But as both the fame of the Encyclopédie and the attacks upon it grew, distinguished and expert contributors were attracted, including A.-R.-J. Turgot, Voltaire, J.-F. Marmontel, and Jacques Necker. Diderot himself contributed innumerable articles, especially on philosophy, social theory, and the trades, proving to be both an energetic general editor and the driving force behind the crisis-ridden project. It was he who compiled and supervised the preparation of the work's 3,000 to 4,000 plates, many of which vividly illustrated industrial arts and processes.

In 1782 the publication of a new, enlarged edition departing from the alphabetical arrangement of the first edition was begun under the title Encyclopédie méthodique ou par ordre de matières ("Systematic Encyclopaedia or Arranged by Subject"). Work on this topically arranged encyclopaedia continued through the French Revolution and was completed in 1832 with the appearance of the 166th volume, 50 years after the appearance of the first volume.

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Encyclopédie, (French: "Encyclopaedia, or Classified Dictionary of Sciences, Arts, and Trades"), the 18th-century French encyclopaedia that was one of the chief works of the Philosophes, men dedicated to the advancement of science and secular thought and the new tolerance and open-mindedness of t

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6 minutes to see the size of the universe.

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As the festive period is here once again, a lot of social gatherings and family time are part of the itinerary for most. So this year instead of telling the regular old Christmas cracker jokes why not entertain your friends and family with these pretty amazing space facts instead?

There are thousands of other planets out there.

We have eight planets in our Solar System. However, outside of our Solar System there are thousands of other planets. The extra-solar planets or exo-planets are in orbit around another star. So far we have almost 1800 confirmed new worlds, with another 3000 awaiting confirmation. Astronomers are looking to a star's goldilocks zone for planets that may be habitable, just like the Earth. The majority of planets discovered so far are hot gas giant planets.

2. In space the skin on your feet peels off!

This is a pretty gross fact but in the micro-gravity environment, astronauts are not using their feet to walk. Therefore the skin on their feet starts to soften and flakes off. As laundry facilities do not exist in space, astronauts will wear the same underwear and socks for a few days. Those socks then need to be taken off very gently. If not those dead skin cells will float around in the weightless environment.

3. On Venus a day is longer than a year.

This is tricky one to get your head around but a year on Venus (that is the length of time it takes to complete one whole orbit around the Sun) is 224.7 Earth days. However it takes 243 Earth days to rotate on its axis just once.

4.The astronauts were placed in quarantine after returning from the moon.

There is a famous image of President Nixon talking to the Apollo 11 crew consisting of Michael Collins, Neil Armstrong and Buzz Aldrin. This continued until after the Apollo 14 crew returned safely. After this it was decided that the Moon did not contain any deadly diseases. The Apollo 13 crew, who had a malfunction and had to return to Earth, did not have to be quarantined after their re-entry as they didn't actually walk on the moon.

5. One million Earths can fit inside the Sun.

Ancient astronomers once believed the Earth was at the centre of the Universe but now we know that the Sun is at the centre of our Solar System and our planets orbit the Sun. The Sun makes up 99.8% of the entire mass of the whole Solar System. One million Earths would be needed to be the same size as the Sun.

6.You become taller in Space.

Another change to the human body in micro-gravity is that spine straightens out, as gravity is not pushing you down. In fact you can be up to as much as 5cm taller in the Space Station.

7. Extreme weather warning!

Some times on the Earth, especially here in Northern Ireland the weather can be a bit rubbish! However our weather is awesome compared to some of the other planets. Jupiter has fast winds and the Great Red spot, a massive hurricane style storm, has raged there for the last 300 years. Mercury and Mars have extreme temperature changes in the same day. Venus is a scorching five times hotter than boiling water. Saturn and Uranus also have extremely fast winds. However Neptune has the fastest ever wind speeds reaching a staggering 1600mph!

8. Space is not that far away.

Space officially begins at the universal marker of the Karman Line. This invisible boundary is 100km above the Earth. In theory if you could drive your car upwards, you could be in space in less than hour.

9. The hottest planet is not the closest planet to the Sun.

Even though Mercury is the closest planet to the Sun, it is not actually the hottest. Mercury does not have any atmosphere meaning that this planet is only hot in the daytime when it is directly facing the Sun. At this stage temperatures can rise to 425°C but at night the planet's temperature can drop down to a freezing -180°C. Venus is the hottest planet. Its thick clouds trap the Sun's heat causing Venus to be a sizzling 500°C all of the time!

10. The moon looks bigger on the horizon

There is an optical illusion which makes the moon appear to be larger the lower it is in the sky. The apparent magnification is not caused by our atmosphere. It is more of a mind trick. When the moon is closer to the horizon, it is closer to objects like buildings and trees which therefore in comparison makes the moon look bigger. However there are times when the moon really is bigger. During its elliptical orbit the moon has times when it is actually slightly closer to the Earth (Perigee) or further from the Earth (apogee). This happens about once a month, due the moon's orbit around the Earth. Usually is not noticeable to the eye. However when a full moon occurs at the same time of the moon's perigee it can be called a Super moon and appears 12-14% bigger than normal!

11. There's a moose loose

Eccentric Astronomer Tycho Brahe (1546-1601) believed that the Moon and Sun orbited the Earth but the other planets orbited the Sun. He catalogued many stars and objects, and has a crater on the moon, and supernova remnant named after him. However his wild antics are perhaps just as interesting. He wore a fake silver nose after losing his real one in a sword fight and he also had a pet moose which died falling down the stairs after one to many drinks. When his body was exhumed and examined in 2010, it is thought that a burst bladder was the cause of his death not mercury poisoning by a jealous colleague which was considered a cause of death.Astronauts are literally star sailors

12. The word astronaut comes from the Greek word "Astron" which means star and "nautes" which means sailor. The Russian cosmonaut has a similar meaning from 'kosmos' meaning universe and again "nautes" sailor.

13. You can cry in space but your tears don't fall

On-board the International Space Station, water floats like bubbles or spheres. However the water will cling to a surface until it is dislodged. This means that tears start to form bubbles around your eyes as the weightless environment is not causing your tears to fall. This sounds really cool but it can be dangerous. ESA astronaut Luca Parmitano suffered a space suit leak whilst on a spacewalk. The water leaked into his helmet covered his eyes and ears, but thankfully he made it back into the Space Station unharmed, but if not he could have drowned in space.

14. Dirty underwear and toilet paper has helped grown plants on the ISS

American astronaut Don Pettit discovered that by folding a pair of underpants into a sphere shape and stitching in some Russian toilet paper (which is thick, wool like gauze), this created a warmer environment for some tomato and basil seeds to start to sprout. Like their socks, underwear is only changed every 3-4 days so he figured the pants might provide some extra nutrients for the plants!

15. There is a dwarf planet named after an Easter island legend

Dwarf planet Makemake was discovered at Easter 2005. The Easter Island Moai figures were the inspiration for its name. Makemake in Rapa Nui mythology was the creator of humanity and the god of fertility. He is also a feature in many rock and cave drawings on the island.

16. Nebulae come in all shapes and sizes

Nebula means cloud in Latin. These are areas in which stars are being created or where a star has died. The cosmic clouds come in all shapes and sizes and are made out of interstellar dust and gases. There is a Christmas tree nebula, a horsehead, a unicorn, a hand, fried egg and lots more. These beautiful clouds which are not visible to the naked eye really highlight the fact there is a lot more happening in the night sky than you can see.

17. The North Star will change...eventually

The North Star used for navigation, a steady point in the night sky will change, however not in our lifetime. The Earth is rotating like a spinning top and therefore the pole of our planet wobbles. Currently it points to Polaris but in the year 13727 our Pole Star will be the star Vega, in the constellation of Lyra. Vega was the also North Star in 12000BCE.

