Sundials,a unique way of teaching concepts of time

Today no one needs a sundial to tell time, yet sundials provide a unique way of teaching children the concepts of time and its measurement, says the Nehru Planetarium Director Piyush Pandey.

The recently installed Sundial (also called shadow dial) at the Nehru Planetarium at Worli in central Mumbai tell time by interpreting the angle at which the shadow of its shadow casting element (gnomon) moves under the Sun.

On May 16 Mumbaikars can witness, at 12.34 pm, the shadow of a vertical pole totally vanishing, Pandey said.

Anyone interested can witness a pole, that could be found in an open playground, football or basketball field. This event will be repeated again on July 28 at 12.44 pm when the Sun will again be at zenith (vertically overhead) in Mumbai, he said.

The popularity of the recently installed Sundial in the Planetarium has also driven officials here to teach the science and art of designing sundials to schoolchildren.

"They may gift it to their respective schools who may in turn decide to convert these cardboard sundials into sturdier ones in stone, marble, steel or other materials that can bear the brunt of sun and rain," Pandey said.

The Nehru Planetarium's Sundial is unique in two ways. The longitude correction for Mumbai has been incorporated in its design.

"In simpler words, our watches are tuned to the central meridian of India. If the Sun is on that meridian now, it would come to Mumbai in the same position 38 minutes later," Pandey said.

This difference has to be accounted for. Secondly, this sundial is very precise and that has been possible because it has been computer generated through a software developed by the Director, Nehru Planetarium.

"We have organised a workshop on May 28 for schoolkids from standards 8 to 10 chosen on first-come-first-get basis. Only 30 students will be admitted to this first sundial workshop of its kind," he said adding that more workshops may be held later.