Tag: Astrolabes

Nicephorus Gregoras’s “περὶ κατασκευῆς … ἀστρολάβου”

An illustration of a rete from a 15th-century copy of Nicephorus Gregoras’s “περὶ κατασκευῆς καὶ γενέσεως ἀστρολάβου,” BN suppl. graec. 0652, fol. 285v.

A nice drawing of the rete from Nicephorus Gregoras’s “περὶ κατασκευῆς καὶ γενέσεως ἀστρολάβου” (“On the Mathematical Origin and Construction of the Astrolabe”). This rete, like other diagrams in copies of Gregoras’s text, lacks stars and finer details. In the few copies I’ve seen that include the stars, the rete closely resembles the one surviving Byzantine astrolabe, especially the number and style of the star pointers.

The only Byzantine astrolabe known to survive dates from the 11th century and reflects the style of other early, Islamic astrolabes. Today this astrolabes is in Brescia.

Interesting, at least to me, is the fact that the illustrations in different copies of Gregoras’s text often label the diagrams in different ways. In this copy diagrams are labeled counterclockwise starting at the 9 o’clock position, e.g., the diagrams on fol. 284v of BN suppl. graec. 0652. In other copies, diagrams are labeled counterclockwise or clockwise from various starting points (the 9 o’clock position is the most common starting point). In one manuscript, diagrams on consecutive folia are labeled in opposite ways. The absence of illustration in many copies of Gregoras’s work makes it challenging to follow the text. In most such cases, the copyist left no room for illustrations, suggesting he was working from an unillustrated copy. In some manuscripts, the copyist left large spaces for the illustrations.

Astrolabes on Iraqi Banknotes

In 2003 the Coalition Provisional Authority that governed Iraq issued a new 250 dinar note decorated with an astrolabe.[1]

In late 2003 the Coalition Provisional Authority governing Iraq introduced new banknotes and coins to replace the Hussein government’s currency. Celebrating the contributions Islamic scholars made to science, the new 250 dinar note was decorated with an engraving of an astrolabe on the obverse (and the Great Mosque of Samarra on the reverse).

Detail of Iraqi 250 dinar note showing the astrolabe on the obverse.

It wasn’t the first time Iraqi currency had celebrated the astrolabe. A decade earlier, in 1993 the Hussein government had issued a 1/2 dinar note with the same engravings on both sides, the astrolabe and the Great Mosque of Samarra. And then in 2002, the government issued a 10,000 dinar note with an astrolabe on the reverse. The astrolabe on this later note is a different engraving.

The similarities between the astrolabe used on the 1993 and 2003 (reissued in 2013 with updated anti-counterfeiting technologies) and typical Persian astrolabes is striking. See, for example, the astrolabe by Muḥammad Amīn ibn Amīrzrā Khān, dated A.H. 996 (1587/8 CE), now at the Museum of the History of Science.

The front of the astrolabe by Muḥammad Amīn ibn Amīrzrā Khān. Note the similar throne and rete design & decoration. MHS Inv. 52399.

  1. In 2005 when I was working on the astrolabes at the Museum of the History of Science, I learned that the new 250 dinar note had an astrolabe on it. So I wrote to the Iraqi government asking how I could acquire one. They sent me eight, which I shared with my colleagues at the Museum. I still have three.  ↩

Astrolabes or Mariner’s Astrolabe—A Primer

Celebrations are afoot in Ontario celebrating 400 years of Francophone presence in the region. An important part of those celebrations is Samuel de Champlain’s exploration of Ontario and his early encounter with First Nations cultures. Simcoe.com has a short post on an exhibit that includes one of Champlain’s navigational instruments: “Historic astrolabe on display in Midland believed to have been Champlain’s.” Unfortunately, there’s a bit of confusion about this instrument, which is not in fact an astrolabe.

