Maryland Archeology Month

-April 2008-

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Stories of Liberty
Archeology in Annapolis

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Archeology Gallery

Astronomer's Ring Dial

Astronomer's Ring Dial

The astronomer's ring dial is an altitude dial constructed of an inner ring and an outer movable ring and is read suspended from a cord. It was in general use from the A.D. 11th century through the end of the A.D. 18th century. The pin hole gnomon (an object that projects a shadow used as an indicator) is cut into a narrow band which fits into a groove in the outside dial. This is set against a calendar scale to adjust for the sun's seasonal change in altitude. Most such dials have two pin hole gnomons, on opposite sides of the ring, for use in summer and winter. The portable dial is designed for use at specific latitude. It has one scale marked S (for the summer months April through September) and one marked W (for October through March). If you look closely, you may see "W" on the lower right portion of the dial. The movable ring with the pin hole gnomons is missing from this specimen.

The illustrated crushed ring dial is made of brass, and is 7.5 cm in length by 1.1 cm in width (4.5 cm in diameter, if the dial was intact). It was found at the Saunders Point Historic Site in Anne Arundel County, Maryland in the spring of 1968. The salvage excavation of a dwelling cellar or trash pit feature, dating to the mid-18th century, was conducted by the Archeological Society of Maryland and the Archeological Society of Virginia, and was directed by Commander Robert and Jane Curts. Artifacts found in association with the ring dial included a carved stone Saunders family coat of arms and fine quality historic ceramics and glass ware.

Rebecca Morehouse, Collections Manager, Jefferson Patterson Park and Museum, relocated the artifact and, using the internet, identified it as an astronomer's ring dial.

Information and photograph provided by Stephen Israel, Central Chapter