Scores of youth and adults participated in a demonstration to simulate the measurement of the earth’s circumference as the sun cast no shadow shortly past noon in Karaikal enclave on Monday.
The Department of Science, Technology and Environment and Pondicherry Science Forum (PSF) had made preparations for a public demonstration of the phenomenon at the Dr. APJ Abdul Kalam Science Centre and Planetarium.
According to PSF coordinator A. Hemavathi, after a perfect sunrise exactly to the east in Karaikal, the sun travels to the zenith and at 12.10 p.m. reaches a point where it causes no shadow. Coinciding with Zero Shadow Day in Karaikal (10.92 degree latitude), a measurement device was set in Puducherry (11.95 degree latitude) similar to the one placed at GHS, Karaikal Medu.
With the aid of the shadow’s height and the distance between Karaikal and Puducherry and applying them in a simple mathematical equation, it was possible to infer the circumference of the Earth, the PSF said.
As early as 200 BC, Eratosthenes, Greek astronomer and the librarian of Alexandria in Egypt had first measured the circumference of the earth on the Zero Shadow Day. Eratosthenes measured the shadow’s length at Alexandria when no shadow formed at a well in distant Syene (now known as Aswan).
In fact, he measured the distance between the two places (about 800 km apart) with estimates of the time it took walkers, specifically trained to measure long distances with consistent strides, to go from one point to another. By using a combination of geometry and trigonometry he calculated the circumference of the earth as 40,000 km which was remarkably only off by 2% of the correct value 40,075 km, PSF said.
