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 Storulvån, Sweden, Göran Strand was able to capture some green and blue flashes around the moon on March 6, 2015.
So how does a green flash 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.
Now, watch a perfect green flash sunset (I did not find any lunar flash, so picked up a solar on):
That was awesome, no?