 All right, so just before I start off, I'd like to take a moment to thank the traditional owners of the land in Canberra, the Nona Wall, and Nambi people. We would like to acknowledge their elders past, present, and emerging. So let's get started and start talking about eclipses and shadows in space. And remember to leave any questions you have in the comment section below. So before we talk about eclipses and shadows in space, let's have a bit of an idea of who's talking to you. Who am I? Well, my name is Ryan. I'm an astronomer. I finished my PhD in astronomy at the Australian National University studying at Mount Strom Observatory, which was an incredible place to study. In my spare time, I make some videos for YouTube. And for my work, I look for exploding stars out in the universe. I'm working at the Space Telescope Science Institute. You may not have heard of this place before, but it's the place in America that handles the operation of space telescopes, like the Hubble Space Telescope. I don't really use the Hubble Space Telescope for my work. I use some other space telescopes like the Kepler Space Telescope, which tragically died and is now drifting in space since 2018. And the Transiting Exoplanet Survey Satellite, which is very useful for finding exploding stuff all across the night sky. But enough about me. Let's start talking about shadows and eclipses. So before we get into shadows, we first need to talk about some kind of light source. In space, this light source is usually a star, like our sun. And these light sources are big shining balls of light in space. And they emit light in every direction. So these stars will just happily shine out light. But what would happen if we put a planet in the way, something that doesn't shine light? A light coming from the star would fall upon the planet and illuminate one side. You'd get daytime and the other side would be nighttime. So you also might think that this planet blocking all this light would cast a shadow that looks like this. Everything in that rectangle behind that planet won't get any light from a star. Well, it's actually a little more complicated than that. And that's not the case because the star is a big ball. And it's complicated like this. If you looked at light coming from the top of the star, a lot of it will run into the planet or move past it. Some of it will move above the planet and some of it will move below it. It could pass on by the planet like that. And likewise, if you had light coming from the bottom of the star, it could pass above and below the planet like that as well. So you end up with this one region, this triangle or cone behind the planet where there's no light coming from the star. It's like a big shadow in space. But it's only this cone. It's not that rectangle that we had before. And either side of this cone, we have two other cones which are partially shaded. We call these different areas the penumbra for the partially shaded areas and the umbra for the completely shaded areas. What would happen though if we put a moon orbiting this planet? Well, the moon would orbit around the planet and sometimes it would pass through the shadow of the planet. In reality, the scales are much more different and it's not so easy to have a moon pass through the shadow of a planet. But in this case, we can just tweak it and make it go where we want. So let's put the moon inside of the penumbra. What we end up with here is a penumbra lunar eclipse. So in this case, the moon is slightly fainter than what it would have been otherwise. But if we move the moon slightly further along and have it obscured by the planet's shadow, then we end up with something called a partial lunar eclipse. And you may have heard of those before where half or part of the Earth's shadow will block out part of the moon. But if we move the moon even further still, we'll get to a total lunar eclipse, where the moon is completely in the Earth's shadow and actually appears this kind of red color from light being bent around by the Earth's atmosphere and shone onto the moon indirectly from the sun. So to see what this looks like in real life, I've got this lovely video here from Colin Legge. So the moon starts and the penumbra shadow moves through to a partial and then to a complete solar eclipse. And then once it's passed to a tally, it'll move to a partial eclipse and back out to a penumbra eclipse. So you can see where the Earth's shadow crossing the moon. And then it turns that lovely red color from all of the light bending through the Earth's atmosphere and falling onto the moon in the Earth's shadow. So the cool thing about this is we've actually got a penumbra lunar eclipse coming up on the 6th of June. So the moon will look a little bit fainter starting at 3.45 a.m. Australian Eastern Standard Time. And I'll reach midpoint through the Earth's penumbra at 5.24 and it will cross out the other side at 7 a.m. So the moon will look a little bit fainter during these times, but if you're up while this is happening, it would be worthwhile to check it out. But it's not just planets that can cast shadows. We can have moons in space and just like a planet, it will block out some light. So the moon will cast a shadow similar to what the planet does as well. And we end up with something looking like this where we have the penumbra here. And if you found yourself inside the penumbra of the moon's shadow, you would be seeing something called a partial solar eclipse. If you were inside the umbra of the moon's shadow, you would be in a total solar eclipse. So again, to show you what this would look like in real life, let's look at another amazing video from again Colin Legg. So this is a total lunar eclipse that happened in 2012 in the northern territory of Australia. You can see that the moon blocks out some for a moment, then moves on again. So this is an incredible event that I haven't seen myself, but I'm often recommended to try and spot a total solar eclipse at some point. So while I'm going through this talk, remember to put your questions down in the comments if you have anything you want me to answer. So it's not just a planet or the earth and moon that have eclipses. You can have eclipses happening all over the place. Here's a cool example of an eclipse happening on a neighboring planet. Jupiter, of course, the biggest planet in our solar system. It has a lot of moons orbiting it and it has four big moons, one of which is shown here is Io. It's the closest moon to Jupiter and you can see that it's casting a very perfect circular shadow onto Jupiter's