Universe Today Video

You probably know we only see one side of the Moon from the Earth. But for the majority of human history, we had no idea what the far side looked like. Billions of years ago, our Moon was formed when a Mars-sized object smashed into the Earth, spinning out a ring of debris. This debris collected into the Moon we know today. It started out rotating from our perspective, but the Earth’s gravity slowed it down until its rotation became locked with the Earth’s, keeping one half forever hidden from our view. It wasn't until the space age that humans finally got a chance to see what’s on the other side. The first spacecraft to image the far side of the Moon was the Soviet Luna 3 probe in 1959, which returned 18 usable images to scientists. And then in 1965, the Soviet Zond 3 transmitted another 25 pictures of higher quality that gave much more detail of the surface. The first humans to actually see the far side with their own eyes, were the crew of Apollo 8, who did a flyover in 1968. We now have high resolution cameras imaging every square meter, even the far side. And here’s the amazing surprise…. You would think that the far side of the Moon would look like the near side, but check out the two hemispheres...They’re totally different. The near side of the has huge regions of ancient lava flows, called maria. While the far side is almost entirely covered in crater impacts. Planetary geologists aren’t sure, but it’s possible that the Earth used to have two Moons. Billions of years ago, the second, smaller moon crashed into the far side of the Moon, covering up the darker maria regions. And just to clarify things with Pink Floyd’s reference to the “Dark Side of the Moon”... Except for the occasional lunar eclipse, half of the Moon is always in darkness and half is always illuminated. But that illuminated half changes as the Moon orbits around us. Just like half of the Earth is always in darkness, and half of every other large object in the Solar System. There’s no permanent “dark side” of the Moon. The side facing towards the Sun is lit up, and the side facing away is in shadows. There are, however, some spots on the Moon which are in eternal darkness. There are craters at the north and south poles deep enough that the light from the Sun never illuminates their floors. In these places, It’s possible that there are reserves of ice that future space colonies could use for their supplies of water, air, and even rocket fuel. Pink Floyd was right if you’re talking radio waves instead of visible light. The far side of the Moon is naturally shielded from the Earth’s radio transmissions, so it makes an ideal spot to locate a sensitive radio observatory. I’ll see you in the permanently shadowed craters of the Moon.

Picture an entire star collapsed down into a gravitational singularity. An object with so much mass, compressed so tightly, that nothing, not even light itself can escape its grasp. It’s no surprise these objects have captured our imagination... and yet, I have a complaint. The name “black hole” seems to have created something of a misunderstanding. And the images that show the gravitational well of a black hole don’t seem to help either. From all the correspondence I get, I know many imagine these objects as magnificent portals to some other world or dimension. That they might be gateways which will take you off to adventures with beautiful glistening people in oddly tailored chainmail codpieces and bikinis. So, if you were to jump into a black hole, where would you come out? What’s on the other side? Where do they take you to? Black holes don’t actually “go” anywhere. There isn’t an actual “hole” involved at all. They’re massive black orbs in space with an incomprehensible gravitational field. We’re familiar with things that are black in color, like asphalt, or your favorite Cure shirt from the Wish tour that you’ve only ever hand-washed. Black holes aren’t that sort of black. They’re black because even light, the fastest thing in the Universe, has given up trying to escape their immense gravity. Let’s aim for a little context. Consider this. Imagine carrying an elephant around on your shoulders. Better yet, imagine wearing an entire elephant, like a suit. Now, let’s get off the couch and go for a walk. This what it would feel like if the gravity on Earth increased by a factor of 50. If we were to increase the force of gravity around your couch up to a level near the weakest possible black hole, it would be billions of times stronger than you would experience stuck under your elephant suit. And so, if you jumped into a black hole, riding your space dragon, wearing maximus power gauntlets of punchiness and wielding some sort of ridiculous light-based melee weapon, you would then be instantly transformed … by those terrible tidal forces unravelling your body into streams of atoms... and then your mass would be added to the black hole. Just so we’re clear on this, you don’t go anywhere. You just get added to the black hole. It’s like wondering about the magical place you go if you jump into a trash compactor. If you did jump into a black hole, your experience would be one great angular discomfort and then atomic disassembly. Here’s the truly nightmarish part. .. As time distorts near the event horizon of a black hole, the outside Universe would watch you descend towards it more and more slowly. In theory, from their perspective it would take an infinite amount of time for you to become a part of the black hole. Even photons reflecting off your newly shaped body would be stretched out to the point that you would become redder and redder, and eventually, just fade away. Now that that is over with. Let’s clear up the matter of that diagram. Consider that image of a black hole’s gravity well. Anything with mass distorts space-time. The more mass you have, the more of a distortion you make....And black holes make bigger distortions than anything else in the Universe. Light follows a straight line through space-time, even when space-time has been distorted into the maw of a black hole. When you get inside the black hole’s event horizon, all paths lead directly to the singularity, even if you’re a photon of light, moving directly away from it. It sounds just awful. The best news is that, from your perspective, it’s a quick and painful death for you and your space dragon. So, if you had any plans to travel into a black hole, I urge you to reconsider. This isn't a way to quickly travel to another spot in the Universe, or transcend to a higher form of consciousness. There’s nothing on the other side. Just disassembly and death. If you’re looking for an escape to another dimension,