18. The Apollo crews did not have any life insurance.

On the chance that the 3 man crew of Armstrong, Aldrin and Collins did not return safely from the moon, they were not covered by any life insurance policy. So before their trip all 3 men signed photographs that could be sold in the event of their death. These Insurance covers were also stamped and posted on the start date of the mission, July 16 th 1969 by a friend.

19. In space metal sticks together

In a vacuum like space, when two pieces of metal touch each other they bond together. This is a process called cold welding. On the Earth because of the oxygen in our environment this does not happen naturally but it is used during some manufacturing processes. It is something to take into account but it is not usually a problem as the astronaut's tools maintain an oxide layer even when leaving Earth.

20. The furthest manmade object is Voyager 1. It has messages for aliens on-board.

In 1977, Voyager 1 and 2 were launched. Their primary mission was to visit Jupiter and Saturn. Voyager 2 continued onto Uranus and Neptune; Voyager 1 has now made its way into interstellar space. Voyager 1 is further away from Earth than the distance between the Sun and Pluto. Both craft carry a golden record on board, which will act like a time-capsule of Earth. It has greetings from Earth as well as different kinds of music. It also has noises of rocket engines, the sea, people talking, animal's sounds and lots of images. All of which sum up the Earth. United States President Jimmy Carter said at the time "This record represents our hope and our determination, and our good will in a vast and awesome universe." These messages have been recorded as electronic impulses which can be translated into written words. If any aliens find it then can enjoy some Louis Armstrong as well some Peruvian panpipes!

Wanted to hear what's on the golden record , have a listen to this .

I hope you have enjoyed these weird and wonderful facts about space or why not also add these to your Christmas repertoire of jokes.

Q. What kind of songs do the planets sing?

A. Neptunes!

Q. Why did the Sun go to school?

A. To get brighter!

Merry Christmas and Happy New Year from Martina Redpath, Senior Education Support Officer

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There are thousands of other planets out there. We have eight planets in our Solar System. However, outside of our Solar System there are thousands of other planets. The extra-solar planets or exo-planets are in orbit around another star. So far we have almost 1800 confirmed new worlds, with another 3000 awaiting confirmation.

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Watch NOVA - The Planets Mars - Educational documentaries on Dailymotion

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Watch NOVA - The Planets Saturn - Educational documentaries on Dailymotion

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Watch NOVA - The Planets Ice Worlds - Educational documentaries on Dailymotion

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See this playlist for the rest of this series content:https://www.dailymotion.com/playlist/x68sly

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Watch NOVA - The Planets Jupiter - Educational documentaries on Dailymotion

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L'encyclopédie des 8-13 ans que chacun peut améliorer !

La guerre de Succession d'Autriche est une guerre européenne qui s'est déroulée de 1740 à 1748.

Le conflit éclate suite au rejet par certains États de la Pragmatique Sanction, qui léguait à la fille de Charles VI du Saint-Empire, Marie-Thérèse, les États héréditaires des Habsbourgs.

La guerre se déroule en Silésie où la Prusse signe un traité de paix en 1742. En Bohême, la Bavière et la France prennent Prague, puis reculent en 1742 ; en 1743, ils subissent des revers pendant leurs retraites. Entre 1744 et 1748, la France concentre alors ses efforts vers les Pays-Bas autrichiens où elle est victrorieuse.

La Guerre se termine en 1748 avec la signature du Traité d'Aix-la-Chapelle en 1748.

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Actualités, interviews... La Gazette de Vikidia propose chaque trimestre les dernières nouvelles sur Vikidia !

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L'encyclopédie des 8-13 ans que chacun peut améliorer ! La guerre de Succession d'Autriche est une guerre européenne qui s'est déroulée de 1740 à 1748. Le conflit éclate suite au rejet par certains États de la Pragmatique Sanction , qui léguait à la fille de Charles VI du Saint-Empire, Marie-Thérèse, les États héréditaires des Habsbourgs.

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* - See the Fact Sheet Notes.

Planetary Fact Sheet in U.S. Units

Planetary Fact Sheet - Values compared to Earth

Index of Planetary Fact Sheets - More detailed fact sheets for each planet

Notes on the Fact Sheets - Explanations of the values and headings in the fact sheet

Schoolyard Solar System - Demonstration scale model of the solar system for the classroom

Author/Curator:
Dr. David R. Williams,dave.williams@nasa.gov
NSSDCA, Mail Code 690.1
NASA Goddard Space Flight Center
Greenbelt, MD 20771
+1-301-286-1258

NASA Official: Dr. David R. Williams, david.r.williams@nasa.gov
Last Updated: 21 October 2019, DRW

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See the Fact Sheet Notes. Planetary Fact Sheet in U.S. Units Planetary Fact Sheet - Values compared to Earth Index of Planetary Fact Sheets - More detailed fact sheets for each planet Notes on the Fact Sheets - Explanations of the values and headings in the fact sheet Schoolyard Solar System - Demonstration scale model of the solar system for the classroom Author/Curator: Dr. David R.

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Carolyn Porco: Could a Saturn moon harbor life?

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Carolyn Porco shares exciting new findings from the Cassini spacecraft's recent sweep of one of Saturn's moons, Enceladus. Samples gathered from the moon's icy geysers hint that an ocean under its surface could harbor life.

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Every time you take a breath of fresh air, it's easy to forget you can safely do so because of Earth's atmosphere. Life on Earth could not exist without that protective cover that keeps us warm, allows us to breathe, and protects us from harmful radiation-among other things.

What makes Earth's atmosphere special, and how do other planets' atmospheres compare? Here are 10 tidbits:

1. On Earth, we live in the troposphere, the closest atmospheric layer to Earth's surface. "Tropos" means "change," and the name reflects our constantly changing weather and mixture of gases. It's 5 to 9 miles (8 to 14 kilometers) thick, depending on where you are on Earth, and it's the densest layer of atmosphere. When we breathe, we're taking in an air mixture of about 78 percent nitrogen, 21 percent oxygen and 1 percent argon, water vapor and carbon dioxide. More on Earth's atmosphere›

In this image taken by the Viking 1 orbiter in June 1976, the translucent layer above Mars' dusty red surface is its atmosphere. Credit: NASA/Viking 1. More on this image›

2. Mars has a very thin atmosphere, nearly all carbon dioxide. Because of the Red Planet's low atmospheric pressure, and with little methane or water vapor to reinforce the weak greenhouse effect (warming that results when the atmosphere traps heat radiating from the planet toward space), Mars' surface remains quite cold, the average surface temperature being about -82 degrees Fahrenheit (minus 63 degrees Celsius). More on the greenhouse effect›

An artist's concept of the surface of Venus, where heat ripples distort the scene in a shimmering heat bath. Credit: NASA/Goddard Space Flight Center Conceptual Image Lab.

3. Venus' atmosphere, like Mars', is nearly all carbon dioxide. However, Venus has about 154,000 times more carbon dioxide in its atmosphere than Earth (and about 19,000 times more than Mars does), producing a runaway greenhouse effect and a surface temperature hot enough to melt lead. A runaway greenhouse effect is when a planet's atmosphere and surface temperature keep increasing until the surface gets so hot that its oceans boil away. More on the greenhouse effect›

Intricate cloud patterns in Jupiter's Northern Hemisphere. Image credit: NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill. More on this image›

4. Jupiter likely has three distinct cloud layers (composed of ammonia, ammonium hydrosulfide and water) in its "skies" that, taken together, span an altitude range of about 44 miles (71 kilometers). The planet's fast rotation-spinning once every 10 hours-creates strong jet streams, separating its clouds into dark belts and bright zones wrapping around the circumference of the planet. More on Jupiter›

An animation of Cassini spacecraft images of Saturn's hurricane-like polar vortex. Credit: NASA/JPL-Caltech/SSI/Hampton

5. Saturn's atmosphere-where NASA's Cassini spacecraft ended its 13 extraordinary years of exploration of the planet-has a few unusual features. Its winds are among the fastest in the solar system, reaching speeds of 1,118 miles (1,800 kilometers) per hour. Saturn may be the only planet in our solar system with a warm polar vortex (a mass of swirling atmospheric gas around the pole) at both the North and South poles. Also, the vortices have "eye-wall clouds," making them hurricane-like systems like those on Earth.

