Far away galaxies look red due to a phenomenon called redshift. This isn't because they are actually red, but because the light they emit is stretched out as it travels through the expanding universe. Here's a breakdown:

* Expansion of the Universe: The universe is expanding, meaning galaxies are moving further apart. This expansion stretches the fabric of space-time.

* Light Waves: Light travels in waves. The color of light depends on the wavelength of these waves: shorter wavelengths are blue, longer wavelengths are red.

* Stretching: As light from distant galaxies travels towards us, the expansion of the universe stretches the wavelengths of that light. This stretching makes the light appear redder.

Think of it like this: Imagine you are holding a rubber band and stretching it out. The rubber band gets longer, and if you were to hold it up to a light, the light would be stretched out too.

Key Points:

* Redshift is a measure of the expansion of the universe. The more distant a galaxy is, the more redshifted its light will appear.

* Redshift doesn't mean galaxies are physically moving away from us. The redshift is caused by the expansion of space itself, not just the movement of galaxies through space.

This phenomenon is crucial to understanding the size and age of the universe. By measuring the redshift of distant galaxies, astronomers can estimate how far away they are and how fast the universe is expanding.