clouds. So if you were to find yourself floating in Jupiter's atmosphere underneath this black shadow, you would see a total solar eclipse just like you would on the earth. So these eclipses can happen all over the place and they happen fairly regularly on Jupiter with all of its lovely moons. But eclipses aren't just property of planets and moons. You can have them on rings as well. Here's another incredible example from Saturn. Now this image is taken by the Cassini space probe, which has burned up in Saturn's atmosphere. But you can see a lot of cool stuff going on. You can see Saturn's shadow being cast on Saturn's rings. And you can also see the rings of Saturn casting a shadow on Saturn itself. So all of these objects in space can cast shadows all over the place. But shadows aren't just pretty things that you might see in space. There can be very useful for science as well. So here's a quick example of how we can use shadows and eclipses in science. And it's to do with finding planets around other stars. So if you imagine a star sitting in the sky and you want to study it very closely, in particular how bright it appears to you. So you might want to measure it and plot it on a graph where the vertical or y axis is the brightness and the x or horizontal axis is time. And if you were just normal, had a normal star, the brightness would kind of mill around, does not really do too much, it'd be very boring. But what would happen if we had a planet? Well, let's see. We'll send the planet across the star. So you can see that as the planet goes across the star, it casts a shadow on us more or less and blocks out some of the light coming from that star. And the brightness of that star dips. Very small amount, but it does dip. And with very sensitive instruments, we can actually detect these things. And so far we've found thousands of planets orbiting distant stars. They're called exoplanets. And there's many thousands more waiting to be discovered. So eclipses are more than just pretty things that we can take pictures of. So just to summarize these things, we talked about the lunar eclipses. There are three different kinds. They're penumbral lunar eclipse, the partial lunar eclipse and the total lunar eclipse. And there's a penumbral lunar eclipse that's going to happen on the 6th of June. And there are solar eclipses, which is when the moon gets between the Earth and the sun or any other star. And we can have lovely eclipses and shadows being cast on anything in the solar system. And they're very useful for finding things out in the universe. So eclipses are generally very interesting, very pretty and very useful objects. So with that said, I'll have some time now to take any questions you might have. So while we're waiting for some questions to come through, I'll just take this moment to show you all about this event that's going to be happening tomorrow afternoon. The Young Stars program has a lecture if you haven't gone enough of astronomy this evening. The universe beginning to end by Professor Brian Schmidt. It starts at 1 p.m. Australian Eastern Standard Time and you can still register for this event through Eventbrite or watch it live on Facebook. All you need to do is search for the Young Stars program and you should be able to find it in either of those places. So let's answer some questions. So one question here is can we detect exo-moons? That is a very good question. And at the moment, there might be, there are some contested claims of exo-moon detection, but it's really tricky to detect it. Let me go back to this slide here where I've kind of exaggerated what happens. In reality, the dip in brightness of a planet going in front of a star is only around 1% or less of the star's total brightness. So we need incredibly sensitive equipment to detect these tiny dips in brightness. And so far we haven't been able to detect conclusively an exo-moon through this transiting method. There are other methods as well of using radial velocity, which is a fancy way of telling us how objects move. Again, there hasn't been any conclusive evidence. So exo-moons might be something or definitely is something left to discover in the future. It's a very hard thing to find. Another question is how often does Australia experience total solar eclipses? Well, total solar eclipses are reasonably common on the Earth, but the tricky thing is most of the Earth is ocean. So almost all of the total solar eclipses will fall somewhere in the middle of an ocean. And I'm not sure exactly when the next one in Australia is. I think there might be one in the 2030s, but I'd need to look that up. Next question is, oh, I've just gotten in some help from the internet. Apparently in the 22nd of July, 2028, over Sydney, thank you, Brittany, is when the next total solar eclipse will happen in Australia. So the next question is if you could see any eclipse in the universe, what would it be? So we can see lots of eclipses in the universe. There are lots of different kinds of things like I showed in the talk. Any object that blocks light from another object that we can see would cause an eclipse. And we can see them from a whole lot of different things, including planets and ones that may not even be around stars. The next question is how frequent are lunar eclipses? Lunar eclipses are pretty common. There's one coming up in the near future in the next year or so. Again, I'm a bit rusty on the dates of these things. So perhaps one of my friendly internet helpers can give me a date on that one. The morning of the 6th, apparently. Yeah, so that's when the next part, the penumbral solar eclipse, will happen in the morning of the 6th of June. Okay, next question. Has Juno captured any eclipses at Jupiter? It has actually. There are lots of amazing photos from the Juno spacecraft for those that don't know. Juno is a spacecraft which is orbiting around Jupiter, trying to understand among many things how Jupiter formed, how the storms operate on Jupiter's big atmosphere. And it does this by taking lots of amazing pictures. And of some of those pictures, some of them are eclipses. There are some I almost put in this talk, but decided on that other one. Okay, next question is, can space junk make a sun or planet less bright? Well, that's an interesting question. They can eclipse things as well. Anything that blocks a light coming from something else can eclipse an object. So there was a YouTuber by the name of Smarter Every Day, who was sharing the American total solar eclipse, found a spot in America where both the moon crossed in front of the sun, and