We recently interviewed Dr. Kevin Grazier, on of the scientist who has worked extensively on the Cassini mission. Here's what he had to tell us about that mission's discoveries. "My name is Kevin Grazier. I am a planetary scientist, and for my research I do long-term integrations or simulations of early solar system evolution. I'm a former scientist on the Cassini mission and a consultant to several TV series such as Defiance, Falling Skies, the movie Gravity, and formerly, Battlestar Galactica." What are Cassini's most amazing discoveries? "Cassini has essentially rewritten the book on the Saturn system. I was on the spacecraft team for 15 years. I worked as a science planner and as the Investigation Scientist on the ISS instrument. (That's Imaging Science Subsystem, not International Space Station.) And of the discoveries we found, I'm trying to think of what I'd call or classify as the most exciting." "One was predicted - the fact that it was believed that there could be ice volcanoes on Enceladus. And as a matter of fact, there are volcanoes on Enceladus, or active venting, however you want to look at that. Those vents create the "E" ring, so we have a ring created by material vented off Enceladus. That's pretty exciting, because we see an active object venting material, and there aren't a lot of active objects in the solar system." "The surface of Titan is really fantastic. We have open oceans or seas of hydrcarbons on Titan. We have the possibility of an open ocean underneath the crust, just like we believe is under the surface of Europa. We have one image which seems to capture what might be a volcanic eruption. That's important, because in the outer solar system, planetary science considers ice a rock. What a rock is defined as depends on where you are in the solar system. So in the outer solar system, ice is a rock. All of the moons in the outer solar system except Io have icy crusts. Now, if you have a volcanic eruption on Titan, we have an eruption of magma, and if ice is a rock, that eruption is water. So we have evidence of magma chambers which could be cauldrons of life-giving water." "How cool is that? How counter-intuitive is that? How science-fiction-y is that? That one of the most interesting places to look for is a lava chamber or magma chamber that could be suitable for sustaining life. I think that's really exciting." You can follow Dr. Kevin on Twitter

All stars die, some more violently than others. Once our own Sun has consumed all the hydrogen fuel in its core, it too will reach the end of its life. Astronomers estimate this to be a short 7 billion years from now. For a few million years, it will expand into a red giant, puffing away its outer layers. Then it’ll collapse down into a white dwarf and slowly cool down to the background temperature of the Universe. I’m sure you know that some other stars explode when they die. They also run out of fuel in their core, but instead of becoming a red giant, they detonate in a fraction of a second as a supernova. So, what’s the big difference between stars like our Sun and the stars that can explode as supernovae? Mass. That’s it. Supernova progenitors - these stars capable of becoming supernovae - are extremely massive, at least 8 to 12 times the mass of our Sun. When a star this big runs out of fuel, its core collapses. In a fraction of a second, material falls inward to creating an extremely dense neutron star or even a black hole. This process releases an enormous amount of energy, which we see as a supernova. If a star has even more mass, beyond 140 times the mass of the Sun, it explodes completely and nothing remains at all. If these other stars can detonate like this, is it possible for our Sun to explode? Could there be some chain reaction we could set off, some exotic element a rare comet could introduce on impact, or a science fiction doomsday ray we could fire up to make the Sun explode? Nope, quite simply, it just doesn’t have enough mass. The only way this could ever happen is if it was much, much more massive, bringing it to that lower supernovae limit. In other words, you would need to crash an equally massive star into our Sun. And then do it again, and again.. and again… another half dozen more times. Then, and only then would you have an object massive enough to detonate as a supernova. Now, I’m sure you’re all resting easy knowing that solar detonation is near the bottom of the planetary annihilation list. I’ve got even better news. Not only will this never happen to the Sun, but there are no large stars close enough to cause us any damage if they did explode. A supernova would need to go off within a distance of 100 light-years to irradiate our planet. According to Dr. Phil Plait from Bad Astronomy, the closest star that could detonate as a supernova is the 10 solar mass Spica, at a distance of 260 light-years. No where near close enough to cause us any danger. So don’t worry about our Sun exploding or another nearby star going supernova and wiping us out. You can put your feet up and relax, as it’s just not going to happen.

