Definition

1. Noun:
   • An astronomical coordinate: Right ascension is the angular distance measured eastward along the celestial equator from the vernal equinox to the point where the hour circle of a celestial object intersects the equator. It is one of the two coordinates used to specify positions on the celestial sphere, analogous to longitude on Earth. It is typically expressed in units of hours, minutes, and seconds, where one hour corresponds to 15 degrees of arc.

Usage

• Right ascension is used in conjunction with declination to precisely locate stars, galaxies, and other celestial objects.
• It is a fundamental coordinate in astronomical catalogs and telescope pointing systems.

Examples

• Noun:
  • The star's position is given as right ascension 05h 55m 10.3s and declination +07° 24' 25".
  • Astronomers use right ascension and declination to map the night sky.
  • One hour of right ascension equals fifteen degrees of angular distance.

Advanced Usage

• "Used with declination": This phrase highlights that right ascension is not used alone. A complete celestial position requires both coordinates.
  • To find the nebula, you need both its right ascension and its declination.

Variants and Related Words

• RA (abbreviation): A common abbreviation for right ascension.
  • The catalog lists the RA and Dec for each object.
• Celestial coordinates: The general system that includes right ascension and declination.
• Hour circle: The great circle on the celestial sphere that passes through the celestial poles and a given celestial object; right ascension is measured along the celestial equator to where this circle intersects.

Synonyms

• Celestial longitude: A descriptive synonym, drawing a direct analogy to terrestrial longitude. (Note: This term is less commonly used in modern professional astronomy than "right ascension").

Related Terms (Not Phrasal Verbs or Idioms)

• Declination: The complementary celestial coordinate, analogous to latitude, measured north or south of the celestial equator.
• Vernal equinox: The reference point (zero point) for measuring right ascension, also known as the First Point of Aries.
• Celestial sphere: The imaginary sphere surrounding Earth, onto which all celestial objects are projected for the purpose of this coordinate system.

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