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The moon crosses the sun in during a partial solar eclipse in space in this view from NASA's Solar Dynamics Observatory in space. The lunar transit lasted nearly an hour, with the moon covering about 89 percent of the sun's disk at the eclipse's peak.

Credit: NASA Goddard Space Flight Center/SDO/Joy Ng, producer

NASA's powerful Solar Dynamics Observatory (SDO) may seem to have a boring job: staring at the sun as a space weather sentinel. But every now and then, the observatory gets a lunar surprise to break up the routine.

That's what happened Thursday (May 25), when the moon passed between SDO and the sun in a brief - but awesome - partial solar eclipse in space. The lunar crossing, or transit, lasted nearly an hour, with the moon covering about 89 percent of the sun at the eclipse's peak.

On Friday (May 26), NASA released an animation of the partial solar eclipse as seen in SDO images. The eclipse began Thursday at 2:24 p.m. EDT (1824 GMT) and ended at 3:17 p.m. EDT (1917 GMT). [ The 8 Most Famous Solar Eclipses in History]

"While the moon's edge appears smooth in these images, it's actually quite uneven," NASA officials wrote in an image description. "The surface of the moon is rugged, sprinkled with craters, valleys and mountains. Peer closely at the image, and you may notice the subtle, bumpy outline of these topographical features."(VideoTag|4902))

SDO's partial solar eclipse view is a teaser of sorts for a grand event coming later this summer. The moon will completely block the sun in a total solar eclipse on Aug. 21 that will be visible from a narrow, 70-mile-wide (113 kilometers) strip of land across 19 states in the United States, stretching from northwest to southeast from Oregon to South Carolina. Observers elsewhere in North America, South America, Africa, Europe and Asia will see a partial solar eclipse, NASA officials said, adding that SDO will also see a partial eclipse.

NASA's SDO spacecraft is one of a fleet of sun-watching observatories monitoring the sun's solar activity.

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NASA Sun Observatory Sees Partial Solar Eclipse in Space

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NASA's powerful Solar Dynamics Observatory (SDO) may seem to have a boring job: staring at the sun as a space weather sentinel. But every now and then, the observatory gets a lunar surprise to break up the routine.

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Being put aboard the ISS to study neutron stars!

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NASA.gov brings you the latest images, videos and news from America's space agency. Get the latest updates on NASA missions, watch NASA TV live, and learn about our quest to reveal the unknown and benefit all humankind.

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Reclassification of the planets and definition of the term planet:

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ESOcast 107 Light: Secondary Mirror of ELT Successfully Cast

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This video is available for download in various formats on: https://www.eso.org/public/videos/eso1715a/ Credit: ESO Editing: Nico Bartmann. Web and technical support: Mathias André and Raquel Yumi Shida. Written by: Lauren Fuge, Hannah Dalgleish, and Richard Hook. Music: Tim Turusov - Saturn Hotline (http://www.turusov.com/). Footage and photos: ESO, SCHOTT.

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http://news.nationalgeographic.com/2016/12/skywatching-sky-guide-2017-top-events-space-astronomy/

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Youtube playlist, only short clips

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Wonders of the Solar System - Trailer - BBC Two

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More about this programme: http://www.bbc.co.uk/programmes/b00qyxfb In this spell-binding series, Professor Brian Cox visits some of the most stunning locations on Earth to describe how the laws of nature have carved natural wonders across the Solar System.

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http://www.skyatnightmagazine.com/feature/how-guide/how-observe-sun-safely

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Explore The Milky Way Galaxy - Documentary HD #Advexon

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https://www.galaxyzoo.org/#/classify

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From Big Bang to formation of our solar system

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Into The Universe With Stephen Hawking   The Story of Everything

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Thanks to Melchior for finding this:
https://www.youtube.com/playlist?list=PL1EVrlgWMPSlSrpzsSlQk-oMJHkdIsSCM

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Author Bio

Elizabeth Howell, Space.com Contributor

Elizabeth Howell is a contributing writer for Space.com who is one of the few Canadian journalists to report regularly on space exploration. She is pursuing a Ph.D. part-time in aerospace sciences (University of North Dakota) after completing an M.Sc. (space studies) at the same institution. She also holds a bachelor of journalism degree from Carleton University. Besides writing, Elizabeth teaches communications at the university and community college level. To see her latest projects, follow Elizabeth on Twitter at @HowellSpace.

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10 Amazing Space Discoveries by the Keck Observatory

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Author Bio Elizabeth Howell, Space.com Contributor Elizabeth Howell is a contributing writer for Space.com who is one of the few Canadian journalists to report regularly on space exploration. She is pursuing a Ph.D. part-time in aerospace sciences (University of North Dakota) after completing an M.Sc. (space studies) at the same institution.

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Barred spiral galaxy...

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Like early explorers mapping the continents of our globe, astronomers are busy charting the spiral structure of our galaxy, the Milky Way. Using infrared images from NASA's Spitzer Space Telescope, scientists have discovered that the Milky Way's elegant spiral structure is dominated by just two arms wrapping off the ends of a central bar of stars. Previously, our galaxy was thought to possess four major arms.

