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1 to 227 of 227 glossary terms
accessory: used here to refer to any associated parts of an instrument such as tripod base and legs.
age of the moon: number of days that have passed since the previous new moon.
alidade: straight rule with sights. An alidade could be used for surveying with a plane table but it also appears in a different form as part of an astrolabe.
almucantars: lines of equal altitude on a projection of the heavens based on the local horizon.
altazimuth theodolite: theodolite for measuring altitude and azimuth simultaneously, see article on the theodolite.
altitude: angle above and perpendicular to the horizon, or an angular elevation above the horizontal direction in the same azimuth.
altitude dial: sundial measuring time from the altitude of the sun.
armillary sphere: set of rings corresponding to the circles of the celestial sphere, see article on the armillary sphere.
aspectarium: aide-memoire which depicts the astrologically significant angles (or aspects) between the planets.
astrolabe: astronomical instrument based on a planispheric projection of the heavens, see article on the astrolabe.
astrolabe quadrant: quadrant that has many of the lines and functions of the ordinary astrolabe, projected for a single latitude.
astrolabum catholicum: type of universal astrolabe, see article on the astrolabe.
astrological houses: 12-part division of the heavens centred on the celestial pole, also called 'houses of heaven', see article on the astrolabe.
astrological instrument: an instrument whose primary use was for astrological purposes, such as casting horoscopes, rather than for observational astronomy.
astronomical clock: a clock incorporating astronomical instruments such as an astrolabe or armillary sphere.
astronomical compendium: several instruments compiled into one device, see article on the astronomical compendium.
astronomical ring dial: a portable astronomical instrument comprising three circles, one to be aligned with the equator, one with the meridian and the third to indicate right ascension and declination. It can be used for astronomical measurement or for telling the time.
azimuth: the arc of the horizon between the meridian and the great circle passing through the zenith and an observed body.
azimuth dial: sundial depending on measurement of horizontal angles, see article on the sundial.
Babylonian hours: system of hour reckoning, see article on time and date.
baseline: measured distance between two positions used as the observing stations for a triangulation survey; angles measured from this line serve to locate the other points in the survey.
Butterfield dial: type of sundial adjustable for latitude, whose gnomon incorporates a latitude pointer often in the form of a bird. This dial type is associated with the 17th-century Paris-based English maker Michael Butterfield.
calendar: system of reckoning dates, see article on time and date.
calendar-zodiac scale: scales relating the sun's position in the zodiac to the date.
caliper: instrument used to take dimensions. One type has two curved legs whose endpoints are used to determine the diameters of spheres.
Cardan suspension: universal mounting attributed to the 16th-century Italian philosopher and physician Girolamo Cardano which, by means of gimbals, allows the supported part to remain horizontal irrespective of the orientation of the rest of the instrument.
cardinal points: the main directions on the mariner's compass, north, south, east and west.
carpenter's rule: measuring ruler carrying one or more scales for calculating the volume of timber or the surface area of board or planking.
celestial globe: globe marked with the positions of the stars.
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.
celestial poles: diametrically opposite points of the celestial sphere about which the heavens are observed to rotate once a day.
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.
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.
chalice dial: sundial where the hour lines are inscribed on the inside surface of a goblet. A second set of lines can be included to allow for refraction, when the goblet is full. See also scaphe dial.
circumferentor: form of surveying compass with fixed sights, where bearings are read from the position of a magnetic compass, see also article on the theodolite.
climates: division into latitude zones of the part of the earth known to ancient geographers, used by Ptolemy.
clinometer: an instrument for measuring inclination.
common hours: system of hour reckoning, see article on time and date.
compass: instrument indicating directions by a magnetic needle, see article on compass.
compass card: card or paper with a printed, drawn or painted compass rose, usually carried above the magnetic needle of a compass.
compass dial: form of azimuth dial.
compass rose: diagram of the points of the compass, often decorated and coloured. North is usually indicated by a fleur-de-lys.
compasses: instrument for drawing circles. see article on drawing instruments.
compendium: several instruments compiled into one device; also see article on astronomical compendium.
conjunction: two planets having the same position (in longitude) in the ecliptic are said to be in conjunction. This relative position had important astrological significance.
cross-staff: instrument for measuring angles between distant objects, mostly altitudes, see article on cross-staff.
