Tully

Definition

Tully, often referred to as Tully-Fisher relation, is an empirical relationship between the luminosity of a spiral galaxy and its rotational velocity. It is a crucial tool for measuring distances to galaxies beyond the Local Group.

5 Must Know Facts For Your Next Test

1. The Tully-Fisher relation was independently discovered by R. Brent Tully and J. Richard Fisher in 1977.
2. It specifically applies to spiral galaxies with well-defined rotation curves.
3. The relationship indicates that more luminous spiral galaxies have higher rotational velocities.
4. The absolute magnitude of a galaxy can be inferred from its rotational velocity using this relation.
5. It is one of the key methods used in constructing the extragalactic distance scale.

Review Questions

Related terms

Hubble's Law:

A law stating that the recessional velocity of a galaxy increases with its distance from Earth, implying an expanding universe.

Cepheid Variables:

A type of star whose brightness varies periodically and is used as a standard candle for measuring astronomical distances.

Redshift:

A phenomenon where light or other electromagnetic radiation from an object undergoes an increase in wavelength, often indicative of an object's motion away from the observer.