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rete: skeletal star map representing the rotation of the heavens on an astrolabe. The rete normally features a projection of the ecliptic and pointers for prominent stars, and can be rotated over a chosen latitude plate. see article on the astrolabe.
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right ascension: angle parallel to the celestial equator, measured eastwards from the spring equinox.
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ring dial: simple form of altitude dial in the shape of a ring, for use in one latitude.
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rule (or ruler): an instrument of multifarious functions in the form of a straight rod of metal, wood or other material; a folding rule is an alternative form with two or more jointed legs.
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Saints' days: anniversary days for Christian saints.
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