Why is it so hard to get a picture of the Milky Way? How much of our galaxy have we mapped? What the heck is a “barred spiral” and what does that have to do with our core? I discuss these questions and more in today’s Ask a Spaceman!

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EPISODE TRANSCRIPTION (AUTO GENERATED)

You know, now that I think about it, I haven't really given Galileo his due in this series. And what are we? 218 episodes in? I've talked about his contemporaries, like Kepler, relentlessly, because Kepler's my boy, and other giants, like Newton, and Maxwell, and Einstein. I've mentioned Galileo in passing because, you know, he's kind of important in the history of science, but I haven't really dug it.

Unfortunately, that is not today's episode. I I'll need to save a full exploration of Galileo's genius for another day, so please ask. But I do get to mention Galileo again today, and I'm gonna kick off today's episode with just one one of his remarkable achievements. He was the first person in the history of humanity to see the Milky Way for what it really is. Now the Milky Way is the name we give to this feature that we see on the sky.

It looks like a, well, like a Milky Way, hence the name. So all sorts of cultures around the world have noticed this because it's kind of big. It kinds of takes up the entire sky. It looks different than other things on the sky. It looks different than the sun or the moon or the stars or the planets.

It's definitely different. Looks kind of like a cloud, but it's definitely not a cloud because it appears in the same position on the sky all the time. And it stretches from one end to the other like a a a road of milk, the Milky Way. And for millennia, humanity across the globe had debated about the true nature of the Milky Way. What is this band of whitish, milkyish stuff that appears in our sky?

Was it in our atmosphere? Was it just past the moon? Was it caused by the earth like refraction in our atmosphere? Was it a reflection of sunlight off of a distant ocean? Around the turn of the 1st millennium, a lot of Islamic astronomers started to guess at the right idea.

We have writings from al Biruni even by a Nassir al Din al Tusi and many others that were starting to argue that maybe maybe the Milky Way is far away because if it was close, we'd be able to measure a parallax distance to it and we can so therefore must be at least farther than the moon. And if you take a bunch of lights like stars and put them very far away, they'll all kind of blend together to give you this cloudy appearance. So this is very solid reasoned arguments. But there were also reasonable arguments against that line of thinking, like how could the stars possibly be that far away? And so the arguments went back and forth for centuries after this point, and then you get to Galileo.

Galileo invents the astronomical telescope, pointed at the sky, and has his mind completely blown. You read his writings. It is just page after page of what's the look at this thing. Look at this thing. Look.

Oh my what is this? Oh, look at this. Look at this. It's just blown away continuously, and one of the things that blew him away was the Milky Way. You look at the Milky Way through a telescope.

Go. If you have a pair of binoculars in your home, go out tonight. Look for the Milky Way. Make sure it's dark enough out. There are no clouds.

You need decently low levels of light pollution to see the Milky Way, and then look at it through binoculars. Likely, your binoculars are more powerful than Galileo's telescope, and you'll see it's full of stars. Countless stars that are so numerous and so far away that they blend together into a diffuse band of light. This was our first taste. Galileo's discovery that the Milky Way is composed made of many, many small and distant stars was the first taste of our galaxy.

The word galaxy itself comes from the Greek word for milk of all things. So, when we say we live in the Milky Way galaxy, we're saying we live in the Milky Way milk thing. It's a bit convoluted, and we're gonna have a hard time explaining that one to the aliens when we finally make contact, and we're trying to we're we're discussing the names we give to everything around us. We say, we call these plants. We call these basketballs.

So we call this, milk. That's gonna be a tough one to explain. And then a direct translation, if they come from another galaxy, we would be asking like, so what milk do you come from? Although I suppose as mammals that question isn't so crazy after all. Anyway, side digression.

Even after Galileo's discovery that the Milky Way is full of stars at the time and still after that time, the Milky Way was just an interesting feature of the sky, but we were starting to realize that there was something special about the Milky Way. And it's especially interesting to us because the Milky Way and here comes the $10 word, so please pay up. Asymmetrical. Asymmetry is one of the most useful tools in astronomy. Symmetry is when everything is nice and even like left is equal to right.

The top is the same as the bottom. The forward is same as the backward. Those are all symmetries. And biologically, we we tend to like symmetries. Aesthetically, we like to we tend to appreciate symmetries.

We like it when our house is the same evenness from room to room. If it starts to tilt, that's an asymmetry. We we don't really like that. When we're hanging pictures, we like to have the pictures up at the same level. We like them to be symmetric.

