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This question came to my mind when I read on NASA's website that an explosion (gamma ray burst, GRB 080913) took place 12.8 billion light years away from us. How do they measure such large distances?

Kyle Oman
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syed_ali_mousvi
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2 Answers2

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Did you mean 12.8 billion light years away?

If so, in this case the distance was estimated by measuring a rough spectrum for the GRB. The NASA article I've linked says:

In certain colors, the brightness of a distant object shows a characteristic drop caused by intervening gas clouds. The farther away the object is, the longer the wavelength where this fade-out begins.

This technique is used where it's hard to get a detailed spectrum and calculate the red shift.

If you're asking a more general question then this is covered in the question How is distance measured to far away stars and galaxies? and your question would be a duplicate.

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John Rennie
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For relatively close objects, the distance can be measured through measurements of parallax (http://en.wikipedia.org/wiki/Parallax ).

akhmeteli
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