Astronomy goes international at Truro High School

Using the sun’s rays in a 2000-year-old science experiment, the girls have been linking up over 100 Egyptian students at the library in Alexandria – who will also be using the same calculation method on Midsummer’s day – to share their findings and calculate the circumference of the earth. With the guidance of Physics teacher, Mr Simon Loosely, and the Director of the Roseland Observatory, Brian Sheen, the girls used the shadow angle of the sun and some basic trigonometry to estimate that the circumference of the earth is 37,960km.  “We were recreating the Eratosthenes Experiment,” explained Simon. “Eratosthenes lived around 2,000 years ago. He studied in Alexandria in Egypt and became librarian of the Great Library there – the centre of science and learning in the ancient world. His experiment was one of the most important of the period; the accepted figure today is only a few percent different from Eratosthenes’ calculations, impressively close for an ancient astronomer without modern tools.” Before they began the experiment Brian told the girls how Eratosthenes arrived at his figure. He knew that on one day of the year the sun shone to the bottom of a well in Aswan and that every day a shadow was cast by the Great Obelisk in Alexandria. He measured the angle of the obelisk’s shadow at the exact time the sun hit the bottom of the well and, using the angle measured with the distance between the obelisk and the well, estimated the circumference of the earth. “Our results were pretty accurate,” said Simon. “It’s a great experiment to get our mathematicians and physicists thinking about astronomy on an international scale. Scientific discovery is all about collaboration so it’s been fantastic to compare results with the students in Alexandria and share in the spirit of enquiry together.” The school is a firm believer in educating girls about the many opportunities Astronomy can offer and regularly undertake special astronomical projects involving school children from across the county and beyond. In partnership with the Roseland Observatory, we are the first school in the UK to have a solar observatory.