Zero Shadow Day

Zero Shadow Day

Subject :Geography

Section: Climatology

Context: On April 25, Bengaluru experienced a ‘Zero Shadow Day’, when vertical objects appear to cast no shadow.

What is Zero Shadow Day?

• ‘Zero Shadow Day’ is an astronomical event that occurs twice a year on specific dates in some parts of the world.
• It is a phenomenon that occurs when the Sun is directly overhead and the shadows of vertical objects such as poles, trees, and buildings disappear completely for a brief period of time.

Why does a Zero Shadow Day happen?

• Uttarayan (movement of the Sun from south to north from winter solstice to summer solstice) and Dakshinayan (back from north to south) happen because Earth’s rotation axis is tilted at an angle of roughly 23.5° to the axis of revolution around the Sun.
• Ramanujam explained that the Sun’s location moves from 23.5°N to 23.5°S of Earth’s equator and back. All places whose latitude equals the angle between the Sun’s location and the equator on that day experience zero shadow day, with the shadow beneath an object at local noon.

When does a Zero Shadow Day happen?

• The dates of Zero Shadow Day vary from place to place, and the event is more likely to occur near the equator. This phenomenon lasts for a small part of a second, but the effect can be seen for a minute to a minute-and-a-half.