Zero Shadow Day

By : Neha Dhyani

Updated : May 12, 2022, 8:39

Zero Shadow Day is a rare celestial occurrence that happens twice a year. When the sun is at its greatest position in the sky, no shadows of any object or living being are visible. On May 21st, 2021, Bhubaneswar, Odisha, observed Zero Shadow Day for roughly 3 minutes.

The days when the sun rises at true east and sets at true west are known as Zero Shadow Days (ZSD). It's a biannual occurrence when the sun is directly overhead and all shadows vanish for a few minutes. When the sun reaches its greatest position in the sky, its rays will strike a specific spot that is exactly parallel to the surface.

History of the Zero Shadow Day

At a specific location, Zero Shadow Day occurs twice a day. It typically occurs between the Tropics of Cancer and Capricorn. When the sun is at its zenith (highest point in the sky), its rays cause any object's shadow to fall exactly beneath it, causing it to disappear.

The Indian states of Chennai, Mumbai, and Pune are located between the Tropics of Cancer and Capricorn, therefore they are likely to have Zero Shadow Day, however, New Delhi is not located between the Tropics of Cancer and Capricorn, so it will not experience Zero Shadow Day.

The Idea behind Zero Shadow Day

Seasons are caused by the Earth's rotation axis which is inclined at 23.5 degrees to the plane of its revolution all around the Sun. In a year, the Sun will move from 23.5 degrees south of the celestial equator to 23.5 degrees north of the equator (Uttarayan) and back (Dakshinayan) at its greatest point of the day.

Facts about the Zero Shadow Day

As a result, one Zero Shadow Day occurs during the Uttarayan (when the Sun goes northwards) and the other occurs during the Dakshinayan (when the Sun moves southwards). The Sun's declination will be equal to their latitude twice for persons living between 23.5 degrees north and 23.5 degrees south latitudes.

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Significance of Zero Shadow Day

It occurs twice a year, in May and July or August, and is commemorated in locations around the world. Although this phenomenon only lasts a fraction of a second, the effect can be seen for up to a minute and a half.

Zero Shadow Day is a rare celestial occurrence when no shadow of an object or being can be seen. When the sun reaches its greatest point in the sky at all points between the Tropics of Cancer and Capricorn, the occurrence occurs twice a year.

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A sub-solar point occurs during Zero Shadow Day when the sun is directly overhead at a specific latitude. When the sun is at its zenith (highest point in the sky), its rays will strike a specific spot on the surface that is perfectly perpendicular to it. This will make any object's shadow fall perfectly beneath it, making it appear as if there are no shadows.

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FAQs on Zero Shadow Day

Q.1. What does "Zero Shadow Day" imply?

At midday, when the sun is precisely at the zenith point, a Zero Shadow Day occurs when the Sun does not throw a shadow on an object. For places between +23.5 and -23.5 degrees latitude, Zero Shadow Day occurs twice a year (between the tropics of Cancer and Capricorn, respectively).

Q.2. Which city experienced Zero Shadow Day?

The city of Bhubaneswar in Odisha experienced Zero Shadow Day.

Q.3. How can you figure out how many Zero Shadow Days there are in a year?

The Sun will be directly overhead twice a year, once during 'Uttarayan' and once during 'Uttarayan', at all areas on Earth between both the Tropics of Cancer and Capricorn, when it is at its highest position in the sky at midday.

Q.4. What is the duration of Zero Shadow Day?

Although Zero Shadow Day only lasts a fraction of a second, the effect can be seen for up to a minute and a half.

Q.5. The Zero Shadow Day occurs how many times a day?

At a specific location, Zero Shadow Day occurs twice a day.