cross-staffs: see article on cross-staff
crucifix dial: form of polyhedral sundial in the shape of a crucifix, see article on sundial.
cylinder dial: type of altitude dial, see article on the sundial.
declination: angle above or below the celestial equator.
declinatory: instrument used in constructing a sundial, to find the declination of a plane.
degrees: the conventional divisions of a circle, one being the 360th part of a circle, and thus the units used to measure and express angles.
diagonals: lines used in the subdivision of divisions of an arc, also known as transversals. Each diagonal line is drawn across the division from its beginning to its end, and is divided linearly either by dots or by concentric arcs. In this way the linear division of a line can be used for the angular subdivision of an arc.
dial: instrument for telling time by the position of the sun (occasionally by the moon), see article on the sundial.
dialling quadrant: instrument in the form of a quadrant used in the construction of a sundial.
diptych dial: type of sundial which, in many cases, could be called an astronomical compendium, in the form of a folding tablet, usually in ivory, with at least a string gnomon and a horizontal dial on the inside, but often with other dials as well.
disc dial: type of sundial belonging in the class of altitude dial.
dividers: instrument with jointed legs for measuring and transferring distances, see article on the dividers.
dominical letter: letter denoting the day of the first Sunday of the year, see article on time and date.
drawing instruments: instruments used for drawing and constructing geometrical figures, see article on drawing instruments.
Easter table: table for calculating the date of Easter, see article on time and date.
ecliptic: line on the celestial sphere representing the annual path of the sun through the stars.
epacts: numbers used in the calculation of Easter, see article on time and date.
equal hours: system of hour reckoning, see article on time and date.
equator: circle on the earth's surface 90 degrees from the poles, or the circle on the celestial sphere 90 degrees from the celestial poles.
equatorial: relating to or based on the equator. Has much the same meaning as equinoctial.
equatorial dial: another name for equinoctial dial.
equatorium: instrument to determine the longitude of one or more of the planets at any given time.
equinoctial: relating to or based on the equator, or relating to the equinox.
equinoctial dial: sundial where the hour plate or circle is set parallel to the equator, see article on the sundial.
equinoctial ring dial: type of sundial, included as an equinoctial dial, comprising two pivoted rings and a bridge for adjusting for solar declination, or of three rings.
equinox: either of two points on the celestial sphere where the equator meets the ecliptic, representing the position of the sun when it is 90 degrees from the poles, or the two dates in the year when the sun is in this position in its annual cycle.
folding rule: see rule.
folding rule and level: a compound instrument combining the functions of both a folding rule and level.
gauging rod: measuring stick, usually with a scale to provide a direct reading of volume, such as the liquid content of a barrel, or the weight of a cannonball.
geographical astrolabe: form of astrolabe, where the lower plate is projected for the earth, while the rete includes the ecliptic.
geographical planisphere: map of the earth, produced by geometrical projection of a sphere on to a flat surface. Included as the more prominent part of the geographical astrolabe.
geometrical square: form of quadrant, with sides divided equally and having an alidade at one corner, used for measuring angles in terms of ratios in the manner of a shadow square on the back of an astrolabe.
globe dial: form of sundial, where the hour lines are on the outer surface of a sphere.
gnomon: the part of a sundial that casts the shadow for indicating the time.
golden numbers: numbers denoting the positions of years in the lunar cycle, see article on time and date.
graphometer: type of surveying instrument, see article on the graphometer.
gunner's caliper: a instrument used to take dimensions in gunnery, such as the diameter of cannons and projectiles.
gunner's compendium: an instrument combining several functions required by the gunner, often incorporating the gunner's sight and gunner's level, along with additional elements.
gunner's folding rule: a folding rule carrying tables or scales specially adapted for the use of gunners.
gunner's gauge scales: scales which provide the weight of a sphere (the shot) from a measurement of its diameter; in gunnery these scales were traditionally provided for iron, lead and stone.
gunner's level: instrument used to set the elevation of a large gun, see article on the gunner's sight and level.
gunner's rule: see rule.
gunner's sight: instrument used to elevate and aim a large gun, see article on the gunner's sight and level.
gunner's sight and level: instrument used to set a large gun to the horizontal, or to elevate and aim it on a target, see article on the gunner's sight and level.
