The cosmological redshift of the light from very distant galaxies is caused by
A) the expansion of space,stretching the photon's wavelength while the photon is traveling toward us.
B) absorption of blue light by interstellar dust between us and the galaxy so that only the red wavelengths reach us.
C) the rotation of the universe around its center (faster at greater distances from us).
D) the Doppler shift,in which the photon's wavelength is stretched as the photon is being emitted by the galaxy's motion away from us through space.

Question

Quizplus · Accepted Answer

The cosmological redshift is caused by the expansion of space, which stretches the wavelength of the photon as it travels towards us. This stretching of the wavelength causes the light to appear redder, hence the term "redshift". This is different from the Doppler shift, which is caused by the motion of the emitter or observer, and can result in either a redshift or blueshift depending on the direction of motion.

The Cosmological Redshift of the Light from Very Distant Galaxies