When light propagates from one medium into another, its speed changes, which causes the light to reflect and refract at the boundary. The index of refraction of water is 1.33 (4/3). As light travels from water to air, it will bend away from the perpendicular to the surface. When the incident angle is greater than 48 degrees, all the light is reflected back into the water (total internal reflection). As your pet goldfish in the aquarium looks up, it will see a reflected view of the sides and bottom of the aquarium beyond the 48 degree angle, while directly above, it sees a compressed view of the outside world. The refraction of light is responsible for many illusions:

   * The shape of a thing you see under the water surface is different from what it really is.
   * A submerged object appears to be nearer the surface than it actually is.

This java applet lets you see the view as seen by your fish, looking up at you.. Pretty weird!

/applet>
Click [b]Pause[/b] to pause the animation, and you can drag eye to different locations.
Try to drag eye below the water surface and you will find another amazing effect!