A cloud of ash from Chile's Puyehue volcano (map), which began erupting on June 4, creates a golden-hued sunset near the mountain resort of San Martín de Los Andes in Argentina on June 12. (Pictures: Chile Volcano Plume Explodes With Lightning.)
The corrosive and obscuring volcanic ash has grounded airplanes all across South America and even in Australia, but the tiny dust and glass particles are also responsible for an optical effect that has lead to spectacular sunsets and sunrises filled with bright gold, fiery orange, and blood red hues around the globe.
"The wavelength of light coming from the sun is being diffracted differently, and that's what causes the visual effect that we see," explained Jay Miller, a volcanologist at Texas A&M University.
The transformed light can range across the color spectrum, but it's usually a dark color, because less sunlight penetrates the atmosphere as a result of the ash cover.
"The two most important things [with respect to] to the variation in hues that we see are how much ash and how high in the atmosphere it gets," Miller said. "A bunch of ash hugging the ground would just make it dark."