Introduction to Astronomy: Crash Course Astronomy #1


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 aren’t doing astronomy, surely. They’re
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 of
“Focus 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 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 you’re not an astronomer? However you define astronomy, humans have
been looking up at the sky for as long as we’ve 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
too… and astrology was born. Astrology literally means “study 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 we’re stuck with “astronomy,”
which means “law 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 astrology… isn’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 in 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 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 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 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 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 we’ve 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? 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 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. 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. 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.