Jantar Mantar is a testament of the architectural brilliance and astronomical innovations of the Rajput era. Built by the Rajput king Sawai Jai Singh II - the founder of Jaipur city, the monument was completed in 1734. Maharaja Jai Singh II was a great scholar and had keen interest in astronomy. The name is derived from Sanskrit language - ‘Jantar’ from ‘yantra’, meaning instrument or machine, and mantar from mantrana meaning to consult or calculate. Therefore, in literal translation, Jantar Mantar means the ‘instrument used for calculation'. Jantar Mantar in Jaipur was restored several times during the British colonial rule. In the year 1948, it was declared a national monument. It was again restored in 2006. Jantar Mantar is managed under the Archeological Sites and Monuments Act of Rajasthan since 1961, and protected as a National Monument of Rajasthan since 1968.

The monument is an imposing collection of nineteen astronomical instruments, constructed out of local stone and marble, and spread over about 18,700 square metres. Each of these astronomical instruments carries an astronomical scale, generally marked on the marble inner lining. Bronze tablets, bricks and mortar, were also used in the construction of these instruments. This stone observatory includes complex instruments whose settings and shapes are scientifically designed, illustrating the glorious past of Medieval Indian astronomy. Jantar Mantar features the world's largest stone sundial - Vrihat Smarat Yantra.

The Jantar Mantar is an observatory comprising of 19 instruments to measure the position and distances of celestial bodies. These 19 instruments are structures carved out of stone, depicting interesting geometric shapes.
Popular structures inside the monument-
Vrihat Smarat Yantra
Vrihat Smarat Yantra is a huge sun dial at the centre of Jantar Mantar observatory. This 27m long structure is the tallest sundial in the world. ‘Samrat Yantra’ meaning ‘supreme instrument’ is an equinoctial sundial and calculates time up to the accuracy of two seconds.
Laghu Smarat Yantra
Popularly known as the small Smarat Yantra, this instrument is smaller in size, and measures the local time up to the accuracy of twenty seconds. The ramp of this sundial points towards the North Pole, so the local time in Jaipur can be easily calculated by measuring the position of ramp’s shadow on the divisions of the carved scale.
Ram Yantra
Ram Yantra measures the elevation and azimuth of Sun and planets, and consists of a pair of tube- shaped structures, open to the sky. Each tube-shaped structure has a pole of equal height at the centre. Scales indicating angles of altitude and azimuth of the celestial bodies are inscribed inside the walls of these structures. Ram Yantra is only found in Jantar Mantar of Jaipur and New Delhi.
Jaya Prakash Yantra
This yantra includes two hemispherical bowls like sundials with graded marble slabs. The elevation, azimuth, hour angles and exact position of heavenly bodies are detected using the inverted image of the sky, and the movement of the inverted shadows on the slabs.
Chakra Yantra
The chakra yantra as the name suggests is a ring instrument that measures the co-ordinates and the hour angle of Sun.
Digamsa
Digamsa is a pillar-like structure in the middle of two concentric outer circles, which is used to predict the sunrise and sunset timings in a day.
Nadivalaya
Consisting of a pair of circular plates, facing north and south, Nadivalaya symbolizes the two hemispheres of Earth.
Karnti Vritya
Karnti Vritya is a special instrument used to measure the solar sign of the Sun in daytime.

If you're someone who likes to glance at the sky to find a tiny star that’s many light years away, and wants to know more about medieval astronomy, then Jantar Mantar in Jaipur is a must-visit for you. You have the option to hire a guide when you visit this place, as it is always fascinating to know more about the history of the monument. However, there are audio guides available as well to help you know the significance of each structure and also gives a background about astronomy. The entry timing for Jantar Mantar in Jaipur is from 9 A.M. to 4:30 P.M. The entry tickets to the monument can be purchased either at the entrance or online. Indians can buy the ticket for Rs 50 and Foreigners for Rs 200.