a spatial location defined by a real or imaginary unidimensional extent

the great circle on the celestial sphere midway between the celestial poles

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

an imaginary line around the Earth forming the great circle that is equidistant from the north and south poles

the great circle on the celestial sphere whose plane passes through the sensible horizon and the center of the Earth

a great circle on the celestial sphere that passes through both celestial poles