Recently, Bengaluru experienced a ‘Zero Shadow Day’, when vertical objects appear to cast no shadow.
Zero Shadow Day happened in Bengaluru at 12.17 p.m. on April 25. On this day, the Sun will be directly overhead and hence any vertical object will not cast a shadow.
As per the Astronomical Society of India, this annual celestial phenomenon occurs twice a year for places between +23.5 and -23.5 degrees latitude. The Sun is almost never exactly overhead at noon but usually transits a bit lower in altitude, a bit to the north or a bit to the south.
What is Zero Shadow Day?
- Zero Shadow Day is a phenomenon that occurs twice a year at every point on Earth located between the Tropic of Cancer and the Tropic of Capricorn.
- During Zero Shadow Day, vertical objects appear to cast no shadow at local noon, when the sun is at its zenith directly above the object.
- It occurs when the sun’s location moves from 23.5°N to 23.5°S of Earth’s equator and back, causing the shadow to disappear beneath objects at local noon.
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.
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