The Simcoe article faithfully reports information from the Sainte-Marie among the Hurons site. Unfortunately for the Sainte-Marie among the Hurons site, the Canadian Museum of History, which owns the instrument, contributed to the confusion. The museum lists the instrument, artifact #989.56.1, as an astrolabe (the museum also identifies its two other similar instruments—artifact #988.58.1 and artifact #LH994.142.1.2 as astrolabes). Buried toward the end of the museum’s description is a passing comment that identifies the instrument as a “mariner’s astrolabe.”

This passing comment is the only place that Champlain’s instrument in correctly identified as a “mariner’s astrolabe.” Although the two instruments share one possible function—determining the altitude of star (usually the sun or the pole star)—that’s it. The astrolabe combined observations and calculations, allowing the user to perform hundreds of operations. It was both a complex, technical device and a status symbol. The astrolabe has been compared to iPhones and more recently to a complex Rolex watch.

Astrolabes—pre-modern Rolex or iPhone, you decide.
Astrolabes—pre-modern Rolex or iPhone, you decide.

These comparisons capture the astrolabe’s status and superabundance of operations its operations. My pamphlet offers a handy introduction to the history, fabrication, and use of astrolabes. Hundreds of astrolabes survive.

The mariner’s astrolabe, by contrast, was utilitarian and singular in function. It allowed the user to determine the height of the polar star or the sun and, thus, the observer’s latitude. The instrument’s design reflects its utilitarian function. Mariner’s astrolabes are typically heavy, made from a thick brass ring (only the limb of astrolabe) to limit them from swinging too much as the ship’s deck swayed and rocked at sea. Some had a ring at the bottom of the instrument from which to hang a weight for added stability. The body of the instrument was often cut away to reduce, scholars claim, the effects of wind blowing on the body of the instrument.

On the left is a typical mariner’s astrolabe from ca. 1600, from the Museum of the History of Science, inventory #54253, found here. On the right is a planispheric astrolabe, usually called simply an astrolabe. This is an early 16th-century astrolabe from the Museum of the History of Science, inventory #52528, found here.
On the left is a typical mariner’s astrolabe from ca. 1600, from the Museum of the History of Science, inventory #54253, found here. On the right is a planispheric astrolabe, usually called simply an astrolabe. This is an early 16th-century astrolabe from the Museum of the History of Science, inventory #52528, found here.

The limb was typically graduated from 0°–90° in the upper quadrants, once again reflecting its use as a basic observational instrument. A simple alidade with rather crude sighting vanes was attached to the front of the instrument. At night the navigator would look through the holes in the alidade to align them with the pole star. Then he could read the altitude of the star from the graduation on the limb, which altitude was, roughly, his latitude. If he wanted to know his latitude during the day, at noon he rotated the alidade until the sun shown down through the holes in the vanes (he would not look at the sun for obvious reasons). He read the sun’s altitude from the scale on the limb, added or subtracted the earth’s tilt based on the day of the year, and subtracted the result from 90° to obtain his latitude.

The mariner’s astrolabe was a nautical/navigational tool. Although an astrolabe could have been used at sea as a navigational tool, it is unclear that they were. The instrument’s many functions and finely graduated limb would have made it unnecessarily complicated and difficult to use on the deck of moving ship. Moreover, the astrolabe’s cost and status make it seem unlikely that a mariner would have owned one when there were other, more specialized and less expensive instruments that did the same thing. There are a few illustrations of astrolabes being used on ships, but whether these are idealized or meant to reflect contemporary practice is unclear. The various instruction manuals that include canons on how to use astrolabes at sea, e.g., Johannes Stöffler’s Elucidatio fabricae ususque astrolabii (1513), do not demonstrate that they were so used. Authors of such manuals sought to distinguish themselves and demonstrate their expertise by cataloging as many possible uses for astrolabes as they could imagine, regardless of whether or not anybody actually used astrolabes in those ways.

