Chakra Yantra, a circular instrument measuring global coordinates of declination and the hour angle of a celestial object, at Jantar Mantar, a monument completed in 1734 built by Maharaja Sawai Jai Singh, founder of Jaipur, featuring 19 architectural astronomical instruments, in Jaipur, Rajasthan, India. The ring in the Chakra Yantra pivots on a polar axis and a sighting tube in its centre moves on a perpendicular axis, allowing the viewing of a celestial object. The instruments allow the observation of astronomical positions with the naked eye. They measure time, predict eclipses, track the location of major stars and ascertain the declinations of planets. Jantar Mantar is listed as a UNESCO World Heritage Site. Picture by Manuel Cohen
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