（Edward Guang Ma)
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.
What is the use of Astrolabe?
In the 10th century, it was said that there are over 1,000 different uses of an astrolabe, in areas as diverse as astronomy, astrology, horoscopes, navigation, surveying, timekeeping, prayer, etc. All of the everyday uses of the astrolabe are not known, but they were certainly used to tell time during the day or night, to find the time of sunrise and sunset and, thus, the length of the day, to locate celestial objects in the sky, as a handy reference of celestial positions and, to determine aspects of horoscopes. Modern astrolabes, such as the Personal Astrolabe, can be used to solve astronomy problems involving sidereal time and can be used with modern civil time.
A Brief History of Astrolabe
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. The first known European metal astrolabe was developed in the 15th century in Lisbon and shoppers started selling astrolabes in his shop in Paris. 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 capabilities and their value for astronomy education.
 For more information, you can go to this website: http://www.astrolabes.org/.
 Dr. Emily Winterburn (National Maritime Museum), Using an Astrolabe, Foundation for Science Technology and Civilization, 2005, from http://en.wikipedia.org/wiki/Astrolabe.
 See Use of the Astrolabe(visited on 9/20/2008), http://astrolabes.org/uses.htm.
 See The Astrolabe An instrument with a past and a future (visited on 9/20/2008), http://www.astrolabes.org/.