Astronomy Online

JACKIE FAHERTY (Senior Scientist, Department of Astrophysics): So let's bring Carter in over here. Before I intro Carter-- hello, Carter--

CARTER EMMART (Director of Astrovisualization): Hey, Jackie.

FAHERTY: --I wanted to say one thing about the program that we're doing today. We're going to be talking about Pluto. And to set this up-- people are probably-- emotions are probably rising up right now because Pluto is a world that gets people emotionally invested. And Carter loves talking about this world and is going to take us through an amazing tour of it.

And one of the things that we're going to be setting up for you is we're going to go there. We're going to see what it looks like. We're going to look at the terrain. We're going to look in what's in the air. And we're going to talk about the kinds of detailed studies that have been going on in this object in recent years since we've had this mission that's flown right by it.

So Carter Emmart, who is a good friend of mine and also the head of-- the director of visualizations at the Hayden Planetarium, the American Museum of Natural History. Carter is here to be your guide. I am going to be taking questions, giving the questions to Carter, helping moderate the chat. Carter, I think we're just about ready to take this flight.

EMMART: Well, thanks, Jackie. We're going to be doing this today, as we've been doing with these astronomy online programs, using OpenSpace. I'll just quickly show my T-shirt here. That's our logo. And this is a NASA-supported-- in other words, your tax dollars at work-- project.

And we were funded in the same year that we flew past Pluto in 2015. And so Pluto is linked to the birth of this software. And so we, however, launched to Pluto in the year of 2006. It took nine and a half years to get to Pluto. So if you're interested in OpenSpace, you can download it for free from openspaceproject.com. And we also have some of our team on board in the chat so that-- if you're interested.

What I'm going to do is move out from the inner solar system. We see Mercury, Venus, Earth, and Mars. And we see the trajectory-- the very fast trajectory-- of the New Horizons' mission, which launched, as I said, January 19 of 2006. It arrived, famously, on July 14 of 2015.

But how do you get to Pluto fast? The Voyager missions that we launched in the late '70s used gravitational assist to actually speed up the spacecraft to go from planet to planet. So when they got to Jupiter, they got an assist to get on to Saturn. And then Voyager 2 went out to Uranus and Neptune. And so launched in the late '70s, Voyager 2 flew past Neptune in 1989.

But what we left off was, basically, what was then considered the ninth planet, or Pluto. And so we're going to look at this trajectory. And you can see, I'm showing you that it does a little, tiny, barely perceptible-- when it moved past Jupiter-- now, this is actually-- the planets are set for the encounter day, which we're about to go see, out to Pluto.

But you can see that the line has a little bend at Jupiter. Going past Jupiter, it picked up 9,000 miles per hour. This is the fastest thing ever launched. And so from the Cape, we used the large Delta [? IV ?] rocket. And the payload, which we'll see in a second, was small. Fastest thing we ever launched.

Pluto is of personal importance to me, in a certain way. On my first scientific meeting when I was 17, I ended up having dinner with Clyde Tombaugh, who discovered Pluto when he was 24. He was 74 at the time. And so it was wonderful.

What I'm going to do is now just target. I have to fly and drive at the same time here, which can be difficult. But let me just target our spacecraft, New Horizons. And so we're going to zoom now quickly out and look at that nine and a half year journey. And as we get out, we can also see the trails of the outer planet orbits.

And I just thought, let me move around to just show you why Pluto is different. It's inclined. Its orbit is inclined about 17 degrees so the rest of the planets line up in a nice plane. And Pluto takes 248 years to make one orbit. And it's also-- I thought some of you might appreciate, just today, to get our heads out of the news a little bit-- 3 billion miles away, on average, to get out to Pluto.

So as I get here and we close in just a little bit, what I'm going to do is just slow up as we get closer. So I just want to turn off this trail outward that we have. And I'll turn off Pluto's trail. And I'm going to turn-- oh, barycentric trail, and turn that off. And also, just as we get closer-- sorry. Let me just come up here. And I'm going to turn on another little trail.

So as we get closer, we're going to see-- actually, we're going to get close to the spacecraft. Let me turn-- and this is basically the encounter trail as the New Horizons spacecraft went past Pluto. And so as I come in, we're just going to see-- zooming in on where the spacecraft is. And we see the Pluto system.

But what I'd like to show is-- let we focus first on just Pluto. So in 1978, astronomers on Earth detected that Pluto had a moon. And so in blue, we see the orbits of, actually, five moons. But here, we see Charon. Some say "share-on." And the pronunciation varies.

But here, we can see Pluto and "care-on," I'll call it today-- and that they have this interesting gravitational dance around one another. And because Charon is half the size of Pluto, they actually orbit a balance point between them. So you might just barely see-- if I come close enough to Pluto, you'll see this little balance point. So we call that the barycenter.

And then also-- oh, I'll just say a word about this bright line that we see of the trajectory of fly-by New Horizons. To get to Pluto, it had to go very fast. It passed Pluto going about seven miles a second, which is very fast. You might think that's extremely fast, but we are going about twice that speed-- the Earth is-- you and I, everybody on the Earth going around the sun. But nevertheless, we came very close to Pluto.

But the Hubble Space Telescope targeted Pluto, and we found four other moons-- Nix, Styx, Hydra, and Kerberos. And because of that, we were worried-- the trajectory and the mission planning was such that we wanted a line that would go nearest this orbit of Charon. Charon goes around Pluto every about-- almost a week-- six and a half days. And so we wanted this line to go past that orbit in case there was a ring of debris around Pluto.

Now, Pluto is about 3/4 the size of our moon, so it is a tiny world. So that's why we call it a sort of dwarf planet. But we do give it a sort of-- it's dwarf planet-- it's a planetary system, because look at all these worlds that are orbiting it.

I'm going to do one more thing here. I want to turn on Pluto's shadow for us and also turn on Charon's shadow. And these are basically-- I'm just highlighting, in gray, the shadow of-- cast by both Pluto and Charon, because the trajectory was also designed to go right through the shadow. Why? Because we had also discovered an atmosphere on Pluto.

Now, we don't have an atmosphere on our moon, but this is very interesting that there's this shadow. And so I'm going to ask if we can have a slide here that was actually a picture taken by New Horizons, which is very beautiful, that shows the atmosphere and the layering to it. And so it's a blue rind. So this picture was taken by the New Horizons spacecraft.

So what I'm going to do now is I want to get close to the spacecraft just so I'll show that briefly. I'm going to target that, swing around. And now I'm going to move closer to it. And as I do, what I'm going to do is turn off its trajectory. So here we are. We're still moving close. I just want to come up. And so I'm going to turn that off.

Now, what is this we're looking at? There we have this line sticking up, as we'll see in just a second, is where the camera is aiming. And there were two main cameras on board, one that had a complicated method of taking colored pictures. But the high-resolution, monochromatic-- or black-and-white-- pictures were coming from this one instrument on board the spacecraft.

Now, the spacecraft is about the size of a grand piano. The dish, which is the communications antenna, is 6 feet in diameter. So think of a tall person. And then, also, it has this black end here, which is the battery. Plutonium is hot. Space is cold. So you run a thermocouple between that's basically like a battery that can run off a temperature difference.

But right here is the LORRI camera, the Long-Range Imaging System-- Reconnaissance Imager. And so that's going off. So it takes these pictures. See that tiny little square in the background? I'll just point to it-- is where it's looking. And so it sees an image about the size of the full moon. So think of a good telescope in your backyard. You're looking at the full moon.

And so now if-- I'm just going to run time here a little bit. We're sort of stuck in time. But if I start to advance time, that-- let me just bring this a little faster. We'll see the telescope is swinging into position. And it's going to take pictures of Pluto.

So what I'm going to do is come down now before the pictures are taken. Now, I've already given it away. We see this beautiful map of Pluto, which was the result of all the imaging on this mission. But what I'm going to do now is going to turn off the labels for Charon and Pluto. I'm going to turn off their shadows. We talked about that. And let me just come down. Pluto, Pluto's shadow-- off. Great.

And another thing that I want to do is show us the best image that we had of Pluto before we got there, taken by the Hubble Space Telescope. So what I'm going to do is just come up and select that. And I just thought, while I do this, I might ask Jackie if there are any questions coming in.

FAHERTY: Yeah, Carter. I was just about to say we've got a couple of cool questions coming in. One-- I wanted to give a shout-out to some people in the chat here. Davis Sparkie, it looks like you're writing us from Kenya. Welcome to the YouTube chat. A lot of kids writing in from various schools. Make sure you tell us what schools you're at, because I can give your school a shout-out in here, too.

Carter, something that's being asked that I think would be good for us to remind people is-- Maia Hure has been asking about how far off Pluto's orbit is. And you've said it, but I think we should just repeat it so people can be reminded, because we're also getting asked the question about--

EMMART: Yes.

FAHERTY: --why Pluto isn't a planet.

EMMART: It's 3 billion miles away, on average. We can think of this in a different way, too. How far away is the sun? The sun is 93 million miles. These numbers are huge. But Pluto is 40 times-- just under 40 times-- the distance of the sun from the Earth. So we really-- we're beyond the orbit of Neptune.

It was discovered by Clyde Tombaugh on a survey. He was actually looking for a tenth planet at the Lowell Observatory in 1930. And he saw a tiny little thing. It looked like a star. And what you do is you take a picture one night, take a picture the next night. And you see that that-- oh, one star has kind of moved. Well, it was tiny Pluto.

Now, looking at it with the Hubble Space Telescope, this is the best image that we have. And that's why I'm showing it to you. A friend of ours, Marc Buie, a scientist at Southwest Research Institute in Boulder, Colorado, which is the team Alan Stern led, the team on New Horizons that-- Marc Buie took 250 Hubble images. That's a lot of telescope time.

And what I'm going to do is-- yeah, I'll just do this. We're going to see what the images from New Horizons look like. I'll slow this down just a little bit. You see the pictures coming in. And changing that map from 250 pictures, put together, he had to build a special computer just to process those 250 images. But it was totally blown away by having a camera sent there, nine and a half years-- New Horizons spacecraft-- to get to Pluto.

I went to the launch. And I was amazed to hear, by Dr. Alan Stern, who launched the mission and organized the whole thing, that some of the ashes of Clyde Tombaugh, who discovered Pluto, were on board the spacecraft. And it was emotional. But here is the imaging campaign carefully planned out while the spacecraft was on its way to Pluto.

And so here, we can see these images revealing a very strange world that-- we knew that it had an atmosphere. And we had detected basically nitrogen-- just as 78% of Earth's atmosphere is nitrogen, so we're breathing it. Then there's oxygen, of course, that we need.

But this nitrogen-rich atmosphere on Pluto, also with methane-- traces of methane and carbon monoxide-- when the scientists started thinking about this-- and the temperatures out here are so cold that what would just be gases, of course, on Earth and in a warmer place in the solar system actually begin to create frost and ices. And otherwise, they'd be volatile and just become vapor. But what we began to see was this amazing world.

