An excellent assembly of architectural astronomical instruments built by Maharaja Jai Singh II is known as Jantar Mantar. Jantar means instrument, and Mantar stands for formula which in this context can be applied as calculation hence Jantar Mantar means calculation instrument.
Fourteen major geometric devices for measuring time, predicting eclipses, tracking stars location as the earth orbits around the sun, ascertaining the declinations of planets, and determining the celestial altitudes and related ephemerides are housed in the facility at Jaipur. Each one of these instruments’ is fixed to the ground and is a tool with specific objective. The Samrat Yantra, the largest instrument, with 90 ft height at an angle of 27° is meant to tell the time of day. The Hindu ‘chhatri’ or small cupola was the platform from where arrival of monsoon and eclipses were announced. All the instruments in the facility were built by the local stone and marble. Each instrument is built in an astronomical scale with marking on inner lining. A walk through Jantar Mantar is like going across solid geometry and facing around an astronomical system meant to communicate with the solar system.
The instruments are huge structures built with a belief that the size would enhance the accuracy; however, they have all been proved to lack any practical significance. Additionally the masons who built these structures had no comprehension of their purpose and had no experience of building anything of that scale either. The observatory is still used to predict weather for farmers and students of astronomy and Vedic astrology take some of their lessons here and it is still considered as representing the Vedic thoughts. However, smaller instruments like the Ram Yantra are appreciated for their innovative design and accuracy.
A quick and brief understanding of the 14 instruments of Jantar Mantar of Jaipur:
1.Samrat Yantra is the Sun Dial meant for calculating the time of the day.
2.Ram Yantra is an instrument used to indicate the altitude and the azimuth or declination of celestial bodies.
3.Jai Prakash Yantra is used to find out the positions of the celestial bodies during days and nights.
4.Dhruva Yantra is used to locate the position of 12 Zodiac signs and also the Pole Star at night.
5.Narivalya Yantra constitutes of two dials used to read time both in southern and northern hemisphere.
6.Kranti Yantra is used for direct measurement of the longitude and latitude of the extraterrestrial bodies.
7.Raj Yantra was used only once a year to calculate the Hindu calendar.
8.Unnsyhsmsa Yantra was used for finding the altitudes of the heavenly bodies.
9.Chakra Yantra gives the angle of an object from the equator.
10.Disha Yantra or the compass that always points to the north.
11.Dakshina Yantra was used for observing the position and movement of heavenly bodies while passing over the meridian.
12.Large Samrat Yantra is ten times larger accurate than the Samrat Yantra. It is used to predict quality of the monsoon locally.
13. Rashivalayas Yantra has 12 sundials for the signs of the zodiac.
14.Jai Prakash Yantra is used for quality check on all the other instruments.