_______________ Variable Stars Are Useful in Measuring the Distance to Globular

Q18: The Sun orbits the center of the

Q19: In the late 18th century, two astronomers,

Q20: Harlow Shapley used observations of globular clusters

Q21: What parts of the galaxy are considered

Q22: Explain how giant molecular clouds give rise

Q24: Spiral arms are clearly visible features of

Q25: What property of a Cepheid variable can

Q26: The center of our galaxy contains a

Q27: Why do astronomers conclude that the spiral

Q28: Population I stars are younger than Population