The Astronomical Ephemeris Volume 1847

The Astronomical Ephemeris Volume 1847

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1843 edition. Excerpt: the given time under the assumed meridian, increased or diminished by the difference (in time) of the two meridians, according as the assumed meridian is to the Westward or Eastward of Greenwich. In a mean Solar day, or 24 mean Solar hours, the Earth, by its rotation from West to East, has caused every meridian in succession from East to West to pass the mean Sun; and since the motion is uniform, all the meridians distant from each other 15 will have passed the mean Sun, at intervals of one mean hour; the meridian to the Eastward passing first, or being, as compared with the Sun, always one mean hour in advance of the Westerly meridian. When it is 6b from mean noon at a place 15 West of Greenwich, it is therefore from mean noon at Greenwich; and it is for this Greenwich time that we must deduce the quantities required from the Ephemeris. If a chronometer adjusted to Greenwich mean time be at hand, the Greenwich time may be immediately obtained by applying a correction, deduced from the daily rate and interval elapsed, and this will be preferable in all cases for obtaining the requisite data from the Ephemeris. The day adopted in this Ephemeris is supposed to begin at mean noon, or at the instant when a clock or chronometer shows 0h 0m 0', Greenwich mean time, and is continued through the 24 hours. to the following mean noon, when another day begins. It may therefore be called the Mean Astronomical Day, although, in practice, astronomers begin the day at the moment the true Sun's centre is on their meridian. In the civil, or common, method of reckoning, the day is supposed to commence at the preceding midnight, and to be counted only to 12 hours or noon, when the 12 hours are reckoned over again to the next midnight. The civil reckoning...
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Product details

  • Paperback | 38 pages
  • 189 x 246 x 2mm | 86g
  • United States
  • English
  • black & white illustrations
  • 1236913000
  • 9781236913005