This annotated artist's concept illustrates the new view of the Milky Way, along with other findings presented at the 212th American Astronomical Society meeting in St. Louis, Mo. The galaxy's two major arms (Scutum-Centaurus and Perseus) can be seen attached to the ends of a thick central bar, while the two now-demoted minor arms (Norma and Sagittarius) are less distinct and located between the major arms. The major arms consist of the highest densities of both young and old stars; the minor arms are primarily filled with gas and pockets of star-forming activity.

The artist's concept also includes a new spiral arm, called the "Far-3 kiloparsec arm," discovered via a radio-telescope survey of gas in the Milky Way. This arm is shorter than the two major arms and lies along the bar of the galaxy.

Our sun lies near a small, partial arm called the Orion Arm, or Orion Spur, located between the Sagittarius and Perseus arms.

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A Roadmap to the Milky Way (Annotated) - NASA Spitzer Space Telescope

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Like early explorers mapping the continents of our globe, astronomers are busy charting the spiral structure of our galaxy, the Milky Way. Using infrared images from NASA's Spitzer Space Telescope, scientists have discovered that the Milky Way's elegant spiral structure is dominated by just two arms wrapping off the ends of a central bar of stars.

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Stargazers in parts of Africa have been treated to a spectacular "ring of fire" in the sky as the sun was almost - but not completely - eclipsed.

An annular eclipse happens when the moon is farther away from the Earth than during a total eclipse.

The result is a bright circle of sunshine surrounding a dark, shadowy core.

The best views were seen in Tanzania, where the event lasted about three minutes.

The eclipse could also be viewed in parts of Gabon, Congo-Brazzaville, the Democratic Republic of Congo, Madagascar, and the French Indian Ocean island of La Reunion.

The moon does not move in a perfect circle around the earth - instead, its orbit is slightly elliptical. That means the distance of the moon varies between around 225,000-252,000 miles (362,000-405,555 km).

When the moon is farther away from the earth, it appears smaller - and does not totally cover the sun's disc during a total eclipse. The result is also known as a "ring of fire" eclipse.

The next eclipse is due to take place in February 2017, and can be seen from parts of South America and Africa.

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Eclipse in Africa: 'Ring of Fire' eclipse wows stargazers - BBC News

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Stargazers in parts of Africa have been treated to a spectacular "ring of fire" in the sky as the sun was almost - but not completely - eclipsed. An annular eclipse happens when the moon is farther away from the Earth than during a total eclipse.

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August's total solar eclipse in the US will almost certainly be the most watched such event in history.

More than 12 million people - from Oregon to South Carolina - live on the path of darkness that the Moon will cut as it sweeps in front of the Sun.

Nearly four times that many live within a two-hour's drive. And then there are all the tourists who will flock to America to witness the spectacle.

It makes the eclipse a wonderful citizen science opportunity.

"By going out and looking at the Sun we take part in this time-honoured tradition of citizen science," says astronomer and artist Prof Tyler Nordgren from the University of Redlands in California.

"Edmund Halley during an eclipse in 1715 in London asked people to go outside, look up and see if they could see the total solar eclipse and measure the length of totality, and by that he was able to help refine the orbit of the Moon," he told BBC News.

You might think that with all the space telescopes trained on the Sun these days there is little the citizen or even the keen amateur can contribute. But total solar eclipses are special because they afford particularly favourable conditions to study the tenuous outer atmosphere of the Sun called the corona.

It is in this superheated "gas" of charged particles that the solar wind originates, and from which billions of tonnes of matter can occasionally burst towards the Earth to disrupt satellites, communications and even electricity grids.

The corona is outshone by the Sun's surface, its photosphere. And satellites will block out this glare using devices called coronagraphs or occulters. But these are usually so wide that they also obstruct a doughnut of light immediately above the edge of the star.

"The spacecraft block out not only the Sun but also a whole lot of light around it, otherwise there would be scattering all over the image. And so we have that whole region uniquely to observe in white light from the ground at total solar eclipse," says Jay Pasachoff from Williams College, a veteran of 65 eclipses.

And he wants members of the public to get in on the act.

One key project in the planning is the Citizen Continental-America Telescopic Eclipse (CATE) project run by the National Solar Observatory.

It is making available 59 identical telescopes and digital cameras to universities, schools and astronomy clubs along the path of the eclipse (another 40 observing kits are available to purchase).

Participants are being trained to gather images of the corona from their locality that can then be spliced together with everyone else's to produce an uninterrupted 90-minute video.

Citizen CATE will rely on dedicated, calibrated equipment. But a similar venture plans to make use of the countless photos that will be taken on the day with general pocket cameras and smartphones.

The Eclipse Megamovie Project is led by the University of California at Berkeley's Multiverse education programme at the Space Sciences Laboratory and Google's Making & Science initiative.

It has a core band of photographers, but the public will be able to participate with the aid of an app that will offer advice on getting the best image quality and provide the means to upload pictures.

The 21 August event is the first coast-to-coast total solar eclipse in the US since 1918.

The Moon's shadow begins its journey across Earth's surface - the path of totality - out in the Pacific.

