Torquetum

The torquetum or turquet is a medieval astronomical instrument designed by persons unknown to take and convert measurements made in three sets of coordinates: horizon, equatorial, and ecliptic.

Its invention has been credited to multiple figures, including Jabir ibn Aflah, Bernard of Verdun and Franco of Poland.

[2] Jabir ibn Aflah of Al-Andalus in the early 12th century has been assumed by several historians to be the inventor of the torquetum, based on a similar instrument he described in his Islah Almajisti.

The astronomer, Peter of Limoges, used this device for his observation of what is known today as Halley's Comet at the turn of the 14th century.

Additionally, Johannes Schoner built a torquetum model for his own personal use in the observation of Halley's Comet in the 1500s.

In his book Astronomicum Caesareum (1540), Apian gives a description of the torquetum near the end of the second part.

[7] The torquetum is a complex medieval analog computer that measures three sets of astronomical coordinates: the horizon, equatorial, and ecliptic.

However, it is a device that requires a thorough understanding of the components and how they work together to make relative positional measurements of certain celestial objects.

The base starts with the tabula orizontis, which is the bottommost rectangular piece in contact with the ground, and this component represents the horizon of the Earth, relative to the point of measurement.

This angle of rotation is created by the stylus, which is an arm mechanism that pins to the slotted holes, which are part of the tabula orizontis.

The midframe of the torquetum consists of a free-spinning disk (unnamed) that can be locked into place, and the tabula orbis signorum, directly hinged to it above.

Similarly, on the outer edge of the tabula orbis signorum is a zodiacal calendar and degree scale, with each of the 12 signs divided amongst it.

The user can now measure altitude of the target celestial body as well as use the base as a compass for viewing the possible paths they travel.

These three differing configurations allowed for added convenience in taking readings and made once tedious and complicated measuring more streamlined and simple.