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celestial equator

n. (context astronomy English) A great circle on the celestial sphere, coincident with the plane of earth's equator.

celestial equator

n. the great circle on the celestial sphere midway between the celestial poles [syn: equinoctial circle, equinoctial line, equinoctial]

Celestial equator

The celestial equator is a great circle on the imaginary celestial sphere, in the same plane as the Earth's equator. In other words, it is a projection of the terrestrial equator out into space. As a result of the Earth's axial tilt, the celestial equator is inclined by 23.4° with respect to the ecliptic plane.

An observer standing on the Earth's equator visualizes the celestial equator as a semicircle passing directly overhead through the zenith. As the observer moves north (or south), the celestial equator tilts towards the opposite horizon. The celestial equator is defined to be infinitely distant (since it is on the celestial sphere); thus the observer always sees the ends of the semicircle disappear over the horizon exactly due east and due west, regardless of the observer's position on Earth. (At the poles, though, the celestial equator would be parallel to the horizon.) At all latitudes the celestial equator appears perfectly straight because the observer is only finitely far from the plane of the celestial equator but infinitely far from the celestial equator itself.

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

  • Pisces (contains the first point of Aries above its southern border)
  • Cetus
  • Taurus
  • Eridanus
  • Orion
  • Monoceros
  • Canis Minor
  • Hydra
  • Sextans
  • Leo
  • Virgo (contains the first point of Libra)
  • Serpens
  • Ophiuchus
  • Aquila
  • Aquarius

Celestial bodies other than Earth also have similarly defined celestial equators.

Usage examples of "celestial equator".

This pertains not only to the very sophisticated astronomical methods that were used - who in ancient Sumer really needed to establish a celestial equator, for example?

And the horizon then must coincide exactly with the circle of the celestial equator.

There was the celestial equator, an invisible line that was a projection of Earth’.

Now the planets move through these houses, that are really segments of the celestial equator.

Mechanism gave him the celestial equator and the degree at which he could expect the Disc-if the Society's calculations were correct.

Mechanism gave him the celestial equator and the degree at which he could expect the Disc—.