great circle - a circular line on the surface of a sphere formed by intersecting it with a plane passing through the centerecliptic - the great circle representing the apparent annual path of the sun; the plane of the Earth's orbit around the sun; makes an angle of about 23 degrees with the equator; "all of the planets rotate the sun in approximately the same ecliptic" equator - an imaginary line around the Earth forming the great circle that is equidistant from the north and south poles; "the equator is the boundary between the northern and southern hemispheres" celestial horizon, horizon - the great circle on the celestial sphere whose plane passes through the sensible horizon and the center of the Earth hour circle - a great circle on the celestial sphere that passes through both celestial poles line - a spatial location defined by a real or imaginary unidimensional extent line of longitude, longitude, meridian - an imaginary great circle on the surface of the earth passing through the north and south poles at right angles to the equator; "all points on the same meridian have the same longitude" vertical circle - a great circle on the celestial sphere passing through the zenith and perpendicular to the horizon |