And then when they tilt, oh my gosh. That's an asymmetry. We don't like that. I actually like, by the way, just a tiny bit of asymmetry in my life. Maybe it satisfies my craving for good data because when you see asymmetries out in nature, that is a sign that there is more information to be had.

We can take advantage of asymmetries to gain better understanding more so than we can when it's just pure symmetries. When there are pure symmetries when when everything's the same, there's not a lot to learn about that object. And the deeper you dig into the asymmetries, the more you learn. Like, if if you the first approximation of the Earth, it is perfectly spherical. It's perfectly symmetric.

Up, down, left, right. The Earth is more perfectly smooth than a billiard ball. Even the tallest mountains, the deepest trenches, the earth is so big. There might as well not be there. It's perfectly symmetrical.

And then there's not a lot to learn about a perfectly symmetrical earth. But once you start digging into the details and you find those asymmetries, you find the mountain peaks, the ocean trenches. You find the differences between land and ocean. You discover there's an atmosphere. All of these are asymmetries, and all of these contain really, really rich information.

In astronomy, we use asymmetries all the time, and the Milky Way is a perfect example of it. In fact, the very fact that the Milky Way is asymmetrical on the sky is a big giant clue that something is different about it. The Milky Way is asymmetrical, which means you can look in one direction on the sky and happen to be looking at the Milky Way. And then if you look in a different direction on the sky, you could be not looking at the Milky Way. That is an asymmetry.

So that right there, the fact that this asymmetry exists means that there's something special about this band of light on our sky that it might represent something more. Prior to the 20th century, we didn't know that other galaxies were a thing. We didn't know that we were living inside of a galaxy. We just thought it was all universe, just one, and it was just full of stuff. And so when we map the sky prior to the 20th century we are simply mapping the universe, and we noticed the milky way, and we noticed it was something interesting an interesting feature of the universe.

But the more we studied the Milky Way, the more the asymmetries popped up, and the more we began to realize that something bigger was going on. In the mid 1700s, the philosopher Immanuel Kant of all people guessed that the Milky Way was a disc of stars rotating together. The disc is pretty obvious. Like, like if you, if you live in a disc and you're embedded inside of the disc, then some directions when you're looking around, you'll be looking through the disc and you'll see a bunch of stuff. And then some directions you'll be looking perpendicular to the disc.

So you won't see a lot of stuff. And so that explains why it appears as a band on our sky. Because when we're looking into the disc of the Milky Way, we're seeing all the stuff. And then if you apply some basic Newtonian physics, rotating disks are really easy to to make in the universe. In fact, easier to make than rotating spheres.

That that's another discussion. In 17/85, the great astronomer William Herschel launched an ambitious program to, you guessed it, map all the stars in the universe. His map, which you can find online, is rather lumpy and awkward looking like a very, very unwell amoeba. But one thing stands out. It's longer than it is wide.

It's definitely not symmetrical. That's odd, isn't it? Why should a survey with our most sophisticated telescopes making a map of the heavens, a complete and total map of the universe, why should it be longer or wider than it is thick? That's odd. That should have clued us in really really early that the Milky Way is not the entire universe, but that wouldn't come until the early 20th century.

In the early 1900, couple more pieces of evidence came in. A couple more asymmetries came in that we that allowed us to start to build a map, build a structure of the universe around us and give us a clue that the Milky Way is different than the universe. In the early 1900, Jacobus captain studied something called proper motions. Proper motions, it's this weird jargon term. Like, the stars move on their own.

They appear to move over the course of the night. They appear to, like, circle around the sky, but we know that motion is due to the the the rotation of the Earth. On top of that, the stars are moving on their own. They're just moving through space. They're just they're just booking.

They're just cruising along. They're just moving, and that kind of motion is called proper motion. It's not like the fake apparent motion due to the our perspective here on a rotating earth. It's their actual movement through the through the universe, through the galaxy, and he discovered that, yeah, stars have all sorts of proper motion. Some are slow.

Some are faster. Some are going up. Some are going down. You know, they're doing whatever they want, but there are 2 general categories. There are some stars that are moving in one direction on the sky, and then another collection of stars that are generally moving the other direction.

It's very asymmetrical. Definitely, maybe, perhaps, for certain something funky is going on. A little while later, Harlow Shapley performed a survey of globular clusters. These are dense collections of stars up to a 1000000 stars, typically dim, old, red stars. They're they're the retirement homes of the galaxy.

