The Sun emits light with a specific wavelength $\lambda_s$. However, at a given moment, the Earth records a spread of wavelengths extending from values below $\lambda_s$ to values above $\lambda_s$. This happens because of the Doppler effect. What might account for this Doppler effect?
- AThe Sun is moving at right-angles to a line joining the Sun and the Earth.
- BThe Sun is moving away from the Earth.
- CThe Sun is moving towards the Earth.
- DThe Sun is rotating.