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Zero Shadow Day

Zero Shadow Day:

A group of students was provided a first-hand experience of the Zero Shadow Day (ZSD) phenomenon at an event organised by the Pondicherry Science Forum (PSF).

  • Zero Shadow Day 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.
  • 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.