When an object, such as a pencil, is partly immersed in water and viewed from above, it appears to bend underwater. This illusion is caused by refraction, the change in direction of a wave as it leaves one medium and enters another. Waves travel with greater velocity in some media than in others, and when a wave enters a new medium at a certain angle, the change in speed occurs sooner on one side of the wave than on the other. What other optical phenomena are caused by refraction? Discuss