CK-12 Foundation
Ck 12: Physics Simulation: Least Time
[Free Registration/Login Required] Explore how Snell's Law arises out of the principle of least time; understand how light rays change direction at interfaces between materials using this interactive simulation. A PDF worksheet and a...
University of Wisconsin
The Why Files: Infra Red Eye Special
A description of the ways in which infra-red is used in astronomy, including an extended example describing how infra-red was used to learn about Pluto's moon, Charon. There are also links to other sites of astronomical interest.