How did Harlow Shapley use the period-luminosity relationship of RR Lyrae variable stars to determine the size of the Milky Way galaxy?
A)He found the distances to open clusters found throughout the disk of the galaxy.
B)He found the distances to individual variables free-floating in the halo of the galaxy.
C)He determined the proper motion of globular clusters in the outer disk of the galaxy.
D)He found the distances to globular clusters distributed about the centre of the galaxy.

Question

Quizplus · Accepted Answer

Harlow Shapley used the period-luminosity relationship of RR Lyrae variable stars to determine the distances to globular clusters distributed about the center of the Milky Way galaxy. By measuring the apparent brightness of these stars, and comparing it to their known absolute brightness, he was able to estimate the distance of these clusters from Earth. This allowed him to determine the size of the Milky Way galaxy, which he found to be much larger than previously believed.

How Did Harlow Shapley Use the Period-Luminosity Relationship of RR