great circle
intersection of the sphere and a plane which passes through the center point of the sphere
equator
great circle that divides a spheroid into northern and southern hemispheres, particularly that line for the planet Earth
vertical circle
optical instrument used to measure angles
ecliptic
apparent path of the Sun on the celestial sphere
celestial meridian
great circle passing through the celestial poles, the zenith, and the nadir of a particular location
lunar mansion
segment of ecliptic through which Moon passes in its orbit around Earth