Definition:Astronomical Triangle

Definition
Let $P$ be a point on the celestial sphere $\CC$.

Consider the following $3$ great circles on $\CC$:


 * the great circle between $P$ and the zenith


 * the great circle between $P$ and the north celestial pole


 * the great circle between the zenith and the north celestial pole.

The spherical triangle formed by these $3$ great circles is called the astronomical triangle $P$.