celestial equator

American  

noun

Astronomy, Navigation.

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

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celestial equator British  

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

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celestial equator Scientific  

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.

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Etymology

Origin of celestial equator

First recorded in 1870–75

Example Sentences

See Examples For:

celestial equator

This region is positioned near the celestial equator and close to the flat disk of the Milky Way, which makes it visible from many locations on Earth during certain seasons.

From Science Daily ● Dec. 25, 2025

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.

From Seattle Times ● Sep. 21, 2023

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.

From National Geographic ● Aug. 23, 2023

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

From Scientific American ● Oct. 20, 2022

Extended to the heavens, it forms a circle called the celestial equator, which in like manner divides the heavens into two equal parts, the northern and southern hemispheres.

From The Sailor's Word-Book An Alphabetical Digest of Nautical Terms, including Some More Especially Military and Scientific, but Useful to Seamen; as well as Archaisms of Early Voyagers, etc. by Sir Edward Belcher