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210 to 219 of 227 glossary terms
tropic of Capricorn: line of geographical latitude and corresponding line of declination coinciding with the sun's position at the autumnal equinox, its most southerly position in the sky.
tympanum: Latin name (plural tympana) for a latitude plate of an astrolabe.
unequal hours: system of hour reckoning, see article on time and date.
universal dial: a sundial that can be used in any latitude.
universal projection: a type of projection of the celestial sphere appropriate for use in any latitude.
vane: upright piece, in this context usually forming a sight and often pierced with a pinhole, a slit, or a slot with a vertical wire.
vertical dial: sundial where the hour lines are marked on a vertical surface, see article on the sundial.
vertical disc dial: sundial where the hour lines are marked on a vertical surface in the form of a disc, see article on the sundial.
volvelle: a device which rotates; usually referring to one or more discs which turn within a circular scale.
wedge: the part of an astrolabe which secures the pin; also called the 'horse'.
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