By what standard technique do astronomers find the luminosity class (I,II,III,IV,or V)of a star?
A) combining the apparent magnitude with the measured distance to the star
B) observing the diameter of the star on a photographic plate or CCD image
C) timing how long it takes for the star to be eclipsed by a companion in an eclipsing binary star system
D) studying the absorption lines in the star's spectrum

Question

Quizplus · Accepted Answer

Astronomers study the absorption lines in the star's spectrum to determine its luminosity class. The strength of certain spectral lines is an indicator of the surface gravity of the star, which is closely related to its luminosity class. This technique is known as spectral analysis, and it allows astronomers to classify the stars into different luminosity classes.

By What Standard Technique Do Astronomers Find the Luminosity Class