An "inferior mirage" green flash. This isn't in IB. Got photos to share? Credit: Wikimedia Commons 
When you're at the beach with your sweetie watching the sunset, listen closely as the sun sets into the water. If you hear cheering, that means that there was a green flash (and that you were watching the sunset at the foot of IB, where the green flash crew watches it every night). According to Wikipedia: 

"Green flashes and green rays are optical phenomena that sometimes occur right after sunset or right before sunrise. When the conditions are right, a green spot is visible above the upper rim of the disk of the sun. The green appearance usually lasts for no more than a second or two. Rarely, the green flash can resemble a green ray shooting up from the sunset (or sunrise) point. Green flashes occur because the atmosphere can cause the light from the sun to separate out into different colors. "

There are a few different types of green (and blue!) flash.

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