Answer :
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.
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.