Definition

1. Noun:
   • An angular coordinate in astronomy: Celestial longitude is the angular distance of a point on the celestial sphere, measured eastward along the celestial equator from the vernal equinox to the point where the object's hour circle intersects the equator. It is one of the two coordinates (with declination) used in the equatorial coordinate system to pinpoint the location of stars and other celestial objects. It is typically expressed in units of time (hours, minutes, seconds), where 24 hours corresponds to 360 degrees.

Usage Examples

• Noun:
  • To locate a star, you need both its celestial longitude (right ascension) and its declination.
  • The celestial longitude of the object was recorded as 5 hours, 34 minutes, and 12 seconds.
  • The vernal equinox serves as the zero point for measuring celestial longitude.

Advanced Usage

• "Right Ascension (RA)": This is the more common modern term for celestial longitude. The two terms are essentially synonymous in contemporary astronomy.
  • The catalog lists the star's position by its right ascension and declination.

Variants and Related Words

• Right Ascension (n): The modern equivalent term for celestial longitude.
• Declination (n): The complementary coordinate in the equatorial system, measuring angular distance north or south of the celestial equator.
• Hour Circle (n): A great circle on the celestial sphere that passes through both celestial poles and a given celestial object.

Synonyms

• Right Ascension (RA)

Notes on Meaning

• While celestial longitude and right ascension refer to the same coordinate, "right ascension" is the standard term used in modern star charts, catalogs, and telescope systems. "Celestial longitude" is an older but still accurate descriptive term that clarifies its conceptual parallel to terrestrial longitude.

Noun

1. (astronomy) the equatorial coordinate specifying the angle, measured eastward along the celestial equator, from the vernal equinox to the intersection of the hour circle that passes through an object in the sky; usually expressed in hours and minutes and seconds; used with declination to specify positions on the celestial sphere
   • one hour of right ascension equals fifteen degrees