... Isaac Newton Explains the Solar System . ... But he went home from Cambridge one summer in 1665, thought a lot about the physical nature of the world, and came back two years later with a revolutionary understanding of mathematics, gravitation, and optics. ... Gliding through the sky on Wednesday evening, February 20th, a first quarter Moon seemed to run over bright planet Saturn as viewed from much of North America. ... Comet Ikeya Zhang . ... Water Ice Imaged in Martian Polar Cap . ...