 Now, I will begin today by talking about explosions and collisions in space. It's one of my favorite things. It's one of the... It's not as dangerous as it seems, but there is a lot that happens in our universe, and we're going to explore that this morning. And firstly, we have to start near the Earth. Now, this is kind of an artistic image by the European Space Agency that maybe you're not usually familiar with, and this is Earth with all the satellites around it. Yes, there's a lot of satellites out there. There's over 6,000 satellites in orbit, more launched every day. Definitely every week. One of the problems that comes with launching satellites is that at some point, eventually, they run out of fuel and they can turn into space junk. And space junk is stuff in space that is human-made, artificial, that we don't have control over, and these things can crash and collide. In fact, in 2009, we saw the very first crash between two satellites. So over Russia, there is this Cosmos satellite, which was a Russian satellite, that they had lost control over, and this crashed into an iridium satellite phone satellite, and this produced thousands and thousands of pieces of debris, almost 10,000 pieces of debris. It was a very large crash or collision in space. And we do worry about this happening. In fact, in February, there's a near-miss between a satellite and an old space telescope coming within a few meters of each other, which in space terms is pretty close. So we do worry about these things. In fact, just two days ago, in the International Space Station, they had to do a maneuver to avoid a piece of space junk, and that was the third such maneuver that they've seen. If you've seen the movie Gravity, where it collides and, you know, we all win because George Clooney turns into space junk. Just kidding, but he does. They were trying to avoid something like that. Not as spectacular, obviously, but they were trying to avoid these impacts, because these impacts and collisions do happen. On the left here, in fact, is an image of glass from the space station, and that hole, which is centimeters deep. So glass in space is bulletproof, right? Because you're traveling into a very harsh place, lots of things. You want to make sure you don't explode, ultimately. Now, this hole was centimeters deep. A piece of paint, a flake of paint created a hole centimeters deep in this bulletproof glass in space. So that is a big collision that it can happen. One of the things we are doing at Mount Stromlo is with electro-optic systems, part of the space environment research center. You may have seen a talk about this this year. We use this laser firing out of one of the domes to track the space junk, track things down to the sides of a couple centimeters, and a new laser that will come online to actually remove that debris and actually burn it up by steering it into the Earth's atmosphere. So really cool post-technology, but collisions do happen in space. But there is another collision, and you may be surprised, and that is the moon. When you look at the moon, it's very beautiful. We obviously like to look at it. Firstly, I think people are surprised how big the moon is. If I were to ask you how big the moon is. Is it bigger, smaller, or about the same size of Australia? What would you say? Well, the answer is it's about the same size as Australia. So here's a picture taken of the far side of the moon. So there isn't a dark side of the moon. There's just a far side. So there's a side that we can't see, but it does get sunlight, as you can see here. And that, in our moon, was actually formed from a big collision billions of years ago. So billions of years ago when the Earth was just a melting planet and this nice ball, something about the size of Mars. It wasn't Mars, but something about the size of Mars crashing the Earth. Then a whole bunch of rock and stuff spilt out of the Earth. This formed a bunch of rock around the Earth that eventually gravity pulled together to form the moon. So in fact, the moon was formed from one of the biggest collisions that has happened on or really around the Earth. But we've seen similar kind of impacts recently. If you recognize this, this is a comet. This is Comet McNaught, sometimes called the Christmas Comets. We had a beautiful view of it about a decade ago here in Australia. And these comets, their comets are essentially kind of like dirty snowballs. There are bits of rock and ice lumped together. They're a couple kilometers wide. Well, in 1994, a particular comet called Shoemaker-Levy 9 crashed into Jupiter. So this video was taken at Siding Spring Observatory. So you can see here, here's Jupiter. Here's the great red spot. Here's one of the moons of Jupiter, Europa. And if we replay this, you can see this big flash on the side. Now, that's not a star. That's not a planet. That's not a moon coming around. That is an explosion from pieces of this comet smashing into Jupiter. And in fact, the Hubble Space Telescope took a bunch of images afterward. And you can see kind of the debris field. You can see these holes, these craters in Jupiter. In fact, the Hubble Space Telescope took a look at Jupiter. And it found this really big hole