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When you look up at the bright stars in the nighttime sky, do you WONDER what's out there? Of course, your science teachers have taught you that there are stars, planets, and entire galaxies out there.

But how do we know this? Man has walked on the Moon, but the Moon is fairly close to Earth when you're talking about . How do scientists study the far reaches of the ?

Over the course of history, man has developed amazing technology to help us see beyond our own planet into the of our and even way beyond. This technology takes the form of some impressive machines and tools that scientists can use to study the heavens.

One of the earliest tools for exploration was the . Using lenses and mirrors to see beyond Earth's borders, telescopes gave scientists their first glimpses of what exists beyond Earth's atmosphere.

What scientists were able to learn with telescopes paved the way for manned exploration. From trips to the Moon to dozens of manned shuttle flights, teams of humans were able to travel in and conduct research on a variety of scientific subjects.

Scientists have always been curious. The more we learn about , the more we realize how much more there is to . This has led scientists to develop even more powerful tools to help them way beyond the places we can go as humans.

For example, the is no longer an Earth-bound instrument . In 1990, the Hubble was launched into . In the last 20 years, it has brought us images of our that couldn't have been captured in any other way.

It's a miraculous piece of technology that's powered by sunlight. With many different cameras and types of scientific instruments, the Hubble has provided scientists with invaluable . In fact, NASA estimates that from the Hubble has been used as the basis of over 10,000 scientific papers in the past two decades!

Since late 2000, scientists have also been able to conduct hundreds of experiments in low-Earth orbit thanks to the International Station (ISS). The ISS is humankind's first station meant to be used for long-term visits from astronauts from a variety of countries. What scientists learn from the ISS will likely be a stepping stone to sending humans on manned missions to Mars and beyond.

In the meantime, scientists have pushed forward with a wide variety of unmanned machines built to the deepest corners of our . Unmanned probes, such as NASA's Cassini , have been sent to other planets. If you've seen a spectacular picture of Saturn recently, you can thank the Cassini .

Astronomers have always been fascinated by Mars, and we know more than ever about Mars today thanks to the Mars Reconnaissance Orbiter and the Mars rovers, Spirit, Opportunity, and Curiosity. The rovers are powerful robots that have helped scientists learn a tremendous amount about the of Mars.

As time marches on, scientists will continue to learn more and more about our using advanced scientific technology to create tools to the depths of . For example, thanks to the Kepler , launched in 2009, scientists now know that there are possibly over 3,000 planets orbiting over 2,000 stars in the Milky Way , none of which were known about until the last couple of years!

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How Do Scientists Explore the Solar System?

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When you look up at the bright stars in the nighttime sky, do you WONDER what's out there? Of course, your science teachers have taught you that there are stars, planets, and entire galaxies out there. But how do we know this?

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Today's Wonder of the Day was inspired by Al. Al Wonders, " What is a supernova? " Thanks for WONDERing with us, Al!

Stars, like the Sun, fill the . The of a star constantly converts , its fuel supply, into . This process, called fusion, makes stars shine so brightly.

After billions of years of burning, a star will eventually use up its fuel supply. When fusion stops, pulls the star inward on itself.

As the star begins to collapse, its inner shell eventually hits the , which creates a huge shock wave. Kaboom! The star explodes, and a supernova is born!

Supernovae (the of supernova) can become billions of times brighter than the Sun. A supernova explosion releases billions of tiny particles called atoms into space. These atoms form a huge dust cloud called a .

Many of the atoms that exist today were originally created inside stars and released into space when the stars became supernovae. In fact, scientists believe much of the , , , , and on Earth came from supernovae.

The first stars became supernovae about 14 billion years ago. To give you an idea of how long ago that was, a billion seconds ago was almost 32 years ago. As you can imagine, 14 billion years was a really, really long time ago!

When a supernova ends, the star can become a white , star, or black hole. Smaller stars (those similar in size to the Sun) become white stars. Medium-size stars (between two to five times the mass of our sun) become stars.

Large stars (more than five times the mass of the Sun) become black holes. The inside black holes is so strong that not even light can escape!

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Today's Wonder of the Day was inspired by Al. Al Wonders, " What is a supernova? " Thanks for WONDERing with us, Al! Stars, like the Sun, fill the . The of a star constantly converts , its fuel supply, into . This process, called fusion, makes stars shine so brightly.

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Do you wash your hands regularly? We hope so! Not only do our hands get dirty throughout the day, they can also become covered with germs that can make us sick. Washing your hands with soap and water helps to get rid of those nasty germs.

Some people hate germs with a passion and avoid them at all costs. These people who fear germs and contamination are often called germaphobes, although the phobia they have is officially known as mysophobia .

If you suffered from mysophobia , where might you go to be safe from germs? Some people might think outer would be a good place to go. After all, there is no air in and all that would have to kill off all the germs, right?

To the surprise of many scientists, many missions to outer over the past several decades have revealed that over 250 different species of and can not only survive, but even thrive in the harsh conditions of outer .

