Ecliptic
Cross-traditionAstronomical factEditorial synthesis
Definition
The plane of Earth's orbit around the Sun, projected onto the sky as a great circle. The Sun, Moon and planets all appear to travel close to it, which is why it is the reference circle astrology measures positions along.
Also called: Plane of the ecliptic · Path of the Sun
In more depth
The ecliptic is an astronomical reference plane, not an astrological idea. It is the plane in which Earth orbits the Sun; drawn onto the celestial sphere it becomes a great circle, tilted about 23.4 degrees from the celestial equator, and the Sun and planets appear to move along or near it. One of the two points where it crosses the celestial equator is the vernal equinox.[1]
Astrology borrows this circle as its coordinate ring. Positions on this platform are reported as a longitude measured along the ecliptic, and the twelve zodiac signs are equal divisions of the same circle. Because the reference plane and its measured quantities are defined in standard astronomical practice, two people using the same convention get the same number.[2]
References
Numbered citations in the text link to the records below; each record links to the full source registry.
- NASA Science. Basics of Space Flight, Chapter 2: Reference Systems. current (living reference page). Astronomical fact View source record
- Sean E. Urban (editor); P. Kenneth Seidelmann (editor). Explanatory Supplement to the Astronomical Almanac. Sean E. Urban and P. Kenneth Seidelmann. University Science Books. 2013. Astronomical fact View source record