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  • The Milky Way is perhaps one of the most striking features in the night sky, especially if you're someplace really dark, during the right season, and even better if you're in the southern hemisphere.

  • And long before humans knew what they were looking at was actually our home galaxy, they used their imagination to comprehend this bright band stretching across the sky.

  • While we may typically be drawn to the bright lights in the Milky Way, in the past, some cultures paid more attention to the darkness.

  • And it turns out that focusing on the dark in the Milky Way is a pretty good place to start to figure out what our galaxy is made of

  • Among those who embrace the dark dusty lanes of the Milky Way, rather than the bright spots, were Aboriginal Australians.

  • They saw the Milky Way asriver in the sky, filled with black water holes filled with fish, or evil spirits.

  • The areas they identified are known as dark constellations.

  • One of the most well known dark constellations is the emu in the sky.

  • Its body is outlined by the bulge in the constellation Scorpius and Sagittarius.

  • Its head is formed by a massive dark nebula closer to the Southern Cross known as the Coalsack.

  • And the Australians weren't alone; all the way across the world, the Incans thought that Earth was floating in a massive cosmic ocean, and that the Milky Way was a connecting river.

  • What's fascinating is that many of the dark areas that attracted these ancient astronomers actually tell us a lot about the makeup of our galaxy.

  • The name "Milky Way" has origins in both Ancient Latin and Greek, both referencing its milky quality.

  • That milky quality comes partly from the billions of stars that stretch out so far in one direction, that it's difficult for our eyes to pick them out individually.

  • This perspective of the Milky Way is actually what helped astronomers figure out what the galaxy looks like, and where we're sitting in it.

  • By measuring the distance to a bunch of these stars and seeing how some move toward us, and others away, we can see that the stars are moving in an overall rotational motion.

  • This tells us that the entire galaxy is rotating in a big uniform spiral.

  • We also know that our sun sits on the edge of one minor arm of the spiral.

  • And the fact that we can see the Milky Way from Earth as a straight line across the sky, with a heavy concentration of stars in the center, means that we're looking at it from just inside the far side.

  • The center of our galaxy is actually something that you can see with the naked eyejust look at the part of the Milky Way right between Sagittarius and Scorpius.

  • Then there are a few layers in the Milky Way: chocolate, caramel, nougat....

  • If there were a caramel layer, it would be that super dense stripe across the middle.

  • So this is called the thin disk, and the thin disk of the Milky Way is where there's a lot more stars. 90% of the mass in the Milky Way exists in the Milky Way thin disk.

  • And this is also where gas settles and forms stars, so that's why there's the dark patches of dust. And if there's gas and dust, there's, you know, a place for possible star formation.

  • This is my friend Dreia Carrillo. She's a galactic archaeologist, yes, coolest title ever! Who studies what the Milky Way is made of.

  • And there's actually a puffier thick disk.

  • So the thin disk and the thick disk are made up of stars born in the Milky Way.

  • The thick disk, was likely thinner, but its stars were heated up and their orbits disrupted.

  • How galaxies form is smaller galaxies get eaten up by larger galaxies, and this is called galactic cannibalism.

  • And this disrupts the stars, making the layer puffy.

  •  And then there's an extended halo around these two layers, made up mostly of stars that were born in other galaxies, like a big stellar graveyard.

  • There's also the bulge, a densely packed region of stars around the center of the galaxy.

  • And, of these layers, the thin disk and the bulge are all you can really see from Earth.

  • Those dark spots in the thin disc that the Aboriginal Australians and the Incans focused on so long ago, are actually massive dust clouds from the formation of new stars in the galaxy.

  • Knowing these different components of the Milky Way is helping scientists like Dreia, figure out how the galaxy formed in the first place.

  • So stars have locked into them some kind of signature of the conditions that they were born in which we see in their chemistry, and that also is different if you're in different parts of the galaxy,

  • or if you're from another galaxy and got cannibalized by the Milky Way.

  • So chemistry is like a very important property that we try to measure in order to kind of backtrackthe formation and evolution of galaxies.

  • It's pretty amazing that we can look up at the Milky Way, from our little planet and know that we're staring at our own galaxy.

  • In fact, every star you can see with the naked eye is within the Milky Way, even the ones not concentrated in the obvious stripe.

  • If the sky is dark enough, you'll be able to pick out the center of our galaxy, the thin disk, some dark dusty nebulae, and the giant emu in the sky.

  • And maybe one day we'll know more about how the galaxy was formed and where all its parts come from.

  • I'm Sarafina Nance, and this is Seeker Constellations.

  • We're going to be covering all kinds of topics to do with the stars and astronomy, so let us know down in the comments if there's something you want us to cover.

  • Thanks for watching.

The Milky Way is perhaps one of the most striking features in the night sky, especially if you're someplace really dark, during the right season, and even better if you're in the southern hemisphere.

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The Milky Way: Dark Constellations, A Black Hole & Our Galaxy

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    林宜悉 posted on 2021/10/17
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