Spherical astronomy

imaginary sphere of arbitrarily large radius, concentric with the observer

in astronomy, angular separation between the Sun and a planet, with the Earth as a reference point

thumb| Upper (oK) and lower culmination (uk) thumb|Method of observation of culminations in ancient Egypt In observational astronomy, culmination is the passage of a celestial object (such as the Sun, the Moon, a planet, a star, constellation or a deep-sky object) across the observer's local meridian. These events are also known as meridian transits, used in timekeeping and navigation, and measured precisely using a transit telescope.

geometry of the two-dimensional surface of a sphere

star that never sets

branch of astronomy about the celestial sphere

the equinox on the earth when the Sun appears to leave the southern hemisphere and cross the celestial equator

the equinox on the earth when the Sun appears to leave the nothern hemisphere and cross the celestial equator

point on the surface of a planet where the sun's rays strike the planet exactly perpendicular to its surface

aspect of a heavenly body in which it makes a right angle with the direction of the Sun

constellation that never set from the viewer's perspective

imaginary point on the celestial sphere exactly opposite the Sun from the viewpoint of an observer

plane used to define orbital elements

Moon stops moving north or south

Spherical triangle used in astronavigation