Video Transcript: The Milky Way

In so many ways, we've lost our connection to the night sky.  I mean, I don't know about you, but I live in a kind of a medium-sized, small-sized city.  And even the lights from that city kind of blind out the faintest things in the sky.  We get what we call light pollution, this light that goes up into the sky from all the street lights and building lights.  And so at night, all I can see is the brightest stars, maybe some of the planets, maybe the moon.  One of the biggest things we lose with light pollution is our ability to see the Milky Way Galaxy; the galaxy that we live in. And when you are at a dark sky location, a place where it's really dark, and you can see all the faintest stars then, even without even letting your eyes get adjusted, you can fairly easily see the Milky Way.  

It looks kind of like this first picture in the gallery.  It's kind of a faint glow of light across the sky, in a particular patch of the sky.  And if you let your eyes get more and more dark adjusted, you can kind of start to see more detail in that glowing light, you can maybe even see what looks to be dark clouds in that glowing light.  And this is the Milky Way.  You can see it with your naked eyes, you can see this galaxy with just your eyes, no telescope.  And ancient people called it the Milky Way because it looked like a stream of milk across the sky.  And then it kind of makes sense; it’s kind of a faint white glow.

Now even at the time of Galileo, people knew or guessed that the Milky Way was glowing because it was lots and lots of stars, and so many stars that you couldn't really see the individual stars but there were so many of them that it caused it to glow.  And when Galileo took his telescope and looked at the Milky Way, he could see that in fact, there were stars there, more stars than he could see with just his eyes. 

Now another way to see the Milky Way that's really cool is if you were to take a picture, a long exposure picture, where you leave the camera open, but you don't just set it there, you have a track along with the sky, right as the sky moves.  Otherwise, you'd get star trails.  So you have to have it move with the stars.  And when you do that on the Milky Way, you get an amazing picture.  Like this image here; like picture number two in the gallery.

This is probably a one-minute exposure, not very much.  And this is a picture of the very center of our galaxy.  You can see not only the glow from all of these stars, so many stars, but also these amazing dark bands, these clouds across the sky.  It's really so cool to see some of the most beautiful pictures, or pictures of the Milky Way, where you see the whole sky and you see this milky way all the way across.  

Now what are we actually seeing here?  We have this unique perspective, because we live on a planet orbiting a star that's inside the Milky Way, so we are like living in this thing, and so when we try to make sense out of what we're seeing, we have to keep in mind that we're inside of it.  You know, it's like, if you were trying to make sense out of a washing machine, but you were inside of the washing machine, you'd probably be like, what is this crazy thing that I am, versus being outside of it and looking at it.  So that's the situation we're in here with the Milky Way; we’re inside of it.  And what we see is that we see a lot of stars across a band of the sky.  And we see a lot less stars when we look away from that band. 

Here's another way to look at that. And you can see that in the picture here, in the second picture of the gallery, where there's this whole dark band with all the stars.  And then as you look away from it, you see way less.  But here's another way to see that.  And the third picture in the gallery.  These are many of these long exposure pictures that have been stitched together.  So this really represents a full 360-degree view of the Milky Way all the way around the sky.  And you'd have to take pictures over the course of an entire year to be able to create a picture like this.  So this is showing us the whole Milky Way as we see it from here from Earth.  

And you can see really well that you know there's all of these stars but as you move up or down away from this disk or this line in the sky, there's less stars.  So it's kind of like this is suggesting that we're living in some kind of pancake-like thing, something that's flat, because when I look along this main line, what we call the galactic equator, just like the equator on the earth, this is the galactic equator, and as we go up in our latitude, our galactic latitude, you look higher and higher above, you see less and less stars.  So it's kind of like we're in a pancake.  And if you were living inside a pancake, maybe you're a little chocolate chip living inside this pancake, well, if you look along the surface of … along the line of a pancake, you just see pancake everywhere.  But if you look up, or you look down, you will see a little bit of pancake, but you'll see out of the pancake.  And that's exactly what's happening in our galaxy.  When we look above or below the Galaxy line, the Milky Way, we're still seeing stars, because we're still in the galaxy.  There are stars that are in our galaxy, but we're seeing way less because we're looking out of the galaxy. 