the International Space Station crossed in front of the sun, and took images and videos of both objects eclipsing the sun more or less simultaneously. So anything in space can block light, but the amount of light that gets blocked by space junk and space stations is incredibly small. So here's another question. Do eclipses occur with other parts of the spectrum? Yeah, so eclipses, whatever kind of light you look at, the object passing in front of something else will pretty much block all the light coming from it. Eclipses can get really interesting, though, if there is an atmosphere surrounding, say, an exoplanet. Atmospheres interact with light. I said earlier that the light coming from the sun gets bent around the earth, and that's why the moon turns red during a total lunar eclipse. The same kind of thing can happen if there's atmospheres around planets orbiting other stars. And the effect of that would be that on the same plot here, if you had observed the transit of a planet in one color, it would take out a certain amount of light. And if you observed with another color, it might take out maybe a little bit more of that light. And you can use computer models and atmospheric simulations to work out exactly what that means the planet's atmosphere is made of. And there have been a few really cool identifications of different atmospheres out there around exoplanets. Okay, do we have any more questions coming through? Ah, does a black hole cause an eclipse? That's a very good question. Right, so Eclipse is another really useful tool for Eclipse which was testing theories of gravity. So we're all used to how gravity works on the earth. If we jump up, we get pulled back down, and we don't go flying off into space. But in extreme environments around stars or around black holes, gravity can do some pretty strange things. It can bend and warp space so that light itself bends as it travels around these objects. Now this principle was observed for the first time during a solar eclipse where stars had shifted position during the solar eclipse that were sitting right next to the sun, from where we expected them to be to where we observed them to be. And that shift was due to the sun's gravitational influence. Now with black holes, because they have extreme gravity, the shifts that they cause light is pretty astounding. And if you've seen a movie called Interstellar, there's a really cool model of a black hole in that where the black hole lenses, it's called, bends light up above and below itself. So if an object sits behind a black hole, copies of that object will get made above and below it. So you could imagine a kind of duplicate image around the black hole. So instead of blocking out the object's light, it will actually amplify the object's light and make it brighter than it would have been without the black hole in the way. On to the next question. Are there exoplanets in our solar system? So in our solar system, we have planets. And the way an exoplanet is defined is it must be a planet orbiting a star that's not our sun. So by definition, we don't have any exoplanets in our solar system. The nearest exoplanet we have is around the nearest star to our sun called Proxima Centauri. And there's a little planet that's about the size of the Earth running around Proxima Centauri, which is about 3.4 or so light years away from us. So that's the nearest exoplanet that we know of. Next question is what kind of mineral deposits may be on the far side of the Moon? That's a very good question and one which starts to stray out of things I know. But in general, the surface of the Moon is made out of the same stuff as the surface of the Earth, or the crust of the Earth. So you would expect to see a lot of the same stuff that the Earth is made of. One of the things that you would also find that's not so common on the Earth is lots of helium on the surface of the Moon. And that's because the Moon catches helium that the Sun emits out in great big solar winds. So particles streaming away from the Sun will land on the Moon and make these little helium deposits. So that's one of the very interesting materials that you might be able to find on the far side of the Moon. The next question is what's space traffic like at the moment? How many astronauts are in space right now? So space traffic is getting more busy. As more and more satellites go up into space, things get more complicated, more crowded, and you've got to be very careful that satellites don't run into other things. So space traffic's okay at the moment, but it may get pretty tricky in the future. At the moment, there are three people on the space station and there are two more which were supposed to be launched into space yesterday but got delayed because a big storm came through and they should be trying to relaunch again. I think it's tomorrow morning. So the next question is where do black holes lead to? Answer one question on black holes and then you're bound to fall into another. So black holes are of course the big exciting mystery of physics and astronomy. There are these strange objects that sit in space which kind of break our understanding of physics because they need to obey the laws of gravity which are defined by general relativity and quantum and the laws of the very small things which are defined by quantum physics and we can't mix those two correctly at the moment. The question of where the black hole leads to is a question that we have no real answer to. If you were to fall into a black hole you would get torn to pieces before you had a chance to see what might be on the other side and if you don't get killed I guess by being torn to pieces by the black hole time will slow down to an incredible crawl that you might never actually fall into the black hole from an outside perspective at least. The last question that we have is can we use the helium on the moon to do nuclear fusion? Yeah, that was actually an argument that's been around for a while is that this helium deposits we have on the moon and specifically helium three is very useful for making fusion reactors. You slam the helium atoms together along with some other things like lithium and you can make a lot of very clean energy that way but it's very tricky to get up to the moon and mine things off the moon so at the moment I don't think I think it will be a while before we can use helium from the moon in nuclear fusion reactors. So anyway thank you all for coming along and listening to my talk I hope you learned a little bit about eclipses and I really enjoyed all the questions you had.