Zero Shadow day

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Overview:

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

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.


Q1: What is the Tropic of Cancer?

It is a latitude approximately 23°27′ N of the terrestrial Equator. This latitude corresponds to the northernmost declination of the Sun’s ecliptic to the celestial equator.

Source: Children experience “Zero Shadow” phenomenon