"Astronomy Class" What is the discussion mainly about?

Narrator: Listen to part of a discussion in an astronomy class. The professor is talking about the solar
   system.
Professor:
Okay, let’s get started. Um, as you know today I promised to take you on a walk through the solar
system, so let’s start here with the central object of our solar system--the Sun. As you can see, the Sun is
about five inches in diameter and that’s about the size of a large grapefruit, which is exactly what I’ve
used to represent it here in our model. So, I’m going to take two steps and that will bring me to the planet
closest to the Sun. That would be Mercury. Two more steps to Venus. And one step from Venus to
Earth. Let’s continue walking three steps from Earth to Mars. And that’s as far as I can go here in the
classroom, but we can visualize the rest of the journey. Don’t bother writing this down. Just stay with me  Q24
on this. So, to go from Mars to Jupiter, we’d have to walk a little over half the length of a football field, so
that would put us about at the library here on campus, and then to get from Jupiter to Saturn, we’d have
to walk another 75 yards, so by then we’d be at Harmon Hall. From Saturn to Uranus, we’d have to walk
again as far as we’d gone in our journey from the Sun to Saturn, and so we’d probably be at the Student
Union. From Uranus to Neptune we’d have to walk the same distance again, which would take us all the
way to the graduate dormitory towers. From Neptune to Pluto, another 125 yards. So, we’d end up
about one third of a mile from this classroom at the entrance to the campus.
   Okay. That’s interesting, but now I want you to think about the orbits of the planets in those
locations. Clearly, the first four planets could orbit fairly comfortably in this room, but to include the others,
we’d have to occupy an area of more than six-tenths of a mile, which is all the way from College Avenue
to Campus Drive. Remember that for this scale, the Sun is five inches, and most of the planets are
smaller than the lead on a sharpened pencil. Okay, with that in mind, I want you to think about space.
Sure, there are some moons around a few planets, and a scattering of asteroids and comets, but really,
there isn’t a lot out there in such a vast area. It’s, well, it’s pretty empty. And that’s what I really want to
demonstrate with this exercise.
   Now, it would really be even more impressive if you could actually make that walk, and actually you
can, if you visit Washington, D.C., where a scale model is set up on the National Mall, starting at the
National Air and Space Museum and ending up at the Arts and Industries MuSeum. I did that a couple
of years ago, and it was, well amazing. Even though I knew the distances intellectually, there’s nothing
like the experience. Has anybody else done that walk?
Student 1:
I have. And you’re right. It’s an eye-opener. It took me about twenty minutes to go from the Sun to Pluto
because I stopped to read the information at each planet, but when I made the return trip, it was about
ten minutes.
Professor: Did you take pictures?
Student 1: I didn’t. But, you know, I don’t think it would have captured it anyway.
Professor:
I think you’re right. What impressed rne about doing it was to see what was not there, t mean, how much  Q25
space was between the bodies inthe solar system, And a photograph wouldn’t have shown that.
   So back to our model. Here’s another thought for you. The scale for our model is 1 to 10 billion.
Now, let’s suppose that we want to go to the nearest star system, the neighbor to our solar system. That
would be the Alpha Centauri system, which is a little less than four and a half light years away. Okay.
Let’s walk it on our model. Here we are on the East Coast of the United States. So if we want to make it
all the way to Alpha Centauri, we have to hike all the way to the West Coast, roughly a distance of 2,700 miles. And that’s just the closest one. To make a model of the Milky Way Galaxy would require a com-
pletely different scale because.., because the surface of the Earth wouldn’t be large enough to
accommodate a model at the scale of 1 to 10 billion.
   Now, let’s stop here for a minute because I just want to be sure that we’re all together on the terms
solar system and galaxy. Remember that our sotar system is a single star; the Sun with various bodies
orbiting around it—nine planets and their moons, and asteroids comets meteors But the galaxy has a  Q26
lot of star systems—probably 100 billion of them. Okay? This is important because you can be off by
almost 100 billion if you get confused by these terms. Not a good idea.
   Okay, then, even if we could figure out a different scale that would let us make a model of the Milky
Way Galaxy, even then, it would be challenging to make 100 billion stars, which is what you’d have to
do to complete the model. How many would that be exactly? Well, just try to count all the grains of sand
on all the beaches on Earth. That would be about 100 billion. But of course, you couldn’t even count
them in your lifetime, could you? If you’d started counting in 1000 B.C.E. you’d be finishing just about
now, with the counting, I mean. But of course, that assumes that you wouldn’t sleep or take any breaks.
   So, what am I hoping for from ths ecture? What deyou think I want you to remember?  Q27
Student 2: Well, for one thing, the enormous distances...  Q23
Student 3: ...and the vast emptiness in space.
Professor:
That’s good. I hope that you’ll also begin to appreciate the fact that the Earth isn’t the center of the
universe. Our planet, although it’s very beautiful and unique, it’s still just one planet, orbiting around just
one star in just one galaxy.