Dr. Ian O'Neill is one of the coolest scientists we know, so we sat him down at the YouTube spaces and asked him a real zinger - when will we humans become an interstellar race, like the ones we're used to seeing on Star Trek? Here's what he had to say to us! "I'm Dr. Ian O'Neill. I work for Discovery News - I'm their space producer. My background is as a scientist - I'm a solar physicist. I got my PhD in Coronal physics. "I think it is possible for humans to become an interstellar race. I think it's possible, but not within my lifetime, not the next hundred years without some really transformative technologies in between. The key one on the International Space Station right now we're testing life support systems, and doing phenomenally well. But the International Space Station is close to earth, so if something breaks down, you can conceivably just hop down and bring something back up, although it is conceivable more complicated than that. As for putting human colonies on other planets, yeah, that's hard, but you've got a gravitational well and you've got a base there, you assume that they've got some sort of infrastructure working." "But if you put everybody onto a space ship and send them out into interstellar space, there is no infrastructure there, no connection to Earth, especially when the years go by and the travel time of messages starts getting very long because of course we're talking about light-years. It could conceivably take several years for one message to get from A to B, so you've got the relativistic issues there as well." "And certainly, without some massive breakthroughs in propulsion technology, I don't think that humans are going to become the Star Trek race we want to be, unless we develop the warp drive. That would be fantastic - then we'll be able to travel around the galaxy at any speed we like. We can even travel faster than the speed of light, with the warp drive. So, ideally, it would be great to create the warp drive." "But within our current understanding of technology and where it is going, the iterative steps that we hope make between that and sending a probe to another star, I just don't see us becoming that space-faring race, not within the next hundred years, not perhaps within the next thousand years. But again, these are timescales that I can't even fathom within my small existence. We're talking about a galaxy that's billions of years old - we're talking about missions that could conceivable take hundreds of years to get to the nearest group of stars. I think we need to start changing the way we think, and science fiction helps - it helps with the warp drive and all that - it kind of pushes us in ways that we wouldn't understand. But in realistic terms, at least a hundred years before that even becomes a possibility." You can circle Dr. Ian O'Neill on G+, follow him on Twitter as @astroengine, read his website here and watch his channel here on YouTube.

Dr. Kevin Grazier was a planetary scientist with the Cassini mission for over 15 years, studying Saturn and its icy rings. He was also the science advisor for Battlestar Galactica, Eureka and the movie Gravity. Mike Brown is a professor of planetary astronomy at Caltech. He's best known as the man who killed Pluto, thanks to his team's discovery of Eris and other Kuiper Belt Objects. We recently asked them about many things - here's what they shared with us about the rings of Saturn. Saturn’s majestic, iconic rings define the planet, but where did they come from? Kevin Grazier: “Saturn’s rings, good question. And the answer is different depending on which ring we're discussing.” That’s Dr. Kevin Grazier, a planetary scientist who worked on NASA’s Cassini mission or over 15 years, studying Saturn’s rings extensively. Mike Brown: “Saturn's rings - the strange things about Saturn's rings is that they shouldn't be there, really, in the sense that they don't last for very long. So, if they are just left over from when Saturn was formed, they'd be gone by now. They would slowly work their way into Saturn and burn up and be gone. And yet they're there. So they are either relatively new or somehow continuously regenerated. 'Continuously regenerated' seems strange and 'relatively new' seems also kind of strange. Something broke up - a large moon broke up, or a comet broke up - something had to have happened relatively recently. And by relatively recently, that means hundreds of millions of years ago for someone like me.” And that’s Mike Brown, professor of planetary geology at Caltech, who studies many of the icy objects in the Solar System. Saturn’s rings start just 7,000 km above the surface of the planet, and extend out to an altitude of 80,000 km. But they’re gossamer thin, just 10 km across at some points. We've known about Saturn’s rings since 1610, when Galileo was the first person to turn a telescope on them. The resolution was primitive, and he thought he saw “handles” attached to Saturn, or perhaps what were big moons on either side. In 1659, using a better telescope, the Dutch astronomer Christiaan Huygens figured out that these “handles” were actually rings. And finally in the 1670s, the Italian astronomer Giovanni Cassini was able to resolve the rings in more detail, even observed the biggest gap in the rings. The Cassini mission, named after Giovanni, has been with Saturn for almost a decade, allowing us to view the rings in incredible detail. Determining the origin and evolution of Saturn’s rings has been one of its objectives. So far, the argument continues: Kevin Grazier: “There's an age-old debate about whether the rings are old or new. And that goes back and forth - it's been going back and forth for ages and it still goes back and forth. Are they old, or have they been there a long period of time? Are they new? I don't know what to think, to be quite honest. I'm not being wishy-washy, I just don't know what to think anymore.” Evidence from NASA’s Voyager spacecraft indicated that the material in Saturn’s rings was young. Perhaps a comet shattered one of Saturn’s moons within the last few hundred million years, creating the rings we see today. If that was the case case, what incredible luck that we’re here to see the rings in their current form. But when Cassini arrived, it showed evidence that Saturn’s rings are being refreshed, which could explain why they appear so young. Perhaps they are ancient after all. Kevin Grazier: “If Saturn’s rings are old, a moon could have gotten too close to Saturn and been pulled apart by tidal stresses. There could have been a collision of moons. It could have been a pass by a nearby object, since in the early days of planetary formation, there were many objects zooming past Saturn. Saturn probably had a halo of material in it's early days that was loosely bound to the moon.”

