Topic summary
Ecliptic longitude
Extracted from the Wikipedia article Ecliptic coordinate system.
Historical use
From antiquity through the 18th century, ecliptic longitude was commonly measured using twelve zodiacal signs, each of 30° longitude, a practice that continues in modern astrology. The signs are approximately the positions on the ecliptic, relative to the position of the Sun on the March equinox, where constellations were on the ecliptic in the year 200 ce ; however the stars of those constellations have precessed eastward and the stars are now shifted by about one-and-a-half 30° signs from the locations of their nominal zodiacal signs. Longitudes were specified in signs, degrees, minutes, and seconds.