Identifier: adolfostahllectu00astruoft (find matches)
Title: The Adolfo Stahl lectures in astronomy, delivered in San Francisco, California, in 1916-17 and 1917-18, under the auspices of the Astronomical Society of the Pacific
Year: 1919 (1910s)
Authors: Astronomical Society of the Pacific Aitken, Robert Grant, 1864-1951
Subjects: Astronomy
Publisher: San Francisco Stanford University Press
Contributing Library: Gerstein - University of Toronto
Digitizing Sponsor: MSN

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out 5° with the ecliptic. Thisexplains why the Moon sometimes rises north of the east point,and sometimes south of it, for the ecliptic itself makes an angleof 235^° with the plane of the Earths equator, and the Sunis south of the equator from the autumnal equinox (aboutSeptember 21) to the vernal equinox (about March 21) andthen north of it through the next six months. Let us note justhere that since the Moon at full is always opposite to the Sun,the full Moon must be north of the equator during our wintermonths, when the Sun is south of it, and south of the equatorduring our summer months. The full Moon therefore rideshigh in the sky and gives us the most light in the winter whenwe have the least sunlight, and rides low in the sky in thesummer. In our latitudes this is not a matter of great con-sequence, but if we were at the North or at the South Pole, itwould be pleasant, at least, to have the Moon above the horizoncontinuously for the 14 days from the first quarter through full
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PLATE XVn. The Moox, 19d. 12.5h. Old. Photograph taken zvith the 36-iiich refractor. Aug. 30, 1893, by A. L.Coltnii and C. D. Ferriiie. The Moon 81 Moon to the last quarter every month during the long polarnight. Next, the ancients learned that the Moons distance from theEarth varies by a sHght amount, corresponding to the slightvariation in its apparent diameter, and that this variationprogresses in a regular manner, completing the cycle of itschanges in the period of a month. This we now know is dueto the fact that its orbit is not an exact circle but is flattened alittle into the form of an ellipse. Of course they also learnedthat the Moon does not shine by its own light but only byretlected sunlight. This led to an understanding of the phasesof the Moon. A careful study of some of the prominent markings on theMoons surface will soon convince any one that they alwaysremain in approximately the same position with respect to thelimb; that is, that the Moon always turns the same face

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