was about 12,000 kilometers wide. Now, 12,000 kilometers wide is a pretty big hole. That is essentially the size of the Earth. So here's the great red spot to scale. And that's that hole. That's that explosion from that collision of that comet. So imagine a comet creating a hole 12,000 kilometers wide, the size of the Earth. Now, that is a big impact. Now, luckily that didn't happen on Earth. But these things have definitely happened in our time. In fact, in 1908, a slightly different event, but related in Tunguska. So Tunguska, Russia, a massive explosion happened, knocking out a whole bunch of trees and forest, devastating a huge area in northern Russia. In fact, still leaving scarves from the event even today. And what we realized was this was actually from an asteroid. So this is a piece of rock or a meteor hit the Earth as it hits the Earth's atmosphere. It essentially exploded. So when you see a shooting star, that's about the size of a grain of sand or a small pebble. It's pretty tiny. Imagine you get a bigger one. They slam into the Earth and they can sometimes explode. We actually saw this back in 2013 as well. Also over Russia, completely overrated, over Chiblitzk. You may have seen the video is caught on dash cam about this meter. So this meteor was about 20 meters wide hitting the Earth's atmosphere. As it hits the Earth's atmosphere, it explodes. It's kind of like doing a belly flop into the water. It stacks the Earth's atmosphere. It explodes. And so this created like, you know, it injured about 1500 people because it shattered windows and all sorts of things. Now no one died. Luckily that was a great thing, but it definitely created some damage. And these are some real impacts that we can happen. You may have heard of the news actually that there was maybe this meteor or asteroid that was going to hit the Earth the day before the U.S. election coming this year. That one's only about two meters wide. So that's 10 times smaller than the one that hit over Chiblitzk in 2013. So it's not one that we necessarily have to worry about. But we do watch for these asteroids because when they hit, they can really cause some big explosions. What you're seeing in this image from NASA is all the yellow points are happening during the day. The blue points happen at night. So the bigger the circle, the bigger the explosion. And we measure this in joules or this case gigajoules. Now to put this in a scale, 63,000 gigajoules. So between this circle and this circle was the amount of energy released from the Hiroshima bomb, that nuclear bomb a long time ago. And you can actually see some of these impacts that someone in Russia we're just talking about are much bigger than a nuclear bomb. So these are things we actually have to think about. And as you see here, you may have asked, well, I talked about two in Russia, they happen all over the place. It just so happens that most of the earth is uninhabited, oceans and Antarctica, places like that. So we don't often see these impacts, but they definitely do happen. These explosions definitely do happen. Now, the coolest explosion I'd love to study are supernova. So supernova exploding stars and they go boom. So one exploding star is equal to 100 million billion billion billion lightning bolts. So imagine one lightning bolt, then imagine 100 million billion billion billion of them. That is what happens when one single star explodes. Now you may be asking, how often do stars explode? Well, in a galaxy like our Milky Way, we expect one about every 100 years. The last one that exploded in our Milky Way was in 1604. So we're actually overdue. Now when we think of all the stuff in the universe, all the two trillion galaxies in the universe and all the stars in those galaxies, about 50 stars explode every second. So 50 stars explode every second in our universe. That is a lot of stuff. That's a lot of explosions. And when these stars explode, it's kind of just like spotting the difference. We take an image, then we take an image a few days later and we look for something to change. So if you'd like playing I spy at home, this is the perfect job for you. And when these stars explode, it's pretty cool. So when the big stars explode, so this is an animation from data we took from the Kepler space telescope. On the inside of the star, the star is being squished into a ball and it's waking up. And at some point, a giant shockwave travels through the star, causing the star to ignite and explode. And you can see here, this happens in minutes. So our sun is too small to explode, but there's lots of big stars out there. In fact, Orion, in the constellation Orion, there's Betelgeuse, and we'll talk about that a little bit later about how you can see it in the nighttime sky, is due to explode any day. Now, when we say any day, we mean 20,000 to 50,000 years. That's as good as we get. But we do think it will explode relatively soon. I really hope it's something we can see. If Betelgeuse explodes, hopefully if I say it three times, it'll explode, it will be bright enough to be seen during the daytime, almost as bright as a full moon. This thing will be very bright. Now, there are some other types of explosions with stars, and