Dr. Thad Szabo is a professor of physics and astronomy at Cerritos College. He's also a regular contributor to many of our projects, like the Virtual Star Party and the Weekly Space Hangout. Thad has an encyclopedic knowledge of all things space, so we got him to explain a few fascinating concepts. In this video, Thad explains the strange mystery of dark energy, and the even stranger idea of the Big Rip. What is the 'Big Rip?' If we look at the expansion of the universe, at first it was thought that, as things are expanding while objects have mass, the mass is going to be attracted to other mass, and that should slow the expansion. Then, in the late 1990's, you have the supernova surveys that are looking deeper into space than we've ever looked before, and measuring distances accurately to greater distances than we've ever seen before. Something really surprising came out, and that was what we'll now use "dark energy" now to explain, and that is that the acceleration is not actually slowing down - it's not even stopped. It's actually getting faster, and if you look at the most distant objects, they're actually moving away from us and the acceleration is increasing the acceleration of expansion. This is actually a huge result. One of the ideas of trying to explain it is to use the "cosmological constant," which is something that Einstein actually introduced to his field equations to try to keep the universe the same size. He didn't like the idea of a universe changing, so he just kind of cooked up this term and threw it into the equations to say, alright, well if it isn't supposed to expand or contract, if I make this little mathematical adjustment, it stays the same size. Hubble comes along about ten years later, and is observing galaxies and measuring their red shifts and their distances, and says wait a minute - no the universe is expanding. And actually we should really credit that to Georges Lemaître, who was able to interpret Hubble's data to come up with the idea of what we now call the Big Bang. So, the expansion's happening - wait, it's getting faster. And now the attempt is to try to understand how dark energy works. Right now, most of the evidence points to this idea that the expansion will continue in the space between galaxies. That the forces of gravity, and especially magnetism and the strong nuclear force that holds protons and neutrons together in the center of an atom, would be strong enough that dark energy is never going to be able to pull those objects apart. However, there's a possibility that it doesn't work like that. There's actually a little bit of experimental evidence right now that, although it's not well-established, that there's a little bit of a bias with certain experiments that dark energy may get stronger over time. And, if it does so, the distances won't matter - that any object will be pulled apart. So first, you will see all galaxies recede from each other, as space starts to grow bigger and bigger, faster and faster. Then the galaxies will start to be pulled apart. Then star systems, then planets from their stars, then stars themselves, and then other objects that would typically be held together by the much stronger forces, the electromagnetic force objects held by that will be pulled apart, and then eventually, nuclei in atoms. So if dark energy behaves so that it gets stronger and stronger over time, it will eventually overcome everything, and you'll have a universe with nothing left. That's the 'Big Rip' - if dark energy gets stronger and stronger over time, it will eventually overcome any forces of attraction, and then everything is torn apart. You can find more information from Dr. Thad Szabo at his YouTube channel.

