The Astrolabe

This page provides a very general overview of astrolabe principles. Links are provided to other pages with more details. The astrolabe in the picture was made by the French scientist and craftsman Jean Fusoris in about 1400 (photo courtesy Adler Planetarium and Astronomy Museum). Click on the image to display a biographical sketch of the maker and large pictures of the front (121K) and back (51K) of the instrument. You can also download The Electric Astrolabe and a template for making a Mariner's Astrolabe.

If, after looking through this site, you find you want to learn more about astrolabes and related pre-telescopic instruments, you might be interested in the author's just published book, The Astrolabe, which explains all types of astrolabes in detail.

Also included is a page describing a monumental sculture based on the anaphoric clock, an astronomical machine from ancient times. The anaphoric star disk is the centerpiece of a restored park in downtown Kansas City, MO and is very likely the largest and most accurate device of this type ever made.

What is an Astrolabe?

The astrolabe is a very ancient astronomical computer for solving problems relating to time and the position of the Sun and stars in the sky. Several types of astrolabes have been made. By far the most popular type is the planispheric astrolabe, on which the celestial sphere is projected onto the plane of the equator. A typical old astrolabe was made of brass and was about 6 inches (15 cm) in diameter, although much larger and smaller ones were made.

Astrolabes are used to show how the sky looks at a specific place at a given time. This is done by drawing the sky on the face of the astrolabe and marking it so positions in the sky are easy to find. To use an astrolabe, you adjust the moveable components to a specific date and time. Once set, the entire sky, both visible and invisible, is represented on the face of the instrument. This allows a great many astronomical problems to be solved in a very visual way. Typical uses of the astrolabe include finding the time during the day or night, finding the time of a celestial event such as sunrise or sunset and as a handy reference of celestial positions. Astrolabes were also one of the basic astronomy education tools in the late Middle Ages. Old instruments were also used for astrological purposes. The typical astrolabe was not a navigational instrument although an instrument called the mariner's astrolabe was widely used. The mariner's astrolabe is simply a ring marked in degrees for measuring celestial altitudes.

The history of the astrolabe begins more than two thousand years ago. The principles of the astrolabe projection were known before 150 B.C., and true astrolabes were made before A.D. 400. The astrolabe was highly developed in the Islamic world by 800 and was introduced to Europe from Islamic Spain (Andalusia) in the early 12th century. It was the most popular astronomical instrument until about 1650, when it was replaced by more specialized and accurate instruments. Astrolabes are still appreciated for their unique capabilites and their value for astronomy education.

Collections

The largest astrolabe collection in North America, and the best displayed in the world, is at the Adler Planetarium and Astronomy Museum in Chicago, IL. The permanent Adler exhibit, "The Universe In Your Hands: Early Tools of Astronomy," includes many of the rare and beautiful astrolabes in the Adler collection along with other pre-telescopic instruments such as sundials and armillary spheres. Other astrolabe collections in North America are at the National Museum of American History division of the Smithsonian Institution (Washington, DC) and Harvard University (Cambridge, MA).

The largest astrolabe collection on public display is at the Musuem of the History of Science, Oxford, UK. Other collections in the UK are in the National Maritime Museum (Greenwich), The British Museum (London), The Science Museum (London) and the Whipple Museum of the History of Science (Cambridge).

European continental museums with astrolabe collections include Museo di Storia della Scienze a Firenze (Florence), Germanisches Nationalmuseum (Nurnberg), Conservatoire National des Arts et Metiers (Paris), Museo Naval (Madrid), Observatorio Astronomica di Roma (Rome) and the Musees Royaux d’Art and d’Histoire (Brussels).

A page with links to other relevant web pages, reference and astrolabe reproductions is attached.

A new page has been added that shows astrolabes made by individuals. Please send us a note if you have made an astrolabe that you would like to have included.

We have accomplished our purpose if these few pages have satisfied or increased your curiosity about astrolabes. In an effort to make astrolabe information more accessible, we offer an inexpensive astrolabe reproduction called The Personal Astrolabe. Even though there is a modest charge for The Personal Astrolabe it is not really a commercial product since it is offered at cost. If you would like to know more about astrolabes, would like to own your own astrolabe or learn more about The Personal Astrolabe, send your mailing address to Janus at the address below or via e-mail to receive free information.

We are now offering a free download of a planetarium program in the form of a planispheric astrolabe called The Electric Astrolabe. Click on the name for a description and download and installation instructions.

Please drop us a note to let us know what you think of these pages, why you visited, how you found them, whether your needs were satisfied or just to say hello. We can handle notes in German, French or English, Italian babytalk and British (if the constructions are kept simple). We answer every single message we receive that asks a question. If you do not get an answer there must be something wrong with your e-mail return address. Try again or send us your mailing address to receive information about the Personal Astrolabe.

This page constructed by:
James E. Morrison, Janus
18 Kingsbridge Road
Rehoboth Beach, DE 19971
USA

(302) 226-5086
janus.astrolabe@verizon.net

In the unlikely event that anyone cares, here is a picture of the author giving an astrolabe tutorial to an eager young student.

Astronomy site of the day 9/2/96

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