celestial longitude

astronomy

Also known as: ecliptic longitude

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June 24, 2026

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Celestial longitude is a coordinate system used in astronomy to measure positions on the celestial sphere. It is measured eastward from the March equinox along the ecliptic, which is the apparent path of the Sun across the sky throughout the year. This system is part of the ecliptic coordinate system, where celestial latitude measures distance north or south from the ecliptic. Celestial longitude is analogous to geographical longitude on Earth and is used in methods like celestial navigation to determine a location.123

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astronomical map
The ecliptic system
Celestial longitude is measured eastward from the ascending intersection of the ecliptic with the equator, a position known as the “first point of Aries,” and the place of the Sun at the time of the vernal equinox about March 21. The first point of Aries…
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Celestial longitude is measured eastward from the ascending intersection of the ecliptic with the equator, a position known as the “first point of Aries,” and the place of the Sun at the time of the vernal equinox about March 21. The first point of Aries…
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ecliptic
…ecliptic system of astronomical coordinates, celestial longitude is measured in degrees east from the vernal equinox along the ecliptic. Celestial latitude is measured in degrees north (positive) or south (negative) from the ecliptic to the ecliptic poles. Each ecliptic pole is 23.44° from the corresponding celestial pole.
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…ecliptic system of astronomical coordinates, celestial longitude is measured in degrees east from the vernal equinox along the ecliptic. Celestial latitude is measured in degrees north (positive) or south (negative) from the ecliptic to the ecliptic poles. Each ecliptic pole is 23.44° from the corresponding celestial pole.
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