[00:00.00]Narrator: Listen to part of a lecture in an astronomy class. [00:05.65]You will not need to remember the numbers the professor mentions.
[00:11.23]MALE PROFESSOR: OK. Let's get going. [00:13.30]Today I'm going to talk about how the asteroid belt was discovered. [00:17.66]And...I'm going to start by writing some numbers on the board. [00:22.00]Here they are: We'll start with zero, then 3,...6,...12. [00:30.08]Uh, tell me what I'm doing.
[00:31.63]FEMALE STUDENT: Multiplying by 2?
[00:33.43]MALE 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...
[00:42.35]FEMALE STUDENT: 48.
[00:43.96]MALE PROFESSOR: 48. Then 96. [00:49.05]We'll stop there for now. [00:50.86]Uh. now I'll write another row of numbers under that. [00:54.32]Tell me what I'm doing. 4, 7, 10...[00:56.33]How am I getting this second row?
[01:02.48]MALE STUDENT: Adding 4 to the numbers in the first row.
[01:05.61]MALE PROFESSOR: I'm adding 4 to each number in the first row to give you a second row. [01:10.40]So the last two will be 52, 100, and now tell me what I'm doing.
[01:17.16]FEMALE STUDENT: Putting in a decimal?
[01:19.42]MALE PROFESSOR: Yes, I divided all those numbers by 10 by putting in a decimal point. [01:24.60]Now I'm going to write the names of the planets under the numbers. [01:28.42]Mercury...Venus...Earth...Mars.[01:35.97]So, what do the numbers mean? [01:38.33]Do you remember from the reading?
[01:40.23]MALE STUDENT: Is it the distance of the planets from the Sun?
[01:43.42]MALE PROFESSOR: Right. In astronomical units–not perfect, but tantalizingly close. [01:48.77]The value for Mars is off by...6 or 7 percent or so. [01:54.54]It's...but it's within 10 percent of the average distance to Mars from the Sun. [02:00.39]But I kind of have to skip the one after Mars for now. [02:04.65]Then Jupiter's right there at 5-point something, and then Saturn is about 10 astronomical units from the Sun. [02:12.40]Um, well, this pattern is known as Bode's Law.
[02:16.28]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. [02:31.52]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. [02:43.04]Then what happened in the late 1700s? [02:46.05]The discovery of...?
[02:47.26]FEMALE STUDENT: Another planet?
[02:48.64]MALE PROFESSOR: The next planet out, Uranus–after Saturn. [02:52.74]And look, Uranus fits in the next spot in the pattern pretty nicely, um, not perfectly, but close. [02:58.92]And so then people got really excited about the validity of this thing and finding the missing object between Mars and Jupiter. [03:06.46]And telescopes, remember, were getting better. [03:09.56]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.
[03:20.96]And Ceres was in the right place–the missing spot. [03:24.85]Uh, but it was way too faint to be a planet. [03:27.52]It looked like a little star. [03:28.99]Uh, and because of its starlike appearance, um, it was called an asteroid.[03:35.25]OK? "Aster" is Greek for "star," as in "astronomy." [03:40.21]Um, and so, Ceres was the first and is the largest of what became many objects discovered at that same distance. [03:48.40]Not just one thing, but all the objects found at that distance form the asteroid belt. [03:54.09]So the asteroid belt is the most famous success of this Bode's Law. [03:59.83]That's how the asteroid belt was discovered.
托福14天冲刺微信战团