The Nautical Almanac and Astronomical Phemeris for the Year 1835 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1833 Excerpt: ...Ascension on January 1, by the proportional part of the daily increase due for the 6h, viz. by one-fourth part, or lm 6-25. This would in all cases be required, even under the meridian of Greenwich, for which the quantities have been specially computed. Let a person be now supposed to be under a meridian 15 West of Greenwich. The positions of the heavenly bodies, as referred to the centre of the Earth, are independent of meridians, and are the same for all places at the same absolute instant; but the relative times at Greenwich and the assumed meridian would be different. If it were lh from mean noon at the one place, it could not be lh from mean noon at the other; for when we speak of time, we mean, as regards a visible phenomenon, the distance of the Sun westxrard from a given meridian, and it the same absolute moment of time the Sun cannot be at the same distance (reckoning westward) from two meridians which are 15 distant from each other. Before we can make use of the Ephemeris, it is therefore necessary to ascertain, in every instance, the distance of the Sun (in time) from the meridian of Greenwich, or what is commonly called the corresponding Greenwich time; and this is evidently equal to the given time under the assumed meridian, increased or diminisfied by the difference (in time) of the two meridians, accordingly 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 compa...