Measuring the Earth’s waist on the longest summer day !

The importance of June 21 might have gone unnoticed by the layman, but for the students of various Delhi schools, it was a big chance to emulate the Greek astronomer Eratosthenes. These students participated in an exercise on Thursday to measure the earth’s circumference on the longest day of summer.
Organised by Science Popularisation of Communicators and Educators (SPACE), the participants took actual measurements of the shadows made by the sun to measure the circumference of the earth as done 2,300 years ago by Greek astronomer Eratosthenes. Eratosthenes was the first person to calculate the circumference of the earth by using a measuring system using stades or the length of stadiums during that time period (with remarkable accuracy).
Thursday being the longest day and the shortest night, we measured the circumference of the earth. After today the duration of the day will be shorter and of the night will be of longer,” said Pooja Kumar of SPACE.
“We are observing the angle of the sun and measuring the shadows. In general, the exact timing of the summer solstice changes from year to year,” she added.
Known as the Project Paridhi ( the word paridhi means “measure “ making it quite apt for the Eratosthenes experiment), the measurement activity went on from 9:30 in the morning to 2 pm at the Jantar Mantar. The project involves participants taking measurement of shadows at noon, at different places on the same longitude, such as Delhi and Bangalore.
“I am measuring the shadow of the sun through an instrument called gnomon meaning ‘indicator’. It is the oldest method to measure direction, time and location by shadows,” said Mehul, a student from Ryan International, Rohini.
“Using the shadow of the sun we will find out the angle of the sun. We are measuring the shadow after every 5 minutes,” Mehul added.
SPACE also partnered with astronomers from Kazakhistan for the conduct of this experiment.
What we have gathered is that Thursday would be 14-hour long day. We measured the sun’s shadow every 5 minutes and we will calculate the earths circumference by the formula known,” said Vibhu Narayan, a student of St. Columba’s school in Delhi.