Calculating Wavelength of H_α for a Receding Star

[azatkgz]

Homework Statement

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?

The Attempt at a Solution

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

 

[BerryBoy]

Homework Statement

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?

The Attempt at a Solution

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

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