equator

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equator Name given to two imaginary circles. The terrestrial Equator lies midway between the North Pole and South Pole and is the zero line from which latitude is measured. It divides the Earth into the Southern and Northern Hemispheres. The celestial equator lies directly above the Earth's Equator, and is used as a reference to determine the position of a star using the astronomical co-ordinate system of right ascension and declination.

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