Another uniquely striking feature is a hexagon-shaped jet stream encircling the North Pole. In addition, about every 20 to 30 Earth years, Saturn hosts a megastorm (a great storm that can last many months). More on Saturn›

An infrared composite image of the two hemispheres of Uranus. Credit: Lawrence Sromovsky, University of Wisconsin-Madison/W.W. Keck Observatory. More on this image›

6. Uranus gets its signature blue-green color from the cold methane gas in its atmosphere and a lack of high clouds. The planet's minimum troposphere temperature is 49 Kelvin (minus 224.2 degrees Celsius), making it even colder than Neptune in some places. Its winds move backward at the equator, blowing against the planet's rotation. Closer to the poles, winds shift forward and flow with the planet's rotation. More on Uranus›

7. Neptune is the windiest planet in our solar system. Despite its great distance and low energy input from the Sun, wind speeds at Neptune surpass 1,200 miles per hour (2,000 kilometers per hour), making them three times stronger than Jupiter's and nine times stronger than Earth's. Even Earth's most powerful winds hit only about 250 miles per hour (400 kilometers per hour). Also, Neptune's atmosphere is blue for the very same reasons as Uranus' atmosphere. More on Neptune›

8. WASP-39b, a hot, bloated, Saturn-like exoplanet (planet outside of our solar system) some 700 light-years away, apparently has a lot of water in its atmosphere. In fact, scientists estimate that it has about three times as much water as Saturn does. More on this exoplanet›

An artist's concept of a hot Jupiter orbiting very close its host star. Credit: NASA/Ames/JPL-Caltech.

9. A weather forecast on " hot Jupiters"-blistering, Jupiter-like exoplanets that orbit very close to their stars-might mention cloudy nights and sunny days, with highs of 2,400 degrees Fahrenheit (about 1,300 degrees Celsius, or 1,600 Kelvin). Their cloud composition depends on their temperature, and studies suggest that the clouds are unevenly distributed. More on these exoplanets›

10. 55 Cancri e, a "super Earth" exoplanet (a planet outside of our solar system with a diameter between Earth's and Neptune's) that may be covered in lava, likely has an atmosphere containing nitrogen, water and even oxygen-molecules found in our atmosphere-but with much higher temperatures throughout. Orbiting so close to its host star, the planet could not maintain liquid water and likely would not be able to support life. More on this exoplanet›

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10 Things: Planetary Atmospheres - NASA Solar System Exploration

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Every time you take a breath of fresh air, it's easy to forget you can safely do so because of Earth's atmosphere. Life on Earth could not exist without that protective cover that keeps us warm, allows us to breathe, and protects us from harmful radiation-among other things.

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It's is no secret that Earth is the only inhabited planet in our Solar System. All the planets besides Earth lack a breathable atmosphere for terrestrial beings, but also, many of them are too hot or too cold to sustain life. A "habitable zone" which exists within every system of planets orbiting a star. Those planets that are too close to their sun are molten and toxic, while those that are too far outside it are icy and frozen.

But at the same time, forces other than position relative to our Sun can affect surface temperatures. For example, some planets are tidally locked, which means that they have one of their sides constantly facing towards the Sun. Others are warmed by internal geological forces and achieve some warmth that does not depend on exposure to the Sun's rays. So just how hot and cold are the worlds in our Solar System? What exactly are the surface temperatures on these rocky worlds and gas giants that make them inhospitable to life as we know it?

Mercury:

Of our eight planets, Mercury is closest to the Sun. As such, one would expect it to experience the hottest temperatures in our Solar System. However, since Mercury also has no atmosphere and it also spins very slowly compared to the other planets, the surface temperature varies quite widely.

What this means is that the side exposed to the Sun remains exposed for some time, allowing surface temperatures to reach up to a molten 465 °C. Meanwhile, on the dark side, temperatures can drop off to a frigid -184°C. Hence, Mercury varies between extreme heat and extreme cold and is not the hottest planet in our Solar System.

Venus:

That honor goes to Venus, the second closest planet to the Sun which also has the highest average surface temperatures - reaching up to 460 °C on a regular basis. This is due in part to Venus' proximity to the Sun, being just on the inner edge of the habitability zone, but also to Venus' thick atmosphere, which is composed of heavy clouds of carbon dioxide and sulfur dioxide.

These gases create a strong greenhouse effect which traps a significant portion of the Sun's heat in the atmosphere and turns the planet surface into a barren, molten landscape. The surface is also marked by extensive volcanoes and lava flows, and rained on by clouds of sulfuric acid. Not a hospitable place by any measure!

Earth:

Earth is the third planet from the Sun, and so far is the only planet that we know of that is capable of supporting life. The average surface temperature here is about 14 °C, but it varies due to a number of factors. For one, our world's axis is tilted, which means that one hemisphere is slanted towards the Sun during certain times of the year while the other is slanted away.

This not only causes seasonal changes, but ensures that places located closer to the equator are hotter, while those located at the poles are colder. It's little wonder then why the hottest temperature ever recorded on Earth was in the deserts of Iran (70.7 °C) while the lowest was recorded in Antarctica (-89.2 °C).

Mars:

Mars' average surface temperature is -55 °C, but the Red Planet also experiences some variability, with temperatures ranging as high as 20 °C at the equator during midday, to as low as -153 °C at the poles. On average though, it is much colder than Earth, being just on the outer edge of the habitable zone, and because of its thin atmosphere - which is not sufficient to retain heat.

In addition, its surface temperature can vary by as much as 20 °C due to Mars' eccentric orbit around the Sun (meaning that it is closer to the Sun at certain points in its orbit than at others).

Jupiter:

Since Jupiter is a gas giant, it has no solid surface, so it has no surface temperature. But measurements taken from the top of Jupiter's clouds indicate a temperature of approximately -145°C. Closer to the center, the planet's temperature increases due to atmospheric pressure.

At the point where atmospheric pressure is ten times what it is on Earth, the temperature reaches 21°C, what we Earthlings consider a comfortable "room temperature". At the core of the planet, the temperature is much higher, reaching as much as 35,700°C - hotter than even the surface of the Sun.

Saturn:

Due to its distance from the Sun, Saturn is a rather cold gas giant planet, with an average temperature of -178 °Celsius. But because of Saturn's tilt, the southern and northern hemispheres are heated differently, causing seasonal temperature variation.

And much like Jupiter, the temperature in the upper atmosphere of Saturn is cold, but increases closer to the center of the planet. At the core of the planet, temperatures are believed to reach as high as 11,700 °C.

Uranus:

Uranus is the coldest planet in our Solar System, with a lowest recorded temperature of -224°C. Despite its distance from the Sun, the largest contributing factor to its frigid nature has to do with its core.

Much like the other gas giants in our Solar System, the core of Uranus gives off far more heat than is absorbed from the Sun. However, with a core temperature of approximately 4,737 °C, Uranus' interior gives of only one-fifth the heat that Jupiter's does and less than half that of Saturn.

Neptune:

With temperatures dropping to -218°C in Neptune's upper atmosphere, the planet is one of the coldest in our Solar System. And like all of the gas giants, Neptune has a much hotter core, which is around 7,000°C.

