Celestial Sphere
If one pictures the sphere we call the Earth, enlarged to embrace the visible heavens, the resulting concept can be called the celestial sphere. If it is a true sphere, any circle drawn around it can be termed a circumference. To locate any particular circle as a circumference, implies the selection of some point of reference. The Horizontal System. If your particular location on the Earth is selected as your point of reference, the point directly overhead is the zenith. The opposite point, below the Earth, is the Nadir. At right angles to these is a plane which is called […]