When the sun is blazing overhead, we instinctively look for shade. But on April 18, residents across parts of Kerala may notice something unusual: there will be no shadow at all.
This rare astronomical event, known as a Zero Shadow Day (ZSD), will occur in Manjeri at around 12:25 pm, with nearby locations experiencing it within seconds of that time.
What is Zero Shadow Day?
A Zero Shadow Day happens when the Sun is positioned exactly overhead (at the zenith, 90° angle). At this moment, vertical objects cast no visible shadow because sunlight falls directly downward.
This phenomenon occurs only in regions between +23.5° and -23.5° latitude, that is, between the Tropic of Cancer and the Tropic of Capricorn. Since Kerala lies within this zone, it experiences this event twice a year.
Manjeri is located at approximately 11.12° North latitude, within the tropical belt. Due to the tilt of the Earth's axis, the Sun appears to move northward and southward across the equator during the year, a motion known as: Uttarayan (northward movement), Dakshinayan (southward movement).
As the Sun crosses directly overhead during this apparent motion, locations like Manjeri experience a Zero Shadow Day.
When will it happen again?
This isn't a one-time event. Kerala will witness another Zero Shadow Day on August 24, during the Sun's southward journey (Dakshinayan).
This sight will be visible only in the locations situated between the Tropic of Cancer (approximately 23.5° North) and the Tropic of Capricorn (approximately 23.5° South), said Unnikrishnan Mangalassery, an astronomer and vice chairman of the Malappuram Amateur Astronomers Society (MAARS).