Equatorial System - A coordinate system, using right ascension and declination as coordinates, used to describe the angular location of bodies in the sky ...
Equatorial System.
Latitudinal Co-ordinate; Declination or Polar Distance. Longitudinal " Right Ascension.
Ecliptic System.
The Equatorial System and the ...
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In the equatorial system, the Earth's equator and poles are projected outward into space to form a celestial sphere with the Earth at the center. The projection of the Earth's equator onto this sphere is called the celestial equator.
equatorial system (NASA SP-7, 1965) A set of celestial coordinates based on the celestial equator as the primary great circle; usually declination and hour angle or sidereal hour angle.
Figure 4. The equatorial system of celestial co-ordinates, showing the right ascension (RA) and declination (dec) of a star.
galactic ~: is used for studying the structure of the galaxy. It is unlikely to be encountered in dialling.
The latitudinal (latitude-like) angle of the equatorial system is called declination (Dec for short). It measures the angle of an object above or below the celestial equator. The longitudinal angle is called the right ascension (RA for short).
This is one of the equatorial system of co-ordinates and it is measured in hours, minutes and seconds. Right ascension is also the difference in time between the culmination of the Vernal Equinox and the culmination of that object.
First Point of Aries (FPA) The Vernal Equinox point, i.e. that where the centre of the Sun, moving northwards, crosses the equator. It is the reference direction for the equatorial system of co-ordinates.
Hipparchus seems to have used a mix of ecliptic coordinates and equatorial coordinates: in his commentary on Eudoxos he provides the polar distance (equivalent to the declination in the equatorial system) and the ecliptic longitude.
 See also: Equator, Coordinates, Earth, Circle, Astronomy
  
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