A Green Flash from the Sun . ... Credit Copyright: Pekka Parviainen ( Polar Image ) Explanation: Many think it is just a myth . Others think it is true but its cause isn't known. ... It's a green flash from the Sun . ... The effect is typically visible only from locations with a low, distant horizon, and lasts just a few seconds. ... The Sun itself does not turn partly green, the effect is caused by layers of the Earth's atmosphere acting like a prism . ... NASA Official: Jay Norris. ...