The No Shadow Day usually happens in locations between the Tropic of Cancer and Tropic of Capricorn. These regions are unique because the Sun’s apparent path in the sky takes it directly overhead twice a year.
As the Sun positions itself directly overhead, its rays fall vertically, causing shadows from upright objects to vanish momentarily. This phenomenon, known as Zero Shadow Day, happens due to the Earth's axial tilt and the Sun’s apparent motion across the sky.
Zero Shadow Day is a phenomenon that occurs twice a year, during which the Sun is exactly overhead, and there is no shadow cast by any object on the ground