galactic equator

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galactic equator

A great circle on the celestial sphere. The galactic plane, which contains the galactic equator, is the plane that passes most nearly through the central plane of the spiral disk of our Galaxy. The galactic plane and celestial equator are inclined at an angle of about 63°. The nominal galactic center lies on the galactic equator in the direction of the constellation Sagittarius and is the zero point for the galactic coordinate system.

Galactic Equator


the great circle along which the plane of symmetry of the Milky Way System intersects the celestial sphere; the center line of the Milky Way coincides with the galactic equator. The galactic equator is perpendicular to the Milky Way System’s axis of rotation. Near the plane of the equator the galactic concentration of stars and interstellar matter reaches its maximum. In galactic space the sun is at a distance of only about 15 parsecs from the plane of the galactic equator and is on the northern side of it. The galactic equator serves as the principal great circle for the galactic system of celestial coordinates. The location of the galactic equator in stellar-astronomical research is often approximated, drawn where the greatest concentration of stars or other galactic objects is noted. In the galactic system of coordinates, however, the galactic equator is defined rigorously and uniquely by the precise position of its poles. The galactic equator forms an angle of 62.6° with the celestial equator. The north pole of the galactic equator lies in the constellation Coma Berenices, and the south pole in the constellation Sculptor.


Kurs astrofiziki i zvezdnoi astronomii, vol. 2. Moscow, 1962.


galactic equator

[gə′lak·tik i′kwād·ər]
A great circle of the celestial sphere, inclined 62° to the celestial equator, coinciding approximately with the center line of the Milky Way, and constituting the primary great circle for the galactic system of coordinates; it is everywhere 90° from the galactic poles. Also known as galactic circle.