Final answer:
The Hubble relation, or Hubble's Law, links the distance of distant galaxies to their velocity of recession, revealing the expanding nature of the universe. It was formulated based on the observation that more distant galaxies move away from us at higher speeds.
Step-by-step explanation:
The Hubble relation links the distance of distant objects in the universe to their velocity of recession. Specifically, this relation, known as Hubble's Law, states that the farther away a galaxy is, the faster it is moving away from us. This phenomenon is due to the expansion of the universe. Astronomers can determine the distances to galaxies using various methods, such as the period-luminosity relationship for cepheid variables and the Tully-Fisher relation. Once the distance and velocity are known, it confirms that the universe is indeed expanding, which was a groundbreaking discovery by Edwin Hubble.
Applying Hubble's Law, we can calculate the distances to remote galaxies by first establishing Hubble's constant. Once we have this constant, simply obtaining a spectrum of a galaxy allows us to determine how far away it is, due to the proportional relationship between distance and redshift, the latter being indicative of the galaxy's velocity of recession.