The triquetrum (derived from the Latin tri- ("three") and quetrum ("cornered")) was the medieval name for an ancient astronomical instrument first described by Ptolemy in the Almagest (V. 12). Also known as Parallactic Rulers, it was used for determining altitudes of heavenly bodies. Ptolemy calls it a "parallactic instrument" and seems to have used it to determine the zenith distance and parallax of the Moon.[1][2]
It performed the same function as the quadrant and was devised to overcome the difficulty of graduating arcs and circles. It consisted of a vertical post with a graduated scale and two pivoted arms hinged at the top and bottom, the upper arm carrying sights. The two arms were joined so that their ends could slide. As a person sighted along the upper arm, the lower one changed its angle. By reading the position of the lower rod, in combination with the vertical length, the zenith distance (or, alternatively, the altitude) of a celestial object could be calculated.[1][3]
The triquetrum was one of the most popular astronomical instruments until the invention of the telescope, it could measure angles with a better precision than the astrolabe.[2] Copernicus describes its use in the fourth book of the De Revolutionibus under the heading "Instrumenti parallactici constructio."[2] The instrument was also used by Tycho Brahe.[4]
A scratch-built version of the device is used by the title character of the 1967 cult series The Prisoner, in the episode "The Chimes Of Big Ben". The scene in which the triqetrum is shown is, however, only present in an alternate pre-release cut of the episode. This version of "Chimes" is readily available on VHS, DVD and Blu-Ray sets of the series.
Notes
- ^ a b Kelley, D., Milone, E., (2005), Exploring Ancient Skies: An Encyclopedic Survey of Archaeoastronomy, pages 77-79. Birkhäuser.
- ^ a b c Gassendi, P., Thill, O., (2002) The Life of Copernicus (1473-1543), pages 118-120. Xulon Press.
- ^ Krebs, R., (2004), Groundbreaking Scientific Experiments, Inventions, and Discoveries of the Middle Ages and the Renaissance, page 225. Greenwood Publishing Group.
- ^ Christianson, J., (2000), On Tycho's Island: Tycho Brahe and His Assistants, 1570-1601, pages 73-75. Cambridge University Press.
|
||||||||||||||||||||
 |
This astronomy-related article is a stub. You can help Wikipedia by expanding it. |
 |
This Ancient Greece-related article is a stub. You can help Wikipedia by expanding it. |
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
