# Astromony question

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?

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

How did you think of to use the Doppler effect?

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".

I see~
Thanks for correcting my spelling mistake!