Zero Shadow Day 2023 Date and Time: What is Zero Shadow Day?
On August 11, 2023What is Zero Shadow Day?
The famous American poet, Sylvia Plath, wrote that shadows were the most beautiful things in the world. But what if there were no shadows?
Zero Shadow Day (ZSD) is a unique and intriguing celestial event which occurs twice in a year, once during the Uttarayan period (Sun’s northward movement) and once during the Dakshinayan period (Sun’s southward movement). It takes place when the Sun is directly overhead at local solar noon. Hence, it will not cast shadows of any vertical object on the Earth’s surface.
On other days, the Sun is never exactly overhead at noon. It usually transits a bit lower in altitude, slightly to the north or slightly to the south.
On ZSD, the Sun reaches its highest point in the sky or zenith. So the length of the shadow will reduce to such an extent that it cannot be seen.
Why does ZSD happen?
ZSD happens due to 2 reasons.
The Earth, as we all know, has a tilted axis. This tilted axis and Earth’s orbit or rotation around the Sun are the two reasons for ZSD. When the Earth orbits the Sun, the angle at which the Sun's rays fall on the Earth's surface keeps changing throughout the year. This casts shadows in different directions and of different lengths.
The tilted axis of the Earth also causes the length of daylight to change across the world, causing the seasons.
The Earth’s axial tilt is around 23.45 degrees. Zero Shadow Day happens when the Sun’s declination is equal to the latitude of the location. Then the rays of the Sun will fall exactly vertical relative to objects on the ground. As a result, it will not cast a shadow of that object.
ZSD happens twice a year in places that are located between the Tropic of Cancer and the Tropic of Capricorn. It occurs near the equator.
In 2023, the first ZSD was on April 25. The second one will be on August 18.
On ZSD, tall structures like buildings, poles, trees, etc., cast no shadows on the ground, though the Sun shines brightly. The reason is – the Sun is directly above our heads. This makes the shadows disappear. All vertical objects will be in alignment with the sunlight.
ZSD may not be the same all over the world. It may vary according to the location of the place on Earth in relation to the Sun.
Why does Zero Shadow Day occur?
At the equator, the Sun's rays are nearly perpendicular to the Earth's surface on two days of the year, causing Zero Shadow Day to occur. In other parts of the world, the angle at which the Sun's rays hit the Earth's surface is not as perpendicular, so Zero Shadow Day does not occur.
Importance of Zero Shadow Day
ZSD is important for many reasons. It helps us to find the exact position of the Sun, which can be important for navigation and other applications. It also offers an opportunity for scientists and astronomers to pursue research on the behavior of sunlight and the effects it has on the Earth's atmosphere. It is also an important cultural event in many countries, as it marks the onset of a new season.
Zero Shadow Day 2023 Date and Time
April 25, 12.17 pm
August 18, mid-day
