File:The elements of astronomy; a textbook (1919) (14779902094).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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steroid, withits perihelion just outside the orbit of Mars, and its aphelion close tothat of Jupiter, its period being a few days less than seven years. 399**. Photography of Comets. — It is now possible to photo-graph comets, and the photographs bring out numerous pecu-liarities and details which are not visible to the eye even withtelescopic aid. This is especially the case in the comets tail.Fig. 100# is from Husseys photograph of Rordames comet of 1893, for which we are indebted to the kindness of Professor Holden, director of the Lick Observatory. As the camera waskept pointed at the head of the comet (which was movingpretty rapidly) the star-images during the hours exposure are drawn out into parallel streaks, the little irregularities beingdue to faults of the driving-clock and vibrations of the tele-scope. The knots and streamers which characterize the comets tail were none of them visible in the telescope, and differ from those shown upon plates taken on the days preceding and
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COMET RORDAME, JULY 13, 1893.Photographed hy W. J. Hussey, at the Lick Observatory. § 399**) PHOTOGRAPHY OF COMETS. 289 following. Other plates, made the same evening a few hours earlier and later, indicate that the knots were swiftly receding from the comets head at a rate exceeding 150,000 miles anhour. Comets have several times lately been discovered by photography in the same way as asteroids, — first by Barnard in 1892. METEORS AND SHOOTING STARS. 400. Meteorites. — Occasionally bodies fall upon the earth out of the sky. Until they reach the air they are usually in-visible, but as soon as they enter it they become conspicuous, and the pieces which fall are called Meteorites, Aerolites, Uranoliths, or simply meteoric stones. If the fall occurs at night, a ball of fire is seen, which moveswith an apparent velocity depending upon the distance of themeteor and the direction of its motion. The fire-ball is generallyfollowed by a luminous train, which sometimes remains visiblefor many

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