Type of quadrant used by medieval Arabic astronomers
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A sine quadrant, known in Arabic as rub‘ul mujayyab
A sine quadrant (Arabic: الربع المجيب, romanized: rub‘ul mujayyab), sometimes known as a "sinecal quadrant", was a type of quadrant used by medieval Arabic astronomers. The instrument could be used to measure celestial angles, tell time, find directions, perform trigonometric computations, and determine the apparent positions of any celestial object for any time. The name is derived from the Arabic rub meaning 'a quarter' and mujayyab meaning 'marked with sine'.[1]
The sine quadrant was described by Muhammad ibn Mūsā al-Khwārizmī in 9th-century Baghdad, and was used throughout the medieval Islamic period to determine the proper times for Islamic prayer.[2] These instruments, with poor angular resolution, were not principally intended to function with stars at night as an astronomical measuring device.[citation needed] It is impractical to sight a star through the front aperture unless it is on a fixed, stabilized mount relative to the half degree width of a very intense Sun.
^"Rub ul Mujayyab". cosmolabe.tripod.com. Retrieved 2021-09-05.
^David A. King, "Islamic Astronomy", in Christopher Walker (1999), ed., Astronomy before the telescope, p. 167-168. British Museum Press. ISBN 0-7141-2733-7.
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