Delhi’s Jantar Mantar observatory on the road to former glory

At the northern wall of “Misra Yantra” or composite instrument, work is currently underway on the “Karka Rashi Valaya”

Pre-telescopic astronomical instruments at Jantar Mantar from the 18th century are among the most popular historical marvels of Delhi, but many are not aware of them due to the instruments lying partially functional or dysfunctional.

A view of the “Samrat Yantra” and “Misra Yantra” (in background). (Sanchit Khanna/HT Photo)

While the observatory may have faded over time, its historical significance has not, as evidenced by the Archaeological Survey of India (ASI) working with a team of experts to restore some instruments that have lost their accuracy and others, their markings.

At the northern wall of “Misra Yantra” or composite instrument, one of three astronomical pre-telescopic instruments at Jantar Mantar, work is currently underway on the “Karka Rashi Valaya”, which roughly translates to “change of seasons”, under the first phase of the restoration undertaken by the Archaeological Survey of India (ASI) since the second half of December 2024.

The “Karka Rashi Yantra” consists of an inverted D arch, marking 180 degrees, and a rod-like structure at the top, which acts as a needle and whose shadow helps with calculations. At the bottom is a slab with calibrations for calculation, which will be replaced with marble and recalibrated.

Aalok Pandya, an expert collaborating with ASI on the restoration work, said the shadow of the needle casts a full shadow over the D-structure on June 21 or the summer solstice, when the day is the longest in a year.

“The needle is supposed to cast a shadow from spring equinox, March 21 to autumn equinox, September 23. After that, we will not see any shadow. Of course, other factors such as cloudy skies and presence of high-rise buildings also affect the shadow,” Pandya, who is a physics and astronomy expert with the Indira Gandhi National Tribal University, Madhya Pradesh, said.

Pandya said that the wall of the instrument must have a southward slope of 5.1 degrees, to mark the difference between the latitude of Delhi (~28.51 degrees) and the Tropic of Cancer (23.5 degrees). “That also contributes to the formation of the shadow and accurate calculations. However, the wall was not uniform and had a slope of 4-6 degrees at different places,” he said.

ASI confirmed that the wall is being replastered. “The marble will be scaled after this, as per the calibrations provided by the experts. Then lead inking of the markings will be done to make it easily decipherable. This work should be done in one and a half months. We want to get it working by March, when the instrument becomes functional,” An ASI official said.

History, working

Among the five observatories built in the 18th century under the guidance of Maharaja Sawai Jai Singh II, the ruler of Amber, Rajasthan (1724-1734), the facility at Delhi was the first to be established, followed by others at Jaipur, Ujjain, Varanasi and Mathura.

However, currently, only the Jaipur observatory is fully functional, an ASI official with the Jantar Mantar sub-circle said. The official said that once the restoration is completed, visitors to Jantar Mantar will be able to experience first-hand the accuracy of instruments and gain accurate information.

During HT’s visit, an official pointed to an instrument titled the “Laghu Samrat Yantra”, which is also part of the “Misra Yantra” and is used to calculate local time.

The second ASI official, pointing to the instrument, said: “Look at the shadow cast on the arch of the instrument. There are faded markings and if you calculate using those, you can tell it is 2.15pm.”

The instrument was 10 minutes late as the time was then 2.25pm, which the official said will be fixed in the ongoing restoration.

The other instruments

The “Misra Yantra” is among one of four astronomical and astrological instruments in place at the observatory. The others are the “Samrat Yantra” or supreme instrument, which is the central structure of the observatory that measures time and declination of the sun; the “Ram Yantra”, which is used to measure the altitude and azimuth of celestial objects and the “Jaiprakash Yantra”, which is an astrological instrument to record details of a person’s birth, with the sun as the reference point.

The second ASI official said restoration plans were in the works for the past six to eight months and in the next phase, restoration of the “Daksinottara Bhitti Yantra” will be taken up. This “yantra” depicts the changing altitude of the sun throughout the year and is the smallest one at the observatory, the official said.

According to ASI, all the instruments originally had markings engraved into slabs of marble. “However, maybe due to vandalism at a later period of time, the marbles were taken out. There was some amount of repair at a later stage and it was fixed up with plaster. The markings were made into plaster, causing them to fade,” a third ASI official, responsible for the conservation of the site, said.