Imagine a really bad day. Perhaps you’re imagining a day where the Sun crashes into another star, destroying most of the Solar System. No? Well then, even in your imagination things aren’t so bad... It’s all just matter of perspective. Fortunately for us, we live in out the boring suburbs of the Milky Way. Out here, distances between stars are so vast that collisions are incredibly rare. There are places in the Milky Way where stars are crowded more densely, like globular clusters, and we get to see the aftermath of these collisions. These clusters are ancient spherical structures that can contain hundreds of thousands of stars, all of which formed together, shortly after the Big Bang. Within one of these clusters, stars average about a light year apart, and at their core, they can get as close to one another as the radius of our Solar System. With all these stars buzzing around for billions of years, you can imagine they’ve gotten up to some serious mischief. Within globular clusters there are these mysterious blue straggler stars. They’re large hot stars, and if they had formed with the rest of the cluster, they would have detonated as supernovae billions of years ago. So scientists figure that they must have formed recently. How? Astronomers think they’re the result of a stellar collision. Perhaps a binary pair of stars merged, or maybe two stars smashed into one another. Professor Mark Morris of the University of California at Los Angeles in the Department of Physics and Astronomy helps to explain this idea. “When you see two stars colliding with each other, it depends on how fast they’re moving. If they’re moving at speeds like we see at the center of our galaxy, then the collision is extremely violent. If it’s a head-on collision, the stars get completely splashed to the far corners of the galaxy. If they’re merging at slower velocities than we see at our neck of the woods in our galaxy, then stars are more happy to merge with us and coalesce into one single, more massive object.” There’s another place in the Milky Way where you’ve got a dense collection of stars, racing around at breakneck speeds… near the supermassive black hole at the center of the galaxy. This monster black hole contains the mass of 4 million times the Sun, and dominates the region around the center of the Milky Way. “The core of the Milky Way is one of those places where you find the extremes of nature. The density of stars there is higher than anywhere else in the galaxy,"Professor Morris continues. "Overall, in the center of our galaxy on scales of hundreds of light years, there is much more gas present than anywhere else in the galaxy. The magnetic field is stronger there than anywhere else in the galaxy, and it has it’s own geometry there. So it’s an unusual place, an energetic place, a violent place, because everything else is moving so much faster there than you see elsewhere.” “We study the stars in the immediate vicinity of the black hole, and we find that there’s not as many stars as one might have expected, and one of the explanations for that is that stars collide with each other and either eliminate one another or merge, and two stars become one, and both of those processes are probably occurring.” Stars whip around it, like comets dart around our Sun, and interactions are commonplace. There’s another scenario that can crash stars together. The Milky Way mostly has multiple star systems. Several stars can be orbiting a common center of gravity. Many are great distances, but some can have orbits tighter than the planets around our Sun. When one star reaches the end of its life, expanding into a red giant, It can consume its binary partner. The consumed star then strips away 90% of the mass of the red giant, leaving behind a rapidly pulsating remnant. What about when galaxies collide? That sounds like a recipe for mayhem. Surprisingly, not so much.

The Universe is expanding. Distant galaxies are moving away from us in all directions. It’s natural to wonder, is everything expanding? Is the Milky Way expanding? What about the Solar System, or even objects here on Earth. Are atoms expanding? Nope. The only thing expanding is space itself. Imagine the Universe as loaf of raisin bread rising in the oven. As the bread bakes, it’s stretching in all directions - that’s space. But the raisins aren't growing, they’re just getting carried away from each other as there’s more bread expanding between them. Space is expanding from the Big Bang and the acceleration of dark energy. But the objects embedded in space, like planets, stars, and galaxies stay exactly the same size. As space expands, it carries galaxies away from each other. From our perspective, we see galaxies moving away in every direction. The further galaxies are, the faster they’re moving. There are a few exceptions. The Andromeda Galaxy is actually moving towards the Milky Way, and will collide with us in about 4 billion years.In this case, the pull of gravity between the Milky Way and Andromeda is so strong that it overcomes the expansion of the Universe on a local level. Within the Milky Way, gravity holds the stars together, and same with the Solar System. The nuclear force holding atoms together is stronger than this expansion at a local scale. Is this the way it will always be? Maybe. Maybe not. A few decades ago, astronomers thought that the Universe was expanding because of momentum left over from the Big Bang. But with the discovery of dark energy in 1998, astronomers realized there was a new possibility for the future of the Universe. Perhaps this accelerating dark energy might be increasing over time. In billions years from now, the expansive force might overcome the gravity that holds galaxies together. Eventually it would become so strong that star systems, planets and eventually matter itself could get torn apart.This is a future for the Universe known as the Big Rip. And if it’s true, then the space between stars, planets and even atoms will expand in the far future. Is this going to happen? Astronomers don’t know. Their best observations so far can’t rule it out, or confirm it. And so, future observations and space missions will try to calculate the rate of dark energy’s expansion. So no, matter on a local level isn't expanding. The spaces between planets and stars isn't growing. Only the distances between galaxies which aren't gravitationally bound to each other is increasing. Because space itself is expanding.

