Astronomical rings (Latin: annuli astronomici), also known as Gemma's rings, are an early astronomical instrument. The instrument consists of three rings, representing the celestial equator, declination, and the meridian.It can be used as a sun dial to tell time, if the approximate latitude and season is known, or to tell latitude, if the time is known or observed (at solar noon). It may be considered to be a simplified, portable armillary sphere, or a more complex form of astrolabe.History
Parts of the instrument go back to instruments made and used by ancient Greek astronomers. Gemma Frisius combined several of the instruments into a small, portable, astronomical-ring instrument. He first published the design in 1534, and in Petrus Apianus's Cosmographia in 1539. These ring instruments combined terrestrial and celestial calculations.Types
Fixed astronomical ringsFixed astronomical rings are mounted on a plinth, like armillary spheres, and can be
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