Written by Adrija Datta
Several districts across West Bengal are set to witness the rare and scientifically significant phenomenon of Zero Shadow Day (ZSD) during the months of June and July this year.
“In Kolkata, Zero Shadow will occur on June 5 and July 7,” said Debapriya Roy, Head of Positional Astronomy Centre of Kolkata.
This astronomical event, which occurs twice a year in regions situated between the Tropic of Cancer and the Equator, takes place when the Sun is positioned directly overhead at local noon, causing objects to cast no shadow for a brief period.
In 2025, the Zero Shadow phenomenon will be observed in multiple districts of the state, including Kolkata, Howrah, Hooghly, Nadia, Medinipur, Bankura, and Purulia.
According to the Astronomical Society of India, the scheduled dates and times for these districts are as follows:
Kolkata: June 5 at 11:35 am and July 7 at 11:41 am
Howrah: June 5 at 11:35 am and July 7 at 11:42 am
Hooghly: June 8 at 11:35 am and July 4 at 11:41 am
Nadia: June 6 at 11:33 am and July 6 at 11:40 am
Medinipur: June 4 at 11:39 am and July 9 at 11:46 am
Bankura: June 13 at 11:42 am and June 30 at 11:45 am
Purulia: June 15 at 11:45 am and June 27 at 11:48 am
Zero Shadow Day occurs when the Sun’s declination—its angular distance north or south of the celestial equator—matches the latitude of a particular location.
At that exact moment, the Sun reaches its highest point in the sky directly overhead, eliminating any visible shadow for upright objects. The effect is most noticeable for a few minutes around solar noon, when the Sun crosses the local meridian.
“Members of our association will be carrying out individual experiments involving vertical objects on this day and will document their observations through photographs. The results of these experiments will later be shared on our social media platforms for public viewing.” said Dipankar Dey of the Sky Watchers Association of Kolkata.
This phenomenon is only experienced in the tropical zone, which lies between the Tropic of Cancer (23.5°N) and the Tropic of Capricorn (23.5°S).
Though the event has no direct meteorological impact, ZSD serves as an observable demonstration of Earth’s tilt and orbital motion, reinforcing fundamental principles of geography and astronomy.
Adrija Datta is an intern with the Indian Express