Zero Shadow Day

About Zero Shadow Day:

• It is a sub-solar point where the sun is directly overhead at a particular latitude.
• When the sun is at the zenith (the highest point in the sky) its rays will be hitting a particular point exactly perpendicular to the surface. This will make the shadow of a person exactly under him, making it look like there are no shadows. 

 When does it occur?

• There are two zero shadow days every year in May and July/August, observed in places that lie between the tropic of Cancer and the tropic of Capricorn.
• One falls during the Uttarayan (when the Sun moves northwards), and the other is during Dakshinayan (when the Sun moves southwards).
• It lasts for a small part of a second, but the effect can be seen for a minute to a minute-and-a-half.