And of course, we had all heard about this heart on Pluto. And so here it is. If I turn it over here, we can see the heart shape, which has been given the name Tombaugh Regio, which means "the region of Clyde Tombaugh," in his honor, who discovered it. And so if I just use my pointer, I will point out-- but in the left side of the heart, is what we call, now, Sputnik Planitia, and named after the first human-made satellite launched by the Soviet Union in 1957, which really--

FAHERTY: Carter--

EMMART: --started the space program. Yes, Jackie.

FAHERTY: I just wanted to bring in, since you're talking about the heart-- and we've had-- even before you brought it up, a lot of people knew about the heart. And so John Bachansky, for instance, who's got two little ones at home-- homeschooling them-- was asking-- they were asking what's in the heart-- and I think you're about to get to that, too-- as well as--

EMMART: Yeah.

FAHERTY: --Thomas Shindler, I want to give you a shout-out, too. You're asking about the heart right now.

EMMART: Hello?

FAHERTY: Yeah. Carter, you can keep going. We can keep talking about the heart.

EMMART: OK. I was just making sure that I had a map I'm going to reveal-- the map I started off with. And we're just going to see that come back up in just a second. So I've got my projections here. I want to see--

FAHERTY: While you do that, I should give--

EMMART: Yeah.

FAHERTY: --a shout-out, too, to-- we've got several students from PS 92, from Edward R. Murrow, from Adrian Hegeman Elementary School with some great questions, including ones that are about the heart right now. It looks like you've got your map back up, but I want everybody to know--

EMMART: I do.

FAHERTY: --we're seeing you on the chat.

EMMART: And I just want to make sure that-- let's see-- that I had this set for-- OK, just a moment. Let's see. Oh, huh. Mm-hmm. OK, [INAUDIBLE]--

FAHERTY: So as you get it set, too, Carter, I could say, since you've just shown this--

EMMART: Very good.

FAHERTY: --transition from Hubble Space Telescope-- very--

EMMART: Really?

FAHERTY: --very nondetailed image all the way to this amazing--

EMMART: Yay!

FAHERTY: --thing--

EMMART: It's brighter now. That's what I wanted.

FAHERTY: There we go. OK, cool.

EMMART: OK. So yes, what's very interesting about this is-- with Pluto-- is that we could also tell, from its size and also its orbits and all this-- we could work out, basically, how heavy it was or its mass. And then we found Charon. And so we knew that, basically, somewhere-- the density, the bulk of all this world-- of these two worlds-- are similar in composition.

They're somewhere between rock-- like silicate rock like we have on Earth, and water-- so a thick layer of water. And out here, it must be ice. And water out here is so, so cold. It's about the tensile strength of steel. And so anything else that might flow on it and so forth, I already talked about the atmosphere.

So let's come in close. But I'm showing Charon in the back here so that we can see how the heart is in view on what is called the encounter hemisphere. In other words, this is the best view we got as we flew by. So if I just draw your attention to the shape of this, it's round. And of course, it has a trail off here. But we think that this might have been a very large crater.

Now, if we come closer to Pluto-- and I'm going to do this so that we can fly over it as we get close-- is that we notice that around it are lots of craters, and-- which looks like the moon. There are dark areas and light areas. And I'll talk all about that. But that Sputnik Planitia-- is what it's called-- is right here-- this smooth area-- is very smooth and has no craters that have been discovered. However, we see all these troughs and these sort of cellular pattern on it.

So what's going on here? Well, let me come down and approach it this way. And I'm going to show you that because we're able to take multiple pictures, and also the technology allows us to look at the shadows and so forth-- between taking multiple pictures, we can extract the elevation of these mountains, allowing us to make maps that are put together like a big puzzle.

So you saw all that mapping strategy before of New Horizons. They also had a complicated color imaging camera on board that gave us the colors. And all this could be merged into what we see here with the mountains sticking up.

And so what I'm going to do is just come down a little bit like this. And I'm going to ask you if we can show this other slide, which was basically the parting shot as New Horizons-- just before it went into the shadow. Look at this wonderful picture. This is the New Horizons lookback picture.

And in it, we see, closest to us, the Norgay Mountains, and in the back, the Hillary Mountains. And so I think if we go back to OpenSpace, I can explain what that means. Tenzing Norgay and Sir Edmund Hillary were the first to climb Mount Everest in 1953, and so they gave the title of these mountains to them.

And so now, that image allows us to calibrate how high the mountains are. I could exaggerate them and make them much bigger. But what I want to do in [INAUDIBLE] time is to fly along to give us this flyover on the edge of Sputnik Planum.

So what we see on the left are dark features. And they map along the equator of Pluto. We're flying northward here. And so Pluto is tipped over. We could see that as we approached, so we came up to it almost like a bull's eye. It's almost facing the sun right now. But along the equator, we have this dark material. We believe that that has been sort of-- that has rained down from the very thin atmosphere of Pluto.

Pluto has an orbit that's a little more elliptical than our very circular orbit around the sun-- with Earth. So Pluto goes through-- basically, it has seasons. And when it's farther from the sun, the atmosphere freezes out. And when it's closer, the atmosphere comes into play.

We're flying over some of this dark and light material. And that dark material, we believe, is a result of its atmosphere of nitrogen and, as I mentioned, carbon monoxide, and also bits of methane-- trace amounts-- and mostly nitrogen. But it gets hit by the ultraviolet light of the sun and can create complex organic chemistry that rains down. This is called tholins. This is one idea of what we're seeing in this dark and reddish material.

And now, also, this cellular structure that we see of the ices of Sputnik Planum. What we believe has happened is that-- and I'll just pull back out for a second to look at the overall view here-- is that Sputnik Planum seems to be this impact, this large crater, and that it's the lowest part of Pluto. And so it creates this basin.

And so this atmosphere that comes and goes with the seasonality essentially concentrates. And when it sort of condenses out and falls into the surface, it condenses into this low area, creating, basically, a sink for a slushy nitrogen ice sea, in a way. Now, it's not liquid. It's not liquid at all. But it's sort of the consistency of Silly Putty.

Notice, also, that what we see here is-- around the ridge-- is we have this edge of the basin. And then we see these blocks. These blocks each are, on average, about 25 miles across. Pluto is about 1,500 miles across. It was about 3/4 the size of our moon. But the width of Sputnik Planitia is about twice the width of Pennsylvania.

And so I'll just come on down again. And we're going to see that these blocks seem to-- they're water ice. They have a spectral reflectance of water ice. And they seem to be moving away from the edge of the basin and rotating that-- they're sort of a jumble.

And I'll just tip over so that we can fly along this a little as we see the cellular structure, that the properties of nitrogen ice and the temperature regimes out of Pluto are such that, if it's warmed from beneath-- and I'll talk about that in a second-- and then it's cold up top, is it would flow like a lava lamp.

And so you see, basically, convective cells, if you've ever boiled water. And advection is another term used. In science, it just means the sideways flow of the material. So it creates these cells of a mushy, nitrogen, icy consistency of Silly Putty or toothpaste. And so because it has this soft character and is flowing, we can see the hard icy ridges of craters. And where there are craters, we can see that those are retained from an earlier time.

And craters have been built up, we believe, in some of the oldest parts of Pluto, perhaps as far as 4 billion years ago, and sort of basically looking at remnants of its formation. We believe that Pluto and other members of-- Pluto is the largest member of the Kuiper Belt, an icy asteroid belt at the edge of the solar system-- is that we believe these worlds formed closer in to the sun. And then the dynamics of Jupiter, Saturn, Uranus, and Neptune were such that it cast these planets further out.

I'm coming up to an area where we can clearly see almost flow features on the right from this action of this slushy environment and low area. And if I come farther down along Sputnik Planitia, we should be able to see areas that are quite interesting in the sense that we get away-- we still see the cellular structure over there. And as we get closer to the shadow area, we can see how they have a little bit of shading. They show these shallow-- they create sort of shallow domes. But--

FAHERTY: Carter--

EMMART: And yes, Jackie. I'm going to come right around to where the glaciers are here. Yes.

FAHERTY: As you do, we've got some great questions in here--

EMMART: Good.

FAHERTY: --one coming from Austin Lin from PS 205. And seeing all these sizes, what is the tallest hill/mountain/bump that we can see on Pluto?

EMMART: So what we saw with those blocks that I flew over-- and also, the Tenzing Norgay and Sir Edmund Hillary mountains are essentially about 16,000 feet tall. So think of, like, if you've ever been out to Colorado and the Continental Divide. Those mountains tend to be about 15,000 feet. But they start from the mile-high city of Denver. So we're only seeing about 10,000 feet of height. So clearly, we're getting into mountains that are very tall-- once again, on a world that is 1/5 the size of Earth or so. Or actually-- yeah, about 1/5 the size of our planet.

Here below us, can you see these swirly patterns? I'll just show you in Sputnik Planitia again-- is that we see what look like-- I'll just navigate down a little bit and rotate like this-- is that we can see this area at the bottom, which is really the left side of the heart-- are these ices that seem to be melting away into this nitrogen, which is then flowing downhill into these glacial flows, creating these flow patterns out into the Planitia.

There are also pits. And we believe that they have to do with the warming underneath and, perhaps, the release of the volatiles, that nitrogen is the main substance, but also the highly-volatile carbon monoxide and methane gas. So we'll see more pits over here.

I'm going to fly us over to-- not only do we see this area where the ices seem to accumulate, but I want to fly us over to a very interesting large feature that's, perhaps, almost as much as about 100 miles across. It kind of looks like elephant skin, I think. And this is this domed feature right here, which, I believe, because of the texture of this-- looks like elephant skin-- looks like it's been built up. And so this could be an icy volcano on Pluto.

And we think we see one crater over here. So where you see craters, it means things are generally older. But what we see in Sputnik Planitia-- because there are no craters, we think that that's very active and young, compared to the rest of Pluto. Also, as I pull out, we can see, over here, craters that are somewhat buried in the ices. So Jackie, I don't know if there are any other questions as I cue this up to fly to another location.

FAHERTY: Yeah, as we're going out, people are noticing a lot of the different features. And we just had one from-- I want to make sure I get your name so we can see your chat up here-- Englander. And it's about how much Pluto might have been hit by meteors and if there's signs of that. With so many craters, you can see that there's clearly something going on. I'm not sure if you know the answer to this, Carter. I know there's been a lot on this since New Horizons.

EMMART: Yeah. So basically, you're seeing craters here. And so this represents an older part of the surface of Pluto. Where you see more craters-- we found, in our studies of the moon, where there tends to be lots of craters, it's older. If you see something smooth, that means that something overrode the craters. And so I talked a bit about how Sputnik Planitia is round, and they think there was this large impact.