Emily Lakdawalla is the senior editor and planetary evangelist for the Planetary Society. She's also one of the most knowledgeable people I know about everything that's going on in the Solar System. From Curiosity's exploration of Mars to the search for life in the icy outer reaches of the Solar System, Emily can give you the inside scoop. In this short interview, Emily describes where she thinks we should be looking for life in the Solar System. Follow Emily's blog at the Planetary Society here. Follow her on Twitter at @elakdawalla And Circle her on Google+ Transcript: My name is Emily Lakdawalla, and I'm senior editor and planetary evangelist for the Planetary Society. There's a lot of different places to search for life in the solar system. If you use liquid water as your proxy for places we should search for life, there's actually liquid water all over the place, because most icy moons of outer planets probably have liquid ocean layers inside them. There might even be some Kuiper belt objects that have liquid oceans - Pluto could have liquid ocean. However, liquid ocean isn't quite enough, because you also need active chemistry, and for that you really need for the ocean to be in contact with rock or some material that is not just more ice, because that is where you can get all kinds of chemical elements to build interesting molecules out of. And so there are a couple of places where we know that's happening. Europa being the big one, where its a large moon that has a thin ocean that's likely in direct contact with a warm rocky core, and it's a world that we know is geologically active, so we know that there's a source of energy coming up from below. And geologic activity brings up all kinds of chemistry - you might have black smoking vents on the ocean floor of Europa, and we know what kinds of cool stuff we find in those environments on Earth, so it would be really awesome to explore Europa and find the same kind of black smoking vents, and who knows - maybe little microbes swimming around. Should we be looking in places other than Europa? Europa's one of the likeliest places to search for life outside of the Earth. A problem, though, is that it's ice shell is very thick, so if you want a place where it's ocean is likely in contact with rock on a geologically active world that is much easier to get to, it's hard to do much better than Enceladus, which a very small moon of Saturn which has these active geysers spewing from it's south pole. Those geysers are salty - it's a salt water ocean, so we basically have a world that is conveniently venting it's ocean out into space. You don't even have to land - you can just fly right through that plume and check to see what kinds of cool chemistry is happening there. So yeah, I think Enceladus would be a really cool place to explore for life.

We enjoy the light from the Sun during the day, and then the comforting glow of the Moon at night. But the light coming from the Moon is an illusion. As you know, you’re actually seeing the reflected light from the Sun, bouncing off the Moon which acts like a mirror. A really terrible mirror. When astronauts walked on the surface, they reported that it was dark grey, the color of pavement. Because of its dark color and bumpy surface, it only reflects about 12% of the light that hits it. Additionally, the amount of light we get from the Moon depends on the point of its orbit. During its first and last quarters, the Moon is half illuminated, but it’s only 8% as bright when it’s full. Just imagine the surface when its only partly illuminated. With the Sun at a steep angle, the mountains cast long shadows. This makes the lunar surface much darker than when it’s directly illuminated. During the full Moon, it’s so bright that it obscures fainter objects in the night sky. Many astronomers put their telescopes away during this phase, and wait for it to go away. When the Moon is highly illuminated, it reflects so much light we can even see it during the day. The brightness of the daytime sky completely washes out the light from the stars, but the Moon is even brighter, and so we can can see it in the sky during the day. The Moon follows an elliptical orbit around the Earth, changing its distance and brightness quite a bit. When it is at its closest point, and it’s full, this is known as a supermoon. This Moon can be 20% brighter than normal. You’ve probably experienced how the Moon can cast shadows. In fact, there are three objects in the sky that can cast shadows. The Sun, of course, the Moon... and Venus. Venus is the next brightest object in the sky, after the Moon. It reflects 65% of the sunlight that hits it. Every few months, Venus reaches its brightest time - that’s when you can see your shadow. On a night with no Moon, head far away from city lights. Let your eyes adjust and watch as your hand casts a shadow on a white piece of paper, illuminated only by Venus. One last thought on reflected light.We talked about how bad a mirror the Moon is, reflecting only 12% of the light that hits it. That’s nothing. Saturn’s moon Enceladus, on the other hand, reflects about 99% of the light that falls on it. If astronauts ever get the chance to walk on the surface of Enceladus, it’ll feel like freshly fallen snow. We have written many articles about the Moon for Universe Today. Here are some interesting facts about the Moon, and here are some Earth and Moon photos. If you'd like more info on the Moon, check out NASA's Solar System Exploration Guide on the Moon, and here's a link to NASA's Lunar and Planetary Science page. We've also recorded an entire episode of Astronomy Cast all about the Moon. Listen here, Episode 113: The Moon, Part 1. References: http://lunarscience.nasa.gov/kids/moonshine http://www-istp.gsfc.nasa.gov/stargaze/Smoon.htm

