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An astrolabe shows the sphere of the heavens; the earth is at the center, showing the movement of the celestial
sphere around the pole and allowing the relative position of stars to be determined at any given. It is, as it were,
a model of the universe that can be held in the hand.
Astrolabes show how the sky looks at a specific place at a given time. 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. Classical astrolabes were usually made of brass and were commonly about six or eight inches (15 to 20
cm) in diameter, although much larger and smaller ones were made. A typical student's astrolabe was made of paper and
wood, but more decorative and sturdier astrolabes were often constructed of brass or other metals.
The astrolabe is an integral tool for practicing the arts of the astrologer and astronomer, and provides a tangible
representation of the celestial sphere. Typical uses of the astrolabe include finding the time during the day or night,
finding the time of as sunrise or sunset and as a handy reference of celestial positions. Essentially, the astrolabe is
an analog computer for finding the position of bodies in the heavens relative to the local horizon. Given the time and
date, a skilled astronomer can use an astrolabe to calculate most of the astrological positions for casting a horoscope,
lacking only the positions of the planets, which would be provided by a set of tables for the appropriate year. |
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