Before revision: the equatorial coordinate system uses the celestial equator; the ecliptic coordinate system uses the ecliptic; the galactic coordinate system uses the Milky Way; and the horizontal coordinate system uses the observer's horizon .
After revision: the equatorial coordinate system uses the celestial equator; the ecliptic coordinate system uses the ecliptic; the galactic coordinate system uses the Milky Way; the horizontal coordinate system uses the observer's horizon