Celestial equator

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The celestial equator is inclined by ~23.5° to the ecliptic plane.

The celestial equator is a great circle on the imaginary celestial sphere, which is actually the plane of the terrestrial equator extended out into the universe (i.e., it could be constructed by extrapolating the Earth's equator until it touches the celestial sphere). The celestial equator is inclined by ~23.5°, with respect to the ecliptic plane; a result of axial tilt.

If an observer stands on the earth equator, he or she sees the celestial equator as a semicircle passing through the zenith. As the observer goes to the north (or south) the celestial equator tilts towards south (or north) horizon. However, because the celestial equator is theoretically infinitely far (on the celestial sphere), irrespective of the observer position, the observer always sees the endings of this semicircle exactly in his/her local east/west horizon.

Celestial objects near the celestial equator are visible worldwide, but they culminate the highest in the sky in the tropics. The celestial equator passes through these constellations: