Zero Shadow Day (ZSD)

News: The Cosmology Education and Research Training Center (COSMOS), Mysuru, of the Indian Institute of Astrophysics observed ‘Zero Shadow Day’ recently. Zero Shadow Day (ZSD).

About Zero Shadow Day (ZSD)

• ZSD is a fascinating astronomical phenomenon that occurs twice a year in locations situated between the Tropic of Cancer and the Tropic of Capricorn.
• All places whose latitude equals the angle between the Sun’s location and the equator on that day experience ZSD.
• This event is a direct result of the Earth’s axial tilt (23.5 degrees) and revolution around the Sun.
• Frequency of phenomenon:
  • First time when the Sun is directly overhead the Tropic of Cancer on 21 June (summer solstice in the northern hemisphere) and then journeys southwards as seen from the Earth, called Dakshinayana.
  • Second time when the Sun is overhead the Tropic of Capricorn on 22 December. It is then seen to journey northwards, called Uttarayana.
  • Hence, the Sun is directly overhead locations between the two tropics twice a year, and this day varies with latitude.
  • When the Sun is directly overhead, the shadow of a vertical object falls under it, and hence no shadow will be seen at local noon.
• Although the exact moment of Zero Shadow occurs instantaneously, the effect can be observed for a short duration, typically lasting for about a minute to a minute-and-a-half.