that is sometimes you can get a very small star, what we call a white dwarf, and it uses its gravity to suck off the atmosphere of another star, and then essentially it eats too much, it swallows too much, and it detonates as a big nuclear bomb. And these nuclear bombs go off and essentially the entire star ignites. And some stars actually even crash together. In this case, we have two white dwarfs, two things our sun will be in billions of years, and they're going to smash into each other, ignite and explode, producing a giant explosion in space. So these are really cool. And as I said, these explosions happen every time. Something else that really collides, that is even more exciting I think recently, are black holes. There's been a lot of talk recently about black holes colliding, something that lots of scientists here at ANU are working on, and all over Australia. And that is if you get two black holes, this kind of looks like an owl almost, near each other, they'll eventually spiral into each other and collide. Now, they don't necessarily produce the biggest explosion, but they kind of produce a bigger black hole. So black holes kind of swallow other black holes. And we see these happening, and sometimes we see even bigger black holes colliding. And these are happening quite often in our universe. And when they do, these collisions produce ripples. So imagine you're standing in a lake and you drop a rock. As the rock causes ripples in the water, that ripples travel through it. And so our universe, what we call space time, it's like a giant sheet, it's like a giant lake. And as these black holes collide, they produce these ripples. Or, you know, if you put a heavy weight on your pillow, the pillow sinks. It's the same thing that happens when these black holes collide, they cause these ripples through space, from these big, massive collisions. And I think Naomi is going to talk a little bit about our neighboring galaxies, a large and small Magellanic cloud and the related activity. And these are examples of galaxies that will collide. Galaxies collide all the time. And I know Naomi is going to touch on this more. And it's an amazing thing to see that these giant things in space can actually collide as well. And so there's really a lot of things that go bump in the night. I think it's kind of cool because we think of the universe as this kind of boring static place, these things where not a lot of stuff happens. But it is, and there's things that are colliding, changing on real time. And even the big things like the Big Bang itself, and the Big Bang wasn't an explosion in the traditional sense, but it was a massive release of energy that gave birth to our universe. And in fact, our universe may end even in another big sort of explosion, what we call the big rip. Our universe is going to end at some point. Now, it could be that we believe for a long time that maybe the universe was going to crunch or collide back on itself. We don't think that's going to happen now. It could be that the universe just keeps growing, something called the Big Freeze or the Heat Death, and it just becomes so big nothing can happen. Or the universe can grow so fast it rips itself apart, releasing all of that energy. So there's a lot of these things that happen, a lot of these big explosions, collisions always happening in space. So I think it's fun. A, we're relatively safe, so don't worry. We're not in that much danger. The sun's not going to explode. We do have to worry about asteroids, but again, not anything to lose sleep over. Now, I know we have lots of questions I don't want to try to answer. Will the universe just become one enormous black hole at the end? One of the things that we think will happen is all of the galaxies will be separated. So ultimately, galaxies start forming, stop forming, and then you're just left with a bunch of supermassive black holes. But black holes actually leak radiation, something we call Hawking radiation over time. So black holes need to feed. So over time, if there's nothing else happens, eventually the black holes will get smaller and smaller and smaller until they eventually dissipate. So we won't end in one enormous black hole, we'll end with a bunch of big black holes that over time will evaporate. Will we see any event signs that beetle Jews are about to explode? The quickest we'll see is on order of maybe seconds to minutes. So one of the things that happens is when a star explodes, a bunch of neutrinos, so particles on the inside are released. And they don't travel fast in the speed of light, but it's kind of the first thing to escape. In 1987, a supernova exploded in the Large Magellant Cloud or neighboring galaxy, and 24 neutrinos arrived on Earth, and then we saw the explosion. So we would see these particles arriving on Earth, realize something's happened and be able to point our telescopes to it, but it won't be that far in advance. It won't be days or months in advance. We're really talking about a very small, short amount of time. But that is a good question. What instrument do we use for supernova hunting? I'd imagine it'd be a wide field to cover as much as possible. Yeah, to find supernova, because we don't