Longitude

The distance, expressed in degrees, or hours, east or west of a given meridian.

Celestial Longitude. The distance of a heavenly body from the vernal equinox, reckoned on the ecliptic. Celestial Longitude is reckoned from the first point of Aries, eastward, from o deg. to 360 deg. and from 0 h. to 24 h.

Difference of Longitude. The difference in degrees, minutes and seconds of arc, or the difference in hours, minutes and seconds of time between two meridians.

Geocentric Longitude. The longitude of a heavenly body as viewed from the earth.

Heliocentric Longitude. The longitude of a heavenly body as viewed from the sun.

Terrestrial Longitude. The distance of any place on the earth's surface, east or west of a given meridian, expressed in arc or time.