What is the Tully-Fisher relation?
A) The more distant the galaxy,the fainter it appears.
B) The more distant the galaxy,the greater the recessional velocity.
C) The brighter the Cepheid,the longer the pulsation period.
D) The brighter the galaxy,the wider the 21-cm radio emission line.

Question

Quizplus · Accepted Answer

The Tully-Fisher relation is an empirical relationship between the luminosity (brightness) of a galaxy and the width of its 21-cm radio emission line. In other words, the brighter the galaxy, the wider the 21-cm radio emission line. This relationship is useful for measuring distances to galaxies and for studying their properties.

What Is the Tully-Fisher Relation