The Jantar Mantar is a collection of architectural astronomical instruments, built by Maharaja Jai Singh II in Jaipur between 1727 and 1734. It is modeled after the one that he had built in Delhi. There are five such observatories in different locations and the one at Jaipur is the largest of these. Initially Jantar Mantar was named as Yantra Mantra, which means instruments and formulae, but due to mispronunciation of the term, it is changed to its current name.
The instruments in Jantar Mantar are wholly constructed with stone and marble with an astronomical scale on the inner lining of each device. The observatory has a remarkable collection of fourteen statistical instruments for measuring time, predicting eclipses and to ascertain other astronomical events. One of the highlights is the Sundial which tells the time to an accuracy of about two seconds in local time of Jaipur. Jantar Mantar was carefully renovated in 1901 and was declared a national monument in 1948.
The Samrat Jantar, the largest instrument in Jantar Mantar is 90 feet high and when its shadow falls on the ground you can tell the time of day. Its face is angled at 27 degrees, which shows the latitude of Jaipur and was also used to predict the length and heaviness of the monsoon for the particular region.. The announcement of eclipses and the arrival of monsoons are done from the small dome shaped cupola on its top.
Other instruments are the Dhruva Yantra which is used to pinpoint the position of 12 Zodiac signs as well as the Pole Star at night, the Narivalya Yantra which is a unique sundial with two dials – the first dial facing south reads time when the sun is inclined towards the Equator and Tropic of Capricorn in the southern hemisphere, between the time period 21st September to 21st March and the other one facing north reads time for the rest of the year when the sun is in the northern hemisphere that is inclined on Equator and Tropic of Cancer, i.e., from 21st March to 21st September.
The Kranti Yantra is used for direct measurement of the longitude and latitude of other heavenly bodies apart from earth. The Raj Yantra or the King of Instruments was used only once a year to calculate the Hindu calendar, the Unnsyhsmsa yantra for determining the altitudes of the heavenly bodies, the Chakra yantra to find an angle of an object from the equator, the Disha yantra or the compass pointing to the north, the Dakshina yantra to observe the position of heavenly bodies when passing over the meridian, the Rashivalayas Yantra has 12 sundials for the signs of the zodiac and the the Jai Prakash Yantra was used to cross check the accuracy of all the other instruments.
