Zero Shadow Day

In News

• At 12:17 PM IST on April 25, Bengaluru and at all places along the 130  north Latitude experienced a ‘Zero Shadow Day’.

What is ‘Zero Shadow Day’(ZSD)?

• A ZSD is a day on which the Sun does not cast a shadow of an object at solar noon, when the sun will be exactly at the zenith position(highest point in the sky)
• ZSD happens twice a year for locations in the tropics (between the Tropic of Cancer at +23.5 degrees of latitude and the Tropic of Capricorn at -23.5 degrees of latitude). So, places north of Ranchi in India does not have Zero shadow day.
• One ZSD falls during Uttarayan (movement of the Sun from south to north from winter solstice to summer solstice) and one other during Dakshinayan (back from north to south).   
• The dates will vary for different locations on Earth.

Why does a ZSD happen?

• Uttarayan and Dakshinayan happen because Earth’s rotation axis is tilted at an angle of roughly 23.5° to the axis of revolution around the Sun.
• When the Sun is at the zenith its rays make the shadow exactly under it, making it look like no shadow.

Source: IE