Tracing The Mystery: Magnetic Equator Shifts Southward From Cherthala And Kollam To Sri Lanka

By G Nandan

Thiruvananthapuram: Remember your school Geography chapter on the 'equator' - that imaginary line dividing the Earth into two halves? Back then, teachers would often joke that the equator was a wavy, wandering line. It took years to understand that that it's actually a precise imaginary circle dividing the planet.

However, very few people know that there's another invisible line, the magnetic equator, and that an European scientist at the Thiruvananthapuram Observatory had wandered more than 20 kilometers in search of it back in the 19th century. As per scientists, its slow southward drift from Kerala to Sri Lanka has been quietly recorded for nearly two centuries at the Observatory here.

The Thiruvananthapuram Astronomical Observatory, located within the city museum premises, was one of the key astronomical observatories established across the world during the 19th century. It played a crucial role in gathering geographical and astronomical data from South India. Dr R Jayakrishnan, the current Director of the Observatory and faculty member at the University of Kerala's Department of Physics, has been documenting this remarkable history, detailing the story of how the observatory traced the path of the magnetic equator.

Studying with a Magnetometer

The geographical equator divides the Earth into northern and southern hemispheres. However, the magnetic equator is determined entirely by the magnetic and gravitational factors of the Earth's core and space environment.

According to Jayakrishnan, the first accurate mapping of the magnetic equator in India was carried out by John Caldecott, the first director of the Thiruvananthapuram Observatory, along with PG Taylor and their research team. Between 1837 and 1839, they conducted measurements on foot, traveling about 20 kilometers across the eastern and western coasts, from Ongole in Andhra Pradesh to Bombay (now Mumbai).

Their observations confirmed that India's magnetic equator then passed through Bolgatty in Ernakulam and Manamelkudi in Tamil Nadu (1839). Based on coastal readings, they concluded that the line ran roughly straight across the subcontinent.

Isoclinical lines in southern India (ETV Bharat/Special Arrangement))

The studies were conducted using a magnetometer, which measured the vertical movement of a suspended magnet. As one moves north, the magnet tilts upward; as one moves south, it dips downward. When reaching the magnetic equator, the magnet becomes perfectly horizontal, showing no tilt, explained Jayakrishnan.

Southward Shift via Cherthala and Kollam

In 1844, engineers of the East India Company found that the magnetic equator had shifted about 20 kilometers south, from Manamelkudi to Pudukottai in Tamil Nadu.

Later, in 1859, John Allan Broun, the second director of the Thiruvananthapuram Observatory, discovered that the magnetic equator had reached Cherthala (in present-day Alappuzha district). He even established a small observatory there. Though that structure was later lost due to lack of preservation, Jayakrishnan has obtained a pencil sketch of the building from the National Library of Scotland.

The Thiruvananthapuram Observatory used to publish a yearly volume titled "Astronomical Aphorisms", containing data on the positions of stars, rainfall, and magnetic equator observations. The first volume, published in 1839, was recently rediscovered in a library in Germany.

Over its years of operation, the observatory published over 100 such volumes, of which 40 have been recovered from libraries worldwide. Analysis of these records shows that the magnetic equator gradually moved southward each year, passing through Cherthala and Kollam before crossing further down.

By 1971, the line had passed through Anchal in Kollam and parts of Tamil Nadu.

By 1991, it had moved through Nagercoil in Tamil Nadu.

By 2025, scientists estimate, it will pass entirely through Sri Lanka.

Explaining the science behind, Jayakrishnan said, "This gradual shift supports the scientific theory that Earth's magnetic north and south poles periodically reverse, flipping positions over long timescales. The Earth's molten core, composed of liquid magma, rotates and flows, causing changes in the magnetic field that lead to the displacement of the magnetic equator."

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