Now, you'll also notice in this picture, that there's a clear difference when you're looking towards the middle of the galaxy, versus when you're looking towards the outer edges of the galaxy.  In fact, I mean, some parts of this line have way more stars than others.  So it kind of gives us a picture, like we can start to tell where are we in this galaxy; where are we in the pancake, if you will.  I mean, imagine a partially transparent pancake, and you'd see way more pancake on one side, and kind of less pancake on the other side.  So you start to say, well, I must not be in the middle, it must be kind of towards the edge because, you know, I see that there's not much pancake behind me.  That's what we see in our Milky Way.  We see a lot of stars in one direction, we see fewer and fewer stars.  This is what early astronomers did, before they had sophisticated equipment is that say, Well, if we just count the number of stars along the Milky Way, we should be able to tell, and even above and below, we should be able to tell exactly where we're located inside our galaxy. 

One of the things they didn't really know to account for is that these dark bands are actually clouds blocking stars, so we can't see.  It's like dust clouds so you can't see the stars that are behind that, so that throws off your counts and things like that, but we can get a pretty good estimate.  I mean, you can just kind of tell roughly we're not in the middle, and we're not at the very edge, we must be somewhere in between.

Now to get more accurate measurements of our location in the Milky Way, we use star clusters. So the fourth picture in the gallery shows a picture of what's called an open star cluster.  This is a group of stars that all formed together out of the same big cloud of hydrogen gas.  Each of these stars was separate, but they kind of formed at the same time.  There are other kinds of clusters called globular clusters.  And those are really spectacular to see.  You should search for a picture of globular clusters.  And they are 100,000 stars that all formed at the same time.  And they form it's almost like a mini galaxy.  It's like this cluster where you get tons and tons of stars in the middle and fewer and fewer as you get out.  These two different kinds of clusters, open star clusters and globular clusters, they allow us to kind of map out the galaxy in a couple of different ways.  

Open Clusters allow us, and we find them throughout our galaxy, they become a map of kind of the skeleton of the spiral of our galaxy, because those open clusters tend to fall more along the spiral arms of the galaxy.  So when we find them, and we find where there's more of them, that helps us to kind of map out a picture of the bones of our galaxy. So we can kind of get a bigger picture. 

Now. The globular clusters, those are evenly distributed, but they're centered around the very center of our galaxy.  So there aren't as many globular clusters near us, mostly, they're a big bubble around the center of our galaxy.  So if we can map out where the globular clusters are, and we find the very middle of where all those Globular clusters are, then that can tell us where the middle of our galaxy is.  So you see how the star clusters can allow us, if we know how far away they are, if we can measure, kind of map them out in three dimensions, then we can figure out exactly where we're located in our galaxy and what our galaxy looks like.  

So astronomers have done this and the fifth picture in our gallery illustrates that.  Now every picture that we've seen in this entire course is from really an area pretty close to our star.  I mean, even that very first pale blue dot picture I showed you the most distant photo ever captured of the earth, that spacecraft was still in our solar system.  It was still orbiting our star.  We cannot escape our galaxy to get a picture of our galaxy from above and say what does the Milky Way look like?  We're stuck here.  We're stuck in the pancake. We can't escape it.  And so how do we know what it looks like?  Well, we use these maps created by clusters, and then we get an artist to draw a beautiful picture. And that's what this is.  The fifth picture is like an artist drawing of what the Milky Way galaxy would look like if you could be above it.

And the idea here is, there's a lot of information that's mapped on here, but you see that the Sun's location kind of matches what we would expect.  We're not in the middle, we're on the farthest outside; we’re kind of partway in between.   And you can see labeled here a number of different spiral arms.  We can map out where it's a denser region where there's more of these clusters.  And we can see pretty accurately how far away we are from the center of the galaxy.

One of the cool things you'll see, and we'll address this a little bit later on when we look at different kinds of galaxies, is that the Milky Way has this unique feature where it has a bar across the middle.  The Milky Way is what we call a barred spiral galaxy.  You see this yellow bar there that goes across the center of the galaxy.  So we live in this particular kind, there are lots of different kinds of galaxies, but ours, it seems, is a barred spiral.  Okay.

One of the other things we can do if we map out the entire galaxy is we can get a sense of how big it actually is.  And that's where things get pretty astounding.  The entire Milky Way galaxy is about 30,000 parsecs across.  So that's 100,000 light years, which means light would take 100,000 years to reach from one side, all the way to the other. So this galaxy is huge, absolutely enormous.  And we'll find that many of the other galaxies we see in our night sky are that big as well. 

Okay, cool. So that's our Milky Way. In the coming videos, we're going to start looking at galaxies in general and some of the amazing things we can see when we look at galaxies in the universe. 

All right, we'll see you next time.