Sunday, May 26 marks Zero Shadow Day in Nagpur and it was observed at the Raman Science Centre & Planetarium in the city. Almost no visible shadow was seen at 12:10 pm sharp in Nagpur. Around 300 people of different age groups including fervent students and general public witnessed this spectacular event. The team of Raman Science Centre & planetarium arranged five different kits to demonstrate the concept of phenomenon from 11.30 am to 12.30 pm. The sun reached the zenith on top of the city at 12.10 pm. Usually, the sun transits by small margins towards the north or south around noon. But on Zero Shadow Day, it was exactly overhead and everyone present was astonished by the diminishing shadow.
A keen observer Swati Jhankare was surprised to know that her shadow could vanish for few seconds. Why this happens on a particular date and who else in the world could experience this event. She was very much interested to solve this puzzle and get the reason behind. To quench such queries various activities were carried out during the workshop organised by the centre.
It happens twice a year, for places between +23.5 (Tropic of cancer) and -23.5 (Tropic of Capricorn) degrees latitude. The Sun is almost never exactly overhead at noon, but usually transits a bit lower in altitude, a bit to the north or a bit to the south. We have all studied in school that the Earth’s rotation axis is inclined at 23.5 degrees to the plane of its revolution around the Sun, which is why we have seasons. This also means that the Sun, in its highest point of the day, will move from 23.5 degrees south of the celestial equator to 23.5 degrees north (Uttarayan), and back again (Dakshinayan), in a year. Of course, the northern most and southern most points are the two solstices, and the crossings of the Sun across the equator are the two equinoxes.
For people living between tropic of cancer and tropic of Capricorn, the Sun’s declination will be equal to their latitude twice – once during Uttarayan and once during Dakshinayan,which also explains why places like Delhi, Allahabad and Srinagar (located away from the Tropic of Cancer) have no zero shadow day.On these two days, the Sun will be exactly overhead at noon and will not cast a shadow of an object on the ground.
This Zero Shadow Day will clearly be different for different places on earth.In India, it is usually observed between April and September. . This phenomenon which occurs twice a year will again be observed on July 17 at 12.20 pm.