Situated within the old city of Jaipur near the City Palace and Hawa Mahal is the UNESCO World Heritage Site of Jantar Mantar. Named after the words "yantra", which in Sanskrit means "instrument", and "mantrana" meaning "to calculate", the Jantar Mantar is an equinoctial sundial that measures the time of the day and the declination of the sun and the rest of the celestial sphere.

There are five Jantar Mantars built all over India during early 18^th century—four of it remains to this day—with the one in Jaipur housing the world's biggest stone sundial. A total of 19 architectural astronomical instruments was placed inside the Jantar Mantar complex in Jaipur during its construction from 1728 to 1738 under the reign of Rajput Maharaja Sawai Jai Singh II.

When the main observatory of the heavenly bodies was transferred from Delhi to Jaipur, the number of astronomers who worked at this site peaked to 23. It continued to become the Rajput Kingdom's main observatory until the death of Singh II in 1743.

Of the four existing Jantar Mantars in Jaipur, Delhi, Varanasi, New Ujjain, this site is considered as among the most prominent because it has the most number of instruments and the world’s largest sundial.

Each of the structural planetary instruments measures celestial positions using the method of “Ptolemaic positional astronomy" used by many older civilizations. It used to supply accurate readings before towering modern buildings blocked the view of the nighttime sky.

Vrihat Smarat Yantra: The World's Biggest Sundial

Occupying the center spot of the Jantar Mantar is a sundial and its gigantic gnomon standing 90 feet high. The "gnomon" is part of a sundial that provides measurement of the sun's position through the shadow it casts.

The Vrihat Smarat Yantra is said to measure time in intervals of a couple of seconds using the shadow casted by the gnomon from the sunlight.

Walking around the Jantar Mantar compound in Jaipur is like being inside a museum where astronomical instruments are displayed. Only in this case, each apparatus appears in a variety of architectural structural forms, each having their own interesting patterns and designs intricately thought out to match the movements of stellar objects in the sky.

Some of the architectural planetary devices that arrested my attention the most are the Laghu Smarat Yantra, which is appear like a stair but is actually a ramp pointed towards the North Pole used to calculate time up to the accuracy of 20 seconds.

Then there's the Ram Yantra, which is like a giant wheel lying on the ground surrounded by pillars in circular formation. It is used to measure the azimuth and elevation of the sun and other planets.

On the photo below, I am shown standing in front of the Nadivalaya Yantra, a structure composed of two sundials facing the south and north hemispheres. It is used to measure time up to an accuracy of less than one minute.

Another interesting instrument is the Jaya Prakash Yantra. It is a hemispherical bowls made of marble slabs used to measure positions of heavenly bodies by the hour.

Just to name a few, each instrument provided me with a new kind of learning and understanding of ancient astronomy and its practitioners who despite without the use of modern equipment, have managed to come up with a more thought-provoking way of studying and measuring the inter-stellar objects in the sky.