An Exhausted-Looking Astronomer Comes Off the Mountain Where Her Observatory

Multiple Choice

An exhausted-looking astronomer comes off the mountain where her observatory is located and tells you she has been doing photometry all night. What has she been up to?

A) taking photos through bedroom windows in the valley below
B) measuring the positions of stars on photographic plates taken over many years
C) putting the light of stars through a spectrograph to measure what elements are present
D) measuring the brightness of different stars
E) counting the number of stars in different star clusters (groups)