know where they're going to happen. We don't know when they're going to go off or where. So we just like to look at a lot of stuff. So we use big telescopes. Sometimes that can see 20 to 30 times bigger than the full moon. So imagine the area of the full moon. You can see 20 to 30 times bigger than the full moon. And we just take image of the sky as much as we can. And we keep doing that repeatedly. And that's how we've tried to find these supernova, because as you're kind of hinting at it, we just don't know where they're going to go off. Sometimes there's a close meteor in the past few days. Yeah, there's kind of meteors happening all the time. There are great news stories because they make, they fit into the theme of 2020. But there are meteors that happen. You probably do see them when you see a bright fireball. And there was a good one over Canberra and the East Coast of Australia earlier this month. Lots of people saw it. That was maybe the size of about a meter. It wasn't actually that big. Another just related question, if Betelgeuse explodes will affect us? No. So that's a great question. So Betelgeuse is far enough away that it's going to be an awesome show, but we don't have to worry about it. It's not anything that's going to cause us any damage or really anything to worry about. And then related, someone asked, what is the closest star that may go supernova in the next few million years? Betelgeuse is one. There's also another star called Eta Carina that we see kind of burping or going through these small eruptions that we expect to explode. So these are thousands of light years away. So still pretty far, but close enough that there'll be the closest ones to us and a pretty good show for at least those people who like explosions, i.e. me. So what happened to the thing that impacted the Moon? So we talked about something crashing to the Earth to create the Moon. We don't know exactly what that is. We've looked for evidence. We think part of it lies in the asteroid belt. There's been groups that have been trying to pinpoint exactly what that is, but we haven't really seen or conclusively said this was the exact object that crashed in the Earth to create the Moon. How wide is Jupiter's red spot? Jupiter's red spot was observed first 130 years ago, and at that time is about five times the size of the Earth. Now it's shrinking. It's just about less than three times the size of the Earth. It is getting smaller over time. What is the closest black hole? Just earlier this year, the closest black hole to the Earth was announced at about a thousand light years away. It's still pretty far. So there is more than one black hole in our galaxy. We have the supermassive black hole. We call Sagittarius A star in the center of our Milky Way. That weighs about four million times the mass of our Sun, but there's lots of smaller ones. There's anywhere between a million or 10 million and 50 million small black holes in our own galaxy, the nearest one being about a thousand light years away. There may be closer ones, but that's the closest one that we found. And the Jupiter's question is a great chance to talk about what we can see in the nighttime sky. So let's talk about some of the things we can do, and let's do a little bit of virtual stargazing. So if you're up early in the morning, or sorry, early in the evening rather, a bit too cloudy tonight. If you look towards the west, and this can be seen all across the world essentially. So about maybe about a half hour after sunset, look towards the western sky where the sun is setting, and you'll notice there's a very bright dot, relatively bright, and that bright dot is Mercury. So right now we can actually see all five visible planets. So there's eight planets in our solar system. Uranus and Neptune are too faint to see, so you cannot just see them with your eyes. We obviously live on Earth, so that kind of doesn't count. So then there's Mercury, Venus, Mars, Jupiter, and Saturn. All five can be seen right around now with our naked eyes at some point. So Mercury only lasts for about an hour after sunset, so it's not very long, but we can definitely see it, and it's a really cool thing to check out. Now, tonight you may have noticed, and I definitely recommend checking it out. So right about 7 p.m., this started to become visible. You would have noticed the Moon, and the Moon is actually sandwiched between Jupiter and Saturn. So this has been happening the past few months that over a few days every month, the Jupiter, Saturn, and the Moon have actually been forming this nice trio. And that's because there's a cool, essentially line-up happening where Jupiter and Saturn are near each other, as viewed from the Earth. In fact, in December, they're all going to be so close. Jupiter and Saturn and the Moon will be all right next to each other that you could actually see it through the same telescope shot. So if you go out right now or anytime tonight, you'll see the Moon in between Jupiter and Saturn. So Jupiter is the bright object on the left, Saturn is the bright object on the right. Now, if you ever want to figure out how to find a planet in the nighttime sky, sorry, I lost my train of thought there, planets