How did Harlow Shapley determine the distances to globular clusters in the Milky Way galaxy?
A. He used the Period-Luminosity Relation of RR Lyrae variable stars so they could be used as standard candles.
B. He used the radial velocity technique as a globular cluster orbits around a companion cluster.
C.He measured the distance to the Galactic center and assumed all clusters were at that same distance.
D. He used the parallax technique with a satellite designed to have a larger baseline than could be achieved from Earth.
E. He used the parallax technique by viewing the clusters at two different times from the orbit of Earth.
Ans: A. He used the Period-Luminosity Relation of RR Lyrae variable stars so they could be used as standard candles.
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