Children experience the ‘Zero Shadow’ phenomenon

Students of Zero Shadow Day program organized by Pondicherry Science Forum on Sunday. | Photo credit: SS KUMAR

A group of students got to experience the Zero Shadow Day (ZSD) phenomenon first-hand at an event organized 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 change position on a piece of white paper.

At 12:09 p.m., all participants joined hands to form a circle under the sun and witness their shadows under their feet.

The event was intended to raise awareness of how the long shadows cast by objects at sunrise become smaller and smaller as the day progresses, until the shadow is smallest when aligned exactly north-south. People between latitudes 23.5 degrees. south (Tropic of Capricorn) and 23.5 degrees. north (Tropic of Cancer) can experience the sun directly overhead at the zenith (an imaginary point directly above a given location) twice a year, once between the December solstice (December 21 and 22) and the June solstice (20 and June 21) and then between the June solstice and the December solstice. (For Pondicherry 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 directly overhead. Twice a year there was no shade around noon, even though the sun was exactly at the zenith. When the latitude of a place is equal to the declination of the sun, the sun’s rays are perpendicular to this latitude and at exactly noon the sun is directly overhead and the shadow of a vertical object falls exactly below it, which is a moment in time without shadow.

Earlier, PSF Chairman R. Madivanan gave a presentation as part of the event. He also interacted with the students and clarified their doubts. Pamphlets were distributed describing everything about the ZSD and its scientific significance.

The next ZSD event in the city will occur on August 19, when the sun, turning from its south-north transit, returns to the opposite trajectory, which the almanacs refer to as ‘Uttarayan’ And ‘Dakshinayan’, said A. Hemavathi, vice president of PSF.

John Paul, vice-principal of the school, and Murugavel and Vijaya Ganapathy of PSF also participated.