Now the globular clusters, he was able to perform a survey of them, which is where are they? And he found they're symmetrical. They're they're they actually are distributed in the shape of a sphere. So unlike the stars, which tended to be clustered in this disk, the globular clusters were scattered all over. It was spherically symmetric, but the center of that sphere, the center of all these globular clusters was tens of thousands of light years away from here.

That's that's an asymmetry right there. So even though the globular clusters themselves are symmetrical, the center of that symmetry is is over there. Tens of 1,000 of light years away. It's not over here. The implication being that the globular clusters are orbiting the center of something that is not us.

And then we discovered that other galaxies exist and it's game over. We need to take a quick break, folks, and mention that this show is sponsored by BetterHelp. And the theme of today is all about collaboration. It's all about relationships. Some of the most powerful satisfying relationships I've ever had in my life are ones with my mentors, with my colleagues who become my friends.

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From then on, after we discovered that there are other galaxies and that we live inside of 1 and that the distances between these galaxies are vast and much bigger than the galaxies themselves. Typical galaxy will be like a 100000 light years across. The distances between them are millions of light years. So these distant galaxies, another name for them, are island universes. Once we discovered the existence of galaxies, once we discovered that we live in one such island, the job of mapping the heavens branched into 2 divisions.

1 was cosmology, which was mapping the whole entire universe and the subject of other episodes, and the other was more locally focused trying to map our own galaxy as a separate entity within the universe. This would be challenging. But even by then, even by the early 20th century, we had taken advantage of so many asymmetries. And by the way, the discovery of galaxies themselves boils down to an asymmetry. You see a collection of stars like the Andromeda Nebula.

And then there are other places on the sky where the Andromeda Nebula is no There's nothing there. There's nothing equivalent. And then you discover after repeated measurements and a lot of work that the Andromeda Nebula is the Andromeda galaxy. There are these islands floating in space in the universe collections that are collections of stars. Stars are not evenly distributed throughout the cosmos.

They're clumped up in the galaxies. That's an asymmetry. That's a imperfection that carries very important useful information. Yes. You can go ahead and tell an astronomer next time you meet one that their entire job is just looking for asymmetries, but by the early 20th century we realize that we live inside of a new kind of cosmological object.

We're gonna go ahead and call them galaxies. Milks. Milk cartons. It's all it's all milk based words here. So we we learned what what did we learn?

That the milky band of stuff in the sky is actually tons of stars. Check. We're part of an island of stars separated from other islands by vast distances. Check. Our island of stars that we're gonna call galaxies from now on is is actually called the Milky Way, which is named after the band of light in the sky.

You know? Notice the slight little name change here. There's the Milky Way sky feature, And then there's also the Milky Way Galaxy. We could have called our home galaxy anything we wanted, but we ended up calling it after the sky feature that we were already familiar with. So the name stuck going from interesting asymmetrical sky feature to the name of our home galaxy.

We learned that this home galaxy, the Milky Way, has a Patreon page, but you should donate to mine instead. It's patreon.com/pmsutter. That's p m s u t t e r. I can't thank you enough for all of your contributions. And reminder, I am running a promotion through the end of March.

Any contribution at $25 and up, you get a free autograph copy of my book. As soon as I get those copies in, I will send them to you. You can even just do it once for 1 month and then just drop it. I will write it down, and I will get you a copy of the book. That's patreon.com/pmser.

The book is Rescuing Science, Restoring Trust in an Age of Doubt. We also learned that the Milky Way galaxy has got a lot more stars than we can count even if we use our fingers and our toes. There are a lot of stars. So that's the early 20th century. That's how we discovered the basic bare bones of our milky way galaxy.

Now, if you if you go on a search engine and type in Milky Way galaxy, you'll get a picture or at least a diagram of the Milky Way. And if I say Milky Way galaxy, a particular image probably pops in your head. It probably has a dense core, probably has beautiful spiral arms and a dazzling array of stars. Well, how do we get that picture with that much detail? Well, the truth is we don't.

We actually only have a dim and vague understanding of what the Milky Way looks like. You know, imagine flying a 1000000 light years away and looking down from above on the Milky Way galaxy. What what would you see? Well, the truth is I can't tell you what you would see with any significant amount of certainty or detail. I can tell you a few things, though.

It's not a lot. It's not a lot, but we've worked really hard for it, and we should be proud of what we've learned because it wasn't easy to get. Because mapping the interior of the milky way is hard, as in enormously challengingly hard for a few reasons. 1, it's big. 100,000 light years across.

