The coordinate system based on the position of the observer. The horizontal plane is the fundamental plane and the coordinates are altitude and azimuth.
The angle under which the radius of the Earth at the place of observation would be seen from a celestial body when it is in the horizon (at the instant of rising or setting). The amount varies with th
e latitude since the Earth is not exactly spherical, and is greatest at equator.
A pointed, mountain peak, typically pyramidal in shape, bounded by the walls of three or more cirques. Headward erosion has cut prominent faces and ridges into the peak. When a peak has four symmetric
al faces, it is called a Matterhorn.