Astron. the arc of the ecliptic measured eastward from the vernal equinox to the point where the ecliptic is intersected by the great circle through the star, planet, etc. and the poles of the ecliptic
Celestial longitude. (n.d.). In YourDictionary. Retrieved from https://www.yourdictionary.com/celestial-longitude
The position of a celestial object east of the vernal equinox along the ecliptic. Celestial longitude is measured in degrees eastward from the vernal equinox (0°) to the point where a great circle drawn through the object and the poles of the ecliptic intersects the ecliptic.