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cardinal points: the main directions on the mariner's compass, north, south, east and west.
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carpenter's rule: measuring ruler carrying one or more scales for calculating the volume of timber or the surface area of board or planking.
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celestial globe: globe marked with the positions of the stars.
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celestial planisphere: map of the heavens, produced by geometrical projection of a sphere on to a flat surface. A common example of the use of a form of planisphere is the rete of an astrolabe.
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celestial poles: diametrically opposite points of the celestial sphere about which the heavens are observed to rotate once a day.
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celestial sphere: sphere in the heavens on which the celestial motions are considered to be moving for the purpose of positional measurements from earth. It is far enough away for the earth's size to be negligible in relation to the distance of the stars, so that all observers can be considered to be at the centre of the celestial sphere.
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celestial spheres: system of concentric, rotating orbs centred on the earth, proposed by Aristotle and others as constituting the physical construction of the heavenly system of planets and stars.
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