Which law describes the relationship between the distance of an object and its recessional velocity?

The law that describes the relationship between the distance of an object in the universe and its recessional velocity is Hubble's Law. According to this law, the farther away a galaxy is, the faster it appears to be moving away from us. This relation indicates that the universe is expanding, and it was first observed by Edwin Hubble in the late 1920s. Hubble's Law is often expressed mathematically as v = H₀d, where v is the recessional velocity, d is the distance, and H₀ is the Hubble constant, a measure of the rate of expansion of the universe.

The significance of Hubble's Law lies in its implications for cosmology, providing a direct relationship that helps in estimating distances to faraway galaxies based on their observed velocities. This foundational principle supports the Big Bang theory by indicating that galaxies are moving away from each other as the universe expands.