People who live in inherently hazy and urban environments can go their entire lifetimes without seeing one.
But those fortunate enough to live where the air is typically pristine can see the colorful shimmering and emerald glints when there is a dense atmospheric inversion.
Green flashes are optical phenomena that are enhanced by mirage, which increases refraction of light into various color components, similar to prisms.
Rarely, a green beam of light can be seen shooting up during the final seconds of sunset.
The sequence of images to the right show the evolution of one such green flash as seen on northern Sweden’s Frösön island at sunset on June 21, 2012.
Astrophotographer Göran Strand took the photos during the sunset’s final moments as the solar disk disappeared behind a distant tree line.
The air was so clean and the atmosphere configuration so favorable that time that an even more ellusive “blue flash” can also be seen in conjunction with the green in the last three images.
An even more remarkable video of the sunset can be viewed here.
Images: © 2012 Göran Strand - Astrofografen