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출처:https://youtu.be/0rHU DWjR5gg7:32(-4:40)12:12But astrology led people to really study the sky, and find the patterns there, which led to a more rigorous understanding of how things worked in the heavenly vault.It wasn’t overnight, of course.This took centuries.Before the invention of the telescope, keen observers built all sorts of odd and wonderful devices to measure the heavens, and in fact it was before the telescope was first turned to the sky that a huge revolution in astronomy took place. It’s patently obvious that the ground you stand on is fixed, rooted if you will, and the skies turn above us. The sun rises, the sun sets. The moon rises and sets, the stars themselves wheel around the sky at night. Clearly the earth is motionless, and the sky is what is actually moving. In fact, if you think about it, geocentrism makes perfect sense that all the objects in the sky revolve about the Earth , and are fixed to a series of nested spheres , some of which are transparent , maybe made of crystal , which spin once per day . The stars may just be holes in the otherwise opaque sphere , letting sunlight though .
Sounds silly to you, doesn’t it?Well, here’s the thing: If you don’t have today’s modern understanding of how the cosmos works, this whole multi-shells-of-things-in-the-sky thing actually does make sense. It explains a lot of what’s going on over your head, and if it was good enough for Plato, Aristotle, and Ptolemy, then by god it was good enough for you. And speaking of which, it was endorsed by the major religious of the time , so maybe it ‘ s better if you just nod and agree and don ‘ t think about it too hard .
But a few centuries ago things changed. Although he wasn’t the first, the Polish mathematician and astronomer Copernicus came up with the idea that the sun was the center of the solar system, not the Earth. His ideas had problems, which we’ll get to in a later episode, but it did an incrementally better job than geocentrism. And then along came Tycho Brahe and Johannes Kepler, who modified that system, making it even better. Then Isaac Newton – oh, Newton – he invented calculus partly to help him understand how objects moved in space. Overtime, our math got better, our physics got better, and our understanding grew. Applied math was a revolution in astronomy, and then the use of telescopes was another. Galileo didn’t invent the telescope, by the way, but made them better. Newton invented a new kind that was even better than that, and we run from the idea there .
Then , about a century or so ago , came anotherrevolution : photography . We could capture much fainter objects on glass plates sprayed with light – sensitive chemicals , which revealed stars otherwise invisible to us , details in galaxies , beautiful clouds of gas and dust in space .
And then the latter half of the last century, digital detectors were invented, which were even more sensitive than film. We could use computers to directly analyze observations, and our knowledge leaped again. When these were coupled with telescopes sent in orbit around the Earth – where our rolling and boiling atmosphere doesn’t blur out observations. We began yet another revolution. And where are we now? We ‘ ve come such a long way !
What questions can we routinely ask that our ancestors would not have dared , what statements made with a pretty good degree of certainty ? Think of this: The lights in the sky are stars! There are other worlds. We take the idea of looking for life on alien planets seriously, and spend billions of dollars doing it. Our galaxy is one of hundred billion others. We can only directly see 4% of the Universe. Stars explode, and when they do they create the stuff of life: the iron in our blood, the calcium in our bones, the phosphorus that is the backbone of our DNA. The most common kind of star in the Universe is so faint you can’t see it without a telescope. Our solar system is filled to overflowing with worlds more bizarre than we could have dreamed. Nature has more imagination than we do. It comes up with some naughty stuff. We’re clever too, we big-brained apes. We’ve learned a lot… but there’s still a long way to go. So with that, I think we’re ready. Let’s explore the universe.
[wrapping up the video]Today you learned what astronomy is, and that astronomers aren’t just people who operate telescopes, but include mathematicians, engineers, technicians, programmers, and even artists. We also wrapped up with a quick history of the origins and development of astronomy from the ancient observers to the Hubble Space Telescope.Crash Course is produced in association with PBS Digital Studios .
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