Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2004 March 21
See Explanation.  Clicking on the picture will download
 the highest resolution version available.

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. 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 was caught in the above photograph in 1992 from Finland. The Sun itself does not turn partly green, the effect is caused by layers of the Earth's atmosphere acting like a prism.

Tomorrow's picture: near miss

< | Archive | Index | Search | Calendar | Glossary | Education | About APOD | >

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Web Site Statements, Warnings, and Disclaimers
NASA Official: Jay Norris. Specific rights apply.
A service of: LHEA at NASA / GSFC
& Michigan Tech. U.