ce·les·tial sphere
səˈlesCHəl sfir/
An imaginary sphere of arbitrarily large radius, centered on Earth, onto which all celestial objects are projected for observational and mathematical purposes.
In astrology and astronomy, the celestial sphere serves as a useful model for mapping the positions of the Sun, Moon, planets, and stars as if they were located on its surface. It provides the framework for key reference circles such as the celestial equator, the ecliptic, and the horizon. Astrologers rely on the celestial sphere to define coordinates (right ascension, declination, altitude, azimuth) and to visualize planetary movement relative to Earth. Though not a physical object, the celestial sphere remains a fundamental tool for chart construction, spherical astronomy, and understanding the apparent motions of the heavens.
Source: Cindy McKean