Final answer:
The Tully-Fisher relation is a means to determine the intrinsic luminosity of a spiral galaxy, aiding in the measurement of its distance.
Step-by-step explanation:
The Tully-Fisher relation is a method used by astronomers to determine the intrinsic luminosity of a spiral galaxy based on its rotational speed. This empirical relation is valuable for measuring Galactic distances by comparing the galaxy's intrinsic brightness with its apparent brightness. However, the Tully-Fisher relation is limited to spiral galaxies, and other methods must be employed to measure the distance to elliptical galaxies. Although the Tully-Fisher relation is useful, it is just one among various methods, such as the period-luminosity relationship for cepheid variables and the observation of type Ia supernovae, used to gauge distances in the universe, each with its own limitations and applicable scenarios.