Hipparchus explains how two numbers can describe the position of a point on a sphere. He then explains stereographic projection: how can one draw a picture of the Earth on a piece of paper?
To subscribe your Apple's iPhone or ITunes
to the feed click on the right!
To subscribe your Zune go to
The videos are now also enable for iPhone,iPod and iPad so you will be able to enjoy them directly from this site in any of these devices.