Sine quadrant
This article needs additional citations for verification. (September 2021) |
A sine quadrant (
The sine quadrant was described by
Description
The instrument is a quarter of a circle made of wood or metal (usually
At the apex—where the two graduated straight sides of the grid pattern meet in a right angle—is a thin cord strung through a pin hole and weighted with a small bead. The cord is called a khait and is used as a
Traditionally, the line from the beginning of the arc to the apex is called the jaibs and the line from the end of the arc to the apex is called the jaib tamams. Because the arc is numbered in both directions, these labels are not attached to one straight side or the other, but are instead relative to the measurement or calculation being performed.
Like the arc, both the jaibs and jaib tamams are divided into 60 equal units gathered in groups of five, numbered in both directions to and from the apex. The sixty lines parallel to the jaibs are called sitheeniys or sixtys, and the sixty lines parallel to the jaib tamams are called juyoobul mabsootah. The reason for sixty divisions along the jaibs and jaib tamams is that the instrument uses the sexagesimal number system. It is graduated to the number base 60 and not to the base 10 (decimal system) presently used. Time, angular measurement, and geographical coordinate measurements are about the only holdovers from the Sumerian/Babylonian number system that are still used.
On one of the straight edges of the non-maritime quadrant (solid sheet form) are two alignment plates called hadafatani, each with a small central aperture (pinhole). These two apertures form an optical axis through which the user sights an inclined object, such as a star at night.
The maritime (navigation) version of these devices is skeletal in design rather than a solid sheet form, so as to limit buffeting or movement of the instrument from wind while in the operator's hand.
Measuring the Sun's altitude
During the day, the Sun's
The second aperture also attenuates (darkens) the incoming sunlight by masking any
Typically, the instrument is orientated such that the user faces looking slightly down upon the scale, with the Sun at the user's left and the right hand placed in such a way that a finger functions as a projection screen. When the apertures are optically aligned with the Sun, the user reads the angular measurement of the point where the graduated arc is bisected by the hanging plumb line.
A misconception by non-astronomers and non-navigators is that using the instrument requires two people: one to take the sight and one to read the plumb line's angular position.[citation needed] Actually, when measuring the Sun's altitude, the instrument is held flush (face on) and below eye level by a single user, meaning they can read the cord's angular position on the face of the instrument. However, it does help to have another person to write down the scale readings as they are taken; the device cannot be held sufficiently stable (retaining the optical alignment) with just one hand.
Gallery
-
Ottoman sine quadrant
-
Sine quadrant
-
Wooden sine-cosine quadrant (1840)
-
Reverse side of wooden quadrant, featuring an astrolabe quadrant
References
- ^ "Rub ul Mujayyab". cosmolabe.tripod.com. Retrieved 2021-09-05.
- ISBN 0-7141-2733-7.
External links
- Deconstructing the Sine Quadrant-Part 1: Introduction – The Astrolabe Project