It makes landfall near Newport in Oregon at 10:16 local time (17:16 GMT; 18:16 BST); and leaves the continent close to the Atlantic coastal city of Charleston, South Carolina, at 14:49 local time (18:49 GMT; 19:49 BST).

The location that will experience full darkness for the "greatest duration" is just outside the town of Carbondale, Illinois. Totality there will last 2 minutes and 40.2 seconds.

So many people are expected to try to view the eclipse that the American Astronomical Society has set up a taskforce to advise urban and rural communities on how to prepare for the expected population surge.

Prof Nordgren works a lot with the National Parks Service: "I'm going to be at John Day Fossil Beds National Monument in eastern Oregon.

"They have six parking spaces and a porta-potty, and yet they're expecting maybe 20,000 people to come there on that day."

And taskforce colleague, Angela Speck from the University of Missouri, added: "We need to have communities ready for the influx of people that are coming, and that means things like emergency services, road traffic control, food and water. Especially water - the eclipse is in August."

Nordgren, Speck, and Pasachoff were speaking here in Boston at the Annual Meeting of the American Association for the Advancement of Science (AAAS).

Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos

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Eclipse to be turned into megamovies - BBC News

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August's total solar eclipse in the US will almost certainly be the most watched such event in history. More than 12 million people - from Oregon to South Carolina - live on the path of darkness that the Moon will cut as it sweeps in front of the Sun.

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Gravitational waves are 'ripples' in space-time caused by some of the most violent and energetic processes in the Universe. Albert Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity. Einstein's mathematics showed that massive accelerating objects (things like neutron stars or black holes orbiting each other) would disrupt space-time in such a way that 'waves' of undulating space-time would propagate in all directions away from the source. These cosmic ripples would travel at the speed of light, carrying with them information about their origins, as well as clues to the nature of gravity itself.

The strongest gravitational waves are produced by cataclysmic events such as colliding black holes, supernovae (massive stars exploding at the end of their lifetimes), and colliding neutron stars. Other gravitational waves are predicted to be caused by the rotation of neutron stars that are not perfect spheres, and possibly even the remnants of gravitational radiation created by the Big Bang.

The animation below illustrates how gravitational waves are emitted by two neutron stars as they orbit each other and then coalesce (credit: NASA/Goddard Space Flight Center). Note that gravitational waves themselves are invisible. They are made visible here to illustrate their propagation away from the source.

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Though Einstein predicted the existence of gravitational waves in 1916, the first proof of their existence didn't arrive until 1974. In that year, two astronomers, Russell Hulse and Joseph Taylor, using the Arecibo Radio Observatory in Puerto Rico discovered a binary pulsar 21000 light years from Earth. This was exactly the type of system that general relativity predicted should radiate gravitational waves. Knowing that the system could be studied to test Einstein's prediction, Taylor and two colleagues (Joel Weisberg and Lee Fowler) began tracking the radio emissions from the stars to measure how their orbital period changed over time. After just four years, they first reported seeing a change in the period that verified that the stars were getting closer to each other at the rate predicted by general relativity (GR) if they were radiating gravitational waves (the rate predicted by GR agreed with the observed rate to within one half of one percent). In 1993, Hulse and Taylor would receive the Nobel Prize in Physics " for the discovery of a new type of pulsar, a discovery that has opened up new possibilities for the study of gravitation".

Since then, many astronomers have studied pulsar radio-emissions (pulsars are neutron stars that emit beams of radio waves) and found similar effects, further confirming the existence of gravitational waves. But these confirmations had always come indirectly requiring that one infer the existance of GWs.t.

All of this changed on September 14, 2015 when LIGO physically sensed the undulations in spacetime caused by gravitational waves generated by two colliding black holes 1.3 billion light-years away. LIGO's first detection will go down in history as one of humanity's greatest scientific achievements.

While the processes that generate measurable gravitational waves are extremely violent, by the time the waves reach Earth they are thousands of billions of times smaller (due to the 'stiffness' of space), and much smaller when they reach us, much as sounds are weaker when you move further from the source. In fact, by the time gravitational waves from LIGO's first detection reached us, the amount of space-time wobbling they generated was a 10,000 times smaller than the nucleus of an atom! LIGO was designed to make such inconceivable, exquisitely small measurements. To learn how LIGO achieves this seemingly impossible task, visit LIGO's Interferometer.

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The pull of gravity on a distant star can now be measured more accurately, shedding light on other worlds, say astronomers.

The method makes it possible to study even the faintest of stars.

"Our technique can tell you how big and bright is the star, and if a planet around it is the right size and temperature to have water oceans, and maybe life," said Prof Jaymie Matthews.

The findings appear in the journal, Science Advances.

Surface gravity is the intensity of the force that pulls everything on the surface of a star or celestial body towards the centre.

It is usually calculated by measuring a star's light or brightness - but this only works well for the closest, brightest stars.

A team led by Thomas Kallinger of the University of Vienna used data from the Kepler space telescope - which is searching for other worlds like the Earth - to show that variations in the brightness of distant stars can give more accurate measurements of surface gravity.

