The Jantar Mantar, in Jaipur, is an astronomical observation site built in the early 18th century. It includes a set of some 20 main fixed instruments. They are monumental examples in masonry of known instruments but which in many cases have specific characteristics of their own. Designed for the observation of astronomical positions with the naked eye, they embody several architectural and instrumental innovations. [Source: Vistara, catalogue of the exhibition]

Among the massive masonry structures in Jaipur’s Jantar Mantar are Jaiprakash Yantra, which consists of two hemispherical cavities partially sunk in the ground. It is used for marking the position of the stars. In background is sundial Narivalayas Yantra.
Among the massive masonry structures in Jaipur’s Jantar Mantar are Jaiprakash Yantra, which consists of two hemispherical cavities partially sunk in the ground. It is used for marking the position of the stars. In background is sundial Narivalayas Yantra. © Vistara, Catalogue of the Exhibition
“Unwrapped” spherical panorama from within the Jai Prakash at the Jaipur observatory. The sighting guide is visible against the sky.
“Unwrapped” spherical panorama from within the Jai Prakash at the Jaipur observatory. The sighting guide is visible against the sky. © Barry Perlus
An “unwrapped” rendering of a 3600 spherical panorama taken from the top of the east quadrant of the Samrat Yantra at the jaipur observatory,
An “unwrapped” rendering of a 3600 spherical panorama taken from the top of the east quadrant of the Samrat Yantra at the jaipur observatory, © Barry Perlus

The Jai Prakash may well be Jai Singh’s most elaborate and complex instrument. It is based on concepts dating to as early as 300 B.C. when the Greco-Babylonian astronomer Berosus is said to have made a hemispherical sundial. Hemispherical dials also appear in European Church architecture during the Middle Ages, and at the observatory in Nanking, China in the late 13th-century. The Jai Prakash, however, is much more elaborate, complex, and versatile than any of its predecessors.

Rashivalayas Yantra, a collection of 12 instruments, each corresponding to a sign of the zodiac. The instruments are used to make observations of celestial bodies.
Rashivalayas Yantra, a collection of 12 instruments, each corresponding to a sign of the zodiac. The instruments are used to make observations of celestial bodies. © Vistara, Catalogue of the Exhibition

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"Manthana – The changing myth." In Vistāra - The Architecture of India, Catalogue of the Exhibition, edited by Carmen Kagal. The Festival of India, 1986.
Ganju, MN Ashish. "The Jantar Mantar at Jaipur, Rajasthan." In Architecture in India, 64-69. Paris and Milan: Electa Moniteur, 1985.
City plan of Jaipur. Jaipur State, Undivided India, 1734.