1. The problem statement, all variables and given/known data Find the radii of the umbra and penumbra circles drawn drawn perpendicular to the EMS axis, formed at a distance equal to that of the moon from the Earth. 2. Relevant equations (From: http://www.opticiansfriend.com/articles/equations.html#Shadows) D2 / L1 = (P + U) / (L1 + L2) D1 / L1 = P / L2 Total Shadow = 2P + U D1 = Diameter of light source D2 = Diameter of object between light source and Shadow L1 = Length from light source to L1 L2 = Length from L1 to Umbra U = Umbra P = Penumbra 3. The attempt at a solution I substituted 12,576 km for D2 as the diameter of earth and 149.6 million km for the distance between the earth and sun. My calculations revealed that P+U= 1305010.784. Am I misguided in the belief that these equations give my the area of the circles from which I can extrapolate the radii?