Astronomy Practice Exam 2025 – Complete Preparation Guide

Redshift is an important concept in astronomy that refers to the phenomenon where light from an object is shifted to longer wavelengths, which appear redder to observers. When we observe the light from distant galaxies, a redshift indicates that the wavelengths of light are stretched, which occurs when the source of that light is moving away from us.

This effect is a consequence of the Doppler effect, which describes how the frequency of waves changes in relation to an observer who is moving relative to the wave source. In the context of galaxies, as the universe expands, galaxies are generally moving away from each other. Therefore, when we detect redshift in a galaxy's light, it signifies that the galaxy is receding due to this expansion.

Additionally, significant redshift is often utilized as a measure of the velocity at which the galaxy is moving away; the greater the redshift, the faster it seems to be receding. This has profound implications in cosmology, particularly in relation to the Big Bang theory and the expanding universe model.

In contrast, if a galaxy were moving closer to us, we would observe a blueshift, where the wavelengths are compressed, appearing bluer. If a galaxy were not moving at all relative to us, there would be