There's one other point I want to make about this before we go off to Charon. But that's a really good question. How many craters and so forth? It's interesting. There's not much material out here. There's a lot of stuff in the Kuiper Belt, but it's farther away from the sun. Material is more spread out. And so we think that this number of craters, perhaps, is an indication of forming a little bit closer to the sun and then getting cast out by the dynamics of the gravitational interactions with the larger planets.

There's a big crater up here, and I must show it. It's right here. And it's subtle. It has other craters inside it. And this is named Venetia Burney after-- she was 11 years old when she named Pluto. So when Clyde discovered Pluto, there was a name contest that went out. And Venetia Burney in England named it. So she was 11 years old at the time. And so she named it Pluto after, of course, the gods of the underworld.

And so we also see fractures. You can see those cracks. That crack right here-- this is a crack. And it seems to be in line with, perhaps, this impact. Now, I want to point out something that's really, really interesting. And it's interesting not only for Pluto but for other Kuiper Belt worlds that we haven't been to yet.

The fact that there is this very interesting part of Pluto that is low and seems to be where the ice is accumulated, and also is where the atmosphere gets rejuvenated from, is that it's this-- oh, but it faces right-- it faces in the opposite direction from Charon, or "care-on." And they basically-- these worlds are so close to one another.

You know how we have tides on Earth, and the water goes up and down depending on where the moon is and how it-- we rotate under the moon every 24 hours. And the moon rises and sets. There are tides. And that's going to be even greater of an effect out here where you have such a large moon that's so close. So to have this impact basin with all the ices diametrically just right across-- directly across-- from Charon indicates that we believe, now, that the icy crust of Pluto may be decoupled from a warm, rocky interior.

And that rocky interior is warm, just like the interior of Earth is warm, because of radioactive decay. And so that slightly warms what could be the covering above it. But because this is directly opposed-- is that this seems to be evidence that, underneath the icy crust, that water is actually liquid and that there's a liquid ocean underneath the icy crust of Pluto.

This is very interesting, because where there's water, or liquid water-- and we know that there's liquid water underneath the ices of Europa, the smallest moon of the major four Galilean satellites around Jupiter-- is that, could there be life? What we see are organic compounds that make up the basis of life in the atmosphere, in the ices of Pluto. But it's very cold. But it has this large moon.

I'd like to take us out to Charon. But before I do, I want to show the effects of, possibly, the weather and climate on Pluto. And the last thing I want to show here is this bladed terrain, Tartarus Dorsa. This is a region where you have basically 15,000-foot mountains. So that question about the height-- these are actually very high.

But they seem to have, at least the spectral signature-- of methane ice that's deposited on the top. And we believe that that's-- because it's so high up that it allows, basically, the methane to freeze out. And so we're looking at these bladed terrains that are possibly built up over a great deal of time.

And there's a beautiful shot right here in the lower part-- is that we can see the shadow of these bladed terrains, long shadows across an embayment, or how it almost looks like a part of Sputnik Planitia just cast aside. And then also this large fracture. The large fracture could be the effects, once again, of these dynamics of both the impact as well as tidal interaction.

So we're going to go off tidal interaction with Charon. So let's go out to Charon. I'll target it, and we'll fly off there. What did we find at this world half the size of Pluto? We found that it's darker. We also see that it has a spectral signature of ice. So it's not covered. It doesn't have an atmosphere. So it doesn't have this nitrogen covering. It seems to just be mainly water ice.

But it has this strange eye on the top of it. This is a north pole. And it's called Mordor Macula. Macula means spot. And what could this be? It seems to be reddish and seems to be, perhaps, some of this material perhaps caught in a stream of material that has escaped Pluto and has made it over to and frozen out the North Pole of Charon. Very interesting.

And then we have this huge canyon here, and also this strange set of other craters, and some more craters in a-- not more craters than Pluto. But we don't see any smooth area-- as smooth as we see of Sputnik Planitia. But we do see an area that's lower than these mountains here in this giant fracture.

For those of you who are science fiction fans, and depending on your age, they'll sort of test your science fiction knowledge. But maybe if some of the parents out there were Star Trek fans, I'll just point out that this is Spock Crater from, of course, Star Trek. And over here is Captain Kirk Crater. But also-- let's see. A couple other characters over here is Uhura Crater and Sulu Crater right here.

And so also, if you're old enough to know the movie 2001-- A Space Odyssey, in honor of the creator-- the director of the movie is Kubrick. This is Kubrick Mons. And over here is Clarke Mons. So Arthur C. Clarke wrote the story 2001-- A Space Odyssey. Stanley Kubrick made the film.

And so what we see is, in this lower area-- so this, through here, is this low plane that we think is part of this fracturing process that Charon had-- this resurfacing through here-- and perhaps was a flow inundating mountains that already existed. Well, why would this happen? Is it tidal frictions with Pluto? Perhaps not. Perhaps it's just that water freezing out-- of course, when it freezes, it expands. And so it could have created the fraction that we see.

We see a large canyon in here. This is called the Serenity Chasma. So this is right here. And then also, the naming of some of these features, kind of bowing to [INAUDIBLE] science fiction. So if you're a Star Wars fan, I'll just point out this-- a couple-- there's a dark and a light crater up here. So this is Darth Crater, and this is Skywalker Crater. And then if you were a fan of the movie Alien, this is Ripley Crater in here. And this canyon right here is Nostromo, named after the spaceship that they were in in Alien.

Also of note is something interesting, that we see a signature of ammonia in these bright craters that have come in. And so ammonia is that terrible-smelling cleaning agent your mom or dad might be using out there. But it's interesting. When you have ammonia with water, it lowers the freezing temperature. And so there is a thought that that elephant skin-- Wright Mons volcano that we saw on Pluto may actually have ammonia as a part of it to lower the temperature of the water ocean on Pluto, and allowing it to remain liquid. So very interesting set of conditions.

Jackie, how are we doing for time? I could go on and on, but I'm sure there are tons of questions.

FAHERTY: Yeah, we do have lots of questions. We have a very engaged audience.

EMMART: Great.

FAHERTY: I'm so glad to see this. And we probably only get a couple of minutes left here. And with that, we might want to grab some of these questions. We've had a lot of chat in here about moons in general. And I wanted to highlight a question that was just asked by Matt--

EMMART: OK.

FAHERTY: --Matthew Tagoe. And it's [INAUDIBLE] philosophical. And it's about, can you get another moon? It appears that-- is it possible to get another moon? I think he's referring to Earth here. Since Pluto's got Charon and all these other moons--

EMMART: Yeah, you know, that's a--

FAHERTY: --we've just got one.

EMMART: --really good question. And there's a question, like with Mars, it has Deimos and Phobos that seem to be like asteroids. So could they have been captured? That's a question. We see that Nix, Styx, Hydra, and Kerberos have reflectance similar to Charon, the water ice. Pluto is the exception in that we have nitrogen, and carbon monoxide, and methane. So those smaller bodies are icy.

We actually have a slide of that, if we could bring up the slide that shows the relative size in the smaller amounts as imaged by New Horizons. So here, the images have all been placed in proper size to one another. So you can see that Styx and Kerberos are really small. But Nix and Hydra are about 30 miles across. And then you see Charon underneath, which is half the size of the 1,500-mile or so diameter-- 1,477 or so-- of Pluto, and just about half that for Charon.

So the idea of capturing is an idea that-- could they have been captured? But most likely, the notion is that the Pluto system may have been formed by a collision. And we now think that the Earth and moon system was formed by a collision, as well, during the planetary building process.

I wanted to say one last thing in closing-- is that Pluto, of course-- if it was demoted to minor planetary status, it's certainly a planetary system. I'll just tip-- I'll show you how it's tipped over in the solar system just by coming around like so, that we can see that it's almost-- as it parades around the sun, that it has seasons just like the Earth being tilted. Pluto is tilted. But it really is this largest member, as far as we can tell, of a group of icy worlds at the edge of the solar system called the Kuiper Belt.

So what I'm going to do is pull out a little farther. And as I do, what I'm going to do is probably bring back, in a moment-- let's see if I've still got my labels up for-- OK, I think I have them on-- because I want to demonstrate the Kuiper Belt in just the last minute or so. I might take another question as I do this, Jackie.

FAHERTY: Yeah, one more, and I think we have reached the end. And I just want to note that the moon did have-- it was in the news a bit, maybe six months ago-- pre-COVID, so more than six months ago. It was discovered the moon had captured a new rock around it for a little while. We were calling it a new moon for the Earth. So that helps answer one of--

EMMART: Bring it on.

FAHERTY: --these questions. And this goes to another question, maybe as our last question, which is, what is the smallest moon possible that one might have?

EMMART: Well, basically, when Sputnik was launched-- it was just about 18 inches in diameter or so-- by the Soviet Union-- was that it was called Earth's second moon. And arguably, it was. So a satellite can be tiny. A fleck of paint off a satellite orbiting the Earth is technically another moon.

So right here, what I'm showing you is the trajectory of the New Horizons spacecraft out to Pluto. And what we see here are trans-Neptunian Kuiper Belt objects. Now, those of you may know that New Horizons went on. And January 1, 2019, we encountered Arrokoth, formerly named Ultima Thule, otherwise known as MU69. It was-- you can see right here. A campaign was launched to look for possible worlds to fly on to.

And the last thing I want to do here is just run-- let's see-- days per second. And so let's see if my time is running, and that we may see New Horizons fly on out to-- let's see if we-- as time evolves here. Jackie, I might take another question just as I do this. I want to get this going even faster.

FAHERTY: I think this will have to be the last thing we do because I'm getting the cue that we should wrap up.

EMMART: OK.

FAHERTY: And this is a good moment, too, Carter, as you're turning it on, to remind people that if this is really interesting for you and you want to take a deeper dive on some of these things, especially this object Carter is pointing out, that you should tune in on Wednesday, November 18 at 7:00 PM. We're having a Frontiers in Astrophysics lecture, Pluto-- Glaciers, Mountains, and Dunes, Oh My! I think, Carter, you're going to be hosting that program, correct?

EMMART: Yes, thank you, with Cathy Olkin, one of the fine scientists on the New Horizons mission, along with John Spencer. And they're both from the Southwest Research Institute in Boulder, Colorado. They're both close friends. And so we'll be discussing, at length, a lot of the science that they can present much better than I.

Here, we also see things that look like comets, but they're part of icy worlds that come in close. And then you can see the parade of the Kuiper Belt, the first one being found in 1992, which was really not that long ago. And so the number of these grow-- and that we can see that the largest of them, like Pluto, having an ocean. It's possible these icy worlds also possibly have liquid water.

Could there be life out there? We don't know. That's why we have to go out and find out. And for the younger members out there, this is your future insofar as what we can look for and look forward to in the future. So thanks so much for joining us. This has been a lot of fun.

