The celestial sphere is a device used to represent the direction of celestial objects for observation. For example, someone in Beijing would see the Moon’s position a little differently from someone in Hong Kong, due to parallax of the observing locations. Therefore, it only make sense to have a different celestial sphere for each for observer. Another example is the satellite or space station, which, due to there close distance from Earth, depends greatly on the location of the observer.
Where is the Center of Celestial Sphere?
