00:00A long time ago, we believed that the entire universe revolved around our own little blue
00:08planet. It's called a geocentric model. We thought that the sun, the stars, and all those twinkling
00:15celestial bodies all danced around us. This theory was super popular in ancient Greece and Rome.
00:21Famous geniuses like Aristotle and Ptolemy really loved this idea. Why did people believe this in
00:27the first place? Well, first of all, we have a massive ego. Second of all, there were a couple
00:33of things that seemed to support it. For example, if you stand on earth and look up at the sun,
00:37it seems like the sun is spinning around us once every day. The moon and the planet seem to be doing
00:42the same thing. The obvious conclusion is, oh, they're probably twirling around the earth.
00:47Then there's the fact that earth feels pretty steady when you're standing on it. It just doesn't feel
00:59like it's moving, you know? And because of the stability beneath our feet, people thought that
01:04the earth was unmoving. But even back then, there were ancient Greek and Roman philosophers that were
01:09onto something cooler. They paired the geocentric model with the idea that earth was actually a round
01:15ball floating in space, not a flat disk. They started connecting the dots. And after a while,
01:22astronomer and mathematician Aristarchus of Samos had a game-changing idea. He thought that the earth
01:27might not be the center of everything. He proposed that everything revolved around the sun.
01:34Funny to think that back in the days, this idea was considered insane.
01:37That's why for a while, most people stuck to their geocentric views. It took us many centuries
01:49to finally accept the heliocentric model, where all the planets in our solar system revolve around
01:54the sun. This idea was brought to life by people like Copernicus, Galileo, and Kepler. This change
02:01wasn't easy for people. It was hard to let go of our space crown. But gradually, we came to terms
02:08with it. And by letting go of this idea, we discovered a whole new world. This journey led us
02:15to an astonishing realization. Not only we're not the center of the universe, we're nothing but a
02:20little speck in it. We're a microscopic dot, sprawling galaxy called the Milky Way. The discovery
02:28of the Milky Way started right from our own backyards. If you've ever gazed up at the stars
02:33on a clear night, you might have noticed a faint, luminescent band stretching. It's like
02:39a shimmering celestial ribbon woven with stars. That is our galaxy. It was named Milky Way because
02:47it looks like someone spilled milk on a road. It was perfectly depicted in the 90s by Voyager
03:02One. NASA's spacecraft took a picture called the Pale Blue Dot. That tiny little pixel that's
03:08almost impossible to see is our planet. The photo was taken from a chilling 3.7 billion miles
03:14away from the sun. On a universe scale, this distance is nothing. But for us, it's unimaginable.
03:22So when scientists discovered the Milky Way, they armed themselves with telescopes. Their
03:27goal was to map the uncharted territories of the night sky. And of course, to find our place
03:32in this gigantic world. To do that, first, we had to unlock the secrets of our galaxy's structure.
03:40Okay, so we can clearly see that it has some band-like formation. That probably means that
03:47our galaxy is not a big, round ball like the planets and stars. In reality, it's more like
03:53a giant pancake. A flattened disk. And we can see that we're not above it and not below it.
04:00We're right on the plate.
04:10The next step is to travel across the Milky Way to map it. There's a little problem, though.
04:15To do that, we'd have to traverse thousands of light years perpendicular to this pancake-like
04:20plane. Just to put things in perspective, think of Voyager 1, the one that took the pale blue
04:26dot picture. That spacecraft has been journeying through space for almost half a century. It
04:33left the solar system years ago. You know how many light years it traveled? 0.002. And how
04:39many light years is the Milky Way? 100,000. You get the picture. But the lack of fancy technology
04:47didn't stop us. In the 18th century, a bold astronomer named William Herschel decided to
04:52explore our galaxy. With nothing but a telescope, this Indiana Jones of astronomy started mapping
04:58the stars in the night sky. As a result, he discovered Uranus, more than 2,000 nebulas,
05:04and created the first map of the Milky Way that depicted it as a disk. The map wasn't super
05:10accurate, but still very impressive.
05:15Unfortunately, he didn't know about something called interstellar dust. It's like space fog
05:24that can block our view of stars in the center of the Milky Way. This dust made the central
05:29region of the Milky Way appear less crowded than it actually is. Now, let's go all the
05:34way to the 20th century. Henrietta Swan-Levitt, an American astronomer, was another curious stargazer.
05:41But she focused her attention on a special kind of star called Cepheid variables. These stars had
05:47a unique quirk. They pulsed, getting brighter and dimmer in a predictable pattern. Levit's job at the
05:54observatory was like being a librarian. She cataloged these special stars, and in doing so, she stumbled
06:01upon something incredible. A direct link between the brightness of these stars and the rate of their
06:09pulsations. This discovery is now known as Levit's law. It meant that by simply measuring how quickly
06:16these stars pulsed, astronomers could figure out how far away they were. These pulsating stars became
06:23the rulers for measuring distances.
06:33Before the 1920s, most scientists believed that our Milky Way was the only galaxy in the universe.
06:40But as telescopes improved, some astronomers started realizing that this isn't the case.
06:46We started finding more and more galaxies.
06:48But if the Milky Way was just one of many galaxies, where exactly were we within it?
06:55Meet the scientist named Harlow Shapley. Armed with a powerful telescope, Shapley turned his attention to
07:00globular clusters. These are tightly packed groups of ancient stars that gather together in spherical
07:06shapes. That's when he noticed something interesting. The oldest stars around us weren't scattered all over
07:12the canvas. They were clustered around the center of the Milky Way, and they were pointing in the direction
07:18of certain constellations like Sagittarius and Scorpius.
07:27It turns out that the origin of our galaxy began from the center. It was the heart of the Milky Way,
07:33and the most ancient guys were hanging out there, which means we're not even at the center of our own galaxy.
07:41Seems like our importance becomes less and less with each new discovery, huh?
07:47Anyway, Shapley found out that we were positioned somewhere on the outskirts of our galaxy.
07:53Shapley's calculations weren't perfectly accurate, but he got pretty close.
07:57Luckily, now we have very precise and cool tools. Since then, we've since pinpointed our precise location.
08:05We're located near a partial arm of the Milky Way called the Orion Arm. It's about 26,000 light years
08:11from the heart of our galaxy. And that was the story of how we found out where we are in the Milky Way.
08:16You think our story is over? Oh, absolutely not. Meet Gaia, the European Space Agency's
08:30celestial cartographer. Launched in 2013, Gaia embarked on a daring mission. It has to map the
08:37Milky Way in unprecedented detail. Not just some rough map, but a photographer capturing every nuance of
08:44our galaxy. Gaia is piecing together the positions and motions of about 1 billion stars. And it's like
08:501% of the stars in the Milky Way. But even that tiny fraction is enough to create a masterpiece of
08:57cosmic cartography. What a grand journey it was. It led us from thinking Earth was the center of the
09:03universe to realizing we're less than a speck in the grand scheme of things. But what's more important
09:10is that this story shows humanity's drive to uncover the mysteries of the world. And there's always
09:15something new to explore. Discoveries just keep coming, so stay tuned and keep looking at the night sky.
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