Great circle.A circle that passes through the center of the sphere and divides the sphere into two equal parts
Celestial equatorThe intersection of the earths equatorial plane and the celestial sphere.
Vernal equinoxThe point where the sun crosses the celestial equator on its journey from south to north.
Autumnal equinoxThe point where the sun crosses the celestial equator on its journey from north to south.
AzimuthThe angle moving east along the celestial horizon from the north point to the vertical circle passing through the object.
Celestial horizonIts the great circle perpendicular to gravitatoinal direction and coinciding to the observer's line of sight.
Celestial meridianThe imaginary circle passing through the observers zenith and intersecting the north and south points.
Declination.The angle between the object and the celestial equator along an hour circle.
Diurnal motionThe apparent daily motion of celestial bodies around the north celestial poles as a result of the earths rotation.
EclipticThe apperent path of the sun on the celestial sphere.