WEBVTT - How do astronomers measure distance?

0:00:00.520 --> 0:00:03.600
<v Speaker 1>Welcome to brain Stuff from how stuff works dot com

0:00:03.600 --> 0:00:14.760
<v Speaker 1>where smart Happens. Hi, I'm Marshall Brain With today's question,

0:00:15.320 --> 0:00:18.640
<v Speaker 1>how are astronomers able to measure how far away a

0:00:18.800 --> 0:00:22.279
<v Speaker 1>star is? It turns out that measuring the distance to

0:00:22.400 --> 0:00:25.880
<v Speaker 1>a star is an interesting problem. Astronomers have come up

0:00:25.920 --> 0:00:29.200
<v Speaker 1>with two different techniques to estimate how far away any

0:00:29.240 --> 0:00:34.680
<v Speaker 1>given star might be. The first technique uses triangulation or parallax.

0:00:35.240 --> 0:00:38.040
<v Speaker 1>The Earth's orbit around the Sun has a diameter of

0:00:38.080 --> 0:00:41.640
<v Speaker 1>about a hundred eighty six million miles or three hundred

0:00:41.680 --> 0:00:45.120
<v Speaker 1>million kilometers. By looking at a star one day and

0:00:45.159 --> 0:00:48.800
<v Speaker 1>then looking at it again six months later, and astronomer

0:00:48.880 --> 0:00:51.800
<v Speaker 1>can see a difference in the viewing angle for the star.

0:00:52.400 --> 0:00:55.960
<v Speaker 1>With a little trigg, the different angles yield a distance.

0:00:56.400 --> 0:00:59.560
<v Speaker 1>This technique works for stars that are about four hundred

0:00:59.640 --> 0:01:03.600
<v Speaker 1>light is away from Earth or closer. There's no direct

0:01:03.680 --> 0:01:07.520
<v Speaker 1>method currently available to measure the distance two stars further

0:01:07.680 --> 0:01:11.959
<v Speaker 1>than four light years from Earth, so astronomers instead use

0:01:12.120 --> 0:01:16.280
<v Speaker 1>brightness measurements. It turns out that a star's color spectrum

0:01:16.400 --> 0:01:20.320
<v Speaker 1>is a good indication of its actual brightness. The relationship

0:01:20.400 --> 0:01:24.440
<v Speaker 1>between color and brightness has been proven using the several

0:01:24.480 --> 0:01:27.200
<v Speaker 1>thousand stars that are close enough to Earth to have

0:01:27.319 --> 0:01:31.320
<v Speaker 1>their distance measured directly. Astronomers can therefore look at a

0:01:31.400 --> 0:01:35.360
<v Speaker 1>distant star and determine its color spectrum. From the color,

0:01:35.480 --> 0:01:39.000
<v Speaker 1>they can determine the star's actual brightness, and then, by

0:01:39.080 --> 0:01:42.120
<v Speaker 1>knowing the actual brightness and comparing it to the apparent

0:01:42.200 --> 0:01:45.839
<v Speaker 1>brightness seen from Earth, that is, by looking at how

0:01:45.920 --> 0:01:49.160
<v Speaker 1>dim the star has become once it's light reaches Earth,

0:01:49.480 --> 0:01:54.400
<v Speaker 1>they can determine the distance to the star. For more

0:01:54.480 --> 0:01:57.000
<v Speaker 1>ONNS and thousands of other topics. Does that how stuff

0:01:57.000 --> 0:01:59.160
<v Speaker 1>works dot com and don't forget to check out the

0:01:59.160 --> 0:02:01.200
<v Speaker 1>brain stuff block on the house stuff works dot com

0:02:01.240 --> 0:02:04.080
<v Speaker 1>home page. You can also follow brain stuff on Facebook

0:02:04.160 --> 0:02:08.760
<v Speaker 1>or Twitter at brain stuff h s W. The house

0:02:08.800 --> 0:02:12.040
<v Speaker 1>Stuff Works iPhone app has arrived. Download it today on

0:02:12.080 --> 0:02:12.600
<v Speaker 1>iTunes