gunnery instrument: see gunner's compendium.
hodometer: device for measuring distance by means of a wheel, pushed along the ground, attached to a geared movement with a dial or other form of distance register.
horary quadrant: quadrant used to tell the time, usually from a measure of solar altitude, see article on the quadrant.
horizon obliquus: line denoting the local horizon on an astrolabe latitude plate, see article on the astrolabe.
horizon rectus: east-west line on an astrolabe latitude plate, see article on the astrolabe.
horizontal dial: sundial where the hour lines are marked on a horizontal surface, see article on the sundial.
hour lines: the time divisions on a sundial or other astronomical instrument.
hour ring: the part of a sundial marked with the time divisions, where this part is in the form of a ring or broken ring.
inclining dial: type of sundial projected as a horizontal dial for a particular latitude, but which can be inclined for use in a range of other latitudes.
Italian hours: system of hour reckoning, see article on time and date.
Jacob's staff: name for a cross-staff, especially when used for surveying, see article on the cross-staff.
Julian calendar: calendar introduced by Julius Caesar and used in Europe until the sixteenth century, or later, see article on time and date.
latitude: angle above or below the equator to indicate position on the earth. The celestial latitude, however, is an angular distance with respect to the ecliptic.
latitude plate: part of an astrolabe with a projection of altitude and azimuth lines on to the equatorial plane, see article on the astrolabe.
latitude projections: projection of altitude and azimuth lines on to the equatorial plane, see article on the astrolabe.
level: name for different types of instrument used in surveying for determining the horizontal direction and differences in height, and in gunnery and elsewhere for adjusting something to the horizontal. See also gunner's level.
level and sight: instrument used to set a large gun to the horizontal, or to elevate and aim it on a target, see article on the gunner's sight and level.
limb: the outermost part or edge of a circular or part-circular instrument carrying a scale, usually divided in degrees.
longitude: angle parallel to the equator to indicate position on the earth. The celestial longitude, however, is an angular distance parallel to the ecliptic.
lunar dial: dial where the shadow is cast by moonlight instead of sunlight, see article on the sundial.
lunar volvelle: volvelle indicating the age of the moon, which typically converts between the time indicated by the shadow of the moon on a sundial and solar time.
magic square: square grid with a number in each cell for which the sum of each row, column and diagonal is the same.
magnetic compass: instrument indicating directions by a magnetic needle, see article on the compass.
magnetic deviation: the angle between geographical north and the direction indicated by a compass needle.
magnitudes: numbers in a scale of the relative brightnesses of the stars, 1 being the brightest.
mariner's astrolabe: altitude-measuring instrument for finding latitude at sea, having a heavy brass or bronze ring, suspended by a shackle and ring, with a degree scale and a centrally-pivoted alidade.
mater: part of an astrolabe, see article on the astrolabe.
mathematical compendium: compound instrument for performing various functions in practical mathematics.
mathematical instruments: collections of instruments of assorted kinds for performing functions in practical mathematics.
measuring rod: an instrument used to measure distances or depths. See also gauging rod.
measuring rods: see measuring rod.
meridian: the plane containing the observer and both celestial poles, or containing the observer, the zenith and the pole, or, more colloquially, the north-south line at a particular position on the earth.
meridian circle: circular scale of degrees which in use is aligned with the meridian.
mining instruments: in this period mining instruments were principally for surveying, adapted for the special conditions of working underground in mines.
nautical circle: generic term for a circular mathematical instrument of use in navigation, but likely to carry a range of mathematical and astronomical scales.
nautical hemisphere: a combination of graduated arcs and circles used for navigational calculations, see article on the nautical hemisphere.
navicula dial: type of altitude dial in the shape of a ship.
nocturnal: instrument for finding the time at night from the orientation of the stars, see article on the nocturnal.
nocturnal and quadrant: compound instrument which combines both the functions of a nocturnal and quadrant, usually on two different sides of the same instrument, with equal importance given to each.
nocturnal and sundial: compound instrument which combines both the functions of a nocturnal and sundial, usually on two different sides of the same instrument, with equal importance given to each.
nonius: a way of subdividing a quadrant of a circle to provide fine discrimination of parts of degrees, comparable in purpose to the later vernier scale. The name comes from the latinized surname of the 16th-century Portuguese mathematician Pedro Nu?ez.
