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Speaker 1: Welcome to brain Stuff from how stuff works dot com

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Speaker 1: where smart Happens. Hi, I'm Marshall Brain With today's question,

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Speaker 1: how are astronomers able to measure how far away a

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Speaker 1: star is? It turns out that measuring the distance to

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Speaker 1: a star is an interesting problem. Astronomers have come up

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Speaker 1: with two different techniques to estimate how far away any

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Speaker 1: given star might be. The first technique uses triangulation or parallax.

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Speaker 1: The Earth's orbit around the Sun has a diameter of

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Speaker 1: about a hundred eighty six million miles or three hundred

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Speaker 1: million kilometers. By looking at a star one day and

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Speaker 1: then looking at it again six months later, and astronomer

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Speaker 1: can see a difference in the viewing angle for the star.

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Speaker 1: With a little trigg, the different angles yield a distance.

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Speaker 1: This technique works for stars that are about four hundred

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Speaker 1: light is away from Earth or closer. There's no direct

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Speaker 1: method currently available to measure the distance two stars further

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Speaker 1: than four light years from Earth, so astronomers instead use

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Speaker 1: brightness measurements. It turns out that a star's color spectrum

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Speaker 1: is a good indication of its actual brightness. The relationship

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Speaker 1: between color and brightness has been proven using the several

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Speaker 1: thousand stars that are close enough to Earth to have

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Speaker 1: their distance measured directly. Astronomers can therefore look at a

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Speaker 1: distant star and determine its color spectrum. From the color,

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Speaker 1: they can determine the star's actual brightness, and then, by

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Speaker 1: knowing the actual brightness and comparing it to the apparent

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Speaker 1: brightness seen from Earth, that is, by looking at how

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Speaker 1: dim the star has become once it's light reaches Earth,

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Speaker 1: they can determine the distance to the star. For more

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Speaker 1: ONNS and thousands of other topics. Does that how stuff

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Speaker 1: works dot com and don't forget to check out the

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