Why does the Cepheid distance method fail us beyond about 20 Mpc?
A) The intergalactic dust reddens the Cepheid's light and apparent brightness.
B) Distant galaxies are younger than our Milky Way; too young to have Cepheids yet.
C) The periods of Cepheids grows longer as the distances increase.
D) Distant galaxies are seen in the past, and Cepheids evolve with time.
E) Even with the HST, the most luminous Cepheids are too faint to be seen beyond 20 Mpc.
E
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Fill in the blank(s) with the appropriate word(s).
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A. It moves toward the centerline. B. It moves away from the centerline. C. It doesn't change.
The ancient Greeks noted that the planets
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A) 10 B) 200 C) 100 D) 20 E) 6.022 × 1023