Science / Tides and Currents / Longitude: Angular distance along a great circle of reference reckoned from an accepted origin to the projection of any point on that circle. Longitude on the Earth's surface is measured on the Equator east and west of the meridian of Greenwich and may be expressed either in degrees or in hours, the hour being taken as the equivalent of 15° of longitude. Celestial longitude is measured in the ecliptic eastward from the vernal equinox. The mean longitude of a celestial body moving in an orbit is the longitude that would be attained by a point moving uniformly in the circle of reference at the same average angular velocity as that of the body, with the initial position of the point so taken that its longitude would be the same as that of the body at a certain specified position in its orbit. With a common initial point, the mean longitude of a body will be the same in whatever circle it may be reckoned.
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Science / Astrology / Longitude, Zodiacal: The position of a given point along the ecliptic expressed in terms of the zodiac. MORE
Science / Astrology / Longitude, Geographical Or Terrestrial: The distance in arc a given point on Earth lies east or west of the prime meridian, which passes through Greenwich, England (0° longitude). Geographical longitude is measured from 0° to 180°. See a MORE