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Celestial Sphere An imaginary sphere surrounding the Earth, concentric with the Earth's center. Collimation The act of putting a telescope's optics into perfect alignment. D - Declination (DEC) The angular distance of a celestial body north or south of the celestial equator. It may be said to correspond to latitude on the surface of the Earth. E - Ecliptic The projection of the Earth's orbit on to the celestial sphere. It may also be defined as "the apparent yearly path of the Sun against the st