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133 to 181 of 227 glossary terms
octant: the eighth part of a circle or an instrument measuring up to 45 degrees.
old quadrant: type of horary quadrant, see article on the quadrant.
opposition: two planets 180? from each other in the ecliptic are said to be in opposition. This relative position had important astrological significance.
ordinary hours: system of hour reckoning, see article on time and date.
orthographic planisphere: flat map produced by orthographic projection.
pedometer: device worn by a walker to measure distance by counting paces.
pendant sundial: a form of sundial suspended by a cord and possibly hung around the neck.
perpetual calendar: calendar covering a number of years, see article on time and date.
phase of the moon: the changing appearance of the moon throughout its approximately monthly cycle, from the thin crescent of new moon to the complete circle of full moon and back again.
pillar dial: type of altitude dial, see article on the sundial.
pin gnomon: the part of a sundial which casts the shadow, where this part is in the form of a pin.
plane table: type of surveying instrument, see article on the plane table.
plane table alidade: an alidade specially adapted for use with a plane table.
planetary hours: system of hour reckoning, see article on time and date.
planetary temperaments: astrological character of the fixed stars; as assigned in classical astrology, each star had a nature and effect similar to one or more of the planets.
planisphere: a representation of a spherical body on a flat surface, commonly a map of the earth or of the heavens.
planispheric astrolabe: astronomical instrument based on a planispheric projection of the heavens, see article on the astrolabe.
plate: part of an astrolabe with a projection of altitude and azimuth lines on to the equatorial plane, see article on the astrolabe.
plumb level: device for determining a horizontal level or an angle of elevation by a plumb line or plummet.
plumb line: a suspended thread with a weight at its end, indicating the vertical.
plummet: a form of plumb line in which the 'line' and weight are a single rigid piece.
polar dial: type of sundial, see article on the sundial.
polyhedral dial: sundial with hour lines on various faces of a solid figure, see article on the sundial.
prime vertical: celestial great circle passing through the east and west points and the zenith.
primum mobile: instrument for finding the sines and versed signs of angles, see article on the primum mobile.
projection: translation of a figure on to a plane or curved surface using straight lines in a systematic way. For example, a spherical surface can be projected on to a plane (the plane of projection) by means of straight lines drawn from all points on the surface to a certain defined point (the point of projection) and marking where they intersect the plane. In a stereographic projection, such as is used for the ordinary astrolabe, points on a containing circle are projected on to an equatorial plane from one pole; in an orthographic projection, such as is used in a Rojas design of universal astrolabe, the point of projection is at infinity and the projection lines are parallel.
proportional compasses: drawing instrument consisting of two legs each with points at either end; used for transferring dimensions in enlarged or reduced ratio.
proportional dividers: drawing instrument consisting of two legs each with points at either end; used for transferring dimensions in enlarged or reduced ratio.
proportional instrument: unusual instrument used to mechanically perform functions in trigonometry.
protractor: instrument for setting out and measuring degrees.
quadragesima: the 40 days of Lent or the first Sunday in Lent.
quadrans vetus: type of horary quadrant, see article on the quadrant.
quadrant: instrument based on a quarter of a circle, see article on the quadrant.
quadratum nauticum: diagram for finding course directions from latitudes and longitudes, see article on the astrolabe.
quatrefoil: decorative form with four leaves or petals.
radio latino: instrument for measuring angles in surveying and gunnery, see article on the radio latino.
ramming rods: long rods, often in wood, intended for use in gunnery and used to push the projectile inside a cannon, or to compress the powder in an arquebus.
reduction compass: a drafting instrument with two pivoting arms which sits parallel to a drawing surface, held up by its fixed points. The arms have no scales but can be divided at any given position by moveable points.
Regiomontanus-type dial: design of portable altitude dial adjustable for any latitude.
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.
right ascension: angle parallel to the celestial equator, measured eastwards from the spring equinox.
ring dial: simple form of altitude dial in the shape of a ring, for use in one latitude.
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.
Saints' days: anniversary days for Christian saints.
scaphe dial: sundial where the hour lines are marked on a concave hemisphere or part hemisphere.
sector: calculating instrument using pairs of lines on the faces of two hinged arms, see article on the sector.
sexagenarium: an instrument in the form of a volvelle for planetary calculations.
shadow square: a form of geometrical quadrant, where two sides of a square are divided into equal parts and a plumb line or alidade from the opposite corner is used for measuring angles in terms of ratios (that is, tangents). Where a plumb line is used, one side has a pair of fixed sights. The name comes from the fact that a measurement of the altitude of the sun, expressed as a ratio, applied to the length of the shadow cast by an upright structure, yields its height. See also under astrolabe.
sight: a device through which an object of interest can be viewed. Sights appear on surveying and astronomical instruments and in a more specialised form in the gunner's sight.
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