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A Jantar Mantar (Hindustani pronunciation: [d͡ʒən̪t̪ər mən̪t̪ər]) is an assembly of stone-built astronomical instruments, designed to be used with the naked eye. There were five Jantar Mantars in India, all of them built at the command of the Rajah Jai Singh II, who had a keen interest in mathematics, architecture and astronomy; The largest example is the equinoctial sundial belonging to Jaipur's assembly of instruments, consisting of a gigantic triangular gnomon with the hypotenuse parallel to the Earth's axis. On either side of the gnomon is a quadrant of a circle, parallel to the plane of the equator. The instrument can be used with an accuracy of about 2 seconds by a "skilled observer" to measure the time of day, and the declination of the Sun and the other heavenly bodies. It is the world's largest stone sundial, known as the Vrihat Samrat Yantra. The Jaipur Jantar Mantar is a UNESCO World Heritage Site.
The Jantar have like[clarification needed] Samrat Yantra, Jai Prakash, Ram Yantra and Niyati Chakra; each of which are used to for various astronomical calculations. The primary purpose of the observatory was to compile astronomical tables and to predict the times and movements of the sun, moon and planets.
List of instruments:
● Samrat Yantra ● Jai Prakash Yantra ● Disha Yantra ● Rama Yantra ● Chakra Yantra ● Rashiwalya Yantra ● Dingash Yantra ● Utaansh Yantra
The name "Jantar Mantar" is at least 200 years old, finding a mention in an account from 1803. However, the archives of Jaipur State, such as accounts from 1735 and 1737–1738, do not use this as Jantra, which in the spoken language is corrupted to Jantar. The word Jantra is derived from yantra, instrument, while the suffix Mantar is derived from mantrana meaning consult or calculate. The words jantar and mantar (or yantra and mantra) mean calculation instrument.
- Smithsonian (2013). Timelines of Science. Penguin. p. 136. ISBN 978-1465414342.
- Archaeological Survey of India, various authors, Nomination of The Jantar Mantar, Jaipur, for inclusion on World Heritage list, p.14 
- Unesco listing for Jantar Mantar accessed July 30 2021
- Sharma, Virendra Nath (1995), Sawai Jai Singh and His Astronomy, Motilal Banarsidass Publishers Pvt. Ltd., pp. 98–99, ISBN 81-208-1256-5
- Anisha Shekhar Mukherji (2010), Jantar Mantar: Maharaja Sawai Jai Singh's Observatory in Delhi, Ambi Knowledge Resource, ISBN 978-81-903591-1-5, retrieved 23 July 2013
- Jantar Mantar - The Astronomical Observatories of Jai Singh II, "a project initiated by Cornell University Professor of Art, Barry Perlus"
- Pictures with French text
- Jantar Mantar Jaipur Timings, Entry Fee
- India's mysterious gateway to the stars BBC Travel (2022-05-31)