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
00:14twinkling celestial bodies all danced around us. This theory was super popular in ancient
00:20Greece and Rome. Famous geniuses like Aristotle and Ptolemy really loved this idea. Why did
00:26people believe this in the first place? Well, first of all, we have a massive ego. Second
00:32of all, there were a couple of things that seemed to support it. For example, if you
00:36stand on Earth and look up at the sun, it seems like the sun is spinning around us once
00:40every day. The moon and the planet seem to be doing the same thing. The obvious conclusion
00:44is, oh, they're probably twirling around the Earth.
00:55Then there's the fact that Earth feels pretty steady when you're standing on it. It just
00:59doesn't feel like it's moving, you know? And because of the stability beneath our feet,
01:03people thought that the Earth was unmoving. But even back then, there were ancient Greek
01:08and Roman philosophers that were onto something cooler. They paired the geocentric model with
01:13the idea that Earth was actually a round ball floating in space, not a flat disk. They started
01:19connecting the dots. And after a while, astronomer and mathematician Aristarchus of Samos had
01:25a game-changing idea. He thought that the Earth might not be the center of everything.
01:30He proposed that everything revolved around the sun. Funny to think that back in the days,
01:36this idea was considered insane.
01:44That's why for a while, most people stuck to their geocentric views. It took us many
01:49centuries to finally accept the heliocentric model, where all the planets in our solar
01:53system revolve around the sun. This idea was brought to life by people like Copernicus,
01:58Galileo, and Kepler. This change wasn't easy for people. It was hard to let go of our space
02:05crown. But gradually, we came to terms with it. And by letting go of this idea, we discovered
02:12a whole new world. This journey led us to an astonishing realization. Not only we're
02:18not the center of the universe, we're nothing but a little speck in it. We're a microscopic
02:23dot, sprawling galaxy called the Milky Way. The discovery of the Milky Way started right
02:29from our own backyards. If you've ever gazed up at the stars on a clear night, you might
02:35have noticed a faint luminescent band stretching. It's like a shimmering celestial ribbon woven
02:41with stars. That is our galaxy. It was named Milky Way because it looks like someone spilled
02:48milk on a road. It was perfectly depicted in the 90s by Voyager 1. NASA's spacecraft
03:04took a picture called the Pale Blue Dot. That tiny little pixel that's almost impossible
03:09to see is our planet. The photo was taken from a chilling 3.7 billion miles away from
03:15the 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
03:32place in this gigantic world. To do that, first, we had to unlock the secrets of our
03:39galaxy's structure. Okay, so we can clearly see that it has some band-like formation.
03:45That probably means that our galaxy is not a big round ball, like the planets and stars.
03:51In reality, it's more like a giant pancake. A flattened disk. And we can see that we're
03:58not above it, and not below it. We'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
04:26Pale Blue Dot picture. That spacecraft has been journeying through space for almost half
04:31a century. It left the solar system years ago. You know how many light years it traveled?
04:39Two. And how many light years is the Milky Way? 100,000. You get the picture. But the
04:45lack of fancy technology didn't stop us. In the 18th century, a bold astronomer named
04:51William Herschel decided to explore our galaxy. With nothing but a telescope, this Indiana
04:57Jones of astronomy started mapping the stars in the night sky. As a result, he discovered
05:02Uranus, more than 2,000 nebulas, and created the first map of the Milky Way that depicted
05:07it as a disk. The map wasn't super accurate, but still very impressive.
05:18Unfortunately, he didn't know about something called interstellar dust. It's like space
05:24fog that can block our view of stars in the center of the Milky Way. This dust made the
05:28central region of the Milky Way appear less crowded than it actually is. Now, let's go
05:34all the way to the 20th century. Henrietta Swan Leavitt, an American astronomer, was
05:39another curious stargazer. But she focused her attention on a special kind of star called
05:44Cepheid variables. These stars had a unique quirk. They pulsed, getting brighter and dimmer
05:51in a predictable pattern. Leavitt's job at the observatory was like being a librarian.
05:57She cataloged these special stars. And in doing so, she stumbled upon something incredible.
06:05A direct link between the brightness of these stars and the rate of their pulsations. This
06:10discovery is now known as Leavitt'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
06:22stars became the rulers for measuring distances.
06:30Before the 1920s, most scientists believed that our Milky Way was the only galaxy in
06:38the universe. But as telescopes improved, some astronomers started realizing that this
06:44isn't the case. We started finding more and more galaxies. But if the Milky Way was just
06:51one of many galaxies, where exactly were we within it? Meet the scientist named Harlow
06:56Shapley. Armed with a powerful telescope, Shapley turned his attention to globular clusters.
07:02These are tightly packed groups of ancient stars that gather together in spherical shapes.
07:08That's when he noticed something interesting. The oldest stars around us weren't scattered
07:12all over the canvas. They were clustered around the center of the Milky Way. And they were
07:17pointing in the direction of 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
07:33the Milky Way, and the most ancient guys were hanging out there, which means we're not even
07:38at the center of our own galaxy. It seems like our importance becomes less and less
07:44with each new discovery, huh? Anyway, Shapley found out that we were positioned somewhere
07:51on the outskirts of our galaxy. Shapley's calculations weren't perfectly accurate, but
07:56he got pretty close. Luckily, now we have very precise and cool tools. Since then, we've
08:02since pinpointed our precise location. We're located near a partial arm of the Milky Way
08:07called the Orion Arm. It's about 26,000 light-years from the heart of our galaxy. And that was
08:14the story of how we found out where we are in the Milky Way.
08:21You 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
08:37to map the Milky Way in unprecedented detail. Not just some rough map, but a photographer
08:42capturing every nuance of our galaxy. Gaia is piecing together the positions and motions
08:48of about 1 billion stars, and it's like 1% of the stars in the Milky Way. But even that
08:54tiny fraction is enough to create a masterpiece of cosmic cartography. What a grand journey
09:00it was. It led us from thinking Earth was the center of the universe to realizing we're
09:05less than a speck in the grand scheme of things. But what's more important is that this story
09:11shows humanity's drive to uncover the mysteries of the world. And there's always something
09:16new to explore. Discoveries just keep coming, so stay tuned and keep looking at the night sky.
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