They say that a man’s shadow is his most trusted companion. It’s his faithful follower, the pattern-shifter; the one that runs and stops with him. But for Mumbaikars, May 15 was no ordinary day. In the hot scorching afternoon at 12.36 pm, the shadow left its master for a few minutes in what was explained as Zero Shadow Day.

So, what’s this phenomenon all about? Well, “Zero Shadow Day” is that moment when the shadow of a person or an object disappears for a few minutes. It occurs twice a year when the sun is at 90 degree angle to the earth surface or overhead. The sun rays fall vertically on different latitudes on different dates and those living on that particular latitude witness their shadows disappearing below their feet when the sun is right over their heads.

Mathematically, it should be one particular day, but one can ‘see’ this phenomenon of zero shadow a day before or after in the city. This is because the sun is not a point (or dot) source but it has a size. Those who live between the latitudes 23.5 degree south (the tropic of Capricorn) and 23.5 degree north (the tropic of Cancer) can experience the sun right overhead at zenith twice every year.

“A zero shadow day can only be witnessed by those living between Tropic of cancer and the Tropic of Capricorn. This particularly takes place twice a year when sun is overhead,” said Arvind Paranjpye, Director of Nehru Planetarium.

The Zero Shadow Day could be experienced in different cities of Maharashtra, including Pune and Mumbai, between May 6 to May 20. The Mumbaikars can witness this Zero Shadow Day again on May 15 between 12.34 pm to 12.36 pm—and also on July 27, 2017. But then, summer is the best season to witness Zero shadow day because in July, the clouds might hinder the shadow formation.

On May 14, the Pune’s Jyotirvidya Parisanstha (JVP)—one of the oldest association of amateur astronomers—and Mumbai’s Nehru Planetarium demonstrated Zero shadow day for children.