A text-book of general astronomy : for colleges and scientific schools (1888)
Young, Charles A. (Charles Augustus), 1834-1908 · Boston ; London : Ginn & Company · leaf 168
27.21 days —about 2 hours and 38 minutesshorter than the sidereal revo-lution of the moon, since thenodes always move westward,completing the circuit in about19 years. 250. 2. Libration in Lon-gitude. The moons orbitbeing eccentric, she movesfaster when near perigee,and slower when near apo-gee ;… … Fig. 81. — The Libration in Longitude. 156 THE MOON. surface which is directed toward the earth at perigee will nothave revolved far enough to keep it directed toward the earth whenshe is half-way (in time) between perigee and apogee, as is evidentfrom Fig. 81. For in the quarter-month next…
Astronomy
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