celestial equator

noun

Astronomy, Navigation.

1. the great circle of the celestial sphere, lying in the same plane as the earth's equator.

celestial equator

noun

1. Also called: equinoctial.  equinoctial circle. the great circle lying on the celestial sphere the plane of which is perpendicular to the line joining the north and south celestial poles

celestial equator

1. A great circle separating the northern and southern hemispheres of the celestial sphere and lying in the same plane as the Earth's equator. The celestial equator is a projection of the Earth's equator outward onto the celestial sphere and is used as the reference point in determining a celestial body's declination.

Word History and Origins

Origin of celestial equator¹

First recorded in 1870–75

Example Sentences

Fall officially kicks off Friday at 11:50 p.m. with the fall equinox, the moment the sun crosses the celestial equator, an imaginary line above earth’s equator.

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Standing by the Hunter’s foot, the Great Dog is an easy-to-find constellation visible from most areas of the world, thanks to being positioned just south of the celestial equator.

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And whereas Ptolemy based his coordinate system on the ecliptic, Hipparchus used the celestial equator, a system more common in modern star maps.

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This makes the sun appear at its farthest below the celestial equator when viewed from Earth.

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At the instant of the equinox — and it’s only an instant — the sun will beam directly above the celestial equator, that imaginary line that divides the planet in two.

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