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How do the horizon, galactic, ecliptic, and equatorial coordinate systems differ?
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Astronomical map
Star trails over banksia trees, in Gippsland, Vic., Austl. The south celestial pole, located in the constellation Octans, is at the centre of the trails.
To pinpoint the position of a celestial object on an astronomical map, astronomers use various celestial coordinate systems. These systems differ primarily based on their reference planes and points of origin:
- Horizon System: This system is based on the observer's local horizon. Its coordinates are altitude and azimuth, which change depending on the observer's specific location on Earth and the time of observation.12
- Equatorial System: This system is based on the celestial equator and poles, which are projections of Earth’s equator and poles into the sky. It uses right ascension and declination, which are analogous to terrestrial longitude and latitude.134
- Ecliptic System: This system is measured relative to the ecliptic, which is the plane of Earth's orbit around the Sun.15
- Galactic System: This system is used to map the Milky Way Galaxy. It uses galactic latitude and longitude, measured relative to the Galaxy's fundamental plane of symmetry, with the zero point of longitude aligned toward the galactic centre.6