Wooden horary quadrant, Persian, 18th century.
© Science Museum / Science & Society Picture Library
This unsigned Islamic horary quadrant was made in Persia (part of modern day Iran). Made of wood, it has hand-drawn painted scales and inscriptions and was used for finding local time by sighting either the Sun or a bright star at night. Held vertically, a measurement could be taken from the position on the scale of a moveable bead on the thread of the plumb bob of the instrument. Horary is an archaic term meaning 'of or relating to hours'. The horary quadrant was derived from the astrolabe and first appeared during Medieval times. Like its predecesor, it includes a two-dimensional depiction of a celestial sphere that is reduced to a quarter.