Why do you see stars if you bump your head?

Monday 18th July 2011
Submitted by hashworth1

Familiar from cartoon strips, this bizarre phenomenon is caused by the generation of so-called phosphenes – illusory flashes of light caused by pressure on the light-receiving cells in our eyes. The simplest – and least painful – way of generating them is by gently pressing on your closed eyelids then opening your eyes. Isaac Newton came up with another method while investigating the nature of light: sliding a bodkin (a think, blunt needle) between his eye and the socket-bone. Not recommended.

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