Zero Shadow Day makes the shadows disappear briefly. (Representational Pic)
Bengaluru will witness a unique celestial event on Tuesday, April 25. For a brief period of time, vertical objects in the city will not be having shadows, due to a phenomenon are calling Zero Shadow Day. The phenomenon will take place at 12:17 pm. The Indian Institute of Astrophysics (IIA) at Bengaluru's Koramangala will organise events at its campus to mark the occasion. Several Bengaluru residents have started tweeting photos getting ready for the event where no shadow of the objects will be visible for a few moments.
What is Zero Shadow Day?
According to Astronomical Society of India (ASI), the Sun will not cast a shadow of an object at solar noon, when it is exactly at the zenith position, causing the phenomenon to occur.
The ASI further said that Zero Shadow Day occurs twice a year for locations in the tropics (between the Tropic of Cancer and the Tropic of Capricorn). For people living in these areas, the Sun's declination will be equal to their latitude both during Uttarayan and Dakshinayan.
Why does this happen?
The ASI said that the Earth's rotation axis is inclined at 23.5 degrees to the plane of its revolution around the Sun, which causes different seasons to occur. This means that the Sun, at its highest point of the day, will move from 23.5 degrees south of the celestial equator to 23.5 degrees north of the equator (Uttarayan), and back again (Dakshinayan), in a year.
Due to this rotational movement, one Zero Shadow Day falls during the Uttarayan (when the Sun moves northwards), and the other falls during Dakshinayan (when the Sun moves southwards). For people living between 23.5 degrees north and 23.5 degrees south latitudes, the Sun's declination will be equal to their latitude twice.
What is the duration of a Zero Shadow Day?
The actual phenomenon only lasts a fraction of a second, but its effect can be seen for up to a minute and a half.
Bhubaneswar in Odisha has also experienced Zero Shadow Day in 2021.