A Green Flash from the Sun.

Many think it is just a myth . Others think it is true but its cause isn't known. Adventurers pride themselves on having seen it. It's a green flash from the Sun . The truth is the green flash does exist and its cause is well understood. Just as the setting Sun disappears completely from view, a last glimmer appears startlingly green . The effect is typically visible only from locations with a low, distant horizon, and lasts just a few seconds. A green flash is also visible for a rising Sun , but takes better timing to spot. A dramatic green flash , as well as an even more rare blue flash , was caught in the above photograph recently observed during a sunset visible from Teide Observatory at Tenerife , Cannary Islands , Spain . The Sun itself does not turn partly green or blue -- the effect is caused by layers of the Earth's atmosphere acting like a prism .

Best Astronomy Images: APOD Editor to speak in Philadelphia tomorrow night and NYC Friday