Variants
of the Astrolabe
.png)
Introduction
The term astrolabe can refer to a planispheric astrolabe in the most general sense, or to several variants of the astrolabe. The planispheric astrolabe can also be combined with other instruments to achieve advanced functions. Together, these instruments form a complex genealogy of ancient mathematical practices.
Planispheric
astrolabe
The planispheric astrolabe is the most common astrolabe, and when unqualified, the term astrolabe refers to it. Planispheric astrolabes are widely circulated and made in a variety of languages. Its internal differences are also great: people at different latitudes will use different climates, the culture of the manufacturer determines the pattern of the rete, and the style of the rule and alidade also varies. There are slight differences, and the diagrams in the cavities on the back or front of the astrolabe are also different, serving different purposes.
Early Arabic astrolabe
Date: late 9th century Place: Syria
Maker: Khafīf, apprentice of ‘Alī ibn ‘Īsā
Inventory no. 47632 in the History of Science Museum, Oxford University.
Arabian decorative arts forbade idolatry. Therefore, there are no animal images on the star network of the astrolabe, and are replaced by complex scrolling leaf patterns.
Arabic astrolabe
Date: 1713/4 Place: Turkey
Maker: ‘Abdī
Inventory no. 39955 in the History of Science Museum, Oxford University.
Persian art style is roughly similar to Arabian art, but more colorful and complex. This is reflected in the astrolabe, which is the winding network of stars.
Persian astrolabe
Date: 1057 A.H. (A.D. 1647/8) Place: Iran/Persia, Asia
Makers: Muhammad Muqim al-Yazdi
Inventory no. 45747 in the History of Science Museum, Oxford University.
Sanskrit astrolabe remains are rare in the world. The instrument on the right is characterized by the fact that the alidade on the back is not just a peephole, but a metal tube runs through it, which becomes a speculum tube. Speculum tubes were used more in ancient China, and early astronomical instruments often used speculum tubes. So there was a saying of “Guan Kui Li Ce”(observe the sky through the bamboo tube and measure the sea with the gourd scoop).
Sanskrit astrolabe
Date: late 18th or early 19th century Place: India
Inventory no. 30402 in the History of Science Museum, Oxford University.
A feature of the European astrolabe was the later adoption of axisymmetric alidade. This improvement eliminates the moment of the alidade on the axis, making it easier for the alidade to stay at the observation position.
Gothic Astrolabe, Replica
Date: 14th century Place: Paris
Inventory no. RE2022008 in the Science Museum, Tsinghua University.
Reproduced from the inventory no. 1264 in the Whipple Museum of the History of Science, Cambridge University
The astrolabe on the right is a representative of the art of the European high season astrolabe. It is golden in color, 30 centimeters in diameter, and beautifully decorated. One side of the astrolabe is a plansipheric astrolabe, and the other side is a modified Zachary universal astrolabe by Gemma Frisius.
Arsenius Astrolabe
Date: 1565 Place: Louvain, Belgium
Maker: Regnerus Arsenius
Inventory no. 53558 in the History of Science Museum, Oxford University.
Universal astrolabe
Generally an astrolabe needs several climates corresponding to different local latitudes. While the universal astrolabe can be used at any latitude, without multiple climates. The universal astrolabe is mainly used for the conversion of astronomical coordinates, such as between equatorial and ecliptic coordinates. There are two types of universal astrolabe in history: Saphae Arzachelis and universal astrolabe de Rojas.
The Saphae Arzachelis (also known as Azafea) was developed by the Andalusian astronomer Al-Zarqali (1029–1100) in his book Tratado de la azafea. In this type of astrolabe, the coordinate network is not projected from the south pole to the equatorial plane, but from the vernal equinox on the equator to the meridian plane (passing the north and south poles).
Saphae Arzachelis, or Azafea, Replica
Date: 11th century Place: Iberia
Inventor: Al-Zarqali, 1029–1100
Inventory no. 220207006 in the Science Museum, Tsinghua University.
Based on Alfonso X el Sabio’s Libros del Saber de Astronomía, reference to the astrolabe of Ibn Hudayl in Royal Academy of Sciences and Arts, Barcelona
The universal astrolabe de Rojas was developed by the Spanish mathematician and astronomer Juan de Rojas y Sarmiento (active 1540-1550) in Commentariorum in astrolabium, quod planisphaerium vocant, libri sex (1550). This type of astrolabe applies the orthographic projection, from the equinox on the equator to the meridian (passing the north and south poles), making the latitude lines of the coordinate network parallel to each other, similar to the global map we use now.