FAHERTY: And I think we're going to wrap it up there. So thank you so much, Carter. Thank you, everybody, for being so active in the chat. So many schools that I didn't necessarily give you all shout outs, though. But PS 160, I know you're there. PS 225. Please join us again, first Fridays of the month. If you want the deeper dive-- November 18, 7:00 PM. That might be past or around bedtime for some people-- or, hopefully not bedtime, but close to sleep time.

We'll have a survey that we're putting in the chat now. You can find it right here. We've got it up here. And please fill that out. Let us know how we're doing because we'd like to improve these programs for you if we can. And we hope to see you on the 18th. There'll be a link, also, posted in the chat for you if you want to see about that. And come back here on the first Friday of the month, where you can join us yet again-- 1:00 PM. Thanks, everybody.

EMMART: And get OpenSpace while you can.

FAHERTY: OpenSpace. Download it.

EMMART: Cool. Thank you.

JACKIE FAHERTY (Senior Scientist, Department of Astrophysics): Welcome everybody to another field trip. Sorry about that. I hadn’t muted myself, so you might have heard me twice. Welcome, welcome, welcome to our- what we’re now calling our YouTube spaceship.

 And we are going to take you on a very exciting ride today, on a field trip to the Milky Way, through the Milky Way, through really exciting data sets in the Milky Way.

My name is Jackie Faherty, and I’m an astrophysicist at the Museum, at the American Museum of Natural History. And I’m also in the Education Department, so I do a lot of these public talks. And I am joined today by a very wonderful pilot, a grad student at Columbia University, as well as the Museum—Marina Gemma.

Marina, can you show us your face, that you are real?

MARINA GEMMA (Graduate Student, Department of Earth and Planetary Sciences): I am real. I am here. Hi, Jackie, and hi everybody. I’m excited to take you guys through the Milky Way today. It’ll be fun.

FAHERTY: This is your first time flying through the Milky Way live with an audience, right, Marina?

GEMMA: It is. So, yeah. Cross our fingers.

FAHERTY: Cross our fingers that we don’t have any- any problems, but I’m sure that we won’t. Because this is virtual and we can correct all mistakes. In the chat today we also have two amazing female scientists. And I can say that because they work with me–Johanna Vos and Daniella Bardalez Gagliuffi will be in the chat, answering your questions.

I can see already we’ve got a lot going on in the chat. We’ve got a lot of people saying hello. I will be multi-tasking during this, monitoring the chat to see where- what questions you guys have. I’m going to throw some questions out at you guys.

I can already see we’ve got people from Florida, Oct- Octavio. We’ve got people from Greece, from the Philippines. Thank you all for tuning in. I see Mary Ashtub from New Jersey. Hello, New Jersey. I hope you survived the storm.

Anybody from New York that’s out there that wants to tell us about the blackout, feel free to also put some info about where you are in here. But most importantly, put in the chat any questions you have as we fly.

So, let’s get started on this field trip. Are we ready, Marina? I think we’re ready.

GEMMA: We are.

FAHERTY: Great. So, we’re taking off. We are going to be using for this field trip the same software that we’ve been using in all of our YouTube spaceship field trips, which is called OpenSpace software. It’s NASA funded. It’s all open source. So, you can download this software yourself and play with the data that you’re seeing here.

We’re flying away from the Earth on our YouTube spaceship. Marina has started focused over New York City, hovering over Central Park with the American Museum of Natural History at center stage there.

So, we are now leaving the- leaving the city, leaving the Earth. And we’re going to be hovering around the Earth with the perspective that I’m pretty sure many of us- many of us, maybe in this chat right now, might really want to have right now, which is a viewpoint from space, where we could be looking down onto the Earth and around at the stars.

So, we’re moving away from the planet. And you can see the northeast suburbs, the whole shore of the Northeast just came alive, the oceans are there. We’re seeing the structure of North America come to life. And then the atmosphere comes on. And in OpenSpace, that’s actually a real rendering of the atmosphere as it was four hours ago.

What day do we have it set at right now, Marina, this picture of the Earth?

GEMMA: Thursday, so yesterday. This is yesterday’s atmosphere. 

FAHERTY: So, it’s after the big storm that hit many of us. Okay. So, here’s Field Trip Milky Way. Marina’s got us moved around so that you’re actually seeing that beautiful stream, river of stars, as we call it, coming across your sky.

Now, this is a view of the sky that- You guys can say in the chat if you’ve ever seen a dark sky. Where you’re getting crisp, clear views of the stars. Crisp, clear views of a very small number of stars, actually, that your eye can actually see. So, your eye can actually only see about 2500 stars or so, if you’re in the darkest, darkest place that you can get to.

But even still, it’s a pretty dramatic view. So, Marina’s kind of moving us around here so you can get a viewpoint. And I see people putting in from different parts of the world. Right now we’ve moved into a viewpoint where the Sun is coming into view, but as a reminder, the Northern sky looks a little bit different than the Southern sky. Well, actually, it looks totally different than the Southern sky.

Your- your constellations will be different. Because you’re seeing different parts of the nighttime sky. And now, what’s important and what we can take you on in this YouTube spaceship is we can take you away- away from the stars and see exactly how they’re oriented.

So, the first step in Field Trip: Milky Way is that the stars are what make up the galaxy. And it’s a lot of what we’re going to be talking about. Marina just turned on constellation lines. And this is showing you the shapes that you might see that are the classic shapes. Among the 88 classic shapes that we have decided, astronomers have decided, are the official boundaries of the sky.

Marina’s got us focused on this one in blue, here, which I’m going to come back to a couple of times, is Orion. So, in the chat, if you guys want to respond if you’ve ever seen Orion, even New Yorkers—because I can see we’ve got a lot of New Yorkers here—if you’ve seen Orion. Have you been watching Betelgeuse? Betelgeuse has been- is the red star at the armpit of Orion, here, that has been dimming, that was dimming in the winter.

And now, what we can do is we can actually move away to show you that the perspective changes if you’re further away from Earth or closer to what those constellations look like. So, Marina’s going to zoom us away. Pretty far away. Until you start to see the figures of these constellations come off the wallpaper, as we say.

And notice the stars that made up those constellations are very different distances from each other. So, what we’ve just done for you is on our YouTube spaceship, taken you into three dimensions. And we’re kind of flying you among the stars right now. So, let’s- We’re giving you a little bit of a view here.

The blue- The reason why- I can see some questions here about the blue versus the red lines. The red lines mark the zodiac constellations. The blue lines are just prominent constellations—so, Orion is one, and Ursa Major, or the Big Dipper, is another.

And let’s head back in, Marina. Let’s get back to our regular perspective. And so- so, we’re going to bring the constellations back together. Notice how many stars you’ve been looking at. We had just a question a moment ago about how many light seconds or years have we traveled so far. So, as we come back in, I’m going to give you a distance scale to think about here.

And from this perspective right now, Marina, how far away are we?

GEMMA: We’re about 14,000 AU right now. So, 2.6 light months, about.

FAHERTY: Two-point-six light months. So, 14,000- we call AU—Astronomical Unit. That’s actually the distance between the Earth and the Sun. That’s such a big number that astronomers instead use light travel, in order to talk about distances. So, that was 2.6 light months.

For scale, it takes light leaving the Sun about eight minutes to reach the Earth. And now, the perspective that we’re at here is about 2.5 months in light time away from the Sun. And there’s a reason why I’ve picked this distance away for our next big move of the Milky Way.

So, I’ve- I’ve said that these are the stars, these are the bright stars, the stars that you can see, basically, with your eye. We’ve created a nighttime sky for you. What we’re going to do now is start exposing you to all the stars in the Milky Way that you can’t see, but they’re there.

So, Marina, why don’t we brighten up this new data set that is called the European Space Agency’s GAIA Catalog. If any of you follow me on Twitter, you know I talk about this catalog at all times because it’s super amazing. And I should have given you a pause there to appreciate that. I’d love to hear your reactions in the chat to this.

What do you think of this? These are all stars in the Milky Way that we have mapped that you cannot detect. And this is roughly, as we’re orbiting here at about 2.5 light months away from the Earth, you’re looking at roughly 7 million or so of them.

This full catalog has two billion stars in it. If we brighten all of those up for you, though, it would just be a big, bright mess on your screen right now. It is a very, very exciting, exciting, exciting data set.

I’m seeing a lot of OMGs in the chat and I am OMGing with you from here. Even though I’ve seen this many, many times.

And now I’m going to OMG you again. Because the other important thing that you have to know about stars in the Milky Way is that they all move. And here’s a key—they all move at a rate that you’re never going to see, unfortunately. Because it happens over a time scale that we don’t live long enough to see.

But with this software, we can actually speed time up to show you motions of stars in the Milky Way. And so, we’ve- Marina has turned this on. Marina, how fast are we moving right now?

GEMMA: We’re moving at about 50,000 years per second right now.

FAHERTY: Fifty thousand years every second. So, that’s- what you’re seeing is something that your eye cannot detect. But that our Milky Way galaxy- We’re not static at all. Stars are in constant motion, constant motion here.

And why we’re hanging out at this distance of 14,000 AU or 2.5 light months away is the following- And I’ll throw this into the chat. What do you know of as the closest star to us? And I know that everybody might say the Sun, and so I mean other than the Sun. What is the closest star to our Sun? Answer it in the chat.

And here’s- here’s what I will tell you, after you tell me what it is—in one million years, that is going to change. That is going to change pretty drastically. And I’m seeing some people answering. Pratheeksha Shetty you’ve answered Proxima Centauri correctly. I’m seeing others saying Alpha Centauri. It is that system. That is the closest star to us at four light years away. Four light years away.

But we’re at 2.6 light months away. So, ladies and gentlemen on this YouTube spaceship with me, in a million years there will be a star at 2.5 light months away. As opposed to Proxima Centauri, which is four light years away. How do we know that? We’re basically showing you.

Because we can measure the motions of the stars here. We know where they are. We can move time forward and we can see that in a million years, the Earth and the Sun, our little solar system, will come in a passing in the night kind of moment, with this other star. It’s called Gliese 710.

It’s much lower mass than our own Sun, but it might be carrying its own solar system with it. We certainly are. And so, think of that, that’s really exciting. If you want something to give you hope today or excitement to look forward to in a future that, I know, none of us will live- live towards because it’s in a million years, but still. It’s really, really exciting.

So, that’s why we’ve been hanging out here at this distance and watching these stars fly by. And now, let’s- let’s actually think about more of this, now that we can see the stars moving. The next step is- Okay, let’s talk more about these stars in the Milky Way.

I just mentioned this star Gliese 710 is coming through, but what about not just single stars? What about all the stars in the Milky Way that have more than one? Does this happen? Our Sun has our solar system, but it doesn’t have a partner. It doesn’t have another star that it’s moving with. But many stars do.

