How common is a green flash and how long does it last?

The phenomenon known as a green flash is indeed rare, occurring only under specific atmospheric conditions. It is most often seen at sunset or sunrise when the sun's light is refracted through the Earth's atmosphere, resulting in a brief appearance of a green spot just above the sun.

The duration of a green flash is typically just a few seconds, as the conditions must be perfectly aligned for it to occur, and even then, the visual effect is fleeting. This brief occasion adds to its rarity and allure, making it a coveted sight for those observing the horizon.

Understanding this, the selection stating "rare / a few seconds" aligns perfectly with the characteristics of the green flash, emphasizing both its infrequency and the very short duration one would likely experience it.