For example, the Russian Mir encountered problems with a film growing over its windows, reducing visibility while in orbit. Upon its return to Earth, scientists were shocked to discover numerous and covering the .

Moreover, the microorganisms had done more than just coat the and block astronauts' views of . They had actually corroded the . This concerned scientists, because the was made of in a frame encased in - a combination scientists had thought could withstand just about anything outer could throw at it.

Closer examination of the Mir revealed that microorganisms had also damaged electronic equipment by rusting cables. Scientists also found coating various polyurethane surfaces.

Scientists were so surprised because vehicles are thoroughly cleaned with toxic gases before being sent into . They now suspect that certain and may survive fumigation by hiding under areas where gas does not penetrate. So why do they survive and thrive once in outer ?

Scientists speculate that come out of hiding once in outer . In a sterile environment without competing microorganisms around, they multiply and thrive. Instead of killing them, may also help them to mutate and aggressively grow faster than they normally could on Earth.

These findings were reinforced by recent experiments conducted on the International (ISS). -laden rocks were installed on the exterior of the ISS to see how they would react to the conditions of outer , including wild temperature swings, lacks of air, and extreme exposure to ultraviolet light and .

While some did succumb to these harsh conditions, a group of known as OU-20, which resemble the cyanobacteria genus Gloeocapsa, survived for over a year and a half on the outside of the ISS! Researchers now have samples of these survivors back on Earth for further study.

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Do you wash your hands regularly? We hope so! Not only do our hands get dirty throughout the day, they can also become covered with germs that can make us sick. Washing your hands with soap and water helps to get rid of those nasty germs. Some people hate germs with a passion and avoid them at all costs.

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Today's Wonder of the Day was inspired by Sarah from Houston , TX. Sarah Wonders, " How do the astronauts build a space center in space? " Thanks for WONDERing with us, Sarah !

What's that up there? Right there! Way up high in the , there's a bright moving slowly across the black of the heavens. It's way too high to be an airplane, and it's too steady to be a shooting star. What could it be? It's the International Space Station, of course!

Visible from Earth with the naked eye, the International Space Station (ISS) is that serves as a microgravity laboratory in space. At costs approaching $150 billion, the ISS is arguably the most expensive thing ever built. It's also the largest structure ever built in space by humans.

While aboard the ISS, a of international astronauts conducts science experiments in a wide range of disciplines, from astronomy and biology to geology and physics. Astronauts enjoy a sunrise or sunset approximately every 92 minutes, as the ISS completes 15.5 orbits around Earth each day.

How can the ISS orbit Earth so quickly? Orbiting at an average altitude of 248 miles above Earth, the ISS travels approximately 17,500 miles per hour. That's a of about five miles per second! Over the course of a single day, the ISS travels a distance nearly equal to traveling from Earth to the Moon and back.

Despite its speed, the ISS is visible from Earth with the naked eye, as long as you know when and where to look. That's because the ISS is so big. How big? The ISS consists of modules and connecting nodes that house living quarters and laboratories. It also has large trusses for support, as well as more than an of solar panels that provide power.

In total, the ISS is a little bigger than an American football field. It weighs approximately 900,000 pounds and contains two bathrooms, a gymnasium, and the living space of about a six-bedroom house.

So how did such a humongous man-made object get into space? It would be impossible to launch such a huge object with modern technology. That's why the ISS was built slowly, piece-by-piece by a combination of five different space agencies representing 15 different countries.

The first piece, Russia's Zarya , was launched into space in 1998. Over time, other modules were launched via rockets and the United States space shuttle program. Astronauts connected all the pieces over the course of several missions. The ISS has been continuously occupied since November 2000.

Since that time, more than 200 astronauts from 15 different countries have visited the ISS. Space agencies hope to continue to use the ISS for many years to come. In fact, there are current plans to add even more modules in coming years.

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How Did Astronauts Build a Space Station?

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Today's Wonder of the Day was inspired by Sarah from Houston , TX. Sarah Wonders, " How do the astronauts build a space center in space? " Thanks for WONDERing with us, Sarah ! What's that up there? Right there! Way up high in the , there's a bright moving slowly across the black of the heavens.

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If you hold a pin at arm's length up in the air, the head of the pin covers approximately the amount of sky that appears in the Hubble Deep Field. The iconic 1995 image is crowded, not because it's a broad swath of sky but because it's a broad swath of time. The Hubble Deep Field is more than 12 billion light-years deep...

What makes the Hubble Deep Field an atypical core sample is that rather than observing the material as it is now, the telescope collected images of galaxies as they appeared millions and billions of years ago. Since light can only travel so fast, the telescope is a peephole into the history of the universe.

From Vox, learn why the Hubble Space Telescope 's photo was such an incredible, positive influence on the act of sharing data within the scientific community.

On this site: More Hubble videos, including The Beauty of Space Photography and the largest, sharpest image ever taken of the Andromeda Galaxy.

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The 1995 Hubble photo that changed astronomy

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If you hold a pin at arm's length up in the air, the head of the pin covers approximately the amount of sky that appears in the Hubble Deep Field. The iconic 1995 image is crowded, not because it's a broad swath of sky but because it's a broad swath of time.