don't twinkle, and I've said this before, so planets don't twinkle in the nighttime sky. So stars twinkle, and stars twinkle because they're so far away, single points of light travel through our Earth's atmosphere or Earth's atmosphere turbulent, so the same reason you're a plane shake, bends and wobbles at light. Now, these planets have multiple points of light entering our Earth's atmosphere, and they actually do wobble. If you look through the telescope, you can see it. But because our eye blends it together, they appear as solid points. So if you see a bright object in the sky that's not twinkling, it's likely to be a planet. The other trick is our solar system is essentially a giant disk. And all of the objects in the solar system lie on this imaginary line we call the ecliptic. So this is the same path our sun takes in the sky. So if you can kind of trace how the sun moves to the sky, and as you see it going across, anything that is on that line and not twinkling is going to be a planet. And this alignment that we're seeing, and I see someone just asked this as well, it is actually kind of special. So we will get it the next few months. You'll get it in October and November with the best being in December. But this actually does only happen every 20 years. So if you miss it now, and if you miss it the past few months, it won't happen for 20 years. So isn't that common of a thing? So it's definitely worth taking a chance. And so tomorrow we'll have Jupiter and Saturn with the moon on the right side. The formation will be a bit different. You may have noticed last night the moon was on the left. Tomorrow night the moon will be on the right. And so this is some video I took of the moon the other day. When you look at the moon, it's really amazing. So this is through one of the telescopes we have. You can actually start to see really great detail of the craters. Now the line between the light and the dark is what we call the terminator. And you may notice even in this video that along the terminator, sorry, we're just repositioning it, you see a lot of craters on the terminator, the line between the dark and the light, and maybe less of the places. Now there's craters all over. But because the terminator gives you contrast, you actually see lots of craters. So if you have a telescope at home or pair binoculars, focus along the terminator, because that's where you're going to see the most craters. And that's the best chance of seeing something. And someone just asked, is it true there may be life on Venus? There was the exciting announcement the other week of phosphine. So phosphine is a mixture of phosphorus and hydrogen. Now the exciting thing about that was that after lots of study of Venus, they couldn't determine what or where this phosphine was being created. They measured it about 50 to 60 kilometers in the Venetian atmosphere, the atmosphere of Venus. It could be from life, but it is not necessarily. There's lots of things that could cause phosphine that they're trying to rule out. It just so happens that microbes, bacteria on Earth and caves also produce it. So it's really exciting because it may be a sign of life, but it by no means is from life. But it's a lot of exciting reasons to go and look at Venus. Someone has asked what causes the craters on the Moon that you're seeing here. These are asteroid impacts. These are meteor impacts. Now the Moon essentially has no atmosphere. It has a very, very, very small amount of atmosphere. Now as meteors crash into your atmosphere, they burn up. We see them as shooting stars. There's nothing to slow them down on. There's nothing to slow them down on the Moon. So they just crash and create meteorite impacts. Now let's take a look at some other stuff. This is what Saturn looks like right now. So one of the astronomers, Dave Weldrake, took this of Saturn through our telescope at Mount Stromlo. Saturn is really beautiful to see through a telescope. You can see the beautiful rings. You can see the gaps in the rings even. So you can see that the rings are clearly separated from the main planet body. And you can see that there's even a gap in the middle of this ring. And so the rings of Saturn are rock and ice. That's pretty much what they are. Eventually they could be or were parts of old moons. Saturn does have the most moons in the solar system at 82. Jupiter is second at 79. And when we see them, you can really see the detail. Now actually all four big planets. So the gas giants, Jupiter and Saturn, and what we call the ice giants, Uranus and Neptune. So all four of those outer planets actually all do have rings. Uranus and Neptune's rings are a bit bigger than Jupiter. And Jupiter has a very small rings. But Saturn, even through a small telescope or pair binoculars, you can start to see the rings. And here's obviously Jupiter. Jupiter looks fantastic in the nighttime sky. You can see some of the gas bands. And you can clearly see the Great Red Spot, as someone has asked, that big storm of Jupiter. Now, the Great Red Spot is a cyclone. It's a giant storm spinning hundreds of kilometers an hour. So no different to really the cyclones we get here on Earth. They just last for a really long time. And