Recreating Historical Earth Radius Measurements
A piece of string, a stone, a scale and a cricket stump!
Armed with these, any student in the country can measure the radius of the Earth if we fix upon a day when we could all do it together – every student from any corner of India. Let us choose the 20th of March, the spring equinox, for this wonderful countrywide collaboration.
Before we get into the details of the simple method with which we could do this calculation, it would be worthwhile to meander through history and meet Eratosthenes, the Greek Mathematician, who first made this estimate in the 3rd century BC.
Eratosthenes heard reports from travelers to a place called Syene (modern day Aswan) about the absence of any shadow cast by a vertical pole, on the day of the Summer Solstice. He apparently did make a trip himself and verified this fact. Did not do Internet cut-and-paste, in fact! From the knowledge that the Sun shone vertically above Syene at summer Solstice, a measurement of the angle made by the noonday sun at Alexandria, and the measured distance between Alexandria and Syene, Eratosthenes could estimate the diameter of Earth, from simple geometrical arguments.
Earth Radius Measurements for the Spring Equinox!
Anyone who has made this measurement from the information above could mail the details to planetdl@bol.net.in their data will be uploaded to this site, with credits.
If you missed doing this on the 20th of March, mail at the address above or make an entry in the guest book and help will be provided to make this measurement on another date.
Some preliminary observational results are here
The radius of the Earth is one important ingredient of data required for measuring the Earth-Sun Distance, using the Transit of Venus observations on the 8th of June 2004.