Sizes and Distances in the Sky Astronomers use degrees, minutes, and seconds to measure

Chapter 1, Problem 73

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Sizes and Distances in the Sky Astronomers use degrees, minutes, and seconds to measure sizes and distances in the sky along an arc from the horizon to the zenith point directly overhead. An adult observer on Earth can judge distances in the sky using his or her hand at arms length. An outstretched hand will be about 20 arc degrees wide from the tip of the thumb to the tip of the little finger. A clenched fist at arms length measures about 10 arc degrees, and a thumb corresponds to about 2 arc degrees. (Source: Levy, D. H., Skywatching, The Nature Company.) (a) The apparent size of the moon is about 31 arc minutes. Approximately what part of your thumb would cover the moon? (b) If an outstretched hand plus a fist cover the distance between two bright stars, about how far apart in arc degrees are the stars?