In short, the Solar System runs the gambit from extreme cold to extreme hot, with plenty of variance and only a few places that are temperate enough to sustain life. And of all of those, it is only planet Earth that seems to strike the careful balance required to sustain it perpetually.

Universe Today has many articles on the temperature of each planet, including the temperature of Mars and the temperature of Earth.

You may also want to check out these articles on facts about the planets and an overview of the planets.

NASA has a great graphic here that compares the temperatures of all the planets in our Solar System.

Astronomy Cast has episodes on all planets including Mercury.

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What is the Average Surface Temperature of the Planets in our Solar System? - Universe Today

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It's is no secret that Earth is the only inhabited planet in our Solar System. All the planets besides Earth lack a breathable atmosphere for terrestrial beings, but also, many of them are too hot or too cold to sustain life. A "habitable zone" which exists within every system of planets orbiting a star.

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Online 3D simulation of the Solar System and night sky in real time - the Sun, planets, dwarf planets, comets, stars and constellations

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Browse an exciting collection of scientific, historical and cultural facts about space, galaxies, the planets and other objects in the solar system. The latest discoveries, space-related features, graphics and diagrams can be found on the blog.

Start exploring below:

What is Outer Space

Space is the area beyond the upper limits of Earth's atmosphere. It is where all of the asteroids, comets, planets, stars, solar systems and galaxies in our universe are found. Space is a vacuum, meaning it contains almost nothing, but it is not completely empty.

Interesting Facts about Space

1. Space does not begin at a specific altitude above the Earth, but the Kármán line at 100 km is a commonly used definition.

2. The temperature in the void of space is about −270.45 °C.

3. Space is a hard vacuum, meaning it is a void containing very little matter.

4. There is no sound in space because molecules are too far apart to transmit sound.

5. The space between galaxies is not completely empty but has an average of one atom per cubic meter.

6. There are an estimated 100-400 billion stars in our galaxy, the Milky Way.

7. The universe is observed to be 13.8 billion years old and has been expanding since its formation in the Big Bang.

8. In the observable universe there are an estimated 2 trillion (2,000,000,000,000) galaxies.

9. The International Space Station is the largest ever crewed object in space.

10. Spacecraft have visited all the known planets in our solar system.

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Space Facts - Interesting Facts about Space!

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Interesting facts about space, galaxies, planets, moons and other solar system objects. Explore the universe through interesting diagrams, photos and more!

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How do celestial bodies warp the fabric of space-time and interact with each other?

Create an object to begin exploring.

This experiment works best in Chrome, Firefox, or Safari. Download the latest version of one of these browsers to begin.

Create your universe Download Chrome

National Science & Technology Medals Foundation Powered By

National Science & Technology Medals Foundation Powered By

Press and hold to create an object

Press, hold, and flick to add velocity

Observations

Runaway planet! That object's velocity is faster than any nearby gravitational force.

How fast does a rocket need to travel to leave Earth? Any projectile must reach a speed of seven miles per second to break free of our planet's gravity.

The gravity on Mars' moon, Deimos, is so low that if you jumped you could reach escape velocity!

Your object attained escape velocity. Its initial kinetic energy was large enough to escape from the gravitational energy well of the larger object. Space probes that completely escape from the earth's gravity and travel to other planets are examples of vehicles that achieve escape velocity.

You've created a binary system. These two celestial bodies weave around their common center of mass.

When you look up at the night sky, at least half of all the stars you see are binary stars orbiting one another.

You created an orbit. Orbits are like the Goldilocks of space, set in motion only when mass, distance, and velocity are just right. Orbits or often circular or elliptical. The earth's orbit around the sun, for example, deviates less than 2% from a circle.

Communications satellites aren't the only man-made objects orbiting Earth. Astronauts have left behind tools, gloves, and other space junk that might still be floating around.

Typically comets have elliptical orbits. These "dirty snowballs" come from the outer edge of the solar system, pass near the sun where they start to melt and produce a long tail, then return to the edge of the solar system where they refreeze.

Your object failed to attain escape velocity. Its initial kinetic energy was too little to escape from the gravitational energy well of the larger object. Rockets and missiles that return to earth are examples of vehicles that do not achieve escape velocity.

During the early days of our solar system, there were lots of collisions. The scattered debris mostly formed back together or attached to planets.

Don't worry. Nowadays our solar system is stable, and planets are unlikely to collide. However, you still need to watch for dangerous asteroids!

Some collisions don't break things apart but leave impact craters. Mars has been shaped by impact. Its northern half is smooth and low, its southern half mountainous and rough -- so different they're like two separate planets!

According to Newton, the larger the mass of objects and the shorter the distance between them, the stronger the attraction.

Objects move proportionately to their mass. Tiny planets move great distances. Massive planets may only wobble.

When slow-moving celestial bodies collide, they might fuse together and enlarge, increasing from a few kilometers to a few hundred kilometers in diameter.

Earth-like planets begin as particles formed from the collision of gas and dust and grow by accretion. A mature planet can take thousands or even millions of years to form.

Notice how the universe distorts when a object forms or grows in size? According to Einstein, all celestial bodies warp the fabric of space-time. The resulting curves are gravity.

Two celestial bodies of different masses have distinct effects upon space-time. A massive object creates a greater distortion of space-time and can shift the path of smaller objects if they're close enough.

Gravity penetrates everything and holds the galaxy together.

Everything in the universe - moons, planets, particles, galaxies, even light - is drawn towards everything else by the force of gravity.

Your planetary collision has created a moon, or natural satellite. Moons can be anywhere from centimeters to thousands of kilometers in width.

Over 4 billion years ago, something the size of Mars bumped into Earth and left behind the moon that orbits us.

Moons can also be captured by a hefty planet's gravitational pull. The largest irregular moon in our solar system is thought to be Neptune's moon, Triton, which originated in the Kuiper belt of comets.

Orbit shapes are typically ellipses. Orbiting objects zip towards a gravitational center and slow when pulling away.

An orbit system is a gravitationally-bound collection of celestial bodies.

The Sun is the center of planetary orbit in our solar system. But each planet has its own gravitational field, and most have their own natural satellites.

How do celestial bodies warp the fabric of space-time and interact with each other?

We tend think of gravity as a force of attraction, but it's also been described as a curvature of space-time in the presence of mass. This National Science and Technology Medals Foundation interactive invites you to bend the fabric of space-time and observe the resulting gravitational forces. By adjusting the variables of mass, distance, and velocity, you can trigger orbits, collisions, and escape velocities in space.

The National Science and Technology Medals Foundation celebrates the amazing individuals who have won the highest science, technology, engineering, and mathematics award in the United States.

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How do celestial bodies warp the fabric of space-time and interact with each other? Create an object to begin exploring. This experiment works best in Chrome, Firefox, or Safari. Download the latest version of one of these browsers to begin.

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Le terme de planète n'est pas clairement définit car il recoupe différentes réalités en fonction de ce que l'on prend en compte.

Il existe une définition officielle de ce que l'on appelle planète dans le système solaire et une définition pour les exoplanètes, c'est à dire des planètes qui tournent autour d'autres étoiles que le Soleil.

Définition intuitive d'une planète

Intuitivement, une planète est un corps de forme sphérique en orbite autour d'une étoile.

Cette définition fonctionne pour de nombreux objets de taille modeste mais il existe des objets très massifs qui ne sont pas tout à fait des étoiles mais qui ne sont pas non plus assimilables à l'idée que l'on se fait d'une planète : les super-Jupiter ou naines brunes, des objets faisant plusieurs fois la masse de Jupiter.

On a donc définit une limite supérieure à ce que peut être une planète en précisant qu'une planète est un corps qui n'a pas entamé de fusion du deutérium en son sein. Si c'est le cas, on parle de naine brune.

