The Doppler Effect of light

  • #1

Homework Statement



The light from galaxy NGC 221 consists of a recognizable spectrum of wavelengths. However, all are shifted to the shorter wavelength end of the spectrum. In Particular, the calcium "line" ordinarily observed at 396.85nm is observed at 396.58nm. (a) is this galaxy moving towards or away from the earth? (b) at what speed?

Homework Equations



Fobs=fsourcesqrt(1-v^2/c^2)/(1+v/ccostheta)

The Attempt at a Solution


I think that the galaxy is moving toward the earth, but I'm not sure how to get what speed it's going at. I tried totake the ration of 396.58/396.85 to plug in so the frequencies would cancel out, but I'm getting a very small negative number. This doesn't seem right. Any help would be appreciated!
 

Answers and Replies

  • #2
rl.bhat
Homework Helper
4,433
8
Use the formula
fobs = fsourcesqrt[(c-v)/c+v)]
 

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