Occasionally, if the atmospheric conditions are just right, the sun will spark a bright green hue just as it disappears on the horizon. Called the ‘green flash’, this phenomenon is purported to be caused by the spectral separation of the sun’s colors. The green flash only lasts for a second or two.
Conditions for the Sun’s Green Flash to occur
For the phenomena to occur the atmosphere must be extremely clear. This particular condition allows the light to be refracted, the colors separated producing the astonishing green flash. The phenomena can occur shortly after sunset or right before sunrise. They are typically seen where there is an unobstructed horizon, such as over water, but the phenomenon has been reported over mountain tops too. With an unrestricted view of the horizon, green flashes are regularly seen by airline pilots, particularly when flying westwards as the sunset is slowed
Cause the Sun’s Green Flash
The individual spectral colors of the sun, with purple located at the top and red located at the bottom, appear one by one as the sun slowly sets producing the notable color changes everyone recognizes as our setting sun. As the sun sets each individual color is presented one by one until Green, the last color of the spectrum, produces its brief and unexpected flash.
In addition to atmospheric refraction and lensing, another primary cause of the Green Flash may be due to a phenomenon recently discovered by researchers, which found that when two photons of infrared light collide with a human retina cell, causing what researchers call “a double hit,” it creates the perception of bright neon green. The researchers discovered this inadvertently while working with powerful infrared lasers, which should have been invisible to them, yet the researchers consistently kept seeing bright green flashes from the source of the laser.
Byrd’s 1934 report of Green Flash phenomenon
Members of the Richard Evelyn Byrd party from the Antarctic Little America exploration base in 1934, gave a remarkable report of their spotting of the “green flash” phenomena:
There was a rush for the surface and as eyes turned southward, they saw a tiny but brilliant