Math: A system for locating each point in space by a set of numbers. Astro: Values in a reference system used to relate the position of a body on the
celestial sphere. Four main coordinate systems are utilized in astronomy: the
equatorial, horizontal, ecliptic, and galactic coordinates systems.

An astronomical → coordinate system for indicating
the positions of → celestial objects on the
→ celestial sphere. The system consists of two components,
→ right ascension and → declination.
Right ascension is the angle between the → vernal equinox
and the point where the → hour circle intersects the
→ celestial equator. The right ascension is
always measured eastward from the vernal equinox, in the units of hours, minutes, and seconds.
Declination is the angle between the celestial
equator and the position of the star measured along the star's hour circle.
It is measured in degrees, minutes, and
seconds north or south of the celestial equator.
By definition, the vernal equinox is located at right ascension 0h and
declination 0°. Equatorial coordinates change with time due to the
→ precession of the Earth's → rotation axis.

A → ccordinate system on the surface of the Earth that defines
every location by a set of numbers and letters, indicating the
→ latitude and → longitude.

The coordinate system based on the position of the observer. The horizontal plane
is the fundamental plane and the coordinates are
→ altitude and → azimuth.

A spherical → coordinate system in which the
→ equator is the → supergalactic plane.
Supergalactic longitude, SGL, is measured → counterclockwise
from direction l = 137.37 deg, b = 0 deg (between 0 and 360
deg). The zero point for supergalactic longitude is defined by the intersection of
this plane with the → Galactic plane.
In the → equatorial coordinate system
(J2000) this is approximately 2.82 h, +59.5 deg.
Supergalactic latitude, SGB, is measured from the supergalactic plane,
positive northward and negative southward.
The North Supergalactic Pole (SGB=90 deg) lies at galactic coordinates
l = 47.37 deg, b = +6.32 degrees, corresponding to the equatorial coordinate
system (J2000) 18.9 h, +15.7 deg.