Jantar Mantar literally means 'calculating instrument'. It is an observatory with a collection of fifteen architectural astronomical instruments built by King Sawai Jai Singh II, at the beginning of the 18th century in Jaipur, India. Six of these instruments use sunlight and 11 operate with the reflection of lunar and starlight.
These instruments are designed to measure time, predict eclipses, track the location of the most important stars, determine the declines of the planets and determine celestial altitudes and related ephemerides.
In the photo’s general view, which I took from a Sundial's staircase, we observe the group of twelve Rashivalaya instruments, which are 12 gnomon dials to measure the ecliptic coordinates of stars, planets and 12 systems of zodiacal constellations. Just behind, you see 2 Ram Yantra, cylindrical instruments to measure altitude and azimuth of celestial bodies. A little further back, we have also 02 Ram Yantra of larger size, and among them with a circular shape, Digansha Yantra, an instrument of great precision to determine the azimuth of the sun. Back to the right a solar clock, Kranti Yantra. Closer to the right, there is Kapali Yantra, two concave hemispheres used for graphic resolution of various astronomical problems. In the middle of them, Chakra Yantra, two large metal circles that provide the declination of the Sun at four specific hours of the day, equivalent to four local hours from different parts of the world.
Built with local stone and marble, each instrument has an astronomical scale, usually marked on the interior marble cladding. Bronze tablets, bricks and mortar were also used to build the instruments
The most impressive structure, is the world's largest stone sundial, Samrat Yantra, is 27 meters high, and its shadow moves at 4 meters per hour. You can see a small vaulted dome at the top to detect eclipses and to announce the arrival of the monsoons. This clock measures the time with an accuracy of no more than two seconds of error.
Some young Indians, accompanied me on the tour explaining part of the comments on post. They were very proud of such a wonderful scientific place.