Definition

1. Noun:
   • The great circle on the celestial sphere midway between the celestial poles: The celestial equator is an imaginary circle in the sky, directly above the Earth's equator. It is the projection of Earth's equator onto the celestial sphere, dividing it into northern and southern hemispheres.

Usage

• The is a fundamental reference line in astronomy for mapping the positions of stars and other celestial objects.
• An object's declination is measured in degrees north or south of the .

Examples

• Noun:
  • The Sun crosses the celestial equator twice a year at the equinoxes.
  • Astronomers use the celestial equator as the zero-point for the declination coordinate system.

Advanced Usage

• "To lie on the celestial equator": Describes a celestial object with a declination of 0 degrees.
  • The star's coordinates place it directly on the celestial equator.

Variants and Related Words

• Equinoctial (line/colure) (n): Another, less common, name for the celestial equator, especially where it intersects the ecliptic.
• Declination (n): The angular distance of a celestial object north or south of the celestial equator.

Synonyms

• Equinoctial circle: A synonym emphasizing its relation to the equinoxes.
• Equinoctial line: Another term for the celestial equator.

Related Concepts (Not Phrasal Verbs or Idioms)

• Celestial sphere: The imaginary sphere onto which all celestial objects are projected.
• Celestial poles: The two points in the sky where Earth's axis of rotation, indefinitely extended, intersects the celestial sphere.

Noun

1. the great circle on the celestial sphere midway between the celestial poles