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Ecliptic longitude or celestial longitude (symbols: heliocentric l, geocentric λ) measures the angular distance of an object along the ecliptic from the primary direction. Like right ascension in the equatorial coordinate system , the primary direction (0° ecliptic longitude) points from the Earth towards the Sun at the March equinox .
The geocentric ecliptic system was the principal coordinate system for ancient astronomy and is still useful for computing the apparent motions of the Sun, Moon, and planets. [3] It was used to define the twelve astrological signs of the zodiac , for instance.
Ecliptic coordinates are convenient for specifying positions of Solar System objects, as most of the planets' orbits have small inclinations to the ecliptic, and therefore always appear relatively close to it on the sky. Because Earth's orbit, and hence the ecliptic, moves very little, it is a relatively fixed reference with respect to the stars.
This is a compilation of symbols commonly used in astronomy, particularly professional astronomy. ... Ecliptic longitude; β - Ecliptic latitude; l - Galactic longitude;
The first point of Aries, also known as the cusp of Aries, is the location of the March equinox (the vernal equinox in the northern hemisphere, and the autumnal equinox in the southern), used as a reference point in celestial coordinate systems. In diagrams using such coordinate systems, it is often indicated with the symbol ♈︎.
When paired with declination, these astronomical coordinates specify the location of a point on the celestial sphere in the equatorial coordinate system. An old term, right ascension ( Latin : ascensio recta ) [ 2 ] refers to the ascension , or the point on the celestial equator that rises with any celestial object as seen from Earth 's equator ...
A map of the IAU-defined constellation boundaries with the equal length signs used in tropical astrology overlaid.One can see that, due to precession and the inequality in the sizes of constellations, it appears that the constellations the signs are based on have moved eastward by nearly a month (or 30 degrees).
The zodiac forms a celestial coordinate system, or more specifically an ecliptic coordinate system, which takes the ecliptic as the origin of latitude and the Sun's position at vernal equinox as the origin of longitude. [4] In modern astronomy, the ecliptic coordinate system is still used for tracking Solar System objects.