How do astronomers know that pulsating variable stars are actually expanding and contracting in diameter?
A) it is clear just by looking at the light curve
B) they discover this by looking at an H-R diagram
C) they can measure a regularly varying Doppler shift in the spectral lines
D) they can measure the star's changing pull on a companion star around it
E) astronomers are just guessing; at the distances of the stars, there is no way to show that stars are expanding and contracting

Question

Quizplus · Accepted Answer

Astronomers can measure a regularly varying Doppler shift in the spectral lines of pulsating variable stars. This is because as the star expands and contracts, its surface moves towards and away from us, which causes the lines in its spectrum to shift in wavelength. This shift is periodic and can be used to determine the star's pulsation period and amplitude, as well as its distance and other properties. Therefore, astronomers can use this method to confirm that pulsating variable stars are actually expanding and contracting in diameter.

How Do Astronomers Know That Pulsating Variable Stars Are Actually