Final answer:
Hubble's Law states the velocity of a galaxy moving away from us is proportional to its distance, which is expressed as V = H x d. The Hubble constant (H) can be determined by measuring a galaxy's distance and recessional velocity, allowing for the estimation of distances to other galaxies and supporting the idea of an expanding universe.
Step-by-step explanation:
Hubble's relation between distance and velocity, known as Hubble's Law, states that the velocity at which a galaxy moves away from us (its recessional velocity) is directly proportional to its distance. This relationship can be expressed with the equation V = H x d, where V is the recessional velocity of the galaxy, d is its distance from the Earth, and H is the Hubble constant. To determine the Hubble constant, one would measure the distance to a galaxy and its recessional velocity. For example, if a galaxy is 200 million light-years away and has a recessional velocity of 5,000 km/s, the Hubble constant (H) could be calculated using the formula:
H = V / d = 5,000 km/s / 200 million light-years
Once Hubble's constant has been determined, it can be used to estimate the distances to other galaxies based on their redshifts. The concept of an expanding universe, fundamental to cosmology, is derived from Hubble's Law.