City’s zero shadow moment

CHENNAI, April 25, 2018 01:04 IST

Updated: April 25, 2018 01:04 IST

A special day for residents as sun reaches zenith in sky

It was only natural that a manipulator of light would not pass up the opportunity. So, Santosh Sivan tweeted an image. Uploaded a minute before 1 p.m., it showed four men and a football on a beach. All of them had their reflection on the film of water left by the receding tide. Only the one closest to the camera had a barely visible shadow. The football looked like it had rolled off-centre from its own shadow. It was not some camera trick or special effect.

The shadows were newborns. The 12.07 p.m. zero shadow had just passed. “Zero Shadow Day in Chennai today: and we are filming for CCV in Chennai,” said the tweet. CCV, or Chekka Chivantha Vaanam, is the Silambarasan-starring, Mani Ratnam film that Sivan is now working on.

Demonstration at IIT-M

On April 24, at 12.07 p.m., Chennai experienced its zero shadow moment. Placing a one-metre pole on a white sheet, students at IIT Madras waited for the shadow to disappear and demonstrated the phenomenon.

“This is called a subsolar point,” said Yashodhan Manerikar, head of the physics and astronomy club of IIT Madras. “The sun is directly overhead at the zenith, the highest point in the sky, at a particular latitude, which implies that erect objects will cast no shadow. Today, it is special for Chennai’s latitude, about 13 degrees,” he explained.

The Sun rising in the East and setting in the West is true for only two days in a year — the Vernal and Autumnal Equinox. On the other days, it rises towards the North of East or South of East. In the Northern Hemisphere, during summer, the Sun rises towards the North of East, and during the Summer Solstice, the Sun rises 23.5 degrees North to East.

“On equinoxes, sun rays hit the Equator perpendicularly and on the Summer Solstice, they hit the Tropic of Cancer perpendicularly,” he explains. “Meanwhile, every latitude between the Equator and the Tropics of Cancer will have a time when the rays of the Sun hit it perpendicularly. In Chennai, this phenomenon occurs around April 24 and August 18 every year.