That's our current guess. A 100,000 light. That's that's big. Yes. We observe galaxies from billions of light years away.

Okay? Those galaxies appear as tiny little dots. The the Milky Way is gigantic. Our nearest neighbor star is, like, what? 4 light years away?

And we're talking a 100000 light years away to get at the very edges of the galaxy. It's big to map it all out. There's a lot of stuff. There are 100 of billions of stars. Low range is 1 to 200000000000,000,000.

Upper range is 5 to 600000000000. There are just as many planets, if not more, probably way more. There are innumerable stellar remnants, neutron stars, black holes, planetary nebula. There are open clusters, globular clusters. There are star forming regions, giant molecular clouds.

It's full of charged particles, magnetic fields, cosmic rays, neutrinos, dark matter. The Milky Way galaxy is crammed with stuff, and part of that stuff makes it really annoying to observe because part of that stuff is dust. I should do a whole episode on astronomical dust just to ask. It doesn't sound like the most exciting topic, but it is what occupies the vast majority of time for most professional astronomers. Dust is so annoying.

It's literally dust, grains of molecules all strung together in various arrangements just floating around, not doing anything except blocking light, scattering light, absorbing light, emitting light of its own. If I want to look through the Milky Way galaxy, which is our only vantage point, We can't go a 1000000 light years away and look at it top down. We're inside of it. We have to look through the Milky Way in order to study it. So it's really big.

There's a lot of stuff. So we're trying to look really really far with very high resolution and map lots of stuff. And then there's all this dust that gets in the way that absorbs distant light, scatters it, fuzzes it out. The dust obscures our view of much of the Milky Way. Even if we had, you know, a telescope the size of planet Earth, we couldn't get rid of the dust and the effects the dust has on our observations.

So how do we do it? How do we get any sort of portrait of the Milky Way? Well, we have asymmetry. We'll take any observation we can get. Any clue we can get.

Any kind of asymmetry helps us build a map because we can extract information from the asymmetry and we can use that to make a solid guess of what's going on. Just like we did before. That like just how we discovered that the milky way itself is a galaxy that is so different and unique. It's asymmetrical on the sky. The stars in the disk behave differently than the stars outside the disk.

We can look to other galaxies to get clues of what's going on, to help us understand our own. When we look at other disky galaxies, they tend to have cores and they tend to have spiral arms. And when we look at inside of our own galaxy, we can very quickly deduce Immanuel Kant did it 100 of years ago that we live inside of a disk, that our Milky Way galaxy is in the shape of a disk. Because if it was another shape, it would appear differently on our night sky. We're taking advantage of that asymmetry.

So now that we know we're a disk, we can look to other galaxies that look kind of disky and see what what were the what are they like. And those galaxies tend to have cores and spiral arms. So, gee, we probably live in a spiral galaxy because that is the most common form of disk like galaxy. And then from there, if we wanna dig into those asymmetries, if we wanna dig into all those little nuggets of juicy information, we're gonna have to use and deploy the astronomer's favorite technique, which is brute force. I'm talking surveys.

I'm talking automated scans. I'm talking hard drives full of data. I'm talking years long observation campaigns. You know, just looking around the place and putting pins and everything and mapping as much as we can. There's a lot of galaxy to go around with a lot of stuff in it.

There's a lot of dust blocking our view to a lot of places. So let's just grab what we can, look for any interesting asymmetries, and try to get the job done. The biggest tool that we have for this is Gaia, launched by the European Space Agency back in 2013. It has one main mission, and that is all the stars. Well, not all of them.

You know, there are 100 of 1,000,000,000 of stars in the Milky Way galaxy. We can't see many of them, if not most of them because of the intervening dust. So how about let's just map the ones we can see and get as much information as possible. Get their precise position, their distance from the earth, their proper motions, their brightnesses, their colors, along with anything else, as we're doing this massive survey, this massive census of the local Milky Way galaxy, we'll get all sorts of other stuff too, like stellar remnants, planetary nebula, giant gas clouds, asteroids, comets, you know, whatever. So we can get other kinds of science done as we're performing the survey.

The latest release, the 3rd data release of the Gaia spacecraft has mapped precisely the positions, proper motions, brightness, this color, full catalog information for 1,008,111,000,000 709,711 stars. That's nearly 2,000,000,000 stars cataloged. It is the most complete catalog of our local universe ever. Take that, Herschel in your little catalog. It's also less than 1% of all the stars estimated to live in the Milky Way galaxy.

