what causes the green flash
Often, the green color lasts for a second, thus it is called a green flash. It is usually seen over a distant horizon such as an ocean or a prairie. The sky must be clear and free of clouds all the way down to the horizon. There are several different mechanisms that produce green flashes. I'll start with one common misconception that the green flash is due to a color afterimage then move on to a discussion of the atmospheric optics that produces the simplest Green Flash.