Spectral line

1. Oct 25, 2007

azatkgz

1. The problem statement, all variables and given/known data
One of the most prominent spectral lines of hydrogen is $$H_\alpha$$ line.A bright red light with wavelength of $$656.1\times 10^{-9}m$$.What's the expected wavelength of the $$H_\alpha$$ line from a star receding with a speed of 3000 km/s?

3. The attempt at a solution

Is it just $$\lambda=\lambda_o-\frac{\lambda_ov}{c}$$

2. Oct 25, 2007

BerryBoy

I believe that should be: $$\lambda=\lambda_o+\frac{\lambda_ov}{c}$$

When objects move away from the observer, the doppler shift, increases the wavelength (red-shifts it).

Sam