Zero Shadow Day is a special celestial event that occurs twice a year. During this time, no shadows appear of any object or living being when the sun is at its highest point in the sky.
Odisha, Bhubaneswar witnessed Zero Shadow Day on May 21st 2021 for about 3 minutes. The topic, ‘Zero Shadow Day’ is relevant for candidates preparing for UPSC Prelims since it has been in news recently.
The article aims to provide detailed information on Zero Shadow Day to help candidates prepare for their IAS Exam (Science and Technology) as well as other competitive exams.
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What is Zero Shadow Day?
- Zero Shadow Days (ZSD) are the days when the sun will rise at true east and set at true west.
- It is a biannual phenomenon when the sun is exactly overhead and the shadows of any object disappear for a few minutes.
- A subsolar point happens when the sun is at its highest point in the sky, its rays will be hitting a particular point exactly perpendicular to the surface.
- Zero Shadow Day happens twice a day at a particular place. It usually happens in the regions between the Tropic of Cancer and the Tropic of Capricorn.
- When the sun is at the zenith (the highest point in the sky) its rays make the shadow of any object to be exactly under it, making it look like there are no shadows.
- Indian states of Chennai, Mumbai and Pune fall between Tropic of Cancer and Tropic of Capricorn and so are likely to observe Zero Shadow Day whereas, its capital New Delhi does not fall between Tropic of Cancer and Tropic of Capricorn and so it wouldn’t observe Zero Shadow Day.
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Zero Shadow Day – Concept
- The Earth’s rotation axis is inclined at 23.5 degrees to the plane of its revolution around the Sun, which is why we have seasons.
- Which means that the Sun, at its highest point of the day, will move from 23.5 degrees south of the celestial equator to 23.5 degrees north of the equator (Uttarayan), and back again (Dakshinayan), in a year.
- Hence, one Zero Shadow Day falls during the Uttarayan (when the Sun moves northwards), and the other falls during Dakshinayan (when the Sun moves southwards). For people living between 23.5 degrees north and 23.5 degrees south latitudes, the Sun’s declination will be equal to their latitude twice.
- Zero Shadow Day happens twice a year, in May and July or August, observed in places that lie between the tropic of cancer and tropic of Capricorn.
- 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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