The timescale of turbulence and vibration at a star's surface, based on its brightness variations, tells you its surface gravity, say the researchers.

Future space missions will hunt for planets around distant stars that might be capable of harbouring liquid water oceans and perhaps life.

The method can be applied to data from these searches to help understand the nature of stars like our Sun and to help find other planets like our Earth, says Dr Kallinger.

Earth-sized world

Since surface gravity depends on the star's mass and radius, the method should also help astronomers work out the masses and sizes of distant stars - and any planets orbiting them.

"If you don't know the star, you don't know the planet," said co-researcher Prof Matthews of the University of British Columbia, Canada.

"The size of an exoplanet is measured relative to the size of its parent star.

"If you find a planet around a star that you think is Sun-like but is actually a giant, you may have fooled yourself into thinking you've found a habitable Earth-sized world. "

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Advance in astronomy 'can help find other worlds' - BBC News

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The pull of gravity on a distant star can now be measured more accurately, shedding light on other worlds, say astronomers. The method makes it possible to study even the faintest of stars.

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In Cassini's Grand Finale orbits - the final orbits of its nearly 20-year mission - the spacecraft traveled in an elliptical path that sent it diving at tens of thousands of miles per hour through the 1,500-mile-wide (2,400-kilometer) space between the rings and the planet where no spacecraft had ventured before.

Each of these last 22 orbits took about six and a half days to complete. They began April 22 and ended Sept. 15. When Cassini was nearest to Saturn during each orbit, the spacecraft's speed ranged between 75,000 and 78,000 miles per hour (121,000 and 126,000 kilometers per hour), depending on the orbit.

The Grand Finale orbits were so named because they not only carried Cassini to its end, but because they were truly grand. The spacecraft flew through an unexplored region of the Saturnian system, producing unique images and attempting to solve longtime mysteries, such as the mass of Saturn's rings and the planet's rotation rate - the length of a Saturn day. And then during Cassini's last five orbits, the spacecraft dipped down to directly sample Saturn's upper atmosphere.

The summaries posted on this page for each Grand Finale orbit include only a few highlights of the many unparalleled science investigations that Cassini performed during these unprecedented orbits. Also, because Saturn is a gas giant, Cassini couldn't be described as being a certain distance from the planet's "surface." So, to convey Cassini's distance from Saturn, each summary also includes the spacecraft's closest approach to Saturn's 1-bar level for that orbit. A bar is the atmospheric pressure you experience on Earth at sea level.

A short, animated video describing Cassini's Grand Finale. Download ›

Full List of Orbits:

This first Grand Finale orbit began following a final close flyby of Titan that sent Cassini on its first plunge through the gap between Saturn and its rings.

The orbit provided Cassini with its best look ever at Saturn's north pole with both VIMS and the Composite Infrared Spectrometer (CIRS). And the observations should provide the sharpest near-infrared movies to date of the motion in and around the hexagon.

Before Cassini passed through Saturn's ring plane for the first time in the region between Saturn and its rings, the spacecraft changed its attitude so that its high-gain antenna faced forward (called "HGA to RAM") to help shield the spacecraft from ring particles during ring-plane crossing.

Using its VIMS and Ultraviolet Imaging Spectrograph (UVIS) instruments, Cassini studied Saturn's smallest ring particles as they passed between the sun and the spacecraft.

During the hour leading up to closest approach to Saturn, the imaging cameras (ISS) took a strip-like series of images of features in the atmosphere (which the team refers to as "the noodle"). These images were Cassini's closest views of Saturn thus far, with a resolution up to 10 times higher than before.

During this orbit, Cassini got within 1,840 miles (2,950 kilometers) of Saturn's 1-bar level. Cassini also passed within 2,960 miles (4,760 kilometers) of the inner edge of Saturn's D ring.

During this orbit, Cassini rolled to calibrate its magnetometer (MAG) for the high-intensity magnetic field observations to be performed when the spacecraft was nearest Saturn. This was the first time MAG made this sort of observation.

The spacecraft's Composite Infrared Spectrometer (CIRS) observed Saturn's moon Rhea in infrared to narrow down the composition and structure of the moon's surface material.

During this orbit, Cassini got within 1,820 miles (2,930 kilometers) of Saturn's 1-bar level. Cassini also passed within 2,980 miles (4,780 kilometers) of the inner edge of Saturn's D ring.

During this orbit, Cassini got within 1,680 miles (2,710 kilometers) of Saturn's 1-bar level. Cassini also passed within 3,110 miles (5,010 kilometers) of the inner edge of Saturn's D ring.

During the radio science/gravity observations, the spacecraft's Cosmic Dust Analyzer (CDA) scooped up and analyzed small ring particles to help determine the age of Saturn's rings. Interplanetary meteoroids bombard Saturn's main rings, depositing silicates, organics, and metals in the ring particles. The more of those contaminants the CDA found, the older Saturn's rings probably are.

During this orbit, Cassini got within 1,650 miles (2,660 kilometers) of Saturn's 1-bar level. Cassini also passed within 3,110 miles (5,000 kilometers) of the inner edge of Saturn's D ring.