La limite entre une planète très massive et une naine brune est donc relativement ténue.

Définition officielle de l'Union Astronomique Internationale (UAI)

Un organisme officiel, l'Union astronomique internationale (UAI), a entreprit d'arrêter une définition officielle de ce qu'est une planète dans le système solaire.

Depuis le 24 août 2006, une planète est définit comme étant un corps qui :

est en orbite autour du Soleil,

a une masse suffisamment importante pour avoir une forme relativement sphérique (équilibre hydrostatique)

a dégagé son orbite et son voisinage d'éventuels autres objets

Cette définition, bien qu'officielle, est pourtant critiquée par la communauté des astronomes car ses critères sont arbitraires et sujets à discussion, notamment le 3 point. C'est ce point qui a exclus Pluton des planètes du système Solaire.

Longtemps considérée comme la neuvième planète du système solaire, Pluton a perdu son statut et est devenu le premier objet faisant partie d'un nouveau groupe appelé " planètes naines ".

La raison de cette distinction est que les astronomes se sont rendus compte qu'il devait y a voir de très nombreux objets sphériques en orbite autour du Soleil au-delà de l'orbite de Neptune, dans la ceinture de Kuiper et peut-être encore plus loin. Cette profusion de planètes potentielles a fait craindre une augmentation drastique du nombre de planète ce qui semblait poser un problème aux astronomes. Il leur est donc apparu nécessaire de repenser la classification de façon a pouvoir classer les objets du système solaire de façon compréhensible, bien que l'aspect scientifique semble avoir laissé la place à des considérations plus idéologiques...

Définition des " planètes naines "

La définition de l'UAI a conduit à la création d'un nouveau type d'objet, les planètes naines.

Selon l'UAI, une " planète naine " est un corps qui ne satisfait que les 2 premiers critères de la définition de " planète ".

Les planètes naines sont donc des objets :

en orbite autour du Soleil,

en équilibre hydrostatique (de forme plus ou moins sphérique)

mais qui n'ont pas dégagé le voisinage de leur orbite

Les 5 planètes naines officiellement reconnues sont :

Pluton (ancienne planète mais reclassée depuis 2006)

Cérès, le plus gros objet de la ceinture d'astéroïdes entre Mars et Jupiter

Hauméa, un objet qui bien qu'ovale et non sphérique est tout de même en équilibre hydrostatique

Makémaké

Eris

Il y a plus de 340 candidats potentiel dont Charon, le plus gros satellite de Pluton, Quaoar, Sedna, Orcus, Varuna, Salacie, etc.

Il y aurait des milliers d'objet pouvant correspondre à la définition de planète naine dans le système solaire.

Comparaison du diamètre des planètes du système solaire

Planètes telluriques du système solaire

Les planètes telluriques du système solaire sont les 4 planètes rocheuses situées entre le Soleil et la ceinture d'astéroïdes.

Les 4 planètes telluriques rocheuses sont :

Ce sont des planètes dites rocheuses car elle sont principalement constituées de roches et de métaux.

On parle de planètes telluriques en référence à la Terre, tellurique signifiant " similaire à la Terre ".

Elles sont relativement petites par rapport aux autres planètes du système solaire : les planètes géantes.

Comparaison de la tailles des planètes du système solaire interne

Planètes géantes du système solaire

Les planètes géantes du systèmes solaire sont les 4 planètes situées entre la ceinture d'astéroïdes et l'orbite de Pluton.

Les 4 planètes externes sont :

Ce sont des planètes dites gazeuses, constituées d'une épaisse atmosphère et d'un noyaux constitué de métaux.

Toutes les planètes géantes semblent posséder des anneaux mais ils sont très différents d'une planètes à l'autre. Saturne, la planète aux anneaux est la plus spectaculaire tandis que les anneaux de Jupiter ou de Neptune sont très difficiles à observer et n'ont été découverts que récemment.

Chaque planète géante est un mini-système solaire à lui seul et comporte un grand nombre de satellites naturels dont certains sont plus gros que Mercure.

Planètes géantes

Les 4 planètes du système solaire externe sont appelées des " planètes géantes " mais les astronomes font une différence entre Jupiter et Saturne d'un côté et Uranus et Neptune de l'autre :

Jupiter et Saturne sont désignées comme étant " planètes géantes gazeuses " ou " planètes géantes de gaz "

Uranus et Neptune sont appelées des " planètes géantes de glace ".

Cette distinction n'est pas officielle mais ces 2 sous catégories semblent correspondre aux différences de caractéristiques que l'on observe entre ces 4 planètes.

Comparaison de la tailles des planètes du système solaire externe

Les anneaux des planètes géantes

Toutes les planètes géantes semblent posséder des anneaux mais ils sont très différents d'une planètes à l'autre. Saturne, la planète aux anneaux est la plus spectaculaire tandis que les anneaux de Jupiter ou de Neptune sont très difficiles à observer et n'ont été découverts que récemment.

Cliquez sur les images pour en savoir plus sur les anneaux de chaque planète :

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Planètes et satellites du Système Solaire - Planète Astronomie

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Le terme de planète n'est pas clairement définit car il recoupe différentes réalités en fonction de ce que l'on prend en compte. Il existe une définition officielle de ce que l'on appelle planète dans le système solaire et une définition pour les exoplanètes, c'est à dire des planètes qui tournent autour d'autres étoiles que le Soleil.

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Représentation des différentes planètes du système solaire

Les planètes joviennes (géantes gazeuses)

Représentation des planètes naines connues et des objets célestes étant susceptibles de faire partie de cette catégorie d'astres

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Les planètes ont des caractéristiques communes. Mercure, Vénus, Terre, Mars, Jupiter, Saturne, Uranus et Neptune sont celles du système solaire.

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Selon la nouvelle définition de l'Union Astronomique Internationale, une planète est un corps céleste qui est en orbite autour du Soleil, qui possède une masse suffisante pour que sa gravité l'emporte sur les forces de cohésion du corps solide et le maintienne en équilibre hydrostatique (forme ronde), et qui a éliminé tout corps se déplaçant sur une orbite proche.

Cette définition fut approuvée le 24 août 2006, en clôture de la 26 ème Assemblée Générale de l'UAI par un vote à main levée de 2500 scientifiques et astronomes après dix jours de discussions.

Selon cette nouvelle définition, le système solaire contient donc dorénavant 8 planètes : Mercure, Vénus, la Terre, Mars, Jupiter, Saturne, Uranus et Neptune.

En complément, l'UAI a créé une nouvelle classe d'objets : les planètes naines dont les premiers membres sont Pluton, Eris, Makemake, Haumea et (1) Cérès.

Par extension, tout astre répondant à ces critères et gravitant autour d'une autre étoile est qualifié d'exoplanète.

Le mot planète a pour origine le mot latin planetus, lui-même dérivé du mot grec planeta qui dans l'expression planêtes asteres désigne des " astres en mouvement " (ou " astres errants "), par opposition aux étoiles qui apparaissent immobiles sur la voûte céleste.

Ce mouvement, très apparent à l'œil nu, a été observé très tôt par les hommes de toutes les civilisations, mais sa complexité est longtemps restée un mystère pour les astronomes jusqu'à l'identification de ce mouvement apparent à la résultante des courses elliptiques de la Terre et des autres planètes autour du Soleil.

Si certaines planètes du système solaire sont visibles la nuit dans le ciel, c'est parce qu'elles réfléchissent la lumière du Soleil, contrairement aux étoiles qui brillent de leur propre feu.

La définition d'une planète telle que reprise ci-dessus dit en substance qu'un corps doit présenter une masse d'au moins 5x10 ²⁰ kg et un diamètre d'au moins 800 km pour être considéré comme une planète. Mais ce n'est pas tout. Le barycentre ou centre de gravité du système doit également se situer en dehors de l'astre primaire.

