A group of students was provided a first-hand experience of the Zero Shadow Day (ZSD) phenomenon at an event organised by the Pondicherry Science Forum (PSF).
Using cylindrical PVC pipes placed on a metal plate base, students gathered at the Petit Seminaire Higher Secondary School to watch the shadow of an object shifting position on a piece of white paper .
At 12.09 p.m. all the participants joined hands to form a circle under the sun and witnessed their shadows under their feet.
The event aimed to raise awareness on how the long shadows of objects at sunrise start becoming smaller and smaller as the day progresses until the shadow is smallest when it is exactly aligned north-south. People between the latitudes 23.5 deg. south ( Tropic of Capricorn) and 23.5 deg. north ( Tropic of Cancer) can experience the sun right overhead at zenith (an imaginary point directly above a particular location) twice every year, once between the December solstice (December 21 and 22) and June solstice (June 20 and 21) and then between the June solstice and December solstice. (For Puducherry this falls in April and August).
According to the PSF, locations north of the Tropic of Cancer and south of the Tropic of Capricorn will never experience the sun right overhead. Twice a year, there would be no shadow at noon, when the sun would be exactly at the zenith. When the latitude of a place equals the declination of the sun, the sun’s rays are perpendicular on this latitude and exactly at noon the sun is right overhead and the shadow of a vertical object falls right below to denote a zero-shadow moment in time.
Earlier, as part of the event, R. Madivanan, PSF president, gave a presentation. He also interacted with the students and clarified their doubts. Pamphlets describing all about the ZSD and its scientific significance were distributed.
The next ZSD event in the city will occur on August 19, when the sun which turns from its south-north transit returns in the opposite trajectory, which the almanacs refer to as ‘Uttarayan’ and ‘Dakshinayan’, said A. Hemavathi, PSF vice president.
John Paul, school vice principal and Murugavel and Vijaya Ganapathy from the PSF also participated.
