S: (n) horizon, view, purview (the range of interest or activity that can be anticipated) "It is beyond the horizon of present knowledge"
S: (n) horizon (a specific layer or stratum of soil or subsoil in a vertical cross section of land)
S: (n) horizon, celestial horizon (the great circle on the celestial sphere whose plane passes through the sensible horizon and the center of the Earth)
S: (n) ecliptic (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"
S: (n) 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"
S: (n) horizon, celestial horizon (the great circle on the celestial sphere whose plane passes through the sensible horizon and the center of the Earth)
S: (n) hour circle (a great circle on the celestial sphere that passes through both celestial poles)
S: (n) meridian, line of longitude (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"
S: (n) vertical circle (a great circle on the celestial sphere passing through the zenith and perpendicular to the horizon)