File:The elements of astronomy; a textbook (1919) (14759250446).jpg

Identifier: elementsofastro00youn (find matches)
Title: The elements of astronomy; a textbook
Year: 1919 (1910s)
Authors: Young, Charles A. (Charles Augustus), 1834-1908 Young, Anne Sewell, b. 1871., ed
Subjects: Astronomy Constellations
Publisher: Boston, New York (etc.) Ginn and Company
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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period, ■ 584days, — a year and 7 months. From superior conjunction toelongation on either side is 220 days, while from inferior con-junction to elongation is only 71 or 72 days. The greatestelongation is 47° or 48°. The inclination of its orbit is about 3^-°. 322. Magnitude, Mass, Density, Etc. — The apparent diam-eter of the planet ranges from 67, at the time of inferior 322) TELESCOPIC APPEARANCE, ETC. 225 conjunction, to only 11 at superior, the great difference de-pending upon the enormous variation in the distance of theplanet from the earth. The real diameter of the planet inmiles is about 7700. Its surface, compared with that of theearth, is y9-^; its volume, -f^. By means of the perturbationsshe produces upon the earth, the mass of Venus is found to bea little less than four-fifths of the earths mass. Hence herdensity is about 86 per cent, and her superficial gravity 83 percent of the earths. A man who weighs 160 pounds herewould weigh only about 133 pounds on Venus.
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Fig. 80. — Telescopic Appearances of Venus. 323. General Telescopic Appearance, Phases, Etc. — The tele-scopic appearance of Venus is striking on account of her greatbrilliance, but exceedingly unsatisfactory because nothing isdistinctly outlined upon the disc. When about midway be-tween greatest elongation and inferior conjunction the planetnas an apparent diameter of 40, so that with a magnifying 226 VENUS. § 323) power of only 45 she looks exactly like the moon four daysold, and of the same apparent size. (Very few persons, how-ever, would think so on the first view through the .telescope :the novice always underrates the apparent size of a telescopicobject.) The phases of Venus were first discovered by Galileo in 1610, andafforded important evidence as to the truth of the Copernican Systemas against the Ptolemaic. Fig. 80 represents the planets disc as seen at five points in itsorbit. 1, 3, and 5 are taken at superior conjunction, greatest elonga-tion, and near inferior conju

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