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  • Hello, and welcome to Crash Course Astronomy! I’m your host, Phil Plait, and I’ll be

  • taking you on a guided tour of the entire Universe. You might want to pack a lunch.

  • Over the course of this series well explore planets, stars, black holes, galaxies, subatomic

  • particles, and even the eventual fate of the Universe itself.

  • But before we step into space, let’s take a step back. I wanna talk to you about science.

  • There are lots of definitions of science, but I’ll say that it’s a body of knowledge,

  • and a method of how we learned that knowledge.

  • Science tells us that stuff we know may not be perfectly known; it may be partly or entirely

  • wrong. We need to watch the Universe, see how it behaves, make guesses about why it’s

  • doing what it’s doing, and then try to think of ways to support or disprove those ideas.

  • That last part is important. Science must be, above all else, honest if we really want

  • to get to the bottom of things.

  • Understanding that our understanding might be wrong is essential, and trying to figure

  • out the ways we may be mistaken is the only way that science can help us find our way

  • to the truth, or at least the nearest approximation to it.

  • Science learns. We meander a bit as we use it, but in the long run we get closer and closer

  • to understanding reality, and that is the strength of science. And it’s all around us!

  • Whether you know it or not, youre soaking in science.

  • Youre a primate.(anthropology) You have mass.(physics) Mitochondria

  • in your cells are generating energy.(biology) Presumably, youre breathing oxygen.(chemistry)

  • But astronomy is different. It’s still science, of course, but astronomy puts you in your place.

  • Because of astronomy, I know were standing on a sphere of mostly molten rock and metal

  • 13,000 kilometers across, with a fuzzy atmosphere about 100 km high, surrounded by a magnetic

  • field that protects us from the onslaught of subatomic particles from the Sun 150 million

  • km away, which is also flooding space with light that reaches across space, to illuminate

  • the planets, asteroids, dust, and comets, racing out past the Kuiper Belt, through the

  • Oort Cloud, into interstellar space, past the nearest stars, which orbit along with

  • gas clouds and dust lanes in a gigantic spiral galaxy we call the Milky Way that has a supermassive

  • black hole in its center, and is surrounded by 150 globular clusters and a halo of dark

  • matter and dwarf galaxies, some of which it’s eating, all of which can be seen by other

  • galaxies in our Local Group like Andromeda and Triangulum, and our group is on the outskirts

  • of the Virgo galaxy cluster, which is part of the Virgo supercluster, which is just one

  • of many other gigantic structures that stretch most of the way across the visible Universe,

  • which is 90-billion light years across and expanding every day, even faster today than

  • yesterday due to mysterious dark energy, and even all that might be part of an infinitely

  • larger multiverse that extends forever both in time and space.

  • See? Astronomy puts you in your place.

  • But what exactly is astronomy? This isn’t necessarily an obvious thing to ask. When

  • I was a kid, it was easy: Astronomy is the study of things in the sky. The sun, moon,

  • stars, galaxies, and stuff like that. But it’s not so easy to pigeonhole these days.

  • Take, for example, Mars. When I haul myscope out to the end of my driveway and look at

  • Mars, that’s astronomy, right? Of course! But what about the rovers there? Those machines

  • aren’t doing astronomy, surely. Theyre doing chemistry, geology, hydrology, petrology

  • everything but astronomy!

  • So nowadays, what’s astronomy? I’d say it’s still studying stuff in the sky, but

  • it’s branched out quite a bit from there. Borders between it and other fields of science

  • are fuzzy… a theme I’ll be hitting on several times over this series. Humans might

  • like firm, delineated boundaries between things, but nature isn’t so picky.

  • And that brings us to our first edition ofFocus On…”

  • This week’s topic: Astronomers! Who are we? What do we do?

  • I used to look through telescopes for a living, or at least study the data that came from

  • detectors strapped onto them. But now I talk and write (and make videos) about astronomy,

  • and relegate my viewing to my personal backyard telescope. But I still consider myself an

  • astronomer, so that should give you an idea that there’s a lot of wiggle room in the profession.

  • In fact, when I worked on Hubble Space Telescope, I was actually hired as... a programmer!

