This introduction to Crash Course Astronomy defines science as a body of knowledge and a method of inquiry, emphasizing honesty and the iterative process of observation, hypothesis, and testing. It then introduces astronomy as a science that places humanity in cosmic perspective, exploring its historical evolution from ancient sky-watching to modern astrophysics.
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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 we’ll 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 ever closer
to understanding reality, and that is the strength of science. And it’s all around us!
Whether you know it or not, you’re soaking in science.
You’re a primate. You have mass. Mitochondria
in your cells are generating energy. Presumably, you’re breathing oxygen.
But astronomy is different. It’s still science, of course, but astronomy puts you in your place.
Because of astronomy, I know we’re 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 my ‘scope 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
