Construction of an Astrolabe

Astrolabe of Jean Fusoris (fr), made in Paris, 1400

An astrolabe consists of a disk, called the mater (mother), which is deep enough to hold one or more flat plates called tympans, or climates. A tympan is made for a specific latitude and is engraved with a stereographic projection of circles denoting azimuth and altitude and representing the portion of the celestial sphere above the local horizon. The rim of the mater is typically graduated into hours of time, degrees of arc, or both. Above the mater and tympan, the rete, a framework bearing a projection of the ecliptic plane and several pointers indicating the positions of the brightest stars, is free to rotate. These pointers are often just simple points, but depending on the skill of the craftsman can be very elaborate and artistic. There are examples of astrolabes with artistic pointers in the shape of balls, stars, snakes, hands, dogs' heads, and leaves, among others.[28] Some astrolabes have a narrow rule or label which rotates over the rete, and may be marked with a scale of declinations.

The rete, representing the sky, functions as a star chart. When it is rotated, the stars and the ecliptic move over the projection of the coordinates on the tympan. One complete rotation corresponds to the passage of a day. The astrolabe is therefore a predecessor of the modern planisphere.

On the back of the mater there is often engraved a number of scales that are useful in the astrolabe's various applications; these vary from designer to designer, but might include curves for time conversions, a calendar for converting the day of the month to the sun's position on the ecliptic, trigonometric scales, and a graduation of 360 degrees around the back edge. The alidade is attached to the back face. An alidade can be seen in the lower right illustration of the Persian astrolabe above. When the astrolabe is held vertically, the alidade can be rotated and the sun or a star sighted along its length, so that its altitude in degrees can be read ("taken") from the graduated edge of the astrolabe; hence the word's Greek roots: "astron" (ἄστρον) = star + "lab-" (λαβ-) = to take.

The Astrolabe, East and West

Astrolabes were used in cultures rooted in religious faith and they reflect the sacred character of the cosmos. Examples from Christendom may have calendars with saints' days, and times of prayer were important for Christians and Muslims, but it was in Islam that the astrolabe was particularly adapted to religious observance. It could be used to find the five times of daily prayer and the sacred direction or 'Qibla', so that the faithful could face towards Mecca in prayer. The astrolabe's traditional role in religious observance may explain why it continued to be made and used much later in Islam than in the West. 

Gift to a mosque

An inscription on the back tells us that this instrument was a gift to a mosque in Fez. Inside the mater is a perpetual calendar for the Muslim and Christian years.

Astrolabe, by Muhammad ibn Ahmad al-Battuti, North African, 1733/4 (Inv. 51459)

An inscription on the back tells us that this instrument was a gift to a mosque in Fez. Inside the mater is a perpetual calendar for the Muslim and Christian years.

Times of prayer
 
Curved lines in the top right quadrant of the back of this astrolabe give the times for the beginning and end of the afternoon prayer in the Muslim observance. Inside the mater (not shown) is a gazetteer of the longitude and latitude of 77 places.

Astrolabe, by Muhammad Muqim, Lahore, c.1650 (Inv. 37530)

Astrolabe, by Muhammad Muqim, Lahore, c.1650 (Inv. 37530)

Ancient Navigation: Astrolabe, by Muhammad Mahdi al-khadim al-Yazdi

This astrolabe, by Muhammad Mahdi, is a masterpiece of Safavid metalwork. The profusion of Persian and Arabic inscriptions confer on it a unique semantic character and the dedication on the throne to an important political personality of the Safavid empire confirm its courtly origin.

Astrolabe, by Muhammad Mahdi al-khadim al-Yazdi, Persian, c.1650

The throne, cast in one piece with the mater and rim, is high and triangular in shape and has an elaborately and delicately pierced base. Both sides bear inscriptions to Safi Quli Beg, an Emir at the court of Shah 'Abbas II.

Both sides of this astrolabe have a verse from the Koran and a Shiite invocation around the edge. The inscription in the throne begins "God: there is no god but Him, the Ever Living, the Ever Watchful. Neither slumber nor sleep overtakes Him. All that is in the heavens and in the earth belongs to Him." Inside the mater is a table for finding the direction of Mecca. 

Astrolabe {star- taker} Elaborate inclinomer, by Muhammad Mahdi al-Yazdi, Persian, c. 1660.

The astrolabe represents a mathematical likeness of the heavens and its Greek name is - "Star Taker". This amazing sophisticated scientific instrument has been crafted by Muhammad Mahdi al-Khadim al-Yazdi in brass and was used to solve astronomical problems and to show the positions of stars and planets at different dates, times and latitudes. The Persian calligraphy engraving reads a quotation from the Koran: "The world is decorated with stars".