day-night terminator

autumnal equinox, vernal equinox, celestial coordinate systems,communications satellites, day-night terminator,Earth, Earth shadow, Earth-Moon barycenter, eclipse seasons,ecliptic, ecliptic longitude, geostationary orbit, geosynchronous equatorial orbit, Navaratri, Nowruz, solstice, subsolar point, Sun,

Autumnal Equinox: What Makes Today Special?