What is redshift and what does it tell us about the movement of galaxies?

Redshift is the phenomenon where light from an object is stretched, increasing its wavelength and shifting it towards the red end of the electromagnetic spectrum. This happens when the object emitting the light is moving away from the observer. Think of the sound of a siren as an ambulance speeds away – the sound waves are stretched out, making the pitch lower. Redshift is the light equivalent of this effect.In the context of galaxies, redshift tells us that the vast majority of galaxies are moving away from us. The greater the redshift, the faster the galaxy is receding. This observation is a cornerstone of the Big Bang theory, which posits that the universe is expanding. As the universe expands, the space between galaxies stretches, causing the light traveling between them to stretch as well, resulting in a redshift.It's important to note that redshift can also be caused by other factors, such as the strong gravitational fields of massive objects. However, the redshift observed in distant galaxies is primarily due to the expansion of the universe, also known as cosmological redshift. This redshift provides strong evidence for an expanding universe and allows astronomers to estimate the distances to faraway galaxies and the rate of the universe's expansion.