Hubble's Law states that the velocity at which a galaxy recedes from an observer is directly proportional to its distance from the observer, implying that the universe is expanding. This relationship is fundamental to cosmology and provides evidence for the Big Bang theory, as it suggests that galaxies were once closer together in the past.
Luminosity distance is a measure used in astronomy to relate the intrinsic brightness of an astronomical object to its observed brightness, accounting for the expansion of the universe. It is crucial for determining distances to faraway galaxies and supernovae, enabling the study of cosmic scale and the universe's rate of expansion.
Angular diameter distance is a way to figure out how far away something in space is by looking at how big it seems to us. It's like when you hold your thumb close to your eyes, it looks big, but when you move it far away, it looks small.