Hey folks. We're gonna take another quick break because I need to mention that this episode is presented by Chemists in the Kitchen by LabX, a YouTube video series spotlighting the power of chemistry and how science and food can bring people together. And yes, both can. In each episode, real scientists walk you through things like, are you ready for this? I'm not making it up.

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We're going to combine the Gaia survey, This broad survey, basically every star near the sun, we're going to precisely catalog in this patch of the galaxy, and then we're going to combine that with other kinds of surveys that are much narrower, but much deeper. These are called pencil beam surveys, where we just take a tiny, tiny, small target and try to go really, really far out. We're going to try to capture different wavelengths of light that will capture different kinds of processes. For example, the James Webb is an infrared telescope. It's going after star forming regions, like dense gas clouds that are forming stars right now.

We can't see the stars themselves because of all the dust, but the dust is emitting infrared radiation that the James Webb can see. So the James Webb is great for picking these out in the Milky Way. When there's active star forming, there's stars living and dying. They're gonna spit out x rays, ultraviolet. We'll we'll observe those.

Radio waves can penetrate dust clouds really well. We'll use that. We'll we'll what we're going to do to get a map of the Milky Way is everything we can. So every wavelength we can get our hands on, every kind of survey, the more data, the better. We're going to take the Gaia catalog of our local universe.

Absolutely complete and total information about these stars surrounding us. These 2,000,000,000 stars surrounding us. And then we're going to do lots of narrow pinpricks into the into the Milky Way. Like, we're we're like an ice core sample. We're gonna poke here and see what we can get in this wavelength.

Look for interesting kinds of astronomical features in that direction, in that direction. And then we're gonna throw all this mountain of data into a spreadsheet, the size of Kansas and try to make sense of it all, especially by using asymmetries. We're going to use different aspects or parts of the Milky Way. We're gonna going to see if they look different from the others. So we're going to compare and contrast different parts of the map.

If we do a pencil beam survey deep into the heart near the core of the Milky Way, and we get a sample of the stars in the core of the Milky Way, we can compare that to the Gaia data of our local universe. And if they're different, that tells us something about the core. It tells us there's an asymmetry there that the populations of stars that live near the core are different than the populations of stars that live out here, 25,000 light years away from the core. If we peer into what we think is a spiral arm and we see something different about the stars or gas clouds or the activity rate over there, we compare that to the Gaia catalog of our local universe, then we know whether we live inside a spiral arm or not. By comparing and contrasting, we're going to use asymmetry to help us figure out the shape and contents of our galaxy.

One of the pictures to emerge relatively recently from this kind of program is that the core of the milky way is not a perfect bulge but it's barred. It's like longer on one side than the other. Might even be peanut shaped. How do we know this? Well, comparing to other kinds of spirals.

Many spirals have have elongated core so it's not unheard of. When we look at the core in infrared light, the core is not symmetric left to right. The gas in the core looks like it's pointed more towards us, which we would not see if it was perfectly symmetric. When we look towards the core there's a certain kind of red giant star that happens to live near the core, and those stars are easy to spot because they're big and bright. The light punches through the dust and we can see them from so far away.

This population of red giant stars that lives near the core is split into 2 clumps, and then when we look at the detailed proper motions of stars in our nearby universe from instruments like the Gaia telescope. We can look at these proper motions and we can use our knowledge of the physics of gravity to figure out how these stars are moving in response to all the other matter contents of the Milky Way. And if our core were perfectly symmetrical and a perfectly spherical core, then the stars, even out here 25,000 light years away would be orbiting in a slightly different way. Because they'd be responding differently to the distribution of mass to how the mass is arranged in our core. We're taking advantage of all these asymmetries to discover that, yes, we have a core, because when we look in one particular direction in the milky way we see a lot of stars and they're older stars and they're more densely packed together.

So and then when we look in a different direction we get something else. That's an asymmetry. That's how we know that we have a core and now we know that our core is probably elongated, stretched out, maybe even looks like a peanut, which is just amusing to me. As for the spirals, I mean spirals are kind of important to the overall identity and self worth of a spiral galaxy. We do believe we live in a spiral galaxy.

Like I said it is the most common form of disk galaxy. We are able to spot the spirals even though we live inside the galaxy by taking advantage of asymmetries. Spiral arms are actually not very dense. They're on average only, like 10% denser than their surroundings than the gaps between the spiral. So if you look at a spiral galaxy, if you look at Andromeda through a telescope or a beautiful picture of it, and you look at these beautiful bold bright spiral arms, those arms are only a little bit more dense than average.

