The Jantar Mantar is an equinoctial sundial, consisting 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 is intended to measure the time of day, correct to half a second and declination of the Sun and the other heavenly bodies.
There are five Jantar Mantar monuments in India, of which the largest is in Jaipur which features many instruments along with the world’s largest stone sundial. The Vrihat Samrat yantra is a sundial that can give the local time to an accuracy of 2 seconds. It is a UNESCO World Heritage Site.
In the early 18th century, Maharaja Jai Singh II of Jaipur constructed five Jantar Mantars in total, in New Delhi, Jaipur, Ujjain, Mathura and Varanasi; they were completed between 1724 and 1735.
1. Jantar Mantar of Jaipur
The Jantar Mantar monument in Jaipur, Rajasthan is a collection of nineteen architectural astronomical instruments built by the Rajput king Sawai Jai Singh II, and completed in 1734. It features the world’s largest stone sundial, and is a UNESCO World Heritage site. It is located near City Palace and Hawa Mahal. The instruments allow the observation of astronomical positions with the naked eye. The monument expresses architectural innovations, as well as the coming together of ideas from different religious and social beliefs in 18th-century India. The observatory is an example of the Ptolemaic positional astronomy which was shared by many civilizations.
2. Jantar Mantar of New Delhi
Jantar Mantar is located in the modern city of New Delhi. It consists of 13 architectural astronomy instruments. The site is one of five built by Maharaja Jai Singh II of Jaipur, from 1723 onwards, as he was given by Mughal emperor Muhammad Shah the task of revising the calendar and astronomical tables. There is a plaque fixed on one of the structures in the Jantar Mantar observatory in New Delhi that was placed there in 1910 mistakenly dating the construction of the complex to the year 1710. Later research, though, suggests 1724 as the actual year of construction.
3. Jantar Mantar of Varanasi
Jantar Mantar is an observatory built in Varanasi in the year 1737 by Maharaja Jai Singh II of kingdom of Amber (later called Jaipur). The observatory is one of the five observatories built by Maharaja Jai Singh II.
4. Ved Shala : Jantar Mantar of Ujjain
Vedh Shala or Jantar Mantar is located in the holy city of New Ujjain. It is an observatory built by Maharaja Jai Singh II in 1725 which consists of 13 architectural astronomy instruments. The observatory is one of the five observatories built by Maharaja Jai Singh II when he was governor of Ujjain.
5. Jantar Mantar of Mathura
Raja Jai Singh and his astrologer Pt. Jagannath contributed their invaluable contributions in the spread of this science by composing texts like ‘Yantra type’ and ‘Emperor theory’. He has established 5 observatories in his care, out of which Mathura was the last one. After it, Jai Singh also added Indian astronomy to European ideology. So it would be fair to say that Jaisingh’s observatories became the basis of the constellations of the future in India. Thus a circle of constellations is completed from the observatory and observatories from stone structures.