CitarWHY ARE SUNSETS TURNING PURPLE? Every year, on average, about 60 volcanoes erupt somewhere on Earth, shooting ash and sulfurous gas thousands of feet into the air. Rarely do the plumes make it all the way up to the stratosphere. This summer, however, two volcanoes have done it.

The Raikoke volcano in the Kirul Islands (June 22nd) and the Ulawun volcano in New Guinea (Aug. 3rd) both punched through to the stratosphere, sending material as high as 60,000 ft. And that is why sunsets are turning purple:


Gabriel Cyr of Saint-Elzéar, Quebec, photographed this example on Aug. 25th: "The skies were perfectly clear with no tropospheric clouds visible to the naked eye, making the phenomenon easier to distinguish from a 'regular' sunset," he says.

Fine volcanic aerosols in the stratosphere scatter blue light which, when mixed with ordinary sunset red, produces a violet hue. The purple color is often preceded by a yellow arch hugging the horizon. As the sun sets, violet beams emerge from the yellow, overlapping to fill the western sky with a soft purple glow. High-quality pictures of the phenomenon often show horizontal bands cross-crossing the yellow arch. These bands are the volcanic gas.

Last night, Greg Ainsworth captured many of these elements in a photo he took from Bozeman, Montana:

"On Aug. 26th, I captured the purplish sunset colors, as well as horizontal banding in the yellow/orange area associated with the volcanic aerosols in the stratosphere," says Ainsworth