Context:
On April 25, Bengaluru observed a distinctive astronomical event known as ‘Zero Shadow Day’.
What is Zero Shadow Day?
- A day on which the Sun does not cast a shadow of an object at solar noon.
- Because the Sun is at its zenith (the highest point in the sky) and the shadow is directly under the object.
- For every point on Earth between the Tropic of Cancer and the Tropic of Capricorn, there are 2 Zero Shadow Days every year.
- It is restricted to locations between the tropics; places north of Ranchi in India are out of it.
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.
- All places whose latitude equals the angle between the Sun’s location and the equator on that day experience zero shadow days, with the shadow beneath an object at local noon.
The northern most and southern most points are the two solstices, and the crossing of the Sun across the equator are the two equinoxes.
Equinoxes:
- During the equinox, the sun crosses the plane of Earth’s equator, making night-time and daytime (roughly) equal length all over the world.
- In the Northern Hemisphere, the spring equinox, or vernal equinox, occurs around March 21, when the sun moves northward across the celestial equator. The autumnal equinox occurs around September 22 or 23, when the sun crosses the celestial equator going south. In the Southern Hemisphere, it is vice-versa.
Solstices:
- A solstice is one of the two times of the year when the positioning and tilt of Earth relative to the sun results in the most amount of daylight time or the least amount of daylight time in a single day.
- A solstice is one of the two the exact moments in the year when the sun reaches its northernmost point (around June 21, when the North Pole tilts closest to the sun) or southernmost point (around December 22, during the winter solstice) from Earth’s equator.
- In the Northern Hemisphere, the summer solstice occurs in June and the winter solstice occurs in December. In the Southern Hemisphere, it is vice-versa.
Source: Indian Express
Previous Year Question
In the northern hemisphere, the longest day of the year normally occurs in the:
[UPSC Civil Services Exam – 2022 Prelims]
(a) First half of the month of June
(b) Second half of the month of June
(c) First half of the month of July
(d) Second half of the month of July
Answer: (b)