This article was originally published on Aug 10, 2012. We've updated it and added this cool new video! Sending spacecraft to Mars is all about precision. It's about blasting off from Earth with a controlled explosion, launching a robot into space in...

We owe our entire existence to the Sun. Well, it and the other stars that came before. As they died, they donated the heavier elements we need for life. But how did they form? Stars begin as vast clouds of cold molecular hydrogen and helium left over from the Big Bang. These vast clouds can be hundreds of light years across and contain the raw material for thousands or even millions of times the mass of our Sun. In addition to the hydrogen, these clouds are seeded with heavier elements from the stars that lived and died long ago. They’re held in balance between their inward force of gravity and the outward pressure of the molecules. Eventually some kick overcomes this balance and causes the cloud to begin collapsing. That kick could come from a nearby supernova explosion, collision with another gas cloud, or the pressure wave of a galaxy’s spiral arms passing through the region. As this cloud collapses, it breaks into smaller and smaller clumps, until there are knots with roughly the mass of a star. As these regions heat up, they prevent further material from falling inward. At the center of these clumps, the material begins to increase in heat and density. When the outward pressure balances against the force of gravity pulling it in, a protostar is formed. What happens next depends on the amount of material. Some objects don’t accumulate enough mass for stellar ignition and become brown dwarfs - substellar objects not unlike a really big Jupiter, which slowly cool down over billions of years. If a star has enough material, it can generate enough pressure and temperature at its core to begin deuterium fusion - a heavier isotope of hydrogen. This slows the collapse and prepares the star to enter the true main sequence phase. This is the stage that our own Sun is in, and begins when hydrogen fusion begins. If a protostar contains the mass of our Sun, or less, it undergoes a proton-proton chain reaction to convert hydrogen to helium. But if the star has about 1.3 times the mass of the Sun, it undergoes a carbon-nitrogen-oxygen cycle to convert hydrogen to helium. How long this newly formed star will last depends on its mass and how quickly it consumes hydrogen. Small red dwarf stars can last hundreds of billions of years, while large supergiants can consume their hydrogen within a few million years and detonate as supernovae. But how do stars explode and seed their elements around the Universe? That’s another episode. We have written many articles about star formation on Universe Today. Here's an article about star formation in the Large Magellanic Cloud, and here's another about star formation in NGC 3576. Want more information on stars? Here's Hubblesite's News Releases about Stars, and more information from NASA's imagine the Universe. We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die? Source: NASA