Surely few people used an astrolabe to make the many observations Cosimo Bartoli cataloged in his Del modo di misurare (1564). Google has scanned it here.
Surely few people used an astrolabe to make the many observations Cosimo Bartoli cataloged in his Del modo di misurare (1564). Google has scanned it here.

Whereas traditional astrolabes were expensive, status symbols and were, therefore, collected and displayed, mariner‘s astrolabes were working tools. They were not, as a rule, collected or displayed. Consequently, much rarer today—only about 100 survive and most of those were recovered from shipwrecks (the Museum of the History of Science has a nice audio guide to the mariner’s astrolabe here).

Champlain’s instrument was graduated from 0°–90° in each quadrant. The body has largely been cut away. And on the front is a large alidade for sighting.

From this photo it is clear that Champlain’s instrument was a mariner’s astrolabe. From the Canadian Museum of History description—direct link to photo.
From this photo it is clear that Champlain’s instrument was a mariner’s astrolabe. From the Canadian Museum of History description—direct link to photo.

It is plausible that he brought a mariner’s astrolabe with him as he explored Canada. But the story of Champlain losing his instrument by a lake, it having lain there in the forest for 250 years before a 14-year-old boy found it, and its subsequent sale to different collectors, seems almost too good to be true. And the instrument’s remarkable shape, having spent more than two centuries in the dirt, is equally surprising.[1] Whether or not it was ever owned by Champlain, his instrument is clearly a mariner’s astrolabe.

  1. In its description of the instrument’s provenance, Canadian Museum of History expresses some but not much skepticism about the story (my emphasis):

    In May 1613, Samuel de Champlain, the French explorer-cartographer, travelled up the Ottawa River. To avoid the rapids, he chose a course through a number of small lakes near Cobden, Ontario. Champlain and his men were forced to portage and to climb over and under fallen logs at one particularly difficult point by Green Lake, now also known as Astrolabe Lake. It was here, according to several nineteenth-century authors, that Champlain lost his astrolabe. If this is correct, the astrolabe remained where it had fallen for 254 years. Eventually a 14-year-old farm boy named Edward Lee found it in 1867 while helping his father clear trees by Green Lake. Captain Cowley, who ran a steamboat on nearby Muskrat Lake, offered Lee ten dollars for the astrolabe. Lee never received the money nor saw the astrolabe again. Cowley sold the astrolabe to his employer, R.W. Cassels of Toronto, President of the Ottawa Forwarding Company. He in turn sold it to a New York collector, Samuel Hoffman. The astrolabe was willed to the New York Historical Society in 1942 where it remained until June 1989, when it was acquired by the Department of Communications for the Canadian Museum of Civilization. This astrolabe is unique. It is the smallest of 35 mariner’s astrolabes surviving from the early part of the seventeenth century and the only one from France. It is in excellent condition, except for one missing piece, a small ring on the bottom edge of the disk, to which a weight was likely attached to help keep the instrument plumb. The ring was probably broken off sometime in the late nineteenth century, since it appears in an 1879 photograph of the astrolabe.

    For a more thorough analysis of the connection between Champlain and this instrument, see “The Mystery of Champlain’s Astrolabe” or, more recent, “19th century manuscript sheds new light on ‘Champlain’s Astrolobe [sic]’ thought lost by French explorer.”  ↩

Nikephoros Gregoras and Byzantine Science

In March I am talking on the Byzantine polymath Nikephoros Gregoras and his efforts to establish his scientific authority. In “Empiricism, Prediction, and Instruments: The Creation of Expertise in 14th-Century Constantinople” I will examine the ways that Gregoras tried to distinguish his own expertise by grounding it in precise, empirical predictions and his command of technical knowledge.

This talk forms part of my larger project on Byzantine scientific knowledge. This larger project began from Gregoras’s text “On the Construction and Origin of the Astrolabe” (“Περὶ κατασκευαζῆς καὶ γενἐσεως ἀστρολάβου”).

A digram from Gregoras’s text on how to construct an astrolabe.