Kolkata will have its zero shadow moment on June 5 when there will be no shadow from sunlight at a particular time of the day. This happens twice a year when the sun is exactly overhead, astrophysicist Debiprosad Duari said on Wednesday.
“Any form of visible light falling on an object generally produces a shadow, unless it is exactly above the object. People and any object, all around the world, living between the Tropic of Cancer and Tropic of Capricorn (+23.5 and -23.5 degrees latitude) lose their shadows, though momentarily, twice a year. These two days are called zero shadow days,” he said.
The city is around 2,500 km from the equator and around 93.5 km from the Tropic of Cancer, the imaginary line which passes close to Krishnanagar in Nadia district.
For Kolkata, the first zero shadow day this year will be on June 5, 2022 and the zero shadow moment will be around 11:34 am. However, in other locations, the day of zero shadow will vary depending upon their position between the two Tropics, Duari said.
On its return path (called Dakshinayan), the sun will again be exactly overhead in Kolkata on July 7, at around 11:41 am and it will be the second zero shadow day of the year, he added.
Every year on the zero shadow days, students and astrophiles who are located between the two Tropics erect vertical poles, place different objects and sometimes even stand outside to see the cosmic event for themselves.
Various cities where the zero shadow day has already occurred this year have experienced the zero shadow moment when every object under the sun lost its shadow for a few moments.
Duari said this event also reminds people of the motions and position of celestial bodies with respect to Earth, and this has direct links to events on the planet like change of seasons, tides and eclipses, besides the zero shadow moments.
The sun is almost never exactly overhead at noon, but usually transits lower in altitude a bit to the north or a bit to the south, he added.