Universal astrolabe of Anthoine Mestrel
Date: 1551 Place: Paris
Maker: Anthoine Mestrel
Inventory no. 10190 in History of Science Museum, Oxford University
Spherical astrolabe
Spherical astrolabe is a variation of astrolabe. Instead of using hemispheric projection like ordinary planispheric astrolabes, it just honestly reproduces the equatorial coordinates and the horizontal coordinate with a spherical surface, so its rete and climates are hemispherical. Since it can not be equipped with the alidade, this type of astrolabe is only used for demonstration and calculation, not for observation.
Spherical astrolabe
Date: 1480/1 (A. H. 885) Place: Syria (?)
Maker: Mūsa
Inventory no. 49687 in History of Science Museum, Oxford
Linear astrolabe
The linear astrolabe, also known as the Tusi Staff, was invented by the Islamic mathematician Sharaf al-Dīn al-Ṭūsī (c. 12th century). The principle is to convert the latitude and longitude grid of a flat astrolabe into a straight line and inscribe it on a pole. Two apertures are set at both ends of the staff. When observing, aim at the object through the aperture, and use the suspension line to read the altitude angle of the object. As for calculating, place the rod on a plane, and use the suspension line for geometric graphing to get the desired information. as light as a cane, the linear astrolabe eliminates most of the astrolabe’s structure, yet still achieves basic functions of the astrolabe.
Linear astrolabe, Reconstruction
Date: 12th century Place: Islamic region
Inventor: Sharaf al-Dīn al-Ṭūsī (circa 12th century)
Restorated based on Malakushi's Collection
Nautical Astrolabe，or Mariner’s Astrolabe
The nautical astrolabe was invented by Portuguese navigators in the late 15th century. It is a simplified version of the planispheric astrolabe, which omits structures such as star nets and latitude disks, and only retains the alidade and scale circle used for observation. It also adds thickness and weight to the mater and features a hollow design. These improvements ensured that the astrolabe remained suspended on bumpy and windy decks, thereby improving observation accuracy.
Nautical Astrolabe (or Mariner's Astrolabe), Replica
Date: 16th century Place: Portugal
Inventory no. 220207002 in the Science Museum, Tsinghua University.
reproduced from the collection of the Tudor and Stuart Seafarers Gallery
Mercury Clepsydra
Mercury Clepsydra
Astronomy and timekeeping are closely related, and astrolabes are also closely related to mechanical clocks. The 13th-century Castilian work Libros del saber de astronomia (“Books of the wisdom of astronomy”) contains many contents about astrolabes, including how to make mercury clepsydra as well. The mercury clock is driven by the fall of mercury, and uses the front of the astrolabe as the display. The climate of astrolabe is fixed like a clock dial; the rete of astrolabe rotates, acting as a pointer.
Mercury Clepsydra of Alfonso X, Reconstruction
Date: 11th–12th century Place: Iberia
Maker: Ibn Said (11th–12th century)
Inventory no. 220615013 in the Science Museum, Tsinghua University.
Restorated based on Alfonso X el Sabio’s Libros del Saber de Astronomía
Geared astrolabe
Another distinctive category of astrolabe is the geared astrolabe. There are gears installed on the surface of the astrolabe, so that the movement of heaven and the revolution of sun and moon can be displayed on the surface of the astrolabe simultaneously. This makes the astrolabe have the function of a calendar.
Astrolabe with solar-lunar gear train, Replica
Date: 1295-1305 Place: Paris or Mans, France.
Inventory no. RE2022006 in the Science Museum, Tsinghua University.
Reproduced from the inventory no. 1880-32 in Science Museum, London. Missing and hidden parts are based on the restoration by Martin Bruno.
Equatorium of Francisco Zarzoso, Replica
A planispheric astrolabe involves only the Sun and stars, while an equatorium can be used to calculate the positions of other planets. The latter is based on the planetary theory of Ptolemaic astronomy, which materializes models such as epicycles and deferents, and can quickly provide planetary orientation information when accuracy requirements are not high. The back of a metal planetary positioner is often the front of the astrolabe. On top of that, both instruments had cheap paper versions in history.
Equatorium of Francisco Zarzoso
Date: Late 15th century
Place: southern France or northern Italy
Inventory no. 49847 in the History of Science Museum, Oxford University.