Celestial Coordinates

amateur  astronomy series #4

Coordinate systems can specify a position in 3-dimensional space, for specifying positions of celestial objects: satellites, planets, stars, galaxies, and so on......are analogous to the geographic coordinate system used on the surface of the Earth, with the same fundamental (x,y) plane and primary (x-axis) direction. Each coordinate system is named for its choice of fundamental plane.

A star's galactic (yellow), ecliptic (red) and equatorial (blue) coordinates, as projected on the celestial sphere. Ecliptic and equatorial coordinates share the vernal equinox (magenta) as the primary direction, and galactic coordinates are referred to the galactic center (yellow). The origin of coordinates (the "center of the sphere") is ambiguous

The Coordinate systems in use:

1. Equatorial Coordinates:

Declination (latitude): +90°, -90°

Right Ascension (longitude): hours, minutes, seconds

2. The Horizontal Coordinate System uses the observer's horizon as the plane of reference.

Altitude: angular measure of an object above the horizon.

Azimuth: being measured westward around the horizon from north.

3. Ecliptic Coordinates are based upon the plane of the Ecliptic and uses the measure of,

Celestial Latitude (Ecliptic Latitude): is measured in degrees north and south of the ecliptic.

Celestial Longitude (Ecliptic Longitude) is measured in degrees eastward along the ecliptic from the first point of the Aries.

4. galactic Coordinate System takes the plane of the Galaxy and the Galactic Center (RA 17h 46m dec -28° 56') as it's reference points.

Galactic Latitude is measured from 0° at tghe Galactic Equator to 90° at tghe Galactic Pole, while

Galactic Longitude is measured from 0° to 360° eastwards along the Galactic Equator.

Summary of the main Coordinate systems:

• 1 Coordinate systems
  • 1.1 Horizontal system
  • 1.2 Equatorial system
  • 1.3 Ecliptic system
  • 1.4 Galactic system
  • 1.5 Supergalactic system

Notation

• Horizontal coordinates

• A - azimuth
• a - altitude

• Equatorial coordinates

• α - right ascension
• δ - declination
• h - hour angle

• Ecliptic coordinates

• λ - ecliptic longitude
• β - ecliptic latitude

• Galactic coordinates

• l - galactic longitude
• b - galactic latitude

• Miscellaneous

• λ_o - observer's longitude
• φ_o - observer's latitude
• ε - obliquity of the ecliptic
• θ_L - local sidereal time
• θ_G - Greenwich sidereal time

Coordinate system [1]	Center point (Origin)	Fundamental plane (0º vertical)	Poles	Coordinates		Primary direction (0º horizontal)
				Vertical	Horizontal
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) / center of the Sun (heliocentric)	celestial equator	celestial poles	declination (δ)	right ascension (α) or hour angle (h)	vernal equinox
Ecliptic		ecliptic	ecliptic poles	ecliptic latitude (β)	ecliptic longitude (λ)
Galactic	center of the Sun	galactic plane	galactic poles	galactic latitude (b)	galactic longitude (l)	galactic center
Supergalactic		supergalactic plane	supergalactic poles	supergalactic latitude (SGB)	supergalactic longitude (SGL)	intersection of supergalactic plane and galactic plane

*Note: all pictures thankfully shared from various sources..