Nuremberg hours: system of hour reckoning, see article on time and date.
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.
simple theodolite: surveying instrument for measuring horizontal angles, see article on the theodolite.
sinical quadrant: a quarter of a circle with a scale of degrees at its circumference which carries a pattern of criss-crossing vertical and horizontal lines. The ratio of the length of a given line to the quadrant's radius gives the sine or cosine of the corresponding angle.
solar time: time measured directly from the position of the sun, see article on the sundial.
solstice: either of two points on the ecliptic where the sun achieves its maximum declination. The term also refers to the two dates when the sun reaches this position in its annual cycle. The winter solstice corresponds to the shortest day, the summer solstice to the longest. Near these points the sun's declination changes only slowly, hence the etymological meaning of solstice as 'standing sun'.
star pointer: point marking the position of a star, see article on the astrolabe.
string gnomon: the part of a sundial which casts the shadow, where this part is in the form of a taut string.
sun and moon dial: sundial that can also tell the time from the shadow cast by the moon, see article on the sundial.
sundial: instrument of many different forms for finding the time from the position of the sun, usually by measuring the position of a shadow, see article on the sundial.
sundial and dividers: a compound instrument combining the functions of both a sundial and dividers.
surveying and gunnery instrument: compound instrument combining functions required in the closely-associated fields of surveying and gunnery, such as measuring bearings and finding ranges.
surveying compass: magnetic compass with fixed sights used for measuring horizontal bearings by magnetic azimuth. See also circumferentor.
surveying instrument: surveyors used instruments to take bearings, elevations, distances and other associated measures, as well as, for example, laying out plans and drawing topographical surveys. Included are such instruments as the surveying compass, surveying quadrant, surveying rod, surveying staff, surveyor's cross, surveyor's line, surveyor's square and theodolite. Surveying instruments also include compound instruments embodying several such functions.
surveying instruments: see surveying instrument.
surveying quadrant: quadrant used for land surveying, usually for measuring altitude and azimuth.
surveying rod: an instrument used by surveyors for taking distances and other associated measurements.
surveying staff: an instrument used in surveying to measure elevations.
surveying staffs: see surveying staff.
surveyor's cross: instrument for establishing right-angled lines of sight, by means either of open sights set at the ends of an equal-arm cross or slits in a cylinder.
surveyor's line: a long string or rope used to measure distances for surveying.
surveyor's square: another name for a surveyor's cross.
theodolite: surveying instrument for measuring horizontal angles, and perhaps vertical angles, see article on the theodolite.
theodolite and sundial: an instrument combining the functions of a sundial and a theodolite.
throne: part of an astrolabe, connecting the instrument to the suspension shackle, see article on the astrolabe.
triangulation: surveying technique involving the measurement of a baseline, the location of other stations by taking angles from either end, and perhaps the extension of the survey through the addition of further triangles.
triangulation instrument: instrument with three jointed arms with scales for surveying or range-finding, see article on the triangulation instrument.
trigonus: triangular element in the type of altitude dial known as the 'organum Ptolemai'.
tripod base: base of a tripod (three-legged support) on which to stand an instrument.
tripod legs: legs of a tripod (three-legged support) on which to stand an instrument.
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'.
wegweiser: a circle marked with the points of the compass and a rotating index.
wind names: a nomenclature for dividing an azimuth circle into degrees, where eight 45-degree scales are allocated to eight traditional named winds of the Mediterranean.
wind rose: type of compass rose, where the directions are indicated by the names or initials of the traditional winds of the Mediterranean. May also refer to a whole instrument serving only to indicate the names of the wind directions.
wind vane: flag-like vane mounted on a vertical post free to align itself with, and indicate the direction of, the wind. Also an instrument performing the same function.
zenith: the point on the celestial sphere directly above the observer.
zodiac: a band of 12 constellations of stars straddling the ecliptic; the ecliptic and zodiac are conventionally divided into these constellations, 30 degrees being allocated to each.
zodiacal calendar: pair of circular scales, one of the signs and degrees of the zodiac, the other of the days and months of the year, which yields the date of the sun's position in its annual cycle. Commonly included on the back of an astrolabe.
zodiacal sign: one of the star constellations included in the zodiac.
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