Astronomical Coordinate Converter

Convert between different astronomical coordinate systems including Equatorial (RA/Dec), Horizontal (Alt/Az), Ecliptic, and Galactic coordinates. Essential for astronomy, astrophotography, and celestial observations.

Input Coordinates

Input Coordinate System:

Equatorial Coordinates (J2000)

Right Ascension (RA):

h m s

Declination (Dec):

° ′ ″

Horizontal Coordinates

Altitude (Alt):

Azimuth (Az):

Observer Location (Required for Alt/Az)

Latitude: North is positive, South is negative

Longitude: East is positive, West is negative

Date & Time (UTC):

Ecliptic Coordinates (J2000)

Ecliptic Longitude (λ):

Ecliptic Latitude (β):

Galactic Coordinates

Galactic Longitude (l):

Galactic Latitude (b):

Converted Coordinates

Enter coordinates and click Convert Coordinates to see results in all coordinate systems.

About Coordinate Systems

Equatorial (RA/Dec)

Right Ascension & Declination: The most common celestial coordinate system. Fixed relative to the stars, independent of observer location. RA measures eastward along the celestial equator, Dec measures north/south from the equator.

Use: Star catalogs, telescope pointing, deep-sky observation.

Horizontal (Alt/Az)

Altitude & Azimuth: Observer-centric coordinates. Altitude is angle above the horizon (0°-90°), Azimuth is compass direction (0°-360°, North = 0°). Time and location dependent.

Use: Visual observing, altitude-azimuth telescope mounts, visibility planning.

Ecliptic (λ/β)

Ecliptic Longitude & Latitude: Based on the plane of Earth's orbit around the Sun. Longitude (λ) measures along the ecliptic, latitude (β) measures perpendicular to it.

Use: Solar system objects, planetary positions, eclipses.

Galactic (l/b)

Galactic Longitude & Latitude: Referenced to the plane of the Milky Way galaxy. The galactic center is at l = 0°, b = 0°. Useful for studying galactic structure.

Use: Galactic astronomy, stellar populations, interstellar matter studies.

Important Notes

Epoch: Equatorial, Ecliptic, and Galactic coordinates use J2000.0 epoch (January 1, 2000, 12:00 TT).
Precision: All conversions maintain sub-arcsecond precision suitable for most applications.
Horizontal Coordinates: Alt/Az conversions require observer location (latitude, longitude) and observation time (UTC). These coordinates change continuously as the Earth rotates.
Coordinate Ranges: RA (0h-24h), Dec (±90°), Alt (±90°), Az (0°-360°), λ (0°-360°), β (±90°), l (0°-360°), b (±90°).
Atmospheric Refraction: Not applied. True geometric positions are calculated. For observed positions, apply atmospheric refraction corrections separately.
Proper Motion: Not included. For precise work with moving objects, account for proper motion from J2000.0 to observation epoch.