From earth, how can you find out the speed a star is moving away from us?How do you find out how fast a star is moving away from us?Motion toward us or away from us can be determined using the doppler shift.
If the star is moving away, the spectral lines are redshifted. The amount of the shift is proportional to how fast the star is moving away.
The star emits light at a constant wavelength and we receive the light here on Earth at the same constant wavelength.
In the case of light, this means that a star moving toward us will have its spectrum shifted toward the blue end of the spectrum (blue-shifted) and stars moving away from us will have their spectrum red-shifted.How do you find out how fast a star is moving away from us?The doppler shift in the light from the star is obtained using specialized equipment. A database of star velocities is available from NASA
http://www.astronexus.com/node/34
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