How big is the Earth? I wish to have students repeat the "Shadow of the stick in two locations on Earth" experiment for determining the radius of the planet, using the Internet to coordinate and synchronize the measurement time at two very distant points. Partial list of potential benefits: Internet exposure/use "Pen-Pal" type inter-country networking Exposure to problem solving (Rediscover the method) Exposure to the ancient solution Use of Experimental Techniques Real Results Perhaps I could do the experiment above on my own, but the reason I want PUMAS help is that I see this as one of several similar experiments for which I do not have the necessary background knowledge: How do we earthlings know: How far away the Sun is How big the Sun is How far away any given star is etc. Please teach me the theory and Math for determining these astronomical dimensions. With that knowledge I would love to structure 5 or 6 experiments like the one above. Thanks.