# Astromony question

#### asdf1

There's an astromony question that I'm stuck on~
" A distant galaxy in the constellation Hydra is receding from the earth at 6.12*10^7 m/s. By how much is a green spectral line of wavelength 500nm (1nm=10^(-9) )emitted by this galaxy shifted toward the red end of the spectrum?

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#### neurocomp2003

what knowledge do you have?

#### Andrew Mason

Homework Helper
asdf1 said:
There's an astromony question that I'm stuck on~
" A distant galaxy in the constellation Hydra is receding from the earth at 6.12*10^7 m/s. By how much is a green spectral line of wavelength 500nm (1nm=10^(-9) )emitted by this galaxy shifted toward the red end of the spectrum?
Just use the relativistic doppler effect:

$$\nu_{obs}/\nu_{source} = \sqrt{\frac{1+\beta}{1-\beta}}$$

where $\beta = v/c = .204$ and $\nu_{source} = c/\lambda_{source}$

AM

#### asdf1

How did you think of to use the Doppler effect?

#### Nylex

Probably because the question is about the Doppler effect (well, it's about red shift, which is to do with the Doppler effect). Also, you mean "astronomy", not "astromony".

#### asdf1

I see~
Thanks for correcting my spelling mistake!

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