What is Zero Shadow Day: Bengaluru to witness this rare celestial event on August 18

"I thought the most beautiful thing in the world must be shadow" - Sylvia Plath wrote this line in her novel The Bell Jar. The shadow might be the most beautiful thing, but Zero Shadow Day, when the objects will not cast any shadows, can be stunning too. 

What is Zero Shadow Day? 

Zero Shadow Day is a special celestial event and it occurs twice a year. When the Sun is at its highest point in the sky during this time, neither living creatures nor inanimate objects cast any shadows. 

For areas in the tropics (between the Tropic of Cancer at latitude 23.4° N and the Tropic of Capricorn at latitude 23.4° S), Zero Shadow Day occurs twice a year. Zero Shadow Day basically happens twice a day at a particular place. 

India: Zero Shadow Day on August 18 

In India, Bengaluru, which is the capital and largest city of the southern Indian state of Karnataka, is all set to witness this phenomenon on August 18. It happens for a specific time in the day, In Bengaluru, it will be most noticeable at 12:24 pm (local time). The last time it occurred in Bengaluru was on April 25 this year.

How does it happen? 

This rare event occurs when the Sun's declination matches the location's latitude. When the Sun crosses the local meridian on a day with zero shadows, the Sun's rays fall perfectly vertically relative to an item on the ground, and no shadow of that object is visible. 

The concept of Zero Shadow Day 

We have studied that the seasons exist because the Earth's rotation axis is 23.5 degrees, inclination to the plane of its revolution around the Sun. 

The Sun will shift in a year from 23.5 degrees south of the celestial equator to 23.5 degrees north of the equator (Uttarayan) and back again (Dakshinayan) when it is at its highest point during the day. 

The two equinoxes mark the Sun's passage over the equator and the two solstices mark the northern and southernmost points on the globe. 

Hence, the Sun's declination will be equal to a person's latitude twice for those who live between +23.5 and -23.5 degrees latitude: once during Uttarayan and once during Dakshinayan. 

The Sun will be directly overhead at noon on these two days, and no objects will cast shadows on the ground. Notably, there will be regional differences on this Zero Shadow Day.