So, now we’re going to switch- Now, Marina, we can turn this one down- this data- this data set. And I say the word “data.” These are points that we have acquired through using telescopes. In particular, all of these points that you’re seeing have been carefully measured by a telescope in space.

And for those of us- those that are just joining us right now, we’re about halfway through this program and we are in the middle of a description of stars in the galaxy. My name’s Jackie Faherty. I’m an astronomer at the Museum. Marina Gemma is flying for us with OpenSpace, and we’ve got astrophysicists Johanna Vos and Daniella Bardalez Gagliuffi in the chat taking your questions.

And so, here we are flying around some stars. Let’s turn on a special set of stars that is a complete list of roughly 250,000 stars that you’re looking at that all move with somebody else. And when I say somebody else, I mean another star. They’re pairs.

So, I like thinking of the Milky Way not just as any one thing, but as a collection of different families of stars. And here’s one of your views that you’ll get to see now.

Let’s turn on time a little bit more. And as I do, I want to answer Katie’s question about how did we figure out the motion of these stars. Because I can answer that so carefully because that’s actually what I do, in part, as an astronomer—you take very, very careful images of the stars over a set amount of time. And astronomers have been looking at the sky for long enough that we see very small motion of a star in the sky.

Not something that your eye would pick out, but something that a camera would. And we take pictures, and we look at how those images, the positions of the stars change over time. And then we move- we extrapolate forward so that we can see where those motions are going. So, once you’ve got images taken over a certain amount of time, you can see the direction and the speed that a star is going.

So, Marina has turned time on. Marina, how fast is time moving now?

GEMMA: We’ve sped up to about 500,000 years per second.

FAHERTY: So, 500,000 years a second is going by. We’re still out here at 2.5 light months away because this is a nice perspective, also, to be viewing the stars of the Milky Way. And have a look at this. Have a look at this—every single one of the stars that you’re seeing here moves with at least one other star in here.

And so, you can really see that. Notice also- I want you to be the scientist observer, like I am when I look at data sets like this. Some of them are close to each other. Some of them are farther away from each other. Some of them appear to be moving very fast and some of them slower. Astronomers look to all of those “observables,” as we call them, to figure out what is going on in the galaxy, what kinds of stories do these families tell us.

Have they interacted with other stars? Have they- Are they breaking apart? Have they just recently been captured? Or did they evolve together? These are the stories of these families. And I’m seeing another question from Michelle Stephens—is it possible that our Sun has been paired with another star in the past?

Michelle, I absolutely love that question. It is an excellent one. There is a theory about our own Sun—it’s called the Nemesis Theory—that we do have a low-mass pair of- a partner. But- And astronomers have looked for it. But we’ve never been able to find it. So, at this point, we don’t think the Sun was- has been paired closely.

Now, it could have been born, though, and that leads me nicely into the next set of stars I want to show you. It could have been born with a giant family of stars. So, this- this data that you’re- these stars that you’re looking at are just pairs. Marina, let’s show the full families that are in here.

And I’m- Another excellent question from Michael Reina—why do the stars seem to move in different directions?

You’re basically seeing just sort of bulk motion of stars through the galaxy when we show you that with time turned on at, as Marina said, 50,000 years a second. And when you do that, you’re catching a lot of different motions that might be going on. The bulk of it is in one direction, but sometimes stars get kicked around by an interaction with something, an interaction with a big cloud of gas or dust, or an interaction with another star.

So, you’re seeing the legitimate, like, walking around the galaxy. Where’s everybody going? Think of it as, like, being on the sidewalks of New York City in, like, Times Square. There’s a bulk motion of where people are going, but then there’s others kind of going in other directions. And that’s kind of like what the stars do.

Now, Marina has us set up here where we’re looking at only young stars. And so, we think this is actually how stars form in big families in the galaxy. And they are together in a big group. So, very likely, going back to Michelle’s question, our Sun did form with a whole big family when it was born. But our Sun is 4.5 billion years old.

It’s like middle aged. But it’s lost its family at this point. It’s- it’s- it’s careened away and it’s doing its own thing with us, the solar system, its own little family. But here, we’re moving around at this distance of 2.5 light months.

We’re moving around the families, the young families. This is maybe what our- where our Sun came from, from a little grouping like this. And, Marina, let’s turn the constellation lines on, so we can get some orientation as to where we are.

So, we’ve got- You can see the Milky Way is stretched above us. And right in front of us here, right in front of us is a- actually I’m not totally sure that this is what I think I’m looking at. But I think we’ve got the Scorpion. Actually, I think we’ve got Cepheus right in front of us—a great constellation.

Marina’s going to move us around so that we can get one of the most famous constellations that I pointed out earlier, Orion, in- in the field of view here. Oh, I see a question that I’d love to answer here by Arabella, about why do stars travel in pairs.

And so, we’re not totally sure, but the answer to that does also rely on this picture that we’re beginning with, which is they start as giant families, big groups. And then what probably happens is they start breaking up. The big families break apart.

So, Marina’s left the constellation lines on as we move out to this three-dimensional view of the young factory of stars in our galaxy. Moving away at- you can tell us how far away we’ve reached, Marina. That would be good for people to know how far away we are.

GEMMA: We’re at about a kiloparsec right now from Earth.

FAHERTY: A kiloparsec is about three- So, one- The word “parsec” you can multiply by three to get it in light years. So, we’re at about 3,000 light years away from- away from the Earth. Actually, sorry, it’s the other way around. I just did that in reverse. It’s divided by three.

So, we’re about 300 light years away from the Earth right now. And- So, from this perspective- The reason why we have the constellation lines on, is because at the very center was your perspective at Earth. And the blue lines that you see- Remember, that was the constellation Orion. And so, those show you where Orion is in here.

So, let’s turn these constellation lines off. And- and when you turn it off, focus on Orion there—the youngest star. I mean, sorry- the young- a very young system of stars that’s near us. Every one of the stars that you’re seeing here—and I’m seeing some questions about why- why there are so many stars in here, why there are so few stars in here.

This is a very, very, very important set of stars. And I’ve only turned ones on here that we think are less than maybe 200-300 million years old. Now, that might sound old to some of you. I see a 5-year-old in here, and so- in the chat. So, maybe that sounds kind of old to you, but it’s actually not.

These are the youngest stars in our galaxy. And they’re very close to the Sun. So, what you’re seeing at the center of this ball, which is just a round ball, like a- I’ve taken a sphere and I’ve put it around the Sun and I’ve said, “Tell me where all the youngest stars are.” And so, at the center there would be the Sun. And then these clumps that you’re seeing are the young stars. And these are the star-forming factories.

This is where all the baby planets are near us. This is where the baby- all of- all of the things we want to know, any question you have about what it was like in our solar system back in the day when it was a couple million years old, this is what it would look like.

And what’s amazing- We’ve stopped here with this face-on view. You’re looking at this three-dimensional structure. And just to give you a little bit of a YouTube spaceship pro- special thing, very few people have ever seen it like this. Because we’ve built this into the OpenSpace software, even the researchers who have been studying the stars haven’t quite seen it this way. It’s something special that we can do at the Hayden Planetarium.

And what we can also do is see where these stars are going. So, Marina, why don’t we turn time on and how fast are we moving time now, Marina?

GEMMA: Now, we’re at about 300 million years per second. So, much, much faster.

FAHERTY: Much, much, much faster. And so, you might ask, “Why, Marina and Jackie, have you had to make time move that fast?” And this is also, to answer a couple of your questions about the speeds- Young stars don’t move all that fast. So, we’ve had to speed time up, because they’ve just formed.

And it actually takes time with stars moving through the galaxy for them to speed up. And so, what you’re looking at is us fast-forwarding time to watch what will happen to some of these stars, these groups, these collections. And what I think is amazing when you see this is-

And I’m seeing questions, like James is asking about the bow shape that you see. The bow shape, I’m pretty sure you’re referring to, is what I would call the hook, which is actually the Upper Scorpius association of young stars that kind of like rips apart as you move time forward.

And notice, there’s a clump that stands still in this. That is Orion. And it looks like Orion is coming to a bit of a halt. It’s not moving much. It’s also moving with the Sun, as well. We have the same direction. And so, we don’t see a lot of the motion of Orion here.

And so, that- this is a very impressive way of looking at and thinking about how stars move and change over time. And these structures are where astronomers look. Because I- I have so many questions when I look at this. Where are the stars going? What happens as they dissolve? What happened to our own Sun? Was it a part of a big family that just broke up like this? Do these things interact? Because they’re very dense. 

And this is just the youngest stars. So, like I said, just a couple hundred million years old. And I’m seeing Ernest- Ernest is saying that one bunch of stars is not moving too much in the middle. Yes, Ernest, that’s Orion. Orion is not moving much. It’s an intriguing thing because it is one of the most well-studied star-forming regions that we know of in the Milky Way.

And this isn’t it, either. This is just a couple hundred light years away from Earth. Let’s show you even more structure. So, Marina, why don’t we pause, go back to now, and turn on an even larger data set, which is very unique to this YouTube Field Trip because we have very few people that have actually seen this.

Let’s move around this. So, the black area at the center is where the Sun is. So, that’s the center. You don’t have that many young stars near the Sun, so that’s why it’s very dark around there. But what you’re seeing, now that we’ve moved farther away- And, Marina, how far away are we now?

GEMMA: We’re at about 1.5 kiloparsecs, approaching 2 kiloparsecs.

FAHERTY: Two kiloparsecs. So, remember one parsec means- divide that by three to get it in light years. So, you’re now at- Now I can’t even remember what I just said. But let’s just say we’re at 1000 light years away, something like that. And at this distance, now everything you’re seeing is structure in the nearby area of the Milky Way.

Where you see these strings of stars, these are other family members that are older. So, when we were close in and we were looking at the young stars, we know that they’re young. I said only young stars in that sample. But this larger structure that we’ve gone another thousand or so light years away, what you see here is even more families of stars. So, you can- Next time you think of the galaxy, it’s not just individual stars, it’s all of these giant structures together. All of these giant structures that are together, that are moving.

And let’s move a little bit further back. Actually, Marina, one thing that I’d love to do is also show how these stars move. So, if we get back to our face-on view- Why don’t we turn time on again? So that we can drive this point home—that the young stars we showed how they moved together. We can leave this at, once again, let’s put it at-

This is- Can you remind us of the speed we put it at, Marina?

GEMMA: 300 million years per second.

FAHERTY: 300 million years per second. Okay. And we’re going back. So, now- now you’re seeing these structures moving through the galaxy like giant—I don’t know what to call it—like, I want to say sloths moving. So, the younger stars take longer to break apart. 

Okay, let’s go back to now. And you might be wondering how far away are we from this- from- from the- in terms of the Milky Way, general. How far away are we? So, if we pause here, and we’re going to pull away, let’s see what you guys think as to how far, how distant we are. 

