At midnight, on a clear and moonless night, the number of stars that are distinctly visible to the eye is in the range
A) 2000-5000.
B) 20,000-50,000.
C) 200,000-500,000.
D) 2 million-5 million.
A) 2000-5000.
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What is wavelength?
a. The amplitude of a wave. b. The distance between identical positions on adjacent wave pulses. c. The distance that the wave travels. d. The distance between a wave's crest and its trough. e. Half the distance between identical positions on adjacent wave pulses.
The assumption that from any place in the universe the observer would measure the same physical properties we observe is called
A) Olbers's paradox. B) general gelativity. C) special relativity. D) steady state physics. E) the cosmological principle.
Astronomers believe that dark matter exists because
A. the galaxies in clusters move slower than expected on the basis of the material visible in them. B. they can detect it with radio telescopes. C. the outer parts of galaxies rotate faster than expected on the basis of the material visible in them. D. it is the only way to explain the black holes in active galaxies. E. All of these choices are correct.
The source of a sonic boom may be a
A) whip. B) a high-speed bullet. C) both of these D) neither of these