Come on, admit it, you've had this question. “Since astronomers know that the Universe is expanding, what’s it expanding into? What’s outside of the Universe?” Ask any astronomer and you'll get an unsatisfying answer. We give you the same unsatisfying answer, but really explain it, so your unsatisfaction doesn't haunt you any more. The short answer is that this is a nonsense question, the Universe isn’t expanding into anything, it’s just expanding. The definition of the Universe is that it contains everything. If something was outside the Universe, it would also be part of the Universe too. Outside of that? Still Universe. Out side of THAT? Also more Universe. It’s Universe all the way down. But I know you’re going to find that answer unsatisfying, so now I’m going to break your brain. Either the Universe is infinite, going on forever, or its finite, with a limited volume. In either case, the Universe has no edge. When we imagine the Universe expanding after the Big Bang, we imagine an explosion, with a spray of matter coming from a single point. But this analogy isn’t accurate. A better analogy is the surface of an expanding balloon. Not the 3 dimensional balloon, just its 2 dimensional surface. If you were an ant crawling around the surface of a huge balloon, and the balloon was your whole universe, you would see the balloon as essentially flat under your feet. Imagine the balloon is inflating. In every direction you look, other ants are moving away from you. The further they are, the faster away they’re moving. Even though it feels like a flat surface, walk in any direction long enough and you’d return to your starting point. You might imagine a growing circle and wonder what it’s expanding into. But that’s a nonsense question. There’s no direction you could crawl that would get you outside the surface. Your 2-dimensional ant brain can’t comprehend an expanding 3-dimensional object. There may be a center to the balloon, but there’s no center to the surface. Just a shape that extends in all directions and wraps in upon itself. And yet, your journey to make one lap around the balloon takes longer and longer as the balloon gets more inflated. To better understand how this relates to our Universe, we need to scale things up by one dimension, from a 2-d surface embedded in a 3-d world, to a 3-d volume embedded within a 4-d universe. Astronomers think that if you travel in any direction far enough, you’ll return to your starting position. If you could stare far enough into space, you would be looking at the back of your own head. And so, as the Universe expands, it would take you longer and longer to lap the Universe and return to your starting position. But there’s no direction you could travel in that would take you outside or “off” of the Universe. Even if you could move faster than the speed of light, you’d just return to your starting position more quickly. We see other galaxies moving away from us in all directions just as our ant would see other ants moving away on the surface of the balloon. A great analogy comes from my Astronomy Cast co-host, Dr. Pamela Gay. Instead of an explosion, imagine the expanding Universe is like a loaf of raisin bread rising in the oven. From the perspective of any raisin, all the other raisins are moving away in all directions. But unlike a loaf of raisin bread, you could travel in any one direction within the bread and eventually return to your starting raisin. Remember that our entire comprehension is based on 3-dimensions. If we were 4-dimensional creatures, this would make much more sense. For a much deeper explanation, I highly recommend you watch my good friend, Zogg the Alien explain how the Universe has no edge. After watching his videos, you should totally understand the possible topologies of our Universe. I hope this helps you understand why there’s no answer to “what is the Universe expanding into?” With no edge,

This question comes from Sheldon Grimshaw. "I've heard that there are more stars in our Universe than there are grains of sand on all the beaches on Earth. Is this possible?" Awesome question, and a great excuse to do some math. As we learned in a previous video, there are 100 to 400 billion stars in the Milky Way and more than 100 billion galaxies in the Universe - maybe as many as 500 billion. If you multiply stars by galaxies, at the low end, you get 10 billion billion stars, or 10 sextillion stars in the Universe - a 1 followed by 22 zeros. At the high end, it's 200 sextillion. These are mind bogglingly huge numbers. How do they compare to the number of grains of sand on the collective beaches of an entire planet? This type of sand measures about a half millimeter across. You could put 20 grains of sand packed in side-by-side to make a centimeter. 8000 grains in one cubic centimeter. If you took 10 sextillion grains of sand, put them into a ball, it would have a radius of 10.6 kilometers. And for the high end of our estimate, 200 sextillion, it would be 72 kilometers across. If we had a sphere bigger than the Earth, it would be an easy answer, but no such luck. This might be close. So, is there that much sand on all the beaches, everywhere, on this planet? You'd need to estimate the average volume of a sandy beach and the average amount of the world's coastlines which are beaches. I'm going to follow the estimates and calculations made by Dr. Jason Marshall, aka, the Math Dude. According to Jason, there about 700 trillion cubic meters of beach of Earth, and that works out to around 5 sextillion grains of sand. Jason reminds us that his math is a rough estimate, and he could be off by a factor of 2 either way. So it could be 2.5 sextillion or there could be 10 sextillion grains of sand on all the world's beaches. So, if the low end estimate for the number of stars matches the high end estimate for the number of grains of sand, it's the same. But more likely, there are 5 to 10 times more stars than there are grains of sand on all the world's beaches. So, there's your answer, Sheldon. For some "back of the napkin" math we can guess that there are more stars in our Universe than there are grains of sand on all the beaches of Earth. Oh, one more thing. Instead of grains of sand, what about atoms? How big is 10 sextillion atoms? How huge would something with that massive quantity of anything be? Pretty gigantic. Well, relatively at least. 10 sextillion of anything does sound like a whole lot. If you were to make a pile of that many atoms... guess how big it would be. It'd be about.... (gesture big then gesture small) 4 times smaller than a dust mite. Which means, a single grain of sand has more atoms than there are stars in the Universe.