What is the relationship between red-shift and the distance of galaxies?

The relationship between red-shift and the distance of galaxies is that more distant galaxies exhibit greater red-shift.

Red-shift occurs when the light from a galaxy is stretched to longer wavelengths, making it appear redder. This phenomenon is a key piece of evidence for the expanding universe. When we observe distant galaxies, we notice that their light is shifted towards the red end of the spectrum. This red-shift happens because the space between us and the galaxy is expanding, stretching the light waves as they travel towards us.

The greater the distance a galaxy is from us, the more its light has been stretched, and thus, the greater the red-shift. This relationship was first observed by Edwin Hubble in the 1920s and is now known as Hubble's Law. Hubble's Law states that the velocity at which a galaxy is moving away from us is directly proportional to its distance. This means that if we measure the red-shift of a galaxy, we can determine how fast it is receding and, consequently, how far away it is.

In practical terms, astronomers use red-shift to estimate the distances to faraway galaxies. By analysing the spectrum of light from a galaxy, they can measure the amount of red-shift and use Hubble's Law to calculate its distance. This method is crucial for mapping the universe and understanding its large-scale structure.

In summary, red-shift is a vital tool in cosmology that helps us understand the universe's expansion and the distances to galaxies. The more distant a galaxy, the greater its red-shift, providing a clear and measurable relationship between distance and the stretching of light.