SPACE chennai ZERO SHADOW DAY

For people living between +23.5 and -23.5 degrees latitude, the Sun's declination will be equal to their latitude twice .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,Chennai will measure the length of the shadow cast (which will be almost zero on April 24 at noon, that is when the Sun crosses the local meridian. Local meridian is the imaginary line connecting south, overhead and north) by the vertical stick of standard length (say 30 cm). This is the instance of time at which the shortest shadow occurs.

Local noon may occur at different times at different longitudes. For instance on April 15, at longitude 82.5 degree (i.e. the longitude used for fixing IST), the local noon occurred at 12 noon. On that day the local noon occurred at Chennai at 12:09 pm. From this difference one can measure the longitude of the place and the speed of Earth’s linear rotation at the given longitude.