And as with the previous orbit, the spacecraft's Cosmic Dust Analyzer (CDA) scooped up and analyzed ring particles - this time larger ring particles rather than the relatively small particles - to help determine the age of Saturn's rings. Interplanetary meteoroids bombard Saturn's main rings, depositing silicates, organics, and metals in the ring particles. The more of those contaminants the CDA found, the older Saturn's rings probably are.

During this orbit, Cassini got within 1,680 miles (2,700 kilometers) of Saturn's 1-bar level. Cassini also passed within 3,120 miles (5,010 kilometers) of the inner edge of Saturn's D ring.

Cassini's RADAR instrument performed the first of three parts to an experiment it had never tried before. Scanning inward from the outer edge of the A ring all the way through the innermost C ring, RADAR generated scans of the main rings at resolutions from 4 kilometers down to 100 meters per pixel.

During ring-plane crossing, the spacecraft was oriented such that its high-gain antenna (the big dish) faced forward (called "HGA to RAM") to help shield the spacecraft from ring particles. This orbit's ring-plane crossing was the highest Cassini ever got in Saturn's D ring.

Also during ring-plane crossing, in the six-minute period where impacts were considered most likely, the Radio and Plasma Wave Science instrument "listened" for the impacts of ring particles, which produced detectable plasma clouds when they struck the spacecraft. The antenna protruded several meters beyond the protection of the high-gain antenna, allowing it to interact with ring particles while most of the spacecraft was shielded.

During this orbit, Cassini got within 2,420 miles (3,900 kilometers) of Saturn's 1-bar level. Cassini also passed within 2,370 miles (3,810 kilometers) of the inner edge of Saturn's D ring.

Cassini's RADAR instrument performed the second of three parts to an experiment it had never tried before: Scanning inward from the outer edge of the A ring all the way through the innermost C ring, RADAR generated scans of the main rings at resolutions from 4 kilometers down to 100 meters.

During this orbit's ring-plane crossing, the spacecraft again was oriented such that its high-gain antenna (the big dish) faced forward (called HGA to RAM) to help shield the spacecraft from ring particles.

And again during ring-plane crossing, in the brief period in which impacts were considered most likely, the Radio and Plasma Wave Science (RPWS) instrument "listened" for the impacts of ring particles, which produced detectable plasma clouds when they struck the spacecraft. The antenna protruded several meters beyond the protection of the high-gain antenna and so could still detect impacts.

During this orbit, Cassini got within 2,420 miles (3,890 kilometers) of Saturn's 1-bar level. Cassini also passed within 2,370 miles (3,820 kilometers) of the inner edge of Saturn's D ring.

During the radio experiments, Cassini's Cosmic Dust Analyzer (CDA) scooped up and analyzed small ring particles to help determine the age of Saturn's rings. Interplanetary meteoroids bombard Saturn's main rings, depositing silicates, organics, and metals in the ring particles. The more of those contaminants the CDA found, the older Saturn's rings probably are.

Next Cassini's Visible and Infrared Mapping Spectrometer (VIMS) mapped Saturn's southern hemisphere at some of the highest resolutions of the mission. The instrument looked for changes in winds, cloud structures and perhaps changes in atmospheric chemistry as the rate of atmospheric upwelling changes with seasons.

During this orbit, Cassini got within 2,120 miles (3,410 kilometers) of Saturn's 1-bar level. Cassini also passed within 2,670 miles (4,300 kilometers) of the inner edge of Saturn's D ring.

Cassini's Ion and Neutral Mass Spectrometer (INMS) took priority during ring-plane crossing, measuring the density and composition of neutral particles in that region to study the relationship between Saturn's rings and the planet's atmosphere. INMS also measured ions such as O₂⁺ created on the surface of the rings and transported along field lines to other locations.

The Cosmic Dust Analyzer (CDA) sampled ring particles around ring-plane crossing.

The spacecraft's imaging cameras, the Imaging Science Subsystem (ISS), took a special photo of the rings from the inside out around ring-plane crossing.

During this orbit, Cassini got within 2,080 miles (3,350 kilometers) of Saturn's 1-bar level. Cassini also passed within 2,710 miles (4,360 kilometers) of the inner edge of Saturn's D ring.

During this orbit, Cassini's Composite Infrared Spectrometer (CIRS) observed Saturn's moon Dione to better understand the moon's temperatures and to study the composition and structure of the moon's surface material.

During the radio experiments, Cassini's Cosmic Dust Analyzer (CDA) scooped up and analyzed small ring particles to help determine the age of Saturn's rings. Interplanetary meteoroids bombard Saturn's main rings, depositing silicates, organics, and metals in the ring particles. The more of those contaminants the CDA found, the older Saturn's rings probably are.

The CIRS instrument also observed Saturn's A ring to compare properties of ice in the rings and on Saturn's icy moons.

During this orbit, Cassini got within 2,110 miles (3,390 kilometers) of Saturn's 1-bar level. Cassini also passed within 2,680 miles (4,320 kilometers) of the inner edge of Saturn's D ring.

The spacecraft's Composite Infrared Spectrometer (CIRS) mapped the temperature and composition of Saturn's north polar vortex at the highest resolution of the mission so far.

