Delhi, India - 22 sept 09

We are grade 8 students from Rukmini Devi Public School, located in the capital city-Delhi of India (Latitude: 28.4° N and Longitude: 77.2° E). Our country portrays a landscape of vibrant cultural heritage and spiritual mysticism. Its rich customs and traditions bind its people together. So despite so much of diversity, we live side by side in harmony. We love to celebrate almost every occasion and are good host.

Our school is a Senior Secondary School that caters to the classes pre-primary to higher secondary and age group ranging from 4- 17 years, with the strength of approximate 2000 students. Students here are exposed to the physical, intellectual, socio-cultural, emotional and spiritual learning. We make up a strong bond with our teachers and classmates.

School has rich infrastructure with state-of-the-art facilities and provides us with all modern amenities such as Library; Gymnasium; Science Park; Laboratories- Science Labs, Social Science Lab, Mathematics Lab, Language Lab, Robotics Lab; Auditorium; Technology Based Teaching Labs/Rooms; Computer Literacy Labs; Learning Lab;IT Lab and Video Conferencing Room. We are provided with many choices to develop our mental faculties beyond academics such as Fine Arts- Dance (Classical & Folk), Music (Vocal & Instrumental), Painting/Craft, Sculpture or preparing Electronic & Electrical Gadgets, Photography, Tailoring and Embroidery, Interior Decoration and Dramatics; Sports- Athletics, Basketball, Handball, Kho-Kho, Volley Ball, Badminton, Table Tennis, Swimming etc.

We have been working on various collaborative projects from last few years. It is a real fun to measure the circumference of the earth using a method that was first used by Eratosthenes over 2000 years ago. Hoping forward to have an informative and interesting experience while working on the Noon Day Project.

Firstly, our teacher explained us the set up and steps to measure the angle of the sun and circumference of the earth. We did our experiment on 25 September’ 2009 which was close to the Equinox day i.e 22 September’ 2009. Equinox is the time when the sun crosses the plane of the earth’s equator, making night and day of approximately equal length all over the earth. We were fortunate to have sunny sky.

We were divided into groups of four to measure the angle of the sun. Out of 4 groups, we submitted the data, which was considered as best in comparison to the actual data. Here’s the procedure and measurements taken by that best group:

We started our experiment at 11.45 a.m. We took gnomon of length 19.5 cm and marked the shadow made by it after every 5 minutes of interval until the shadow started increasing. Then, we found the length of shortest shadow which came out to be 11.6 cm, which was cast by the gnomon at 12.15 p.m. Then by making right angle triangle between length of gnomon and shortest shadow of the gnomon, we measured the angle of the sun. The angle of the sun was measured to be 29°.

We took data from website of MacKinnon Middle School situated in NJ, U.S.A to calculate the circumference of the earth, which was done as follows:

Latitude of Delhi, India = 28.38° N Angle of Sun measured = 29°

Latitude of Georgia, USA = 40.89° N Angle of Sun measured = 41°

Central angle = 41° – 29° = 12°

Number of slices needed to make a full circle by central angle = 360 / 12 = 30.

The distance between these two places along a north-south line = 40.89°– 28.38° = 12.51°.

Now, as each angle of latitude = 111 km. Therefore, total distance between these two places along a North-South line = 12.51 x 111= 1388.61 km, which can be taken as 1388 km.

So if the length of the "slice" is about 1388 km and there are about 30 slices, then the projected circumference is 1388 x 30 = 41,640 km.

Therefore, the circumference of the earth came out to be 41,640 km, which is about 4% error, since the average circumference of earth is 40,008 km.

It was a real fun and enriching experience to measure the circumference of the earth using a method that was first used by Eratosthenes.

Through this project, we came to know that angle of sun we measured was equal to the latitude of our place. As a further enhancement to the project, when we will take up this project next time, we would also find longitude by shadow measurements.