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Right ascension is measured eastward up to 24 h along the celestial equator from the primary direction. Right ascension (abbreviated RA; symbol α) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the (hour circle of the) point in question above the Earth. [1]
The longitude of the ascending node, also known as the right ascension of the ascending node, is one of the orbital elements used to specify the orbit of an object in space. Denoted with the symbol Ω , it is the angle from a specified reference direction, called the origin of longitude , to the direction of the ascending node (☊), as ...
Model of the equatorial coordinate system. Declination (vertical arcs, degrees) and hour angle (horizontal arcs, hours) is shown. For hour angle, right ascension (horizontal arcs, degrees) can be used as an alternative. The equatorial coordinate system is a celestial coordinate system widely used to specify the positions of celestial objects.
Coordinates Primary direction (0° longitude) Latitude Longitude Horizontal (also called alt-az or el-az) Observer Horizon: Zenith, nadir: Altitude (a) or elevation Azimuth (A) North or south point of horizon Equatorial: Center of the Earth (geocentric), or Sun (heliocentric) Celestial equator: Celestial poles: Declination (δ) Right ascension (α)
J2000.0 equatorial coordinates approximating the galactic reference points [1] Right ascension: Declination: Constellation: North Pole +90° latitude 12 h 51.4 m +27.13° Coma Berenices (near 31 Com) South Pole −90° latitude 0 h 51.4 m: −27.13° Sculptor (near NGC 288) Center 0° longitude 17 h 45.6 m: −28.94° Sagittarius (in ...
The local hour angle (LHA) of an object in the observer's sky is = or = + where LHA object is the local hour angle of the object, LST is the local sidereal time, is the object's right ascension, GST is Greenwich sidereal time and is the observer's longitude (positive east from the prime meridian). [3]
Like right ascension in the equatorial coordinate system, the primary direction (0° ecliptic longitude) points from the Earth towards the Sun at the March equinox. Because it is a right-handed system, ecliptic longitude is measured positive eastwards in the fundamental plane (the ecliptic) from 0° to 360°.
An object's right ascension and the local sidereal time can be used to determine the time of its culmination (see hour angle). The term meridian comes from the Latin meridies , which means both "midday" and "south", as the celestial equator appears to tilt southward from the Northern Hemisphere .