Pour le dictionnaire, dont les définitions n'ont qu'une valeur académique mais certainement pas scientifique, une planète est un " objet céleste compact, dépourvu de réactions thermonucléaires (ou anciennement : sans lumière propre), gravitant autour du Soleil ou, par extension, d'une étoile ".

Jusqu'en 2006, l'Académie nationale des sciences américaine définissait une planète comme étant un corps de moins de 2 masses joviennes gravitant autour d'une étoile. Mais cette définition ne tenait pas compte des récentes découvertes dont Eris découverte en 2005, de Sedna et d'autres KBO.

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Selon la nouvelle définition de l'Union Astronomique Internationale, une planète est un corps céleste qui est en orbite autour du Soleil, qui possède une masse suffisante pour que sa gravité l'emporte sur les forces de cohésion du corps solide et le maintienne en équilibre hydrostatique (forme ronde), et qui a éliminé tout corps se déplaçant sur une orbite proche.

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There are more planets than stars in our galaxy. The current count orbiting our star: eight.

The inner, rocky planets are Mercury, Venus, Earth and Mars. The outer planets are gas giants Jupiter and Saturn and ice giants Uranus and Neptune.

Beyond Neptune, a newer class of smaller worlds called dwarf planets reign, including perennial favorite Pluto.

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There are more planets than stars in our galaxy. The current count orbiting our star: eight. The inner, rocky planets are Mercury, Venus, Earth and Mars. The outer planets are gas giants Jupiter and Saturn and ice giants Uranus and Neptune. Beyond Neptune, a newer class of smaller worlds called dwarf planets reign, including perennial favorite Pluto.

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Pourquoi y-a-t-il des marées ? - C'est pas sorcier

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Pourquoi y-a-t-il des marées ? Jamy vous explique ! Pour tout savoir sur le Mont Saint-Michel : https://www.youtube.com/watch?v=PtWrL1E-I4k Retrouvez les émissions sur YouTube https://www.youtube.com/user/cestpassorcierftv Suivez-nous sur Facebook https://www.facebook.com/cestpassorcier/ et Twitter @cestpassorcier

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Black holes are some of the strangest and most fascinating objects in space. They're extremely dense, with such strong gravitational attraction that not even light can escape their grasp.

The Milky Way could contain over 100 million black holes, though detecting these gluttonous beasts is very difficult. At the heart of the Milky Way lies a supermassive black hole - Sagittarius A*. The colossal structure is about 4 million times the mass of the sun and lies approximately 26,000 light-years away from , according to a statement from NASA.

The first image of a black hole was captured in 2019 by the Event Horizon Telescope (EHT) collaboration. The striking photo of the black hole at the center of the M87 galaxy 55 million light-years from Earth thrilled scientists around the world.

Related: White holes: What we know about black holes' neglected twins

Black hole FAQs answered by an expert

We asked theoretical astrophysicist Priyamvada Natarajan a few commonly asked questions about black holes.

Theoretical Astrophysicist

First black hole discovered

Albert Einstein first predicted the existence of black holes in 1916, with his general theory of relativity. The term "black hole" was coined many years later in 1967 by American astronomer John Wheeler. After decades of black holes being known only as theoretical objects.

The first black hole ever discovered was Cygnus X-1, located within the Milky Way in the constellation of Cygnus, the Swan. Astronomers saw the first signs of the black hole in 1964 when a sounding rocket detected celestial sources of X-rays according to NASA. In 1971, astronomers determined that the X-rays were coming from a bright blue star orbiting a strange dark object. It was suggested that the detected X-rays were a result of stellar material being stripped away from the bright star and "gobbled" up by the dark object - an all-consuming black hole.

How many black holes are there?

According to the Space Telescope Science Institute (STScI) approximately one out of every thousand stars is massive enough to become a black hole. Since the Milky Way contains over 100 billion stats, our home galaxy must harbor some 100 million black holes.

Though detecting black holes is a difficult task and estimates from NASA suggest there could be as many as 10 million to a billion stellar black holes in the Milky Way.

The closest black hole to Earth is dubbed " The Unicorn" and is situated approximately 1,500 light-years away. The nickname has a double meaning. Not only does the black hole candidate reside in the constellation Monoceros ("the unicorn"), its incredibly low mass - about three times that of the sun - makes it nearly one of a kind.
Related: How many black holes are there in the universe?
Black hole images

In 2019 the Event Horizon Telescope (EHT) collaboration released the first image ever recorded of a black hole. The EHT saw the black hole in the center of galaxy M87 while the telescope was examining the event horizon or the area past which nothing can escape from a black hole. The image maps the sudden loss of photons (particles of light). It also opens up a whole new area of research in black holes, now that astronomers know what a black hole looks like.

In 2021, astronomers revealed a new view of the giant black hole at the center of M87, showing what the colossal structure looks like in polarized light. As polarized light waves have a different orientation and brightness compared to unpolarized light, the new image shows the black hole in even more detail. Polarization is a signature of magnetic fields and the image makes it clear that the black hole's ring is magnetized.

In May 2022, scientists revealed the historic first image of the supermassive black hole at the center of our galaxy - Sagitarrius A*.

Related: The 1st photo of the Milky Way's monster black hole explained in images

What do black holes look like?

Black holes have three "layers": the outer and inner event horizon, and the singularity.

The event horizon of a black hole is the boundary around the mouth of the black hole, past which light cannot escape. Once a particle crosses the event horizon, it cannot leave. Gravity is constant across the event horizon.

The inner region of a black hole, where the object's mass lies, is known as its singularity, the single point in space-time where the mass of the black hole is concentrated.

Scientists can't see black holes the way they can see stars and other objects in space. Instead, astronomers must rely on detecting the radiation black holes emit as dust and gas are drawn into the dense creatures. But supermassive black holes, lying in the center of a galaxy, may become shrouded by the thick dust and gas around them, which can block the telltale emissions.

Sometimes, as matter is drawn toward a black hole, it ricochets off the event horizon and is hurled outward, rather than being tugged into the maw. Bright jets of material traveling at near-relativistic speeds are created. Although the black hole remains unseen, these powerful jets can be viewed from great distances.

The EHT's image of a black hole in M87 (released in 2019) was an extraordinary effort, requiring two years of research even after the images were taken. That's because the collaboration of telescopes, which stretches across many observatories worldwide, produces an astounding amount of data that is too large to transfer via the internet.

With time, researchers expect to image other black holes and build up a repository of what the objects look like. The next target is likely Sagittarius A*, which is the black hole in the center of our own Milky Way galaxy. Sagittarius A* is intriguing because it is quieter than expected, which may be due to magnetic fields smothering its activity, a 2019 study reported. Another study that year showed that a cool gas halo surrounds Sagittarius A*, which gives unprecedented insight into what the environment around a black hole looks like.

Types of black holes

So far, astronomers have identified three types of black holes: stellar black holes, supermassive black holes and intermediate black holes.

Stellar black holes - small but deadly

When a star burns through the last of its fuel, the object may collapse, or fall into itself. For smaller stars (those up to about three times 's mass), the new core will become a neutron star or a white dwarf. But when a larger star collapses, it continues to compress and creates a stellar black hole.

Black holes formed by the collapse of individual stars are relatively small but incredibly dense. One of these objects packs more than three times the mass of the sun into the diameter of a city. This leads to a crazy amount of gravitational force pulling on objects around the object. Stellar black holes then consume the dust and gas from their surrounding galaxies, which keeps them growing in size.

