A green flash is when the sun appears green for a second or two, right at sunset. How does this happen?
If you’ve ever been watching a sunrise or sunset and suddenly the sun turned green for a second, don’t worry, you’re eyes are fine. It’s a real optical phenomenon called a green flash that occurs when conditions are just right. They usually only last for a second or two, but can last up to 15 seconds depending on the conditions.
Green flashes occur because the atmosphere can cause the light from the sun to separate out into different colours. A “green flash” can be one of a few different phenomenon that are all grouped together because they cause the same result, and not all of them are even understood.
Four types are understood, being inferior-mirage flash, mock-mirage flash, sub-duct flash, and green ray, the first two making up 99% of reports. Green rays are different than the rest. As the name suggests, a green ray is observed shooting up from the sunset/rise, lasting several seconds.
There is also a “blue flash” that is even rarer than green flashes. It’s not known how these form, as blue light is much more easily scattered, which is the reason it’s green that we mostly see.