Good luck spotting that. That is an asymmetry, but a really tough one to nail down, but instead the spiral arms are regions of star formation. When you make a lot of stars, you make small ones, medium ones, and big ones. The big ones are bright, they're blue, and so they stand out. So when you see the spiral arms in a beautiful picture of a galaxy, the asymmetry isn't really in the density there.

The asymmetry is in the ages of stars. The spiral arms are populated by younger brighter stars, and so they really pop. And we can take advantage of that asymmetry to map out the spiral arms in our own galaxy because we can look around and look for regions of intense star formation And see if there's a string, a row of regions of intense star formation. Because yeah, there may be a pocket here and there that has nothing to do with anything. But if you are doing these surveys of the Milky Way and you're you're poking here and you're poking there, and it's too big to map the whole thing and too full of dust to just map the whole thing and be done with it, but if you start poking around and you see, oh, there's a star forming region right there.

There are lots of bright blue young stars. There are a lot of star forming regions. There's there are a lot of open clusters. There's lots of recent supernovae signs that there's been a lot of activity there. And then you start looking around like, okay.

I've I identified one region of star formation. Now I'm gonna go a little bit inwards. Do I see it there? No. No.

No. It's like, like playing Battleship. Like, okay. You hit the Battleship there. You found a star forming region.

Now I'm gonna map around the regions around it to see if I can string it along and build at least part of a spiral. We do not have maps of complete maps of the spirals. Instead, we just have pieces of them put together, And we use these pieces to connect the dots. So we see a string of star forming regions over here. And then when we look further a field and get, you know, like, try to get some sort of sense, some sort of map from like 80,000 light years away, and we see another star forming region, and then we try to connect the dots and like build a spiral that connects them.

It's not perfect. It's very fuzzy and vague. What we've come up with is that the Milky Way almost certainly has 2 prominent spiral arms that are anchored on the core, and they make a giant s shape, which is pretty cool. After that, there's not a lot. Well, I mean there's a lot of literature on the subject, but not a lot of certainty.

We might have 2 more medium sized ones. Maybe. It might just be a tangled mess of smaller ones. We know we live in on the spur of a medium spiral arm, by the way. Again, by taking advantage of asymmetries, but we don't know.

It's hard to tell what would be visible and prominent to an alien astronomer. If you were a 1000000 light years away looking down at the Milky Way, you might only see that s, or you might see some other additional spiral arms. It it might look something more like Andromeda. Probably not. Like I said there's not a ton of information.

Any map you see of the milky way is going to be largely conjecture. Like the old school European maps of the new world, where they take the places they know for sure. Add in the stuff that likely inebriated sailors told them about, and then for the rest you just go wild. You just say oh, I'll just draw a coastline here. That's our state of knowledge of the maps of the Milky Way galaxy, but it's the best we've got, and to be honest, we've worked really hard to even get this far.

We've taken advantage of a lot of asymmetries in nature comparing and contrasting to build out this guesswork of what the map could be. And we should be proud of it. And why why bother studying the Milky Way in such detail if we're going to if I mean, we can look at the Andromeda Galaxy it's face on. We could just see all the structure of it right there. Well, the Milky Way is the closest galaxy we've got.

If we wanna understand galaxies, this is it. This is our laboratory. The other galaxies are too far away, and besides, this is our home and it's worth mapping. Thank you to atddfairchild on Twitter, atjanellduncanon Twitter, and calvinl on email for the questions that led to today's episode. And of course, thank you to all my Patreon contributors at patreon.com/pmsutter.

Please, go if you are already a contributor at $25 and up, you're getting a free book whether you like it or not. If you haven't yet, go ahead and sign up, and I will get you a free copy of Rescuing Science, Restoring Trust in an Age of Doubt. And I'd like to thank my top patreon contributors this month. Justin g, Chris l, Barbara k, Alberto m, Duncan m, Corey d, Nyla, John s, Joshua, Scott m, Rob h, Lewis m, John w, Alexis, Aaron j, Gillard m, and Valerie h. Thank you so much to everyone for listening to today's episode.

I can't wait till the next one to share even more cool stuff with you. Please keep the questions coming. It's askaspaceman@gmail.com. The website is askaspaceman.com. Please like, share a review like, share the app and then do all the things.

You know what to do. I'm tripping over my own words. Share the episode. Drop a review on iTunes. I really appreciate it.

Helps get the show get even more visibility, and I will see you next time for more complete knowledge of time and space.

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