Longitude

Definition

Longitude is a coordinate used to specify position. Celestial longitude measures a planet or point eastward along the ecliptic, usually from 0° Aries through the full 360° zodiac. A longitude of 45°, for example, corresponds to 15° Taurus in the tropical zodiac. Geographic longitude instead measures a location east or west of Earth’s prime meridian and is used when calculating a chart for a particular place.

Astrological Meaning

In a horoscope, celestial longitude determines the zodiac sign and degree occupied by the Sun, Moon, planets, angles, and calculated points. Comparing these positions reveals aspects, while tracking changes in longitude allows astrologers to calculate transits and other timing techniques. Longitude does not describe a body’s distance from the ecliptic; that separate coordinate is celestial latitude. The same celestial longitude may also receive a different sign label in tropical and sidereal systems because those zodiacs use different reference frameworks.

Why It Matters

Accurate longitude is fundamental to chart calculation. Even a small difference can affect exact aspect measurements, degree-based techniques, and the timing of planetary contacts. The geographic longitude of the birthplace also helps establish local time, the Ascendant, Midheaven, and house cusps. Understanding the term makes ephemerides and chart tables easier to read and helps distinguish an astronomical position from its later astrological interpretation.

Related Encyclopedia Entries

• Traditional Astrology
• Astrological Terminology
• Natal Chart
• Ecliptic
• Celestial Latitude
• Zodiac Degrees