References

General Devices

Primarily Heaven Models

Astrolabe (5c BCE) - A device that essentially is a flattened armillary sphere, but the portability and readability that results makes it significantly more useful. Both the observer frame (zenith, horizons, cardinal directions) and the celestial frame (right ascension, declination, ecliptic) are reduced to 2D via a stereoscopic projection, and the plate with the celestial frame (the rete) can be rotated to emulate the earth’s rotation.

Armillary Sphere (4c BCE) - A device with an appearance of a skeletal globe, showing the celestial sphere around a geocentric observer. It typically has fixed rings corresponding to the horizon and cardinal meridians, and collectively moving rings corresponding to the celestial equator, tropics, and ecliptic. At center there is often a small ball representing the earth.

Equatorium (5c)- An instrument similar in appearance to an astrolabe but of different function, instead for calculating the positions of the moon, sun, and planets using the Ptolemaic system of epicycles.

Torquetum (12c)- An astronomical device for both taking angular measurements as well as translating them between horizon, equatorial, and ecliptic coordinates. It was an analog alternative to calculating coordinate transforms from a time where the mathematical understanding of spherical trigonometry was not well developed yet.

Planisphere - The modern equivalent of an astrolabe, often using a azimuthal equidistant rather than stereoscopic projection and a clear plastic constellation map instead of a skeletonized rete.

Astrolabe Quadrant - A reduced functionality astrolabe but more compact, essentially folding the full circle of the astrolabe into one quadrant

Cometarium - A very niche instrument showing the path of a comet around the sun. Due to their highly eccentric orbits the normal approximation of circular and constant speed orbit used in Orreries is not valid, so cometaria require some means of approximating Kepler’s Equation to accelerate the motion at perihelion.

Primarily Time-telling

Farmer’s Ring (15c) - An early, latitude specific sundial in the form of a ring.

Astronomical Rings - A device that aligns at least one ring with either the celestial north pole or the solar maximum to act like a handheld equatorial sundial.

Rectangulus - A specific astronomical measuring/calculating device created by Richard of Wallingford, essentially a specialized Torquetum.

Diptych - An early type of folding sundial with a string gnomon. Often includes a compass to orient it north.

Regiomontanus - A sighting dial with a plumb bob that has a movable pivot point to allow adjustment for different times of year and latitudes. A 2D grid of latitudes and times of year is engraved, and the plumb bob pivot is on the end of an articulating arm to be positioned anywhere on the grid.

Navicula - A sighting dial with a plumb bob that has a movable pivot point to allow adjustment for different times of year and latitudes, shaped like a ship. The plumb bob pivot can be slid up and down the mast for adjusting latitude, and the mast tilted to adjust for time of year.

Nocturnal - A sighting instrument used to tell time at night by aligning a central hole with Polaris and rotating an arm to align with other near-polar stars, such as those in Ursa Major.

Scaphe - An early sundial in the form of a hemispherical bowl, with a vertical gnomon in the center and markings on the interior surface. Also referred to as a hemispherium.

Hemispherium - See Scaphe.

Hemicyclium - A sundial similar to a scaphe/hemispherium, but with the southern side and bottom cut away. The gnomon is also horizontal, projecting from the north side to the center.

Phillipi Dial - A specific type of Greek astronomical ring with ring segments for setting latitude and time of year

Nebra sky disc - A bronze age object of astronomical significance, although not entirely understood.

Pillar Dial - A cylindrical sundial with a horizontal gnomon, which can be rotated based on the time of year. A type of altitude dial.

Shepard’s Dial - See Pillar Dial

Navigation and Angle Measurement

Kamal - An simple and early device (primarily for latitude sailing) consisting of a plank of wood of known length held at a fixed distance from the user’s eye by means of a knotted cord held by the teeth.

Shadow Square - A geometric diagram combined with a sight, used to determine the height of an object. Often included on the back of astrolabes.

Sine Quadrant - Variation of a quadrant, but includes scales for calculation of sine, cosine, and their inverses among a couple less common functions.

Dioptra - The ancient precursor to the modern surveyor’s transit or theodolite, a device having a sight and two angles of adjustment.

Triquetrum - A semi-stationary sighting device for taking altitude measurements, of greater accuracy than the small handheld astrolabe

Backstaff - An instrument for measuring altitude of the sun (or moon) by means of a shadow-casting sight system. It is used with the users back to the sun, thus the name.

Octant - An angle measuring device using a rotating mirror on an arm with an angular scale.. It has a scale of 45 degrees, which (due to the reflection) gives it a measurement range of 90 degrees.

Sextant - A successor to the octant which used a 60 degree scale rather than 45 deg, giving it a measurement range of 120 deg and therefore more appropriate for taking measurements of lunar distance.

Bris Sextant - A modern, compact, and simplified reflecting device showing multiple superimposed images at fixed and known angles.

Quadrant - A device in the form of a sector with sights along one edge and a plumb-bob hanging from the vertex. Allows for measuring angles relative to the gravity vector.

Repeating Circle - A surveying instrument similar to a dioptra except that the angle measurement is taken multiple times with the instrument summing them, the average of which allowing for some cancelling of errors for a better overall measurement.

Reflecting Circle - A variant of the Repeating Circle but using mirrors similar to a sextant or octant

Other

Heliostat - Now largely electronically controlled, mechanically driven heliostats were used in experiments where a beam of sunlight was required to be stationary (counteracting solar motion).

Coelostat - Mechanically similar to a heliostat but different in use, having a larger mirror following the sun but in conjunction with a solar telescope which can then be fixed.

Volvelle - A calculating device for determining the location of the moon, in principle adding its phase to the sun position.

Jovilabe - A simple planetarium of Jupiter and its four largest moons (the Galilean Moons), often meant to be viewed from the side to look as though it would from earth.

Meridian circle - A precision telescope system that only moves about the North-Zenith-South meridian and is used to precisely time objects meridian crossing (culmination)

Equatorial ring - A fixed ring that is tilted to match the latitude of the location, the equinox can be determined when the interior surface is fully shaded during the day.