That was a lot of science we just covered. A huge amount of science that we just covered. Young stars, co-moving stars. But have a look at this. As we pull away, that is- this is a view that we have definitely never had, because we’ve never flown this far away from the galaxy. And at this distance away, where we’re getting a bird’s eye view, you’re seeing the structure of the Milky Way through a rendering.

We’ve rendered what we think the Milky Way looks like here. It has spiral arms. It’s got a very, very bright center, where there’s a lot of stars. And the stars that we’ve been talking about in the galaxy, that we’ve learned so much of, they take up just a small fraction of the overall size. Now, we think there are 100, 200, maybe 300 billion stars in the Milky Way.

I was so excited to talk about that data set, which I called GAIA. And that has mapped 2 billion stars, or roughly 2 billion stars. That’s a small percentage of the number of stars in the galaxy. But it is so important to be able to map out even the small fraction at the level that we did. Because we can ask all of our questions about the- how many structures do you see, how many times do you see stars moving with another star, how many times do you see big families of stars out there. And all of that you can ask among that little sample that we have highlighted there.

Because once we can ask and answer the questions about the little data sets that we have in there, we can expand and figure out what’s going on elsewhere. And let’s move away from here, Marina, because I’m seeing some questions about other galaxies.           

For instance, Jaxon asked how close is the Andromeda Galaxy to Earth. And we’re going to fly out towards a distance, which will give you that perspective. It’s about 2.5 million light years away, or so.

Remember, we started this at a perspective about 2.5 light months away, where we hung out there. And now, this view that you’re getting is showing the Milky Way with the Large and Small Magellenic Clouds, which are those LMC and SMC labelled objects in there. Those are satellite galaxies, much smaller than our own Milky Way, that are orbiting us. 

And as we move around- And those are in the Southern Hemisphere, so they’re in your South view. You’ll see Andromeda will come up, because Andromeda is actually in the Northern Hemisphere. You can view it from the North. It’s actually the most distant object that you can see with your unaided eye, with just your eye.

But now, every one of the points that you’re seeing- The Milky Way is still there at the center, that beautiful image—not a real- rendering. It’s not an actual image that we’ve ever taken since we’ve never flown outside of the galaxy. Every single one of these colored points in here is another galaxy with billions of its own stars.

Some of them are labelled in here. You can see Andromeda now, up and to the left. The LMC and the SMC are close by. And I want to end on this note for you, that the- the Milky Way, with all of the stars- And I tried to tell you the story of the Milky Way through the stars. 

The Milky Way is also highly influenced by some of these other galaxies. For instance, we are interacting with those two galaxies at the lower part there—SMC and LMC. The Milky Way is eating some of those stars. And they- and those two galaxies are pulling some of the Milky Way’s stars.

And there’s another galaxy in here called the Sagittarius Dwarf Galaxy the Milky Way is interacting with. The billions and billions of stars that are in these other galaxies are still relevant to think about when you- when we think about our own galaxy. So, from this perspective we’re seeing this- this is now getting more into the larger-scale structure of the universe.

And so, we’re going to end the visual part in here. I’ll take a couple more of your questions because I can see we’ve got a lot of intrigue over this. I see there’s a question from Richard Paul about how thick is the universe from a distance perspective.

I’m not sure I could say how thick the universe is, but I could give you an idea. The Milky Way galaxy- Marina, we could fly in just a little bit so that we could see the- the thinness of the disc of the Milky Way here.

What’s interesting is throughout our observations, astronomers’ observations of the universe, discs are extremely prevalent. So, the Milky Way is something like 150,000 light years across, but it’s very, very thin. So, as we come in, you’ll see it’s more like a pancake.

And that is in part because of the way that the material when it comes together, it collapses into a disc. Similar to how our solar system, it formed as a disc around our Sun. And I’m seeing some- some lovely comments. Cynthia’s saying, “This definitely puts the Earth and other planets into perspective in terms of size.”

I always think of that, as well. That I’m constantly thinking of perspective here. And- in- I love seeing the Milky Way from this perspective because with- A reminder, you can see the small data set that we were playing with that was so important, just off one of the spiral arms there. That’s our home.

And I’ll take just one more question here. Is the center of the Milky Way a lot of stars close together? This comes from Katie. Great question, Katie. Yes, at the center of the galaxy there is most likely a supermassive black hole. We think a supermassive black hole exists at the center of most galaxies.

And that is also the gravitational sink of the galaxy. So, it’s the downtown. It’s where ev- all the bulk of the stars will be. So, you see the highest density of stars out there, in there at the center of the galaxy. And we see this in images of other galaxies, as well.

So, the Hubble Space Telescope has taken amazing images, galleries of images of other galaxies that we think might be reminiscent of what our own galaxy looks like.

Great, so I think we’re out of time here. I want to thank Marina for being such an amazing pilot. Marina, did you have fun on your first Milky Way flight? 

GEMMA: I had a blast, Jackie. Thank you for guiding us through these awesome data sets. 

FAHERTY: And I want to thank Johanna and Daniella, who’ve been answering what I can see was a very busy chat of lots and lots of questions. As a reminder, we do these field trips on Friday and next week at 1pm on our- this same channel, we’re going to be talking about corals and climate.

And check back into our channel for more of our astronomy content as we- as we are pretty regular with our field trips into space. So, I think we’re also going to drop a survey into the- into the chat, so pay attention to that.

And thanks, everybody. Keep looking up, keep paying attention to the stars. And hopefully this gives you a little more perspective on the very galaxy that you live in. 

CARTER EMMART (Director of Astrovisualization): OK. Welcome. Welcome to Earth Day, 50th anniversary. My name is Carter Emmart. I'm the Director of Astrovisualization for the American Museum of Natural History. And we're celebrating the view of Earth from space. This is what gave birth to Earth Day 50 years ago, from the pictures brought back by our lunar explorers that went to the Moon in the Apollo program.

So today when we're all home and looking at the Earth together, this reminds us of our larger moment, which is the planet. And it really became obvious to us when we went out to the Moon that it was lifeless. That looking back at all the life on Earth is what matters. And this is where we are. And it's where we have evolved. And it's where all life that we know of in the universe exists.

So today what we're going to look at is this beautiful blue planet. It's blue because of the atmosphere and the way it scatters the light. And you can see the swirling clouds of weather. And also dominating our view for the most part, 3/4 of the Earth is covered by water. So we see oceans. And then also land, we see green and browns of the land.

But also the Earth spins on an axis. It spins-- imagine spinning a basketball on your finger-- is that you would balance it on the spin point. And that creates a sort of axis of rotation for the Earth. So where it spins, up at the poles, it's cold because it doesn't get a lot of sunlight. But where it's spinning around at the widest part, the equator, is where it gets the most sunlight. And so it's warm. And so what we see here is weather and the clouds, that this sets up these patterns.

I'm going to be joined today by my friend and colleague, astronomer Jackie Faherty, who's going to take questions from the Chat. And so we're here together. Jackie.

JACKIE FAHERTY (Senior Scientist, Department of Astrophysics): Hi, everybody. Yup. I'm here. I'll be monitoring the Chat and taking any questions you have about the Earth, as Carter flies you through some gorgeous parts of the Earth today.

EMMART: So thanks, Jackie. And also silently joining us is our pilot, Micah Acinapura. And what he's piloting is called Open Space. And Open Space is software that's freely available. And if you're interested in knowing more what it's about, our team is on the Chat. So you can ask questions about how to get it. And you can do this yourself.

We're looking at an image of the Earth from April 11. And it comes to us from NASA, and NASA satellite images that we direct into here. And as we get closer-- we're coming in now over South America. We're going to take a quick little tour to about five different, what we call biomes or environments of Earth. So think of mountains, or deserts, or rainforests.

And our first destination here in South America is, as you can see, as we're coming in, a lot of clouds. Can you see the white clouds? And then also to the lower right we can also see some browns. And that brown band is actually the land that's just west of the Andes Mountains mountain chain.

And so the Andes Mountains in South America, that run along the west side of the continent, actually trap the circulation of the moist air coming off the ocean in this tropical region, the equatorial region that we call the Amazon Basin, named after the great Amazon River. Basically, it's the world's largest river. It has the capacity of basically one fifth of all the river water in the world.

And as Micah brings us down lower, we're going to be seeing through the clouds essentially. So Micah, why don't we come on down through the clouds.

FAHERTY: Hey, Carter, as we go in, we've got a question on the age, as we're coming down, the age of the Earth. And if you're looking at younger or older parts of the Earth here?

EMMART: Oh, that's a good question. Well, what we know about the Earth can be inferred from some Moon rocks that we brought back in the Apollo program. They're the oldest rocks found, 4 and 1/2 billion years. And the oldest Earth rock is about 4 billion years. So we've been around a long time.

But what we're seeing here, these continents of Earth that move around, that we found out, and something-- we call it plate tectonics. But the sort of land areas of Earth move about. But as they do, and as they move and sort of collide with one another, it forces up mountains. But then also erosion happens, basically rain. It's brought up. It's moist air that comes up and drops the moisture out as rain over the mountains-- comes down.

And what it does is it erodes the mountains. And so it carries a lot of dirt and a lot of soil. And that comes into these rivers. This is the Amazon River we're chasing. Micah is-- Micah, can we come lower?

And as we do-- Micah, can you tip it over so that we see the atmosphere? And so I'm asking Micah to tip the atmosphere over. The atmosphere is really, really thin. It's only about 20 miles thin. And the Earth itself is about 8,000 miles in diameter. So really what we live in, and the atmosphere, is equivalent to about as thin as a skin on an apple.

Micah is coming into an area here in the river. Micah, let's drop down. I want to see the city of Manaus in Brazil. It's the capital of the Amazonas Region of Brazil, so the Amazon rainforest. The green that we see surrounding this area, beyond the river, is all forest. It's tremendous. It's the largest rainforest in the world, the Amazon.

But we're coming in. We see a city here. It's gray. And this is typical, the color of cities, mainly concrete. But Manaus has a population of about just over a million and a half people. It's about the size of the city Phoenix in Arizona.

So what we're going to do now is we can see actually the Amazon River. Can you see these pictures? These pictures have taken from space, and brought together, and sort of all stitched together like a big quilt. We call it a mosaic. And so sometimes you'll see pictures that maybe have a little clouds and then you might see a little border. But these are how we put this together.

And so NASA takes these pictures. Various satellites take these pictures. And we work with a company called Esri that helps us put this together. And that's what we're showing you now, up close.

But let's fly farther downriver river of the Amazon. We're going eastward through the rainforest. The rainforest is on both sides. And it's in green.

FAHERTY: Carter, as we fly away, the question is the river is always this brown or if it changes color?

