Kolkata: Residents of Kolkata are in for a celestial treat as they will experience zero-shadow days at precisely 11.35 am on June 5 and again at 11.41 am on July 7. According to Bipash Das Gupta, a scientific officer at the MP Birla Institute of Fundamental Research, MP Birla Planetarium, Kolkata, the timing of this phenomenon will only vary by a few seconds across different locations within the city.
Zero-shadow days are biannual events occurring in regions between the Tropic of Cancer and the Tropic of Capricorn.An opaque object typically casts a shadow when illuminated by a light source from behind. On zero-shadow days, however, the Sun’s position directly overhead results in the shadow of any object falling directly underneath it, creating the illusion of no shadow. This phenomenon is closely linked to the Earth’s diurnal and annual motions and offers insights into the seasonal changes and the processes of tides, said Das Gupta.
Zero-shadow day provides an excellent opportunity for scientific observation and photography. People can take sequential photos at regular intervals to document the vanishing and reappearance of shadows.
The Earth’s axis is tilted at an angle of 23.5° to its orbital plane around the Sun. This tilt causes the Sun’s rays to hit different parts of the Earth perpendicularly at different times of the year, leading to zero-shadow days. The Sun’s apparent movement along the ecliptic path, from 23°30' South to 23°30' North, is responsible for this event. When the Sun is at its zenith, directly overhead at local apparent noon, objects and people lose their shadows momentarily, explained Das Gupta.
Zero-shadow day is not just a visual spectacle but also a valuable educational experience. It helps in understanding fundamental astronomical concepts such as the Earth’s rotation, the angle of sunlight, and the changing seasons. For scientists and astronomers, it provides crucial data on the movement and position of the Sun, aiding in the study of the Earth’s tilted axis and the Sun’s path across different regions.
In India, the Tropic of Cancer passes through eight states, including West Bengal. For instance, it crosses the outskirts of Krishnanagar, just 2.5 kilometers away.