Ecliptic longitude

Definition

Ecliptic longitude is the primary coordinate astrology uses to place planets and points on the zodiac. It measures angular distance in degrees along the plane of the ecliptic, counting from zero degrees of Aries (the vernal point) up to three hundred and sixty degrees of a full zodiacal loop. It is the terrestrial longitude projected onto the sky, and it is the standard coordinate from which the classical aspects between bodies in a natal chart get calculated.

In context

If your Sun reads fifteen degrees of Taurus, that is its ecliptic longitude: forty-five degrees from the vernal point, counted along the ecliptic. The whole machinery of the classical aspects by ecliptic (major and minor families alike) is built on differences of longitude between bodies in the natal chart. Declination operates as a complementary second coordinate, but ecliptic longitude remains the primary one of the modern frame and the coordinate that organizes the whole grid of the chart.

To go deeper

Ecliptic longitude organizes the primary coordinate apparatus:

• Declination: the complementary celestial coordinate.
• Parallel: aspect built on equal declination values.
• Natal chart: map where the coordinates apply.