Supermassive black holes - the birth of giants

Small black holes populate the universe, but their cousins, supermassive black holes, dominate. These enormous black holes are millions or even billions of times as massive as the sun but are about the same size in diameter. Such black holes are thought to lie at the center of pretty much every galaxy, including the Milky Way.

Scientists aren't certain how such large black holes spawn. Once these giants have formed, they gather mass from the dust and gas around them, material that is plentiful in the center of galaxies, allowing them to grow to even more enormous sizes.

Supermassive black holes may be the result of hundreds or thousands of tiny black holes that merge. Large gas clouds could also be responsible, collapsing together and rapidly accreting mass. A third option is the collapse of a stellar cluster, a group of stars all falling together. Fourth, supermassive black holes could arise from large clusters of dark matter. This is a substance that we can observe through its gravitational effect on other objects; however, we don't know what dark matter is composed of because it does not emit light and cannot be directly observed.

Scientists once thought that black holes came in only small and large sizes, but research has revealed the possibility that midsize, or intermediate, black holes (IMBHs) could exist. Such bodies could form when stars in a cluster collide in a chain reaction. Several of these IMBHs forming in the same region could then eventually fall together in the center of a galaxy and create a supermassive black hole.

In 2014, astronomers found what appeared to be an intermediate-mass black hole in the arm of a spiral galaxy. And in 2021 astronomers took advantage of an ancient gamma-ray burst to detect one.

"Astronomers have been looking very hard for these medium-sized black holes," study co-author Tim Roberts, of the University of Durham in the United Kingdom, said in a statement. "There have been hints that they exist, but IMBHs have been acting like a long-lost relative that isn't interested in being found."

Research, from 2018, suggested that these IMBHs may exist in the heart of dwarf galaxies (or very small galaxies). Observations of 10 such galaxies (five of which were previously unknown to science before this latest survey) revealed X-ray activity - common in black holes - suggesting the presence of black holes of from 36,000 to 316,000 solar masses. The information came from the Sloan Digital Sky Survey, which examines about 1 million galaxies and can detect the kind of light often observed coming from black holes that are picking up nearby debris.

Binary black holes: double trouble

In 2015, astronomers using the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected gravitational waves from merging stellar black holes.

"We have further confirmation of the existence of stellar-mass black holes that are larger than 20 solar masses - these are objects we didn't know existed before LIGO detected them," David Shoemaker, the spokesperson for the LIGO Scientific Collaboration (LSC), said in a statement. LIGO's observations also provide insights into the direction a black hole spins. As two black holes spiral around one another, they can spin in the same direction or the opposite direction.

There are two theories on how binary black holes form. The first suggests that the two black holes in a binary form at about the same time, from two stars that were born together and died explosively at about the same time. The companion stars would have had the same spin orientation as one another, so the two black holes left behind would as well.

Under the second model, black holes in a stellar cluster sink to the center of the cluster and pair up. These companions would have random spin orientations compared to one another according to LIGO Scientific Collaboration. LIGO's observations of companion black holes with different spin orientations provide stronger evidence for this formation theory.

"We're starting to gather real statistics on binary black hole systems," said LIGO scientist Keita Kawabe of Caltech, who is based at the LIGO Hanford Observatory. "That's interesting because some models of black hole binary formation are somewhat favored over the others even now, and in the future, we can further narrow this down."

If you fell into a black hole, theory has long suggested that gravity would stretch you out like spaghetti, though your death would come before you reached the singularity. But a 2012 study published in the journal Nature suggested that quantum effects would cause the event horizon to act much like a wall of fire, which would instantly burn you to death.

Black holes don't suck. Suction is caused by pulling something into a vacuum, which the massive black hole definitely is not. Instead, objects fall into them just as they fall toward anything that exerts gravity, like the Earth.

The first object considered to be a black hole is Cygnus X-1. Cygnus X-1 was the subject of a 1974 friendly wager between Stephen Hawking and fellow physicist Kip Thorne, with Hawking betting that the source was not a black hole. In 1990, Hawking conceded defeat.

Miniature black holes may have formed immediately after the Big Bang. Rapidly expanding space may have squeezed some regions into tiny, dense black holes less massive than the sun.

If a star passes too close to a black hole, the star can be torn apart.

Astronomers estimate that the Milky Way has anywhere from 10 million to 1 billion stellar black holes, with masses roughly three times that of the sun.

Black holes remain terrific fodder for science fiction books and movies. Check out the movie "Interstellar," which relied heavily on Thorne to incorporate science. Thorne's work with the movie's special effects team led to scientists' improved understanding of how distant stars might appear when seen near a fast-spinning black hole.

Black hole facts

Additional resources

Dive deeper into the mystery of black holes with NASA Science. Watch videos and read more about black holes from NASA's Hubblesite. Discover more about black holes with the National Science Foundation.

Bibliography

Hubblesite: Black holes: Gravity's relentless pull interactive: Encyclopedia. STScI Home. Retrieved May 6, 2022.

NASA. Imagine the universe! NASA. Retrieved May 6, 2022.

Boen, B. (2013, August 29). Supermassive black hole Sagittarius A*. NASA. Retrieved May 6, 2022.

NASA's Chandra Finds Intriguing Member of Black Hole Family Tree. Chandra X-ray Observatory. (2015, February 25). Retrieved May 6, 2022.

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Black holes: Everything you need to know

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Black holes are real, they're some of the strangest objects in space. Discover what black holes are and how they form with our informative black hole guide.

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Carter Emmart: A 3D atlas of the universe

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For the last 12 years, Carter Emmart has been coordinating the efforts of scientists, artists and programmers to build a complete 3D visualization of our known universe. He demos this stunning tour and explains how it's being shared with facilities around the world.

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Planetary scientist Carolyn Porco shows images from the Cassini voyage to Saturn, focusing on its largest moon, Titan, and on frozen Enceladus, which seems to shoot jets of ice.

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The True Size Of The Universe As We Know It

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The Hopewell Rocks - OFFICIAL Time Lapse video of 45.6 foot tide

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Exoplanet Exploration: Planets Beyond our Solar System

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From Kimm Fesenmaier, Caltech
Caltech researchers have found evidence of a giant planet tracing a bizarre, highly elongated orbit in the outer solar system. The object, which the researchers have nicknamed Planet Nine, has a mass about 10 times that of Earth and orbits about 20 times farther from the sun on average than does Neptune (which orbits the sun at an average distance of 2.8 billion miles). In fact, it would take this new planet between 10,000 and 20,000 years to make just one full orbit around the sun.

The researchers, Konstantin Batygin and Mike Brown, discovered the planet's existence through mathematical modeling and computer simulations but have not yet observed the object directly.

"This would be a real ninth planet," says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy. "There have only been two true planets discovered since ancient times, and this would be a third. It's a pretty substantial chunk of our solar system that's still out there to be found, which is pretty exciting."

Brown notes that the putative ninth planet-at 5,000 times the mass of Pluto-is sufficiently large that there should be no debate about whether it is a true planet. Unlike the class of smaller objects now known as dwarf planets, Planet Nine gravitationally dominates its neighborhood of the solar system. In fact, it dominates a region larger than any of the other known planets-a fact that Brown says makes it "the most planet-y of the planets in the whole solar system."

Batygin and Brown describe their work in the current issue of the Astronomical Journal and show how Planet Nine helps explain a number of mysterious features of the field of icy objects and debris beyond Neptune known as the Kuiper Belt.

"Although we were initially quite skeptical that this planet could exist, as we continued to investigate its orbit and what it would mean for the outer solar system, we become increasingly convinced that it is out there," says Batygin, an assistant professor of planetary science. "For the first time in over 150 years, there is solid evidence that the solar system's planetary census is incomplete."