EMMART: Actually, as we came down, Manaus is this area where the Rio Negro, which looks kind of dark, comes together with the brownish-looking Amazon. And the Rio Negro has less dirt in it. And it's actually clear, but looks sort of dark from space. And it flows together just east of Manaus, in this confluence of two-- of the tributary rivers that make up the Amazon.

So now we see where the Amazon drains into the Atlantic Ocean, and so the mouth of the delta of the Amazon River. And so we're now going to move back up and away from the Earth. And this green, this tremendous green, once again is because of all the rain that's come coming down off of this warm belt, right down around the middle of the Earth. That's mostly the sunlight.

And so, again, it's very warm. So it evaporates the water of the ocean. And then that flows and creates the circulation patterns that we see of the weather. Can you see the blue of the ocean, the Atlantic? We're going to fly about 2,000 miles across the Atlantic. So we're going to come across.

The width of the United States is about 3,000 miles. So the distance from New York to Denver, about 2,000 miles. So now we can see the brown of the Sahara Desert. We're coming in on Africa. And so the Sahara occupies about one third of Africa.

You can see in the lower right, we can see clouds over the Congo rainforest. So above that are these desert bands on Earth. And this is caused by-- once again, the equatorial warming causes the air to get hot and buoyant. So it goes up like a hot air balloon.

And then it starts to cool as it gets higher. And it spreads out on both sides of the equator, north and south, and creates these desert bands. So we're coming up to the largest desert in the world, the largest hot band of desert here.

I'm going to ask Micah to go a little bit farther eastward, if you can please. These are the Tibesti Mountains. And so if we go a little bit farther east, these are mountains that are built by volcanoes out in the middle of this desert.

FAHERTY: Carter, just real quick, another question here from eight-year-old Lily, which was on-- since we're on land, but it looked like there was a lot of water. The question is, how much of the Earth is land versus water?

EMMART: About 3/4-- that's a good question, Lily. So 3/4 of the Earth basically is ocean. So we live on sort of one fourth or one third roughly of the Earth that's land. And the land is divided up into deserts, and grasslands, shrublands, and forests. And so we're now coming into this portion of the Earth. About 30% of the Earth is-- of the land area are actually deserts.

So Micah is coming in over the Tibesti Mountains. And these are lava flows that were created by volcanoes. And they've been eroded. Can you see-- when I say that, they've been carved. Can you see that in these darker areas here, this is volcanic rock. And we can see this carving of it in little-- sort of river channels that have been eroded away.

This indicates to us that this area wasn't always this dry. And so about 100,000, 200,000 years ago, and during the ice ages, this was actually a greener environment. But now it's quite dry. And so the oranges-- can you see that sort of yellow orange color-- those are sand dunes.

And so this area had been carved when it was wetter. And it creates these drainages basically where the water flows and erodes that rock that comes down. And the hot winds circulate the sands. And so these sand dunes blow around.

And they're yellowish in color because sand is really made up of like glass. This is silica or sort of the crystal of silicon dioxide. It's glass. It's what we make glass out of. And glass can be clear. But it's coated a little bit with iron and that iron that weathers off. And that creates a kind of orange-reddish color.

FAHERTY: Carter, my question about something that I think is one of your favorites, which is if this looks like how Mars looks since it's so red And little Elliot has heard that that is also a rusty planet.

EMMART: Well, that's-- Elliot, thank you for asking that question. Because, in fact, I was about to mention that, that Mars is essentially a weathered planet that has kind of a rust component that makes it red, reddish-brown, very much like the Sahara Desert. When we fly over the Sahara, we can we sort of pretend that we're on Mars. But it's a lot hotter in the Sahara than it is on Mars.

So I'm going to ask Micah to now fly higher up so that we can go into some other mountainous areas that are in the continent of Asia. So we're going to be flying eastward over the Middle East. And as we elevate higher up, we can see the Mediterranean. Can you see the blue in the top left? That's the Mediterranean Sea. We don't really call it an ocean because a sea is smaller than the oceans. But it's right there between Africa and Europe.

So we're now going to pull away from the Earth. And we're going to fly eastward into Asia. What we can see as we pull back is how the atmosphere kind of comes on. We see that again. And this is from April 11.

And down below, can you see the blue that's stretching from the center, over to the right? That's the Red Sea. It flows down to the Gulf of Aden. And then we see the Arabian Peninsula. And then we're going to go farther east into Asia.

FAHERTY: Carter, a quick question from Maggie. Little Maggie wants to know if there is still atmosphere in this area or if the Earth's atmosphere is gone where we're orbiting here?

EMMART: So the atmosphere-- that is a good question, too. The atmosphere covers the entire Earth. The earth is so big that it can actually-- its gravity can just hold onto air. And that's what it does.

Our Moon doesn't really have air because it's too small. It's about one quarter the diameter of Earth. It's too small to really hold onto an atmosphere. And so the Earth has this beautiful, rich atmosphere that we enjoy.

What we're coming down on-- can you see that river valley, this sort of green river valley, the Indus River Valley, that's running to the bottom of the screen? But we now see a green band. Can you see the green band across the middle? And then also we're going to see snows or the white areas of mountains. And these are the Himalayan Mountains.

These are the tallest mountains in the world. The green that you see, in Nepal and India, is actually forests. And these forests are thanks to the water, once again from the atmosphere that flows up north. Flows up the mountains, cools off, drops off as rain, feeds these forests.

And then when it gets over the mountains, to the left, we have the Tibetan Plateau, which is a tundra. It's dry. It's sort of a desert of itself, high desert.

And so Micah is bringing us down across the top of the Himalayas. And these snows build up. So here we have snow.

And when it melts, it runs off. First, it flows in ice glaciers, alpine glaciers. So the ice flows downhill. But then that melts off into the rivers that come off the Himalaya. And the major rivers of Asia come off of this mountain chain. And it feeds-- basically, the water is responsible for feeding over 3 billion people, India, China, Southeast Asia.

And so now we're coming in to an area where these mountains are the highest in the world, the Himalayas are. And Micah is going to bring us to the highest mountain. Maybe some of you have heard of it. It's called Mount Everest.

And as we come in-- now, can you see that sort of gray little fingers that are coming off the snows here? Those are glaciers. And that's ice that builds up. And actually ice kind of flows. It flows slowly, but it flows down. And when it does, it sort of carves these valleys. And it sculpts the mountains that we see. The Himalayas are still--

FAHERTY: Carter, a question-- before we get in, there's a question from Max and Maddie. And they want to know if we've been also flying over little lakes, too, as we've been going over the mountain?

EMMART: Well, we saw lakes in the Tibetan Plateau. There are tiny lakes up here. So some of them you see. And you'll see them kind of bluish color.

But also these mountains are still growing. They're growing about half an inch per year. Why are they growing?

Well, the whole continent of India-- a smaller continent started to collide with Asia as a continent after the death of the dinosaurs. And they died off. Dinosaurs died off about 60 million years ago. But about 40 to 50 million years ago, these two land areas came together. And they're still colliding, forcing up these mountains.

Micah, let's come closer to Mount Everest. This is beautiful. I want you to drop down lower if you can. We are now to the north of it. That's why we see the sort of shadow from the Sun. And we're looking across the beautiful greens of Nepal and then across, out to India.

And so this is the tallest mountain in the world. And this is a good way to get there, is to fly in Open Space and see it this way. And you might wonder. These pictures are taken from space. But they also-- from space, we can actually get-- an elevation map, we call it.

In other words, we can get the shape of the mountain. And then the picture is put on top of that. So everything you're looking at is basically data that we've gotten from our space program and satellites. And we put it together into this big map.

FAHERTY: Carter, as we fly away, one of my favorite questions-- little four-year-old Eleanor says her mom really wants to hike Mount Everest. Have you ever seen people in any of these images?

EMMART: We can see people. And we don't see anything-- I haven't seen any people in the pictures of Mount Everest. But where the pictures are good enough-- and it varies in quality. So if you come into a place-- well, like in Mecca you can see the people around the Kaaba, which is the black cube that is worshipped in Islam, is full of people. Tiananmen Square in China, you can see people. And I think I can see people, indeed, in Washington, D.C.

So here we see the mountains of the Himalayas. And also this is the great Brahmaputra River. It flows together into the Ganges. And it's one of these river systems that come off the Himalayas.

So now we're flying up-- Micah is going to turn to the right. And we're going to fly down across Southeast Asia, the various countries there, and a favorite part of the world for me. Micah is also-- we're going to just adjust the timing. In other words, we're looking at lighting because the Earth spins day and night. So in the software, we're going to-- rotating the Earth to see the lighting change.

So here we are-- down below us Southeast Asia. And then we're coming-- we're aligning ourselves, so that we're going to come down to Australia. And Australia is a continent about-- it's the smallest continent. But it's about the width of the United States, about 3,000 miles wide. And it's south of the equator.

So the most northern reach, which is closest to the equator, is tropical. And so again we have rainforest in the Queensland area of Australia. And off of that east coast, that northeast coast of Australia, is the largest reef in the world. And this is basically a barrier island chain, which is created basically from shells.

This is life. Over about 10,000 years that life has been building this reef system. And so it basically is a sort of boundary area between land and the oceans. And reefs are responsible for where all our-- a lot of the fish that we eat are actually born. And it's home to thousands of species.

So it's very important for us in how we interact with the Earth. And Micah is going to bring us in closer. We rely, of course, on the Earth, whether we eat only plants or whether we eat plants and animals. We are of the Earth. We're part of this whole ecosystem. The beauty of looking at the Earth this way is that we see the Earth for what it is.

Here, this is called Cape York up there, those beautiful blues, that sort of blue and turquoise water. And then we begin to see the lighter blue. Can you see the lighter blues in here? And they amount to sort of a chain of islands. And these are the barrier islands that sit off the northeast coast, up by Queensland, Australia.

FAHERTY: Carter, a question-- we coming in here. I think it's a nice one, from Charity. Which is, if there's also-- this is such a wet area. Is there also a rain forest in this area, in Australia?

EMMART: Yes. And I mentioned that Queensland is a rainforest because it's the most northern part of Australia. So it reaches up into the tropics. That island just north, Cape York, I was pointing out, it's sort of in the upper left area-- is basically the island of New Guinea. So it's rainforest on New Guinea and also in the Queensland Peninsula, that's sticking out there. And the green that you see is really green because of the forest and the tropical rainforest.

So we've gone over these various biomes, so the rainforest of Brazil to the rainforest of Queensland and the Great Barrier Reef off of Australia. Of course, we've seen the mountains of the Himalayas and the Sahara Desert. But as we pull out slowly here, we're going to see the clouds come together and completing our sort of picture of the Earth.

And I'm going to ask Micah, as we as we do this movement away from Earth, is that we're going to go into the night side of Earth. When we go into night, we'll be able to see our city lights. And so the city lights show where humans are. It shows where our cities are. It shows where we are.