  • I coded in the language used by the folks helping to build and calibrate a camera that

  • was due to launch into space and be installed onto Hubble by an astronaut.

  • Once the data from that camera are taken and analyzed, you have to know what to do with

  • them. Do the observations fit the physical model of how stars blow up, or how galaxies

  • form, or the way gas flows through space? Well, you'd better know your math and physics,

  • because that’s how we test our hypotheses. And someone who does that is generally called

  • an astrophysicist.

  • Of course, those telescopes and detectors don’t create themselves. We need engineers

  • to design and build them and technicians to use them.

  • Most astronomers don’t actually use the telescopes themselves anymore; someone who’s

  • trained in their specific use does that for them.

  • Some of those instruments go into space, and some go to other worlds, like the moon and Mars.

  • We need astronomers and engineers and software programmers who can build those, too.

  • And then, at the end of all this, we need people to tell you all about it. Teachers,

  • professors, writers, video makers, even artists.

  • So I’ll tell you what: If you have an interest in the Universe, if you love to look up at

  • the stars, if you crave to understand what’s going on literally over your head, then who

  • am I to say youre not an astronomer?

  • However you define astronomy, humans have been looking up at the sky for as long as

  • weve been humans. Certainly ancient people noticed the big glowy

  • ball in the sky, and how it lit everything up while it was up, and how it got dark when

  • it was gone. The other, fainter glowy thing tried, but wasn’t quite as good as lighting

  • up the night. They probably took that sort of thing pretty seriously. They probably also

  • noticed that when certain stars appeared in the sky, the weather started getting warmer

  • and the days longer, and when other stars were seen, the weather would get colder and

  • daytime shorten.

  • And when humans settled down, discovered agriculture, and started farming, noticing those patterns

  • in the sky would have had an even greater impact. It told them when to plant seeds,

  • and when to harvest.

  • The cycles in the sky became pretty important. So important that it wasn’t hard to imagine

  • gods up there, looking down on us weak and ridiculous humans, interfering with our lives.

  • Surely if the stars tell us when to plant, and control the weather, seasons, and the

  • length of the day, they control our lives tooand astrology was born.

  • Astrology literally meansstudy of the stars”; as a word it’s been used before

  • science became a formal method of studying nature. It irks me a bit, since it got the

  • good name, and now were stuck withastronomy,” which meanslaw or culture of the stars."

  • That’s not really what we do! But what the heck. Words change meaning over time, and

  • now it’s pretty well understood that astronomy is science, and astrologyisn’t.

  • Millennia ago, astrology was as close to science as you got. It had some of the flavors of

  • science: astrologers observed the skies, made predictions about how it would affect people,

  • and then those people would provide evidence for it by swearing up and down it worked.

  • The thing is, it really didn’t; the fault of astrology lies in ourselves and not our

  • stars. People tend to remember the hits and forget the misses when predictions are made,

  • which is why they sometimes sit in casinos pumping nickels into machines that are

  • proven to be nothing more than a method for reducing the number of nickels you have.

  • But astrology led to 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 is 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 through.

  • 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 multiple-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 religions 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 well 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 the way objects moved in space. Over time, 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 weve run with the idea from there.

  • Then, about a century or so ago, came another revolution: 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 in 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 roiling and boiling atmosphere doesn’t blur out observations

  • - we began yet another revolution.

  • And where are we now?

  • Weve 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 on 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 a 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 nutty stuff. Were clever

  • too, we big-brained apes. Weve learned a lotbut there’s still a long way to go.

  • So, with that, I think were ready. Let’s explore the universe.

  • 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 ancient observers to the Hubble Space Telescope.

  • Crash Course is produced in association with PBS Digital Studios.

  • This episode was written by me, Phil Plait. The script was edited by Blake de Pastino,

  • and our consultant is Dr. Michelle Thaller. It was co-directed by Nicholas Jenkins and

  • Michael Aranda, and the graphics team is Thought Café.

Hello, and welcome to Crash Course Astronomy! I’m your host, Phil Plait, and I’ll be

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天文學 (Introduction to Astronomy: Crash Course Astronomy #1)

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