Back to Astrolabes

Examples of Calculations with the Astrolabe

Basic Problems

Problems involving stars

• Finding the rising position of a star
• Finding the maximum height of a star
• Finding the length of time a star is above the horizon

Problems involving the sun

• Finding the sun in the Zodiac
• Finding the position of the sun at sunrise (sunset)
• Finding the height of the sun at noon

Problems involving time

• Finding the time of sunrise (sunset)
• Finding the length of day
• Finding the time of day using the sun
• Finding the time of day using a star

Advanced Problems

Problems using seasonal hours

• Finding the seasonal hour using the front of the astrolabe
• Using the seasonal hour arcs

Problems using the shadow boxes

• Calculating the height of the sun from the length of a shadow
• Simple trigonometric calculations using the shadow box

A few notes on time

Learning to Use the Astrolabe

Learning to use the astrolabe requires both practice and patience. A familiarity with the basic motions of the stars and the sun is essential to understanding how the astrolabe works. I recommend consulting an introductory text on astronomy. In the following pages, some worked examples are describes and illustrated. If you find yourself getting discouraged, don't despair. In Medieval times men and women spent months learning to manipulate the astrolabe. Even so, I have found that first year astronomy students can master the basic principles of the astrolabe in just a few hours. More advanced calculations, such as those involving seasonal hours or the shadow boxes, may take some additional time to fully absorb.