Many sunset watchers have witnessed the green flash. Sometimes it's vibrant and obvious, other times it’s subtle. (Yes, non-believers, green flashes do occur.)
Photos, in most cases, do not do the phenomenon justice. But Colin Legg, an astrophotographer from Western Australia, on Monday posted a stunning green flash image titled “Sun Pyramid” to his Facebook page.
The image shows the flash of green light on the sun’s upper rim as it set beyond the Rottnest Island lighthouse in Perth. Legg, who specializes in photographing the night sky, posted video of the same event on Wednesday (see video below).
“Some funky aberrations and distortions in this one,” Legg wrote on Monday. “We had nice seeing in Perth this evening, so I shot a video of the sun setting behind Rottnest Island lighthouse from Cottesloe beach. To avoid wind jitter, I setup at the local rugby tavern and asked the players to not kick in my direction. Pretty impressive view through 23 km of atmosphere.”
Green flashes occur only sporadically and very briefly at sunset, when part of the sun suddenly changes to blue or green.
According to a San Diego State University Web page devoted to the phenomenon, "Green flashes are by-products of the large variations in astronomical refraction near the horizon. Although there are several kinds of green flash, almost every kind is a by-product of a corresponding mirage."
Legg's video reveals multiple blue and green flashes during the final stages of sunset. He was using a Canon 5D Mark II and shooting with a 2,000-millimeter lens.
–Pete Thomas, via GrindTv Outdoor
–Hat tip to EarthSky.org