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Lecture 3.05: An ode to comets
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来自 Caltech 的课程
太阳系科学
317 个评分
从本节课中
Unit 3: Big questions from small bodies (week 1)
与讲师见面
Mike BrownProfessor
Planetary Astronomy
To my mind, one of the most spectacular sights you can see in the night
sky with your eye is a comet.
Now, I hope all of you had a chance to see a comet with your eye at some
point in your life.
It's been more than a decade now since the best one in my lifetime was around,
comet Hale-Bopp, which was bright, sitting in the sky month after month after month.
We don't get ones like that very frequently, but every year or so there is
one that you can see with your eye if you know when to look and where to look.
And I think they're just spectacular.
I will admit, though, that I'm a little bit biased.
The reason I'm a little bit biased is because comets are the thing that really
brought me into studying the solar system.
When I started grad school many years ago,
what I really wanted to do was study the most distinct galaxies in the universe.
It was a very popular thing to want to study.
In fact, back when I was in graduate school in astronomy, and
even to some extent today, if you studied things that were really far away,
you were the coolest person you could possibly be.
If you studied things that were kind of far away,
like galaxies that were next door, you were pretty cool.
If you studied things that were kind of close, like stars in our own galaxy,
you were not really that cool, and
if you studied the solar system, you were totally uncool.
Everybody wants to be cool.
Everybody wanted to study these very distant galaxies.
These days, actually things are different.
The solar system I think has gotten increasingly cool.
Planets around other stars have made planets in general cool, and
close by planets even cooler.
So, things have been mixed around some, but at the time it was very clear.
If you want to be cool, go for the distant most things and
that's what I wanted to do.
And so I went to graduate school at the University of California,
Berkeley and I started working with Hy Spinrad.
If you remember carefully, you have heard that name before.
That is the person who first discovered water vapor in the atmosphere if Mars.
But that was early in his career and by the time I got to Berkeley, what he really
did was studied very distant galaxies, which is what I wanted to do.
But he had always maintained a love for the solar system and
for comets, in particular.
So, even though he looked at these very, very distant galaxies he still, every time
a nice bright comet came by, he went to the telescope, collected a spectrum of it.
Wanted to see what it was made out of.
What it looked like.
His wife claimed it was because he liked fuzzy things in the sky.
And galaxies are fuzzy and comets are fuzzy.
And they look about the same.
I'm not sure I actually believe that that's the main reason.
I think he actually just liked comets.
And he really just liked telescope and instruments and observing things.
And comets are cool.
The interesting thing, though, is that because none of the students
wanted to work on comets, because the solar system, too close,
not cool, what he would do is, whenever you started working with Hy Spinrad, and
you wanted to work on distant galaxies, he would force you to work on comets.
Maybe for a summer just to get you some exposure in something else and
to have some help along with his commentary work.
So, I arrived at Berkeley and wanted to work on distant galaxies, and
immediately there was this moderately bright comet in the sky, Comet Austin in
1990 and we set off to the telescope to go observe it.
And this is a moment I think I'll always remember.
We swung the big telescope.
This was the three meter Shane Telescope at the Lick Observatory just up
the mountain from San Jose, California.
It was the biggest telescope I'd every seen in my life at the time.
We swung that big telescope around,
pointed it at where Comet Austin was supposed to be in the sky.
Couldn't really see it, but we had the coordinates,
pointed it there, started collecting the photons coming in, getting a spectrum,
learning what it was made out of.
And I walked out onto the dome floor, and
I stood there, looking up in the direction that the telescope was pointed.
And squinted and let my eyes adjust, and I could see it.
I could see that very faint fuzzball that we were actually collecting light from.
This was an astounding thing.
If you study the most distant galaxies in the universe, you do not see them.
You don't see them with your eye.
You don't see them with binoculars.
You don't see them with a backyard telescope.
You don't see them.
They're sort of abstract.
They are coordinates on the sky, they aren't things that are in your life, and
yet, it was this comet that was there, I could see it.
We went the next night, it was in a different place.
You could see it moving.
The fact that the solar system was so visceral is what really finally
drew me in and made me decide to stay in this region of doing,
looking at comets, looking at Jupiter.
You can look up and see Jupiter, see the moons of Jupiter,
which is what I did my PhD thesis on.
And night after night, they're there moving around the sky.
They become just part of your life in
a way that distant galaxies I don't think ever can.
You might get a different story from someone who studies distant galaxies, and
thinks of them as part of their life, too.
But at least that's my story for
why I am now firmly entrenched inside the solar system.
So comets, I think are cool.
I'm biased.
But comets are interesting scientifically in two sort of separate ways.
One is, if you can figure out what comets are made out of, just like when we trying
to figure out what Mars is made out of, what Jupiter was made out of.
If you figure out what comets are made out of,
you're learning something about a piece of the solar system,
a time in the solar system history when these things were being created.
And second, if you can figure out where comets come from,
you've connected that what they're made out of, where they came from.
And you are once again starting to put together the history of the formation of
the solar system.
