A pencil sketch discovered in a notebook at the National Library of Scotland has rekindled interest in the historic Thiruvananthapuram Observatory’s pivotal role in geomagnetic research.
The sketch, depicting a magnetic observatory once located in Cherthala, was unearthed by a research team led by Prof. R. Jayakrishnan, the present director of the Observatory (then the Trivandrum Observatory).
This discovery prompted a detailed investigation into the scientific legacy of the observatory, culminating in a research paper titled ‘162 years of rendezvous with the Magnetic Equator by the Travancore Observatory’, published in the Indian Journal of History of Science.The paper chronicles the observatory’s contributions to mapping the magnetic equator in India and tracking its gradual southward migration toward Sri Lanka.
The first-ever magnetic equator map in India was published in 1839 through the collaborative efforts of John Caldecott, then director of the observatory, and T.G. Taylor of the Madras Observatory. Their findings revealed that the magnetic dip equator (a position where the Earth’s magnetic field is perfectly horizontal, and the magnetometer shows a ‘zero’ reading for the vertical component) lay at Bolghatty in Ernakulam in the west coast and Manamelkudi in Pudukkottai, Tamil Nadu in the east coast.
Over two centuries
Subsequent studies by East India Company engineers and Trivandrum Observatory scientists, including the renowned John Allan Broun, documented the equator’s continued migration. Over nearly two centuries, the observatory had meticulously traced this magnetic shift, while providing rare data that point to a possible geomagnetic reversal, a phenomenon where Earth’s magnetic poles gradually switch places.
When the Travancore kingdom became part of the country, the Trivandrum Observatory was taken over by the Central government. In 1961, the observatory’s geomagnetic work transitioned to institutions like the National Geophysical Research Institute (NGRI) and later the Indian Institute of Geomagnetism (IIG) in 1971. Despite closure of the original magnetic facility in 1999 and its relocation to Tirunelveli, the Thiruvananthapuram Observatory’s historic archives remain a treasure trove of data.
“We managed to retrieve some 40 documents from global repositories including Munich University, which include the second Almanac printed for the observatory for the year 1839, but we will lack the first Almanac for 1838. Compiling data from the Almanac from the year 1839 to 1941 we have made the discovery that Thiruvananthapuram Observatory recorded the movement of the magnetic equator both in the southward and northward direction in those 98 years,” Prof. Jayakrishnan said.
He added that the Thiruvananthapuram Observatory is the only in the world that may have recorded the migration of the magnetic equator over its geographical location.
Published – November 02, 2025 09:19 pm IST
