Take a look at the following picture: enter image description here

Why does the light at the bottom of the water form this pattern? I have also seen the same phenomenon in all the swimming pools I've ever visited, of whatever depth they may be. How does this happen?

  • 3
    $\begingroup$ I'd like to propose that you replace "weird" with "friggin awesome" in your question title. $\endgroup$ Sep 17, 2013 at 1:56
  • 5
    $\begingroup$ The patterns are known as caustics. See en.wikipedia.org/wiki/Caustic_(optics) for more info. $\endgroup$ Sep 17, 2013 at 10:17
  • $\begingroup$ Observing caustics is one way of identifying exoplanets. $\endgroup$
    – Farcher
    Apr 15, 2017 at 17:21
  • $\begingroup$ This pattern, caustics, is now seen in space as the fibrous connections between galaxies through the dark matter spaces between those galaxies but it's in 3-D. The universe is so marvelous and a wonder of God's creation. $\endgroup$ Feb 3 at 3:28

1 Answer 1


The pattern on the bottom of the pool it caused by the sides of ripples or waves on top of the water refracting the light of at large angles so they don’t reach the bottom but the peak of the wave refracts the light down so you get the concentrated light showing the formation of the waves on the bottom of the body of water. An OK metaphorical example of this would be how a magnify glass has a central focus point at the centre of the lens (the peak of the wave) and the outsides of the lens magnify light weaker and actually dulls the light (the sides of the wave). I hope this helps.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.