Saturn's actually really asked a good question. When was the last meteorite impact on the moon? We've actually seen them in recent times. Some small ones and big ones. There is even one captured during an event where people were monitoring the moon a couple of years ago. So we do see them, even if they're small. Would you be able to see a meteorite impact? It would have to be pretty big. I mean, you can't see the meteorite craters with your naked eye. So if you had a telescope, maybe. If it was a big one, that probably wouldn't be good because it would be a big meteorite impact. But hopefully, we don't have many of those. So it would probably be tricky to see one of those. But Jupiter, as we were just looking at, looks fantastic. Here's a little time lapse video of it. And you will notice it's a bit fuzzier and wobblier. So this is the turbulence of the atmosphere. Just because you can't see it with your eyes, it is happening. So if we kind of add all of these images together and take a nice, deep, still image, that's the one we get over here. Now there's some other things to see. Around 11 p.m., Mars is rising. So if you're up late or you're up early in the morning and you look straight above you, you'll see this nice red dot. And that is the planet Mars. And Mars looks like a red dot because it is red. That's what Mars is. Through a telescope, you can start to see detail on Mars. You can even notice this white thing. So this white thing is what we call the ice caps. Mars does have ice caps. We don't often think about it, but Mars does have an ice cap. And you can see it even through a good-sized telescope. Now some of the other things that you can see in the nighttime sky. We have the Southern Cross. This is just taken with my iPhone. Here's the Southern Cross. If you look next to the Southern Cross, we have Alpha and Beta Centauri, what we call the pointers. Now Alpha Centauri is quite cool because it's the nearest star to us. And we can use the pointers and the Southern Cross to find south. And this is always a favorite thing I like to point out to people. And there's kind of two cool ways. One, you take the long part of the cross and you go three times. One, two, three. That point is the South Celestial Pole. So if you look behind me, the Earth is rotating. And the stars appear to be going in a circle. That is the South Celestial Pole. That is the point our Earth is rotating. And so directly below it is south. The other way is you draw a line through the long part of the cross and along between the two pointers. And the line or the point those intersect is the South Celestial Pole as well. So it's another great thing to actually see in the nighttime sky. Near Alpha Centauri, which is here and here. That's Beta Centauri. It's a Mega Centauri. So if you kind of form a triangle from Alpha Centauri or Rigel Centaurus to this kind of object to the top of the Southern Cross, you may see there's this bright object. And that bright object is not actually even an object at all. It's a faint fuzzy ball called a Mega Centauri. And a Mega Centauri is what we believe to be an old dwarf galaxy. It's a globular cluster that's full of millions of stars. That through a telescope, as you see here, you can really see it. So all these little pinpoints of light are stars. Now before we move on to Naomi, I'll just take one or two more questions. Do most meteorites come from Saturn's rings? No, most meteorites come from the asteroid belt. So the asteroid belt, it is chaotic. There are a lot of asteroids. Sometimes they bump into each other. Bits of those asteroids break apart. They travel through space and sometimes hit the Earth's atmosphere. So it is something that really can happen. And it does happen that often. Where do the water for the ice come from and all the loose space debris? So it's actually been realized for a long time that water ice is quite common in the outer solar system. Moons of Jupiter and Saturn are rich in water. And so a lot of these things happen. So when you just have hydrogen and oxygen, that mixes to H2O. It is kind of as simple as that. And you can freeze it and condense it on these objects in space. But also ice is not just water ice. Ice is any gas that is frozen. So you can get methane ice. You can get carbon dioxide ice. So ice doesn't just necessarily apply to water ice. And I'll probably make this the last question because it's a great one. What would happen if the Earth didn't have a moon? We would be a very different place. So the moon obviously affects our tides. It also affects our daytime, how fast we spin. In fact, the moon is slowly moving away. So about every year, the moon is four centimeters further. And as the moon goes away, it is actually slowing down the Earth's rotation. So as the moon drifts away, the Earth is slowing down. So our days are getting longer. So yes, every Monday scientifically is a fractionally longer than the previous Monday. Not by something necessarily you can measure, but it really is happening. Millions of years ago, the day was much shorter. In fact, scientists have actually measured using things in the ocean that the day around the end of the dinosaurs were about 23 and a half hours long.