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Mercury, March/April 2005 Table of Contents

Photo courtesy of the author.

by Nick Kanas

People always have been fascinated by the movement of objects in the sky. The ability to accurately locate the heavenly bodies and to predict celestial events had practical applications for many early cultures. For the ancient Egyptians, the heliacal rising of the star Sirius predicted the flooding of the Nile, signaling the optimal time for planting. For the classical Greeks, accurately locating a heavenly body in the sky using their skill with spherical geometry satisfied their urge to understand the structure of the Cosmos. For the Medieval Christians, knowing the time of the full Moon after the Vernal Equinox for a given year helped them calculate the date of Easter Sunday every year. For Islamic peoples, understanding the location of objects in the heavens helped them determine the direction of Mecca, which they needed to face several times a day during prayer. Thus, events in the sky were important for the day-to-day life of many early civilizations.

To measure and calculate the location and movement of heavenly bodies in the sky, as well as to tell time and determine one’s location in latitude on Earth, a number of instruments were developed, such as the astrolabe and the armillary sphere. However, such instruments were made of metal or wood, were expensive to produce, and were used mainly by scholars who had the incentive to purchase them. But with the advent of moveable type and the development of printing in Europe in the 1450s, an opportunity arose to incorporate principles of these instruments into books, which could be produced more cheaply and could reach more people. This led to the popularization of moveable devices on the printed page that were called volvelles.

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