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On June 3, 1965, after America's first spacewalk was complete, the two Gemini IV astronauts, spacewalker Edward H. White II and command pilot James A. McDivitt, had trouble getting the hatch closed. They managed to, and got back to Earth safely, but what had caused the hatch to stick? Was it due to something called cold welding?

Cold welding or contact welding is a solid-state welding process... Unlike in the fusion-welding processes, no liquid or molten phase is present in the joint.

Cold welding was first recognized as a general materials phenomenon in the 1940s. It was then discovered that two clean, flat surfaces of similar metal would strongly adhere if brought into contact under vacuum. Newly discovered micro- and nano-scale cold welding has already shown great potential in the latest nanofabrication processes.

"The reason for this unexpected behavior is that when the atoms in contact are all of the same kind, there is no way for the atoms to "know" that they are in different pieces of copper. When there are other atoms, in the oxides and greases and more complicated thin surface layers of contaminants in between, the atoms "know" when they are not on the same part." -  Richard Feynman, The Feynman Lectures, 12-2 Friction

In the end, the Gemini IV mission didn't have a cold welding challenge as much as a stuck door challenge, but cold welding is still an issue in space. Veritasium's Derek Muller explains in this video on Welding in Space.

From ESA: More info on cold welding (pdf). Riveting related reading: 50 Years Ago, The First Spacewalk Nearly Ended In Tragedy (but didn't), a story about cosmonaut Alexey Leonov.

Next: Anodizing Titanium - The Rainbow Metal, plus more about metal, more astronauts, and more from Veritasium on this site.

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On June 3, 1965, after America's first spacewalk was complete, the two Gemini IV astronauts, spacewalker Edward H. White II and command pilot James A. McDivitt, had trouble getting the hatch closed. They managed to, and got back to Earth safely, but what had caused the hatch to stick?

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In 1995, scientists pointed the Hubble Telescope at an area of the sky near the Big Dipper. The location was apparently empty, and the whole endeavor was risky - what, if anything, was going to show up? But what came back was nothing short of spectacular: an image of over 1,500 galaxies glimmering in a tiny sliver of the universe.

From TED Ed and Alex Hofeldt, take an animated look at NASA's Hubble Deep Field and eXtreme Deep Field (XDF) images: How small are we in the scale of the universe?

Next: The 1995 Hubble photo that changed astronomy, The Hubble Ultra Deep Field in 3D, The Most Astounding Fact, Solar System, Milky Way, Laniakea: Our home supercluster, and how do we measure the universe?

Bonus: Building the solar system to scale in the Nevada desert.

This Webby award-winning video collection exists to help teachers, librarians, and families spark kid wonder and curiosity. TKSST features smarter, more meaningful content than what's usually served up by YouTube's algorithms, and amplifies the creators who make that content.

Curated, kid-friendly, independently-published. Support this mission by becoming a sustaining member today.

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How small are we in the scale of the universe? | The Kid Should See This

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In 1995, scientists pointed the Hubble Telescope at an area of the sky near the Big Dipper. The location was apparently empty, and the whole endeavor was risky - what, if anything, was going to show up? But what came back was nothing short of spectacular: an image of over 1,500 galaxies glimmering in a tiny sliver of the universe.

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Fly by the moon Phobos towards Mars, and then fly across the Red Planet's surface thanks to NASA's High Resolution Imaging Science Experiment (HiRISE) imagery and three months of digital imaging work by Finnish filmmaker Jan Fröjdman: A Fictive Flight Above Real Mars.

The anaglyph images of Mars taken by the HiRISE camera holds information about the topography of Mars surface. There are hundreds of high-resolution images of this type. This gives the opportunity to create different studies in 3D. In this film I have chosen some locations and processed the images into panning video clips. There is a feeling that you are flying above Mars looking down watching interesting locations on the planet...

The colors in this film are false because the anaglyph images are based on grayscale images. I have therefore color graded the clips. But I have tried to be moderate doing this. The light regions in the clips are yellowish and the dark regions bluish. The clips from the polar regions (the last clips in the film) have a white-blue tone. There are a lot of opinions and studies of what the natural colors on Mars might be. But the dark regions of dust often seems to have a bluish tone. Please study this issue on e.g sites by NASA.

This film is not scientific. As a space enthusiast I have just tried to visualize the planet my way.

Next: To Mars and Back In 150 Seconds, In search of water on Mars, and What did Mars look like 4 billion years ago?

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Fly by the moon Phobos towards Mars, and then fly across the Red Planet's surface thanks to NASA's High Resolution Imaging Science Experiment (HiRISE) imagery and three months of digital imaging work by Finnish filmmaker Jan Fröjdman: A Fictive Flight Above Real Mars. The anaglyph images of Mars

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DK Find Out! | Fun Facts for Kids on Animals, Earth, History and more!

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Visit DK Find Out! to learn about dinosaurs, space, animals, nature & more. Fun learning activities for kids with videos, quizzes & galleries at DKFindOut.com