Definition

1. Noun:
   • The great circle on the celestial sphere whose plane passes through the sensible horizon and the center of the Earth: This is the astronomical horizon, an imaginary circle on the celestial sphere that is level with the observer's eye and divides the visible sky from the invisible sky. It is the projection of the Earth's horizon onto the celestial sphere.

Usage

• The term "celestial horizon" is used in astronomy, navigation, and observational contexts to describe a fundamental reference line in the sky.
• It is a precise, technical term. In everyday language, people typically just say "horizon."

Examples

• Noun:
  • To calculate the star's altitude, the astronomer first located the celestial horizon.
  • The sun appeared to sink below the celestial horizon at dusk.

Advanced Usage

• "True celestial horizon": Sometimes used to distinguish it from the "visible" or "sensible" horizon, which can be affected by terrain and atmospheric refraction.
  • For precise calculations, navigators use the true celestial horizon, not the visible one.

Variants and Related Words

• Horizon (n): The more common, general term for the line where the earth and sky appear to meet.
• Sensible horizon (n): The apparent horizon seen by an observer, as opposed to the theoretical celestial horizon.
• Astronomical horizon (n): Another term for the celestial horizon.

Synonyms

• Astronomical horizon: A direct synonym with identical meaning.
• Rational horizon: Another technical synonym used in astronomy and geodesy.

Related Phrases

• Above the celestial horizon: Refers to objects in the visible sky.
  • All constellations you can see are above the celestial horizon.
• Below the celestial horizon: Refers to objects not currently visible from the observer's location.
  • The other half of the celestial sphere is below the celestial horizon.

Noun

1. the great circle on the celestial sphere whose plane passes through the sensible horizon and the center of the Earth