## The Nautical Almanac and Astronomical Ephemeris for the Year ... (Google eBook) |

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Page 600 - ... distance, to obtain the approximate Greenwich mean time corresponding to the given distance. If the distance between the Moon and a Star increased or decreased uniformly, the Greenwich...

Page 591 - Astronomers, with a view of obtaining a convenient and uniform measure of time, have recourse to a mean solar day, the length of which is equal to the mean or average of all the apparent solar days in a year. An imaginary Sun, called the mean Sun, is conceived to move uniformly in the Equator with the real Sun's mean motion in Right Ascension, and the interval between the departure of any meridian from the mean Sun and its succeeding return to it is the duration of the mean solur day.

Page 595 - Greenwich, the sidereal clock ought to show oh om o9, and at the succeeding return of the star, or the equinox, to the same meridian, the clock ought to indicate the same time. The sidereal time here given is that in common use among astronomers, and expresses the actual hour angle from the meridian, westward, of the true equinoctial point at the moment of observation. It is therefore affected by the equation of the equinoxes ; and is not, strictly speaking, a mean or uniformly increasing quantity.

Page 612 - The hours and minutes of Right Ascension, and the degrees and minutes of Declination, are placed at the heads of the columns as constants, and belong equally to all the numbers below them. This arrangement has rendered it necessary, in...

Page 595 - 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 shown by a sidereal clock at Greenwich, when the mean time clock indicates oh om o*.

Page 603 - Satellite is at some Distance from the Body of Jupiter, except near the Opposition of Jupiter to the Sun, when the Satellite approaches nearer to his Body.

Page 600 - 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. They are arranged...

Page 597 - Moon's limo, as in all cases of altitudes or lunar distances. The latter, for computing the horizontal parallax of the Moon at any given latitude on the Earth, considered as a spheroid; also for finding the parallax in altitude, Right Ascension, &c., for...

Page 607 - ... the meridian, is denominated Sidereal Time at Mean Noon, this may, by analogy, be termed the Mean Time at Sidereal Noon. It is the time which ought to be shown by a mean time clock adjusted to the Greenwich meridian, at the moment that a clock, adjusted to sidereal time, indicates exactly oh om o*.

Page 597 - The Logarithm of the Radius Vector of the Earth is the logarithm of the distance between the centre of the Earth and the true place of the centre of the Sun at mean noon, the mean distance, or the semi-axis major of the orbit, being considered unity. The Mean Time of Transit of the First Point of Aries is the distance of the mean Sun from the meridian, at the instant when the true point of intersection of the ecliptic...