Suppose an Observer Were Far from a Planet That Had $\alpha$

Multiple Choice

Suppose an observer were far from a planet that had a very strong gravitational field, and a light wave reaches the observer from a source of hydrogen (H _$\alpha$ ) light on the surface of the planet. For an H _$\alpha$ light source in the observer's own spaceship, the wavelength is 656.3 nm. What wavelength does the observer see when looking at the light source on the planet?

A) shorter than 656.3 nm
B) longer than 656.3 nm
C) infinite, since the source is in a gravitational field
D) 656.3 nm, the same as from the spaceship's light source