In order to calculate the unknown reaction force, we need to know that the sum of forces pointing down is equal the sum of the forces pointing up, so all forces will be in equilibrium.
So we have:
Answer:
They appear to recede from our viewpoint.
That is, their emitted spectra are shifted toward the red (red-shift).
The wave-lengths that are received on earth are somewhat longer because of the "Doppler" shift of the receding atoms.