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How to Use an Astrolabe to See Stars Moving

An astrolabe can show the changes in star positions throughout the calendar year. The tool can be used to pinpoint the exact star and constellation position for a given night. Instead of the date being referred to in Gregorian calendar time, it is determined by where the sun is positioned in the astrological zodiac. After this measurement is taken, the astrolabe is then used to chart where particular constellations fall over an extended period of time. The astrolabe can be used to watch the stars move during the span of one night, as well; they are observed in regard to the degrees shifted from the horizon line. The astrolabe is used from the perspective of an observer who is on the earth's surface.

Things You'll Need

Astrolabe
Paper
Pencil or pen
Greenwich Mean Time (GMT) conversion chart

Instructions

- 1
  Convert the time you begin to take measurements into GMT, also known as Coordinated Universal Time. Use a GMT conversion chart to adjust the time. The GMT time must then be converted to military time using the 24-hour clock; for example 10:00 pm GMT would be translated to 22.00. Make note of the converted time on a piece of paper.
- 2
  Find the astrological date of your first measurement by using the back of the astrolabe as a reference; the common Gregorian dates are listed with their corresponding astrological dates. Make note of the date. Find the astrological date on the rete section of the astrolabe, in the front. Rotate the rule of the astrolabe to this position.
- 3
  Read the stars' positions with the astrolabe. The common line on the astrolabe is the horizon line, just beneath the rete; all calculations will be based on this line. Everything inside this line will be visible above the horizon. The diagram will show how the sky will look at this particular moment in time. The central 90-degree point on the astrolabe points to directly overhead, to the zenith of the sky. The numbered rings portray how high to look in the sky. Make note of a particular star to study.
- 4
  Keep track of the specified star's movement. Notice how the astrolabe coincides with its movement throughout the night and into the early morning. Keep track of these movements and the larger movements of a season's time to see how the star moves throughout the elliptical.

Astronomy