Post-concussion syndrome. Post-concussion syndrome, also known as postconcussive syndrome or PCS, is a set of symptoms that may continue for weeks, months, or a year or more after a concussion â a mild form of traumatic brain injury (TBI).
The Equatorial (Celestial) Coordinate System. Equatorial coordinates, also called simply celestial coordinates, are the standard coordinate system for the sky. It is meant for the fixed sphere of the stars within which the Earth and Sun move.
In astronomy, the celestial equator is the great circle in which the plane of the terrestrial Equator intersects the celestial sphere; it consequently is equidistant from the celestial poles. When the Sun lies in its plane, day and night are everywhere of equal length, a twice-per-year occurrence known as equinox.