The Green Flash

Now that summer’s here lots of us will be looking at sunsets – so keep your eyes peeled for the green flash!  This happens when the sun dips below (or rises above) the horizon and a momentary flash of green light will occur. Not many of your companions will have seen a green flash.  The rarity of a green flash sighting can, wrongly, lead people to suspect that the green flash is an old wives tale or an urban legend.  That doesn’t mean you can always see one though as most often atmospheric conditions aren’t right.  Here are some tips to give you a chance to spot a green flash and a little of the science that explains how a green flash occurs.

The best opportunity to see a green flash is at sunset (or sunrise) with a clear horizon and no obstructions, such as a flat sea.  When the conditions are right, a green spot is visible above the upper limb of the Sun’s disk just as it dips below the horizon.  The green appearance usually lasts for only a second or two.  Rarely, the green flash can resemble a green ray shooting up from the sunset point.

Green flashes are optical phenomena enhanced by mirage, which increase refraction.  A green flash is more likely to be seen in stable, clear air when more of the light from the setting sun reaches the observer without being scattered.  They can be observed at any latitude.  Most airline pilots will tell you they have seen the flash and it may be viewed from mountain tops, deserts and ice fields too.

Jules Verne described a green flash in the Green Ray.
“…it will be ‘ green,’ but a most wonderful green, a green which no artist could ever obtain on his palette, a green which neither the varied tints of vegetation nor the shades of the most limpid sea could ever produce the like! If there be green in Paradise, it cannot but be of this shade, which most surely is the true green of Hope!”

The sun does have a green upper rim every sunrise and sunset.  The best time to see a green rim above the sun is 10 minutes before sunset.  Note that as the sun gets closer to the horizon, the green rim becomes fainter due to atmospheric reddening.  However, take care, as magnification will be required to see the green rim and without proper protection, even a glimpse of the sun through a telescope or binoculars can burn the eye’s retina leaving a permanent blind spot.  To avoid this a magnified image can be projected onto a sheet of paper for safe viewing.  Hold a white card or paper a foot or two behind the eyepiece of a telescope or a pair of binoculars on a tripod.

An old saying tells that if you see a green flash you will never go wrong in affairs of the heart!

References:

1 “Green Flash” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 25 June 2017. Web 17 July 2017.
2 “Mirage of astronomical objects” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 27 May 2017. Web 17 July 2017.

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