November 04, 2009
Helo Halo
Luminous halos twirled above a Boeing CH-47 Chinook on a recent night around 11:30 p.m. local time at Forward Operating Base Jackson in Sangin, Helmand Province, Afghanistan, as helicopters ferried casualties and supplies in and out of the base. The photographer was independent journalist Michael Yon, a former U.S. Army Special Forces soldier now traveling the world's war zones with a camera. Helicopter pilots don't have a name for the effect, but one explained to Yon, "Basically it is a result of
static electricity created by friction as...dissimilar material strike against each other. In this case, titanium/nickel blades moving through the air and dust." Scientists call it a "triboelectric" or "piezoelectric" effect. Depending on the viewing angle,
it creates dazzling little galaxies. An even longer exposure
reveals stars and another aircraft marked by a string of lights at upper left of center; Yon suspects this aircraft was a Predator or Reaper UAV, which, unlike manned military aircraft, fly with their lights on in the Afghan night to avoid collisions. Yon, who made these shots with a Canon 5D Mark II with a 50 mm lens at an ISO of 800, claims that the night was far darker than his sensitive camera conveys, as evidenced by the green chemlights on the ground to guide the pilots. He was moved to create a name, the
Kopp-Etchells Effect, for the rotor phenomenon to honor a pair of fallen soldiers,
U.S. Army Corporal Benjamin Kopp and British Army Corporal Joseph Etchells, who died one day apart in July after fierce fighting in Helmand (Kopp had been evacuated to the U.S. before he died). "The tent in the foreground is a medical tent," says Yon, "so that casualties can be kept in a tent until the last minute. A substantial number of British casualties in Helmand have been lifted off of this exact spot...because this is probably either the most dangerous place in Afghanistan, or nearly the most dangerous."
######
{loadposition user8}
More...
Smithsonian Air&Space on Kopp-Etchells Effect