And so as we pull away from Australia, again we can see the swirly nature of the clouds, so the weather. Again, that's all set up because of the day/night cycle of Earth. When the Earth rotates, the night side is cooler. It comes around into the day side. It warms up from the Sun. We have evaporation of the oceans. And then that goes up higher in the atmosphere, cools off, creates the clouds.

There we can see India beneath us. We're going to come around. And Micah, can we go into nighttime here, if we could? So he's going to rotate the Earth.

FAHERTY: Carter, as we're kind of coming down, I know we had one before. But we're getting a lot of questions in the Chat on size. So could we remind people-- Riley and Rory are actually asking this right now, about how big is the Earth? Can we tell everybody?

EMMART: So it's 8,000 miles in diameter. It's very big. And think about that. In math class, if you take a diameter of a circle and multiply times 3.14, which is pi, you get the circumference of the circle. So 8,000 times 3 is 24,000 miles around. And we rotate in 24 hours.

We're now looking at-- Micah has come down over a beautiful-- almost the shape of a rose. You see that. It's almost like a stem going up to a rose. Well, what that is-- we are looking at the city lights now of humans.

And in this case, that rose pattern is basically-- the stem is the Nile River Valley. And there are almost 100 million people that live right here in Egypt. This is Egypt. And where it fans out, making the rose, is the Nile River Delta.

And you can see where the stem connects with the top of the rose there and it's kind of brighter. Micah, let's move in a little bit. That's where most of the people in Egypt live. And that's the city of Cairo.

And then just off to the right of the rose is-- we can see the coastline of Israel, and further up into Lebanon. And we see cities of Jordan and Syria. And over-- so Micah is moving in closer now. And so we're going to see some of these city lights. So we see the patterns of where we live, basically because we light ourselves up at night.

FAHERTY: Carter, we had a question from Matteo, which is an interesting question. Do people ever live on the water there?

EMMART: Well, people live-- it's a good question. Do people live on the water? In some communities around the world, yes, they do. But they live typically close to land because-- of course, cruise ships and things like that go out onto the ocean.

But few people actually live out there on the ocean. We live typically close to water. And notice how everybody was living along the river. Well, that's because that's where the water is.

So Micah is now flying a little bit westward, which is nice. We see the lights of Turkey in the upper right; the lights of Athens, right in the middle of the screen there now. But then coming into view, can you see the sort of shape that's coming up? And it's rather distinct. It kind of looks like a boot.

And that boot is the boot of Italy. It's the shape of Italy. We can see the night lights sort of outline that. And the two bright spots you can see along the boot, or maybe the boot buckles, are Naples to the right. And farther up is Rome. And even farther up is the city of Milan and the Po River Valley that flows into Venice and Florence-- all these beautiful places there in Italy.

So we're going to bring the day back around. And we're going to finish up by going up to a polar region. And we've talked about the hot desert of the Sahara, around the equator. But look at the poles. Even though they're ice covered, that it's actually quite dry because of the way the atmosphere flows.

It goes up to the pole. It basically cools off. And then it comes-- because it cools off, it gets heavier. Then it comes down and sweeps out, winds, and sort of dries off that ice. So what we're going to do now is we're going to come in-- coming north. And we can see here in this image--

FAHERTY: Carter, as we come down, too, because it's such a beautiful part of the Earth, we've had a lot of questions about the shape of the Earth. And Lanier is asking if the Earth is a perfect circle or not? It's such a good view from here, to talk about that.

EMMART: It looks like a perfect circle. If you're a geophysicist-- that's how I was trained through my undergraduate years-- it's not a perfect sphere. And we have this concept called the geoid, which is sort of the shape of the planet. But from where we are and how we see it, it's nearly a perfect circle, a circular shape, spherical shape. But that's a really good question because it does vary. And, of course, the mountains are bigger here and there.

So we're looking now at the continent-- or the sort of subcontinent of Greenland. OK. All right.

FAHERTY: Maybe while we wait, since we're now waiting for our Earth to come back up, I can shoot you a couple more. We've had a very, very active chat with people--

EMMART: That's great.

FAHERTY: --in here. And some off-the-wall questions, that I'm going to throw a couple of them at you.

One from Matteo, who's 4. Do you know how-- can you explain how gravity works, how people are kept on the planet?

EMMART: So, boy, that's-- gravity is one-- this is a great question. We can describe how gravity works. In other words, we understand that gravity happens because if you have a lot us stuff somewhere, like the Earth, that attracts other stuff. And we're small stuff. So we'd stick onto the big stuff. So the Earth is big. And you can jump up and down and try and get away from Earth. But it really takes a rocket to get away from Earth.

So what we understand is more stuff has more gravity. Why it has gravity, we don't really know. That's a real good question. And some of the greatest physicists in the world have thought of this question. We wonder why? Why does gravity happen?

This is kind of a mystery to us. But how it works, we can describe in great detail. And we that by experiments.

FAHERTY: It's a good point. And as astronomer, we think about gravity a lot. Oh, it looks like we've got our planet back on.

EMMART: So the eastern coast of Greenland-- and every year at this time, in spring, the ice sheet begins to melt at the edges. And so the ice starts to come off in chunks. And if we come in close-- Micah, this is great-- we're going to actually see chunks that are almost the size of cities, that are breaking off. And these become icebergs. And they begin to float around.

Now, you also see a lot of things. There's a lot of white. You see the blue. The blue is the ocean. But what we see are clouds. Clouds are white. And we also see the ice of-- the ice sheet of Greenland, which is in the upper left. And so that's like snow.

And then we can kind of see some mountains in here. And we can also see-- again, we can see valleys that have been shaped by glaciers and by meltwater. But then also the finest detail that we see in these little, swirly patterns is actually ice floating on the ocean. So the difference between the clouds and the ice, the ice sheet, it's all white. It's kind of like trying to tell-- you've got a polar bear in a snowstorm. It might be difficult because they're both white. But in this case, we can see this. And that creates these beautiful patterns that we see every year at this time.

FAHERTY: Carter, on this cue we had several people ask questions. The last one I saw came from JD on whether or not the Earth could get bigger? And seeing the glaciers break off and contributing to the ocean might be a good point to talk to JD and the others about that.

EMMART: So it's interesting. The Earth doesn't get bigger. It was sort of formed billions of years ago, about 4 and 1/2 billion years ago. And so the stuff that we have of the Earth is here. We have occasionally things fall to Earth. In fact, last night I guess is the Lyrid meteor shower.

And so we still collect stuff because we-- again, we have big gravity because we're big. And so stuff is attracted to us and falls in occasionally. So we get slightly bigger by those things falling in.

But we can get bigger if we have a lot of stuff falling on us. But that really happened in the formation of the Earth. But since then, we've been dealing with what we got. And so this budget of different things, that the lighter stuff kind of rose to the top, and the hot dense core in the middle, actually creates a magnetic field. And we're not seeing that. Join us later today when we talk with Professor Martha Gilmore about what makes Earth so special-- but our magnetosphere that's created.

But what we're seeing here right now is the air. We can see-- that beautiful blue edge to the Earth, it's from what we call the scattering of the light from the oxygenated atmosphere. We're really about-- sort of 3/4 of our atmosphere is nitrogen, about 20% is oxygen. But that oxygen creates is beautiful blue glow. And that's reflected in the ocean. So we really do call Earth the blue planet.

And we're coming back now. Micah is lining us up. So that we can finish off this program, coming into where Jackie, and I, and our team come from, from the American Museum of Natural History. So we're going to close in to New York.

And when we do this, remember at the beginning of the program I showed you a city. We saw briefly the city of Manaus, out in the middle of Brazil. And it was kind of gray. And it's gray because concrete roads, buildings, things like that. And as Micah comes in closer now, what we see is-- we can see the green of North America.

Notice that light blue that we see in the ocean. And then it gets darker blue. That's because there's something called the continental shelf. So we're seeing lighter blue where the ocean is not as deep. And then deeper blue in the lower right now, from where it falls off into the abyssal depths of the ocean.

Now, we're coming in. We can see Long Island. Can you see Long Island? It's sort of stretching from the middle. Micah is centering in on the gray patch which is New York. And in the upper right, we see Cape Cod. That's where I'm sitting and talking to you from. And also Boston is just off the top of the screen up there.

But now as we come into the head of the sort of fish-shaped Long Island, we could see the five boroughs of New York. We see Connecticut. And we also see New Jersey. That's where I grew up.

And so we come in closer now. And we see this beautiful harbor-- it's an amazing harbor, and the Hudson River that runs north. And the city grew because this harbor was a goldmine for transport of all the riches of the New World several hundred years ago.

Now, we come in. We can see Brooklyn to the lower right. We can see the island of Manhattan. And it's between the Hudson River and the East River. And as we come in closer, we might be able to see some darker patches at the tip-- of the southern tip of Manhattan. That's where all the tall buildings are.

And again, Midtown, all those tall buildings in New York City right there, in Midtown, it makes it kind of darker because of the shadows. But we also see Central Park. And also can you see the blue in the middle of Central-- Central Park is green. And it forms a rectangle dead ahead of us.

And then off-- you can also see Roosevelt Island. That's that long, little island in the middle of the East River over there. But in the middle of Central Park, can you see that blue? There's a sort of blue thing. That's called the reservoir.

FAHERTY: Carter, if I could just jump in for second because I know we're just right at our edge of time.

EMMART: OK.

FAHERTY: I want to give one shout-out here as we look at Manhattan, with this beautiful grid, to the event that happens-- starts to happen in Manhattan in one month. Right now the Sun is getting itself-- and we're getting in ourself-- in a position where we're going to have a line up a setting Sun, with this beautiful grid of Manhattan, for an event we call Manhattanhenge, which hopefully will be able to celebrate. It's always wonderful to see the grid and the view here. I know where we're at our 12:40 breaking point.

EMMART: I'll just do one last point. The George Washington Bridge, which is out there in the background, is exactly one mile. So the Hudson River is about a mile wide. And Central Park is just a little shy of that. But right in the middle is the American Museum of Natural History, our home, and the home of this proper Open Space.

I want to give a shout-out to our colleagues in Sweden, who help us to develop this. And also to our NASA support, that has helped us build Open Space and bring it to you today. And it's been a lot of fun, hasn't it Jackie? It's fantastic.

FAHERTY: It's been great. I know we had students from all over, Montclair Kimberlee Academy, Lockhart Air Academy, I know you both were in the Chat. Thank you for joining us, kids. And you can look forward to more educational content from the museum all day long, including an event we're going to do in the evening at 6:00 o'clock for those that want a little bit more on Venus and Earth.

And tune in right after this for a super-cut video on Earth Day that you can watch from the American Museum of Natural History.

EMMART: Thanks, Jackie. And thank you all.