How to Aim an Armillary

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Armillary spheres were first used in ancient Greece, China and the Middle East as models for teaching astronomy. Larger armillary spheres were also sometimes used for observing the skies. The armillary sphere consists of bands of metal that form rings to create an open sphere. Sometimes a small globe, which represents Earth, is at the center.

Three main rings, perpendicular to one another, represent the equator, the solstices, and the equinoxes. Other rings represent the Arctic Circle, the Antarctic Circle, the Tropics of Cancer and Capricorn and the ecliptic. Finally, an axis rod passes through the sphere and usually has an arrowhead which points towards Polaris, the North Star.

Things You'll Need

  • armillary sphere
  • compass
  • level

Determine where to put your armillary sphere. Both outdoor armillaries and decorative indoor armillaries are available. Set an outdoor armillary sphere on a flat surface. Use a level to help set the armillary straight. Make sure that the stand is not leaning and is firmly anchored. Place an indoor armillary in a place where it will not be moved or knocked over.

Find true north with your compass. Aim the axis (or gnomon) arrow of the armillary north. In the northern hemisphere, at night this arrow should point towards Polaris, the North Star.

Find your latitude by using a map or the Internet. Adjust the meridian ring on the armillary sphere by turning it so that it makes an angle with the horizon that matches your latitude. For example, a person living at a latitude of 37 degrees north would have their meridian ring set at an angle of 37 degrees.

Bolt an outdoor armillary sphere to a deck or other platform to keep it from falling over. Set the stand in concrete if you want a permanent installation. Double-check the sphere’s alignment with true north before anchoring the sphere permanently.

Tips & Warnings

  • Use a quality compass.
  • Some armillary spheres are decorative only and not adjustable.
  • Make sure your armillary is aimed correctly before you permanently mount it to anything.

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