American war correspondent and photographer Michael Yon named the halo that is caused by dust striking helicopter blades the Kopp-Etchells effect after two soldiers, one American, the other British -- Cpl. Benjamin Kopp and Cpl. Joseph Etchells -- who died in Afghanistan in July 2009. Usually only seen overseas because it requires large, powerful helicopters (often military) and lots of dust, the Kopp-Etchells effect occurs because sand particles are harder than the metal abrasion strips, typically titanium or nickel, placed on helicopter rotor blades. When the sand hits the metal, the surface begins to erode and sparks fly.
View more Pictures of the Day.
We want to hear what you think about this article. Submit a letter to the editor or write to firstname.lastname@example.org.