History of Computers - Astrolabe
--Rbeckner 09:24, 10 September 2010 (CDT)
Astrolabes are the basic analog computers primarily used to predict the position of celestial bodies. Astrolabes were also used to calculate local time by determining latitude and had surveying applications.
Origin
The first astrolabe found was made in 150BCE, and attributed to the Greek astronomer Hipparchus. The earliest astrolabes fueled Greek prowess in astronomy and astrology[1].
Construction
The basic astrolabe is composed of a central disc, called the mater, which is used to hold one or more flat plates called climates. The climate is made for a specific latitude representing a section of the celestial sphere above the local horizon. The rete a free-rotating framework bearing the path of the sun across the sky as well as the location of the brightest stars is located above the mater and climates. The rete is primarily a star chart and by rotating the rete, predictions can be made about the location of the sun and other planets. Many astrolabes held charts and graphs of the back to help the user translate this raw data into other information, such as the latitude and longitude of the user, or the time[2].
Significance
Astrolabes are used to locate stellar landmarks and divine the time. With the advent of large-scale sailing, the mariner's astrolabe was invented in 1295 to allow for ease of use on board rocking boats. The mariner's astrolabe allowed sailors to navigate more efficiently as they were able to determine their position by the stars in the sky. The astrolabe was of importance to astronomers, astrologers, and enabled navigators to easily ascertain their position[3].
Links
http://en.wikipedia.org/wiki/Astrolabe
http://www.ifa.hawaii.edu/tops/astl-hist.html
