Green flashes from the Sun at sunset are a rare phenomenon, but even rarer are green flashes from a setting Moon. With the unique atmospheric conditions at Cerro Paranal in Chile, a photographer from ESO’s Very Large Telescope managed to what are likely the best images ever taken of the Moon’s green flash. ESO Photo Ambassador Gerhard Hüdepohl took a series of images of the setting full Moon crossing the horizon, taken on a clear early morning from the Paranal Residencia.
What happens that makes the green flashes appear?
The Earth’s atmosphere bends, or refracts, light, like a giant prism. The effect is greater in the lower denser layers of the atmosphere, so rays of light from the Sun or Moon are curved slightly downwards. Shorter wavelengths of light are bent more than longer wavelengths, so that the green light from the Sun or Moon appears to be coming from a slightly higher position than the orange and red light, from the point of view of an observer. When the conditions are just right, with an additional mirage effect due to the temperature gradient in the atmosphere, the elusive green flash is briefly visible at the upper edge of the solar or lunar disc when it is close to the horizon.
Hüdepohl works as an Electronics Engineer at ESO’s Very Large Telescope. He said he was surprised and delighted to catch the stunning green flash from the Moon.
You can read an article we did about green flashes from the setting Sun here.