Rajasthan: Jantar Mantar of Jaipur

Jantar Mantar, built between 1728 and 1734, literally means the ‘instruments
for measuring the harmony of the heavens’. Jai Singh, the brain behind the grand project, chose stone with marble facing. This was the biggest of all his observatories and the only one built of stone. He used it daily, often with his astronomy gurus Pandit Jagannath and Kewal Ram. In all there are 17 instruments in the Jantar Mantar complex. The function of each instrument is rather complex but serves a particular function where time plays the main theme.

• Astronomical instrument at Jantar Mantar

• The Ram Yantra

The twin circular sundials of the Ram Yantra remind viewers of dueling Roman Coliseums. Used to measure the altitude and azimuth of celestial objects such as the sun and stars, these monumental instruments are in fact perfect complements of one another – the solid portions of one Ram Yantra’s floor correspond to open spaces in that of its partner. 

The cut-outs allow observers to note the precise positions of shadows cast by a central gnomon without inadvertently blocking the light. Should the shadow fall into a space inside one Ram Yantra, the observer simply moves to the other instrument. This pattern is repeated with several other calculating instruments of the Jantar Mantar.

• Impressive instruments at the outdoor observatory.

The Chakra Yantra is the pair of upright metal circles in the photo. They stand between a pair of hemispheres (bowl shapes) lowered into the ground in front of and behind the metal circles. The pair of hemispheres is the Kapali Yantra, discussed on the next page.

As for the Chakra Yantra, it is an instrument for finding the right ascension and declination of a planet or other celestial body observed at night.

To understand these coordinates, it may help if you visualize the earth's lines of longitude and latitude projected up onto the sky, such that the north star corresponds to earth's north pole. Earthly latitude is the angular distance north or south of the equator, and earthly longitude is the angular distance around the polar axis as measured from any arbitrary starting point - in this case, the meridian of Jaipur.

• Samrat Yantra