Green ray - Definition and Overview

The green ray or green flash occurs shortly after sunset or even at dawn. Just as the sun sets/rises, a green ray shoots up. This is a rare optical phenomenon.

Its explanation lies in refraction of light in the atmosphere and is enhanced by atmospheric layering. It is usually observed from a low altitude where there is an unobstructed view of the horizon, such as on the ocean. Whilst we would expect to see a blue light, the blue is dispersed (this is why the sky is blue) and the green flash is visible from a fraction of a second to a couple of seconds duration.

With slight magnification the effect can be seen on the top limb of the solar disk on most clear-day sunsets. However the flash effect requires a stronger layering of the atmosphere.

External links

• Straight Dope Article on the Green Flash (http://www.straightdope.com/classics/a880408.html) from Cecil Adams
• A Green Flash Page (http://mintaka.sdsu.edu/GF/index.html), Andrew T. Young's page with comprehensive explanations.
• Green flash (http://www.weather-photography.com/Photos/gallery.php?cat=optics&subcat=green_flash)
• Astronomy Picture of the Day (http://antwrp.gsfc.nasa.gov/apod/ap040321.html) from NASA
• Green Flash Pictures (http://humane.sourceforge.net/pictures/green_flash.html)