托福听力TPO2分类之天文学

2022-06-09 04:28:06

  

  TPO 2 Lecture 4 Astronomy

  Narrator

  Listen to part of a lecture in an astronomy class. You will not need to remember the numbers the

  professor mentions.

  Professor

  OK. Let’s get going. Today I’m going to talk about how the asteroid belt was discovered.

  And . . . I’m going to start by writing some numbers on the board. Here they are:

  We’ll start with zero, then 3, . . . 6, . . . 12. Uh, tell me what I’m doing.

  Female student

  Multiplying by 2?

  Professor

  Right. I’m doubling the numbers, so 2 times 12 is 24, and the next one I’m going to write after 24

  would be . . .

  Female student

  48.

  Professor

  48. Then 96. We’ll stop there for now. Uh, now I’ll write another row of numbers under that. Tell

  me what I’m doing. 4, 7, 10 . . . How am I getting this second row?

  Male Student

  Adding 4 to the numbers in the first row.

  Professor

  I’m adding 4 to each number in the first row to give you a second row. So the last two will be 52,

  100, and now tell me what I’m doing.

  Female Student

  Putting in a decimal?

  Professor

  Yes, I divided all those numbers by 10 by putting in a decimal point. Now I’m going to write the

  names of the planets under the numbers. Mercury . . . Venus. . . Earth. . . Mars. So, what do the

  numbers mean? Do you remember from the reading?

  Male Student

  Is it the distance of the planets from the Sun?

  Professor

  Right. In astronomical units—not perfect, but tantalizingly close. The value for Mars is off by . . . 6

  or 7 percent or so. It’s . . . but it’s within 10 percent of the average distance to Mars from the Sun.

  But I kind of have to skip the one after Mars for now. Then Jupiter’s right there at 5-point

  something, and then Saturn is about 10 astronomical units from the Sun. Um, well, this pattern is

  known as Bode’s Law. Um, it isn’t really a scientific law, not in the sense of predicting gravitation

  mathematically or something, but it’s attempting a pattern in the spacing of the planets, and it

  was noticed by Bode hundreds of years ago. Well, you can imagine that there was some interest

  in why the 2.8 spot in the pattern was skipped, and um . . . but there wasn’t anything obvious

  there, in the early telescopes. Then what happened in the late 1700s? The discovery of . . . ?

  Female Student

  Another planet?

  Professor

  The next planet out, Uranus—after Saturn. And look, Uranus fits in the next spot in the pattern

  pretty nicely, um, not perfectly, but close. And so then people got really excited about the

  validity of this thing and finding the missing object between Mars and Jupiter. And telescopes,

  remember, were getting better. So people went to work on finding objects that would be at that

  missing distance from the Sun, and then in 1801, the object Ceres was discovered.

  And Ceres was in the right place—the missing spot. Uh, but it was way too faint to be a planet. It

  looked like a little star. Uh, and because of its starlike appearance, um, it was called an

  “asteroid.” OK? “Aster” is Greek for “star,” as in “astronomy.” Um, and so, Ceres was the first

  and is the largest of what became many objects discovered at that same distance. Not just one

  thing, but all the objects found at that distance from the asteroid belt. So the asteroid belt is the

  most famous success of this Bode’s Law. That’s how the asteroid belt was discovered.

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