The road to the theoretical discovery was not straightforward. In 2014, a former postdoc of Brown's, Chad Trujillo, and his colleague Scott Sheppard published a paper noting that 13 of the most distant objects in the Kuiper Belt are similar with respect to an obscure orbital feature. To explain that similarity, they suggested the possible presence of a small planet. Brown thought the planet solution was unlikely, but his interest was piqued.

He took the problem down the hall to Batygin, and the two started what became a year-and-a-half-long collaboration to investigate the distant objects. As an observer and a theorist, respectively, the researchers approached the work from very different perspectives-Brown as someone who looks at the sky and tries to anchor everything in the context of what can be seen, and Batygin as someone who puts himself within the context of dynamics, considering how things might work from a physics standpoint. Those differences allowed the researchers to challenge each other's ideas and to consider new possibilities. "I would bring in some of these observational aspects; he would come back with arguments from theory, and we would push each other. I don't think the discovery would have happened without that back and forth," says Brown. " It was perhaps the most fun year of working on a problem in the solar system that I've ever had."

Fairly quickly Batygin and Brown realized that the six most distant objects from Trujillo and Shepherd's original collection all follow elliptical orbits that point in the same direction in physical space. That is particularly surprising because the outermost points of their orbits move around the solar system, and they travel at different rates.

"It's almost like having six hands on a clock all moving at different rates, and when you happen to look up, they're all in exactly the same place," says Brown. The odds of having that happen are something like 1 in 100, he says. But on top of that, the orbits of the six objects are also all tilted in the same way-pointing about 30 degrees downward in the same direction relative to the plane of the eight known planets. The probability of that happening is about 0.007 percent. "Basically it shouldn't happen randomly," Brown says. "So we thought something else must be shaping these orbits."

The first possibility they investigated was that perhaps there are enough distant Kuiper Belt objects-some of which have not yet been discovered-to exert the gravity needed to keep that subpopulation clustered together. The researchers quickly ruled this out when it turned out that such a scenario would require the Kuiper Belt to have about 100 times the mass it has today.

That left them with the idea of a planet. Their first instinct was to run simulations involving a planet in a distant orbit that encircled the orbits of the six Kuiper Belt objects, acting like a giant lasso to wrangle them into their alignment. Batygin says that almost works but does not provide the observed eccentricities precisely. "Close, but no cigar," he says.

Then, effectively by accident, Batygin and Brown noticed that if they ran their simulations with a massive planet in an anti-aligned orbit-an orbit in which the planet's closest approach to the sun, or perihelion, is 180 degrees across from the perihelion of all the other objects and known planets-the distant Kuiper Belt objects in the simulation assumed the alignment that is actually observed.

"Your natural response is 'This orbital geometry can't be right. This can't be stable over the long term because, after all, this would cause the planet and these objects to meet and eventually collide,'" says Batygin. But through a mechanism known as mean-motion resonance, the anti-aligned orbit of the ninth planet actually prevents the Kuiper Belt objects from colliding with it and keeps them aligned. As orbiting objects approach each other they exchange energy. So, for example, for every four orbits Planet Nine makes, a distant Kuiper Belt object might complete nine orbits. They never collide. Instead, like a parent maintaining the arc of a child on a swing with periodic pushes, Planet Nine nudges the orbits of distant Kuiper Belt objects such that their configuration with relation to the planet is preserved.

"Still, I was very skeptical," says Batygin. "I had never seen anything like this in celestial mechanics."

But little by little, as the researchers investigated additional features and consequences of the model, they became persuaded. "A good theory should not only explain things that you set out to explain. It should hopefully explain things that you didn't set out to explain and make predictions that are testable," says Batygin.

And indeed Planet Nine's existence helps explain more than just the alignment of the distant Kuiper Belt objects. It also provides an explanation for the mysterious orbits that two of them trace. The first of those objects, dubbed Sedna, was discovered by Brown in 2003. Unlike standard-variety Kuiper Belt objects, which get gravitationally "kicked out" by Neptune and then return back to it, Sedna never gets very close to Neptune. A second object like Sedna, known as 2012 VP113, was announced by Trujillo and Shepherd in 2014. Batygin and Brown found that the presence of Planet Nine in its proposed orbit naturally produces Sedna-like objects by taking a standard Kuiper Belt object and slowly pulling it away into an orbit less connected to Neptune.

But the real kicker for the researchers was the fact that their simulations also predicted that there would be objects in the Kuiper Belt on orbits inclined perpendicularly to the plane of the planets. Batygin kept finding evidence for these in his simulations and took them to Brown. "Suddenly I realized there are objects like that," recalls Brown. In the last three years, observers have identified four objects tracing orbits roughly along one perpendicular line from Neptune and one object along another. "We plotted up the positions of those objects and their orbits, and they matched the simulations exactly," says Brown. "When we found that, my jaw sort of hit the floor."

"When the simulation aligned the distant Kuiper Belt objects and created objects like Sedna, we thought this is kind of awesome-you kill two birds with one stone," says Batygin. "But with the existence of the planet also explaining these perpendicular orbits, not only do you kill two birds, you also take down a bird that you didn't realize was sitting in a nearby tree."

Where did Planet Nine come from and how did it end up in the outer solar system? Scientists have long believed that the early solar system began with four planetary cores that went on to grab all of the gas around them, forming the four gas planets-Jupiter, Saturn, Uranus, and Neptune. Over time, collisions and ejections shaped them and moved them out to their present locations. "But there is no reason that there could not have been five cores, rather than four," says Brown. Planet Nine could represent that fifth core, and if it got too close to Jupiter or Saturn, it could have been ejected into its distant, eccentric orbit.

Batygin and Brown continue to refine their simulations and learn more about the planet's orbit and its influence on the distant solar system. Meanwhile, Brown and other colleagues have begun searching the skies for Planet Nine. Only the planet's rough orbit is known, not the precise location of the planet on that elliptical path. If the planet happens to be close to its perihelion, Brown says, astronomers should be able to spot it in images captured by previous surveys. If it is in the most distant part of its orbit, the world's largest telescopes-such as the twin 10-meter telescopes at the W. M. Keck Observatory and the Subaru Telescope, all on Mauna Kea in Hawaii-will be needed to see it. If, however, Planet Nine is now located anywhere in between, many telescopes have a shot at finding it.

"I would love to find it," says Brown. "But I'd also be perfectly happy if someone else found it. That is why we're publishing this paper. We hope that other people are going to get inspired and start searching."

In terms of understanding more about the solar system's context in the rest of the universe, Batygin says that in a couple of ways, this ninth planet that seems like such an oddball to us would actually make our solar system more similar to the other planetary systems that astronomers are finding around other stars. First, most of the planets around other sunlike stars have no single orbital range-that is, some orbit extremely close to their host stars while others follow exceptionally distant orbits. Second, the most common planets around other stars range between 1 and 10 Earth-masses.

"One of the most startling discoveries about other planetary systems has been that the most common type of planet out there has a mass between that of Earth and that of Neptune," says Batygin. "Until now, we've thought that the solar system was lacking in this most common type of planet. Maybe we're more normal after all."

Brown, well known for the significant role he played in the demotion of Pluto from a planet to a dwarf planet adds, "All those people who are mad that Pluto is no longer a planet can be thrilled to know that there is a real planet out there still to be found," he says. "Now we can go and find this planet and make the solar system have nine planets once again."

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Far beyond Pluto, a possible Planet Nine awaits discovery

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From Kimm Fesenmaier, Caltech Caltech researchers have found evidence of a giant planet tracing a bizarre, highly elongated orbit in the outer solar system. The object, which the researchers have nicknamed Planet Nine, has a mass about 10 times that of Earth and orbits about 20 times farther from the sun on average than does Neptune (which orbits the sun at an average distance of 2.8 billion miles).

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5) Les planètes et lunes du système solaire

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5) Les planètes et lunes du système solaire