Coordinate Systems

Four coordinate systems are supported by the near-position (cone) search. The coordinate systems are Equatorial, Ecliptic, Galactic, and Supergalactic. The Equatorial system gives declination (Dec) measured relative to the celestial equator, set by the Earth's rotational axis at either the B1950.0 or J2000.0 equinox (the two most commonly used). The right ascension (RA) in this system is measured in hours, minutes, and seconds, relative to the first point of Aries, where the ecliptic crosses the equator at the specified equinox. The Ecliptic system gives latitude measured relative to the ecliptic, defined by the projection of Earth's orbit around the sun. The longitude in this system is measured in hours, minutes, and seconds, relative to the first point of Aries. The Galactic system gives latitude measured relative to the Galactic plane and longitude measured relative to the Galactic center. The Supergalactic system is defined relative to the plane of the Virgo Supercluster. Note that changing the Equinox has no effect for the Galactic or Supergalactic systems.