Cassini's Visible and Infrared Mapping Spectrometer (VIMS) captured a movie of Saturn's south polar region. It was the closest and sharpest near-infrared movie to date of the intricate structure and complex movements of features in and around the south polar vortex.

*(UPDATED) During this orbit's ring-plane crossing, the spacecraft was originally planned to be oriented with its high-gain antenna (the big dish) facing forward to help shield the spacecraft from ring particles. However, during the two earlier dives through the D ring (orbits 276 and 277), the ring particle environment was found to be benign. Because of this, mission planners decided to remove the shielding requirement for this orbit. The antenna was once again be used as a shield on the following orbit (orbit 282)

After ring-plane crossing, Cassini completed an engineering checkout of the spacecraft's sun sensor assembly to be sure it wasn't damaged when the high-gain antenna shielded the spacecraft during ring-plane crossing.

During this orbit, Cassini got within 2,320 miles (3,720 kilometers) of Saturn's 1-bar level. Cassini also passed within 2,480 miles (3,980 kilometers) of the inner edge of Saturn's D ring.

During this orbit, Cassini's Ultraviolet Imaging Spectrograph (UVIS) stared at the star Kappa Canis Majoris, as parts of the C ring and A ring pass between the spacecraft and the star. The spacecraft's Composite Infrared Spectrometer (CIRS) observed the occultation as well.

Cassini's UVIS instrument also studied small-scale structures in the rings.

During this orbit's ring-plane crossing, the spacecraft was oriented such that its high-gain antenna (the big dish) faces forward (called "HGA to RAM") to help shield the spacecraft from ring particles.

Also during ring-plane crossing, in the brief period in which impacts were most likely, the Radio and Plasma Wave Science (RPWS) instrument "listened" for the impacts of ring particles, which produced detectable plasma clouds when they struck the spacecraft. The antenna protruded several meters beyond the protection of the high-gain antenna and so still detected impacts.

During this orbit, Cassini got within 2,320 miles (3,730 kilometers) of Saturn's 1-bar level. Cassini also passed within 2,470 miles (3,980 kilometers) of the inner edge of Saturn's D ring.

During this orbit, Cassini's Composite Infrared Spectrometer (CIRS) observed the lit side of the middle A-ring to determine its composition and structure. The CIRS instrument then targeted the point where Saturn's shadow falls across the B-ring, studying how the ring's temperature changes as it crosses into Saturn's shadow. These CIRS observations should reveal details about the structure of the ring particles themselves, which were too small for Cassini's cameras to resolve.

Cassini's imaging cameras, the Imaging Science Subsystem (ISS), observed some of Saturn's known ring propeller features. The ISS also performed a high-resolution scan of Saturn's C ring and inner B ring

With Cassini about 31,100 miles (50,000 kilometers) from Saturn's lower atmosphere, the Ion and Neutral Mass Spectrometer (INMS) sampled the exosphere and ionosphere of Saturn and of the atmosphere-ionosphere of Saturn's rings. On a later orbit (Orbit 288), the INMS sampled Saturn's visible, much denser atmosphere for the first time.

During this orbit, Cassini got within 1,780 miles (2,860 kilometers) of Saturn's 1-bar level. Cassini also passed within 3,020 miles (4,850 kilometers) of the inner edge of Saturn's D ring.

When Cassini was in the segment of this orbit in which it was nearest to Saturn, the spacecraft rolled so that the Magnetometer (MAG) could collect unique measurements that will lead to a better understanding of Saturn's magnetic field, the planet's rotation rate, the size of the central core and other characteristics of Saturn.

Then the Visible and Infrared Mapping Spectrometer (VIMS) led an observation of Saturn's southern hemisphere at night.

During this orbit, Cassini got within 1,740 miles (2,790 kilometers) of Saturn's 1-bar level. Cassini also passed within 3,050 miles (4910 kilometers) of the inner edge of Saturn's D ring.

During this orbit Cassini's imaging cameras, the Imaging Science Subsystem (ISS), took priority to observe Saturn's moon Titan for two periods, each lasting several hours, to image the moon's atmosphere and surface, in particular to watch Titan's clouds form and change. The spacecraft's Composite Infrared Spectrometer (CIRS) and Visible and Infrared Mapping Spectrometer (VIMS) observed Titan as well.

The Ultraviolet Imaging Spectrograph (UVIS) observed swaths of both Saturn's northern and southern auroral zones, with the north in sunlight while the south was in darkness.

During this orbit, the spacecraft rolled to calibrate Cassini's magnetometer (MAG) for its high-intensity magnetic field observations to be performed when the spacecraft is nearest Saturn.

Cassini's Radio and Plasma Wave Science (RPWS) instrument was active during the MAG rolls to capture "whistlers" produced by Saturn lightning.

During this orbit, Cassini got within 1,750 miles (2,810 kilometers) of Saturn's 1-bar level. Cassini also passed within 3,040 miles (4,890 kilometers) of the inner edge of Saturn's D ring.

Cassini's Visible and Infrared Mapping Spectrometer (VIMS) observed Saturn's aurora during this orbit as well. This observation was the closest and highest-resolution auroral observation VIMS made during Cassini's entire mission.

