Text-book on Practical Astronomy

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John Wiley & sons, Incorporated, 1917 - Spherical astronomy - 205 pages

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Page 100 - Zodiac," are Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricornus, Aquarius, and Pisces.
Page 189 - SUBTRACT from the time of west elongation om. 16 for every degree north of 40. Reverse these operations for correcting times of east elongation. E. To refer to any other than the tabular longitude: ADD om.
Page 20 - The hour angle of a point is the arc of the equator between the observer's meridian and the hour circle through the point. It is measured from the meridian westward (clockwise) from o* to 24* or from o to 360. In Fig. 16 the declination of the star S is AS (negative); the hour angle is M F1G.
Page 19 - The first coordinate of a point is its angular distance north or south of the equator, measured on an hour circle; it is called the Declination. Declinations are considered positive when north of the equator, negative when south. The complement of the declination is called the Polar Distance. The second coordinate of...
Page 189 - The astronomical day begins twelve hours after the civil day, ie, begins at noon on the civil day of the same date, and is reckoned from 0 to 24 hours. Consequently an astronomical time less than twelve hours refers to the same civil...
Page 189 - ... to 24 hours. Consequently an astronomical time less than twelve hours refers to the same civil day, whereas an astronomical time greater than twelve hours refers to the morning of the next civil day. It will be noticed that for the tabular year two eastern elongations occur on January 12 and two western elongations on July 12.
Page 40 - A solar day is the interval of time between two successive upper transits of the sun over the same meridian. The solar time at any instant is the hour angle of the sun at that instant.
Page 165 - In making the observation the instrument is set up at one end of the line whose azimuth is to be determined, and the plate vernier set at o. The vertical cross hair is set on the mark and the lower clamp tightened. The sun glass is then put in position, the upper clamp loosened, and the telescope pointed at the sun. It is not necessary to observe on both edges of the...
Page 10 - While the direction of the earth's rotation axis is so nearly constant that no change is observed during short periods of time, there is in reality a very slow progressive change in its direction. This change is due to the fact that the earth is not quite spherical in form but is spheroidal, and there is in consequence a ring of matter around the equator upon which the sun and the moon exert a force of attraction which tends to pull the plane of the equator into coincidence with the plane of the...

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