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Astronomy 101

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- Tue, 10 Mar 2015 16:45:18 EST ng5PGFH1 No.55120
File: 1426020318482.jpg -(119531B / 116.73KB, 847x845) Thumbnail displayed, click image for full size. Astronomy 101
I need your help, I'm completely clueless.
If Hydrogen has a spectral line of 656nm and it is measured in a distant galaxy at 705nm, how would you find the recessional velocity of the galaxy?
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Edmond Halley - Wed, 11 Mar 2015 18:13:34 EST rjqBmvyM No.55125 Reply
Wouldn't you need at least one other line? A given spectrum could be translated as well as stretched/compressed, and a single line wouldn't be able to distinguish those, right?
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Edwin Salpeter - Sat, 14 Mar 2015 10:41:12 EST kB08C8qN No.55130 Reply
>>55125
Wavelength dependent effects are rare and in the optical almost always destroy the lines. Just treat it all as a velocity, it's the safest bet.

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