The spacecraft's Composite Infrared Spectrometer (CIRS) observed the south polar region of Saturn's moon Enceladus during this orbit, studying winter temperatures on the moon's surface. This was the instrument's last opportunity of the mission to study the temperatures on Enceladus, to help researchers understand how they change over time.

During this orbit, Cassini got within 1,820 miles (2,920 kilometers) of Saturn's 1-bar level. Cassini also passed within 2,980 miles (4,790 kilometers) of the inner edge of Saturn's D ring.

The spacecraft's imaging cameras, the Imaging Science Subsystem (ISS), performed the first of two final observations of one of Saturn's tiny, irregular moons, named Kiviuq, which completed about 80 percent of one rotation during Cassini's observation. The observation was intended to improve models of the moon's shape and other of Kiviuq's characteristics.

Also during this orbit, the spacecraft rolled to calibrate Cassini's magnetometer (MAG).

During this orbit, Cassini got within 1,830 miles (2,940 kilometers) of Saturn's 1-bar level. Cassini also passed within 2,960 miles (4,760 kilometers) of the inner edge of Saturn's D ring.

Cassini had just five orbits of Saturn remaining before the mission ends.

During this orbit, Cassini's Composite Infrared Spectrometer (CIRS) observed the edge of Saturn's atmosphere to determine different temperatures at different altitudes.

The spacecraft's imaging cameras, the Imaging Science Subsystem (ISS), then observed mysterious features informally called "streaks" in Saturn's C ring.

This was the first of five orbits in which Cassini's elliptical orbit carried it so low that the spacecraft passed briefly through Saturn's outermost atmosphere. Cassini's reaction control thrusters were at the ready to correct the spacecraft's orientation in case Saturn's atmosphere pushed on the spacecraft hard enough to cause any rotation.

During the period in which the spacecraft was nearest Saturn, Cassini's Ion and Neutral Mass Spectrometer (INMS) performed the first ever direct sampling of Saturn's atmosphere. The instrument measured densities of different species of molecular hydrogen, helium and a variety of ions in the immediate vicinity of the spacecraft.

Cassini's RADAR instrument operated at the same time as INMS, studying Saturn's atmosphere in a passive mode to study the small-scale structure and ammonia concentration of Saturn's atmosphere.

Cassini had just three orbits of Saturn remaining before the mission ends.

During this orbit Cassini's Composite Infrared Spectrometer (CIRS) mapped Saturn's northern hemisphere to study temperatures in the upper troposphere and the Visible and Infrared Mapping Spectrometer (VIMS) created a map of Saturn's equatorial region. The CIRS instrument also performed its final Saturn limb observation of the mission.

The spacecraft used its RADAR instrument in active mode to study Saturn's atmosphere.

This was the third of five orbits in which Cassini's elliptical orbit carried it so low that the spacecraft passed briefly through Saturn's atmosphere. Cassini's reaction control thrusters were at the ready to correct the spacecraft's orientation in case Saturn's atmosphere pushed on the spacecraft hard enough to cause any rotation. This was the deepest Cassini dipped into Saturn's atmosphere during the "Final Five" orbits.

During the period in which the spacecraft was nearest Saturn, Cassini's Ion and Neutral Mass Spectrometer (INMS) performed its second session directly sampling Saturn's upper atmosphere. The instrument measured densities of different species of molecular hydrogen, helium and a variety of ions in the immediate vicinity of the spacecraft.

Cassini had just two orbits of Saturn remaining before the mission ends.

The VIMS instrument and Cassini's Composite Infrared Spectrometer (CIRS) worked together to study Saturn's atmosphere.

This was also the fourth of five orbits in which Cassini's elliptical orbit carried it so low that the spacecraft passed briefly through Saturn's atmosphere. Cassini's reaction control thrusters were at the ready to correct the spacecraft's orientation in case Saturn's atmosphere pushed on the spacecraft hard enough to cause any rotation.

During the period in which the spacecraft was nearest Saturn, Cassini's Ion and Neutral Mass Spectrometer (INMS) performed its third session directly sampling of Saturn's upper atmosphere. The instrument measured densities of different species of molecular hydrogen, helium and a variety of ions in the immediate vicinity of the spacecraft.

This was Cassini's final full orbit of Saturn before the mission ended.

During this orbit, Cassini's Composite Infrared Spectrometer (CIRS) and Visible and Infrared Mapping Spectrometer (VIMS) instruments worked together to determine the abundance of helium in Saturn's atmosphere.

This was the fifth of five orbits in which Cassini's elliptical orbit carried it so low that the spacecraft passed briefly through Saturn's atmosphere. Cassini's reaction control thrusters were at the ready to correct the spacecraft's orientation in case Saturn's atmosphere pushed on the spacecraft hard enough to cause any rotation.

During the period in which the spacecraft was nearest Saturn, Cassini's Ion and Neutral Mass Spectrometer (INMS) performed its fourth session directly sampling Saturn's upper atmosphere. The instrument measured densities of different species of molecular hydrogen, helium and a variety of ions in the immediate vicinity of the spacecraft.

At the end of this orbit, Cassini made a distant flyby of the Mercury-size moon Titan, whose gravity altered the spacecraft's trajectory one final time. This gravitational nudge, which the team calls "the goodbye kiss," ensured that the spacecraft was disposed of in a controlled manner. Instead of passing safely into and out of Saturn's outermost atmosphere on the next orbit, Cassini instead dipped so deeply into the atmosphere that the spacecraft burned up like a meteor.

During this partial orbit, when Cassini was three and half hours from its expected end of mission, data from the spacecraft's Composite Infrared Spectrometer (CIRS), Ultraviolet Imaging Spectrograph (UVIS), and magnetospheric and plasma science instruments were transmitted to Earth in nearly real time, just seconds after each observation was made. Cassini usually held onto those data for hours or days before turning its high-gain antenna toward Earth to transmit them.

Unlike the preceding orbits, where the Cassini's lowest altitudes were chosen to avoid tumbling, the spacecraft trajectory on this orbit intentionally continued all the way into Saturn.

Cassini continued transmitting as long as possible until the force of Saturn's atmosphere overpowered the spacecraft's thrusters and Cassini could no longer point its antenna precisely enough to maintain contact with Earth.

When the spacecraft's signal was lost, the Cassini mission ended.

Go to the Grand Finale Overview page.

For additional details about Cassini's recent activities, see Saturn Tour Dates for 2016 & 2017

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In Cassini's Grand Finale orbits - the final orbits of its nearly 20-year mission - the spacecraft traveled in an elliptical path that sent it diving at tens of thousands of miles per hour through the 1,500-mile-wide (2,400-kilometer) space between the rings and the planet where no spacecraft had ventured before.

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Official webpage for the TRAPPIST-1 system

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Exam board:
https://qualifications.pearson.com/en/qualifications/edexcel-gcses/astronomy-2009.html

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Best site for revision!
http://www.gcseastronomy.co.uk/

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Gravity's a funny thing. Not only does it tug away at you, me, planets, moons and stars, but it can even bend light itself. And once you're bending light, well, you've got yourself a telescope.

Everyone here is familiar with the practical applications of gravity. If not just from exposure to Loony Tunes, with an abundance of scenes with an anthropomorphized coyote being hurled at the ground from gravitational acceleration, giant rocks plummeting to a spot inevitably marked with an X, previously occupied by a member of the "accelerati incredibilus" family and soon to be a big squish mark containing the bodily remains of the previously mentioned Wile E. Coyote.

Despite having a very limited understanding of it, Gravity is a pretty amazing force, not just for decimating a infinitely resurrecting coyote, but for keeping our feet on the ground and our planet in just the right spot around our Sun. The force due to gravity has got a whole bag of tricks, and reaches across Universal distances. But one of its best tricks is how it acts like a lens, magnifying distant objects for astronomy.
Thanks to the general theory of relativity, we know that mass curves the space around it. The theory also predicted gravitational lensing, a side effect of light travelling along the curvature of space and time where light passing nearby a massive object is deflected slightly toward the mass.

It was first observed by Arthur Eddington and Frank Watson Dyson in 1919 during a solar eclipse. The stars close to the Sun appeared slightly out of position, showing that the light from the stars was bent, and demonstrated the effect predicted. This means the light from a distant object, such as a quasar, could be deflected around a closer object such as a galaxy. This can focus the quasar's light in our direction, making it appear brighter and larger. So gravitational lensing acts as a kind of magnifying glass for distant objects making them easier to observe.

We can use the effect to peer deeper into the Universe than would otherwise be possible with our conventional telescopes. In fact, the most distant galaxies ever observed, ones seen just a few hundred million years after the Big Bang, were all discovered using gravitational lensing. Astronomers use gravitational microlensing to detect planets around other stars. The foreground star acts as a lens for a background star. As the star brightens up, you can detect further distortions which indicate there are planets. Even amateur telescopes are sensitive enough to spot them, and amateurs regularly help discover new planets. Unfortunately, these are one time events as this alignment happens only once.

There's a special situation known as an Einstein Ring, where a more distant galaxy is warped by a nearby galaxy into a complete circle. To date a few partial rings have been seen, but no perfect Einstein Ring has ever been spotted.

Gravitational lensing also allows us to observe invisible things in our Universe. Dark matter doesn't emit or absorb light on its own, so we can't observe it directly. We can't take a photo and say "Hey look, dark matter!". However, it does have mass, and that means it can gravitationally lens light originating behind it. So we've even used the effect of gravitational lensing to map out dark matter in the Universe.

What about you? Where should we focus our gravitational lensing efforts to get a better look in the Universe? Tell us in the comments below.

Podcast (audio): Download (Duration: 4:03 - 3.7MB)

Podcast (video): Download (Duration: 4:26 - 52.8MB)

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What is Gravitational Lensing? - Universe Today

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Gravity's a funny thing. Not only does it tug away at you, me, planets, moons and stars, but it can even bend light itself. And once you're bending light, well, you've got yourself a telescope. Everyone here is familiar with the practical applications of gravity.