## A Treatise on Nautical Astronomy: For the Use of Students |

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### Common terms and phrases

a.m. mean apparent altitude astronomical azimuth calculated celestial concave centre chro chronometer showed colatitude compass error cosec deduced diameter difference of longitude earth ecliptic equal altitudes equinoctial Explain feet Find the Greenwich Find the latitude find the true formula given Greenwich date Greenwich mean heavenly body height of eye hence horizontal parallax hour angle index correction index error interval latitude and longitude latitude by account line of position lunar distance mean noon mean sun meridian altitude meridian passage method moon Nautical Almanac object observed altitude plane point of Aries polar distance prime vertical proportional logarithms refraction right ascension Royal Naval College second observation sextant ship in latitude sidereal day star subtract sun's declination tion transit triangle true altitude true distance tude variation vernier vers zenith distance

### Popular passages

Page 288 - Sun, the larger planets and certain stars as they would appear from the centre of the Earth. When a Lunar Distance has been observed on the surface of the Earth, and reduced to the centre, by clearing it of the effects of parallax and refraction, the numbers in these pages enable us to ascertain the exact Greenwich mean time at which the objects would have the same distance.

Page 141 - Observer' at a salary of 100£ per annum, his duty being 'forthwith to apply himself with the most exact care and diligence to the rectifying the tables of the motions of the heavens and the places of the fixed stars, so as to find out the so much desired longitude of places for the perfecting the art of navigation.

Page 288 - ... in the Ephemeris; the remainder will be the proportional logarithm of a portion of time to be. added to the hour answering to the nearest distance, to obtain the approximate Greenwich mean time corresponding to the given distance.

Page 93 - Sidereal Time at Mean Noon is the angular distance of the first point of Aries, or the true vernal equinox, from the meridian, at the instant of mean noon : it is therefore the Right Ascension of the mean Sun, or the time which ought to be shown by a sidereal clock at Greenwich, when the mean time clock indicates oh om os.

Page 34 - An apparent solar day is the interval between two successive transits of the sun across the meridian.

Page 306 - ... these are known accurately. The last (the corrected distance between the Sun and the Moon) must be estimated. There is no difficulty in doing this with accuracy abundantly sufficient for this investigation. With Greenwich time by account, the distance may be rudely computed from the distances in the Nautical Almanac. Or, without time or calculation, a navigator accustomed to lunar distances may form a shrewd guess of the probable amount of correction. (The effect of a possible error will be exhibited...

Page 141 - Mathematical o>jgraphy.) the arc of the equator, intercepted between the first meridian...

Page 308 - C . cos. a . sin. 6 . cos. c _ — 2 . sin. A . sin. B . sin. C . sin. a . sin. b . sin. c I — 2 sin.

Page 35 - A Solar Day is the interval of time between two successive transits of the sun over the same meridian; and the hour-angle of the sun is called Solar Time.

Page 142 - Fourthly, that the conference recognizes for certain scientific needs and for the service for the great administrations of the means of communication, such as railways, steamship lines, telegraphs, and posts, the utility of adopting a universal hour, side by side with the local or national hours, which will necessarily continue to be employed in civil life. " Fifthly, that the conference recommends, as the point of departure of the universal hour and of cosmopolitan dates, the mean noon of Greenwich,...