Question

According to the Doppler effect, objects moving away from Earth would have a cooling appearance. blue shift. red shift. warming appearance.

Answer 1

When you take the Doppler effect into account, it turns out that
the visible light emitted from a source moving away from Earth
will appear to have a wavelength longer than it really has, that is,
shifted toward the red end of the visible spectrum.

This is the only way we have of measuring whether a source of
light is moving away from us, and how fast.  We measure the
wavelengths of its light, and measure how much longer they are
than they should be. 

The main trick in this whole process is: When you see the light
from a star or a galaxy, how do you know what its wavelength
should be ?

Answer 2

The correct answer is:

redshift.

Explanation:

Redshift and blueshift describe how light shifts approaching shorter or longer wavelengths as objects in space (such as stars or galaxies) move closer or removed away from us. The knowledge is key to charting the universe's expansion. Visible light is a spectrum of colors, which is clear to anyone who has observed at a rainbow.