* Redshift: When light from distant galaxies is observed, its wavelengths are stretched, making them appear redder (hence the term "redshift"). This stretching of light waves is caused by the Doppler effect, similar to how the pitch of a siren changes as it moves towards or away from you.
* Expansion: The fact that galaxies are generally redshifted indicates that they are moving away from us. Since this is observed across the entire universe, it suggests that space itself is expanding, carrying the galaxies along with it.
* Hubble's Law: Astronomer Edwin Hubble observed a direct relationship between the redshift of a galaxy and its distance from Earth. This relationship, known as Hubble's Law, provides strong evidence for the expanding universe.
Key takeaway: The observation of redshift in galaxies is a crucial piece of evidence for the expanding universe. It tells us that the galaxies are moving apart and that the space between them is growing larger.
