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.
The celestial sphere is an imaginary sphere with the earth at its center. The sky overhead is the half of the sphere we see from earth, appearing as a dome (even though the sky extends infinitely into space). The other half of the sphere is below the circle of the horizon.