The Tully-Fisher relation provides a method of determining distances to galaxies by estimating the galaxy luminosity from the measurement of what parameter relating to the 21-centimeter atomic hydrogen radio emission line?
A) Its position and Doppler shift
B) The split between its two components
C) Its width
D) Its intensity

Question

Quizplus · Accepted Answer

The Tully-Fisher relation is based on the assumption that there is a correlation between the width of the 21-centimeter atomic hydrogen radio emission line and the luminosity of a galaxy. Therefore, the parameter that is measured to estimate the galaxy luminosity is the width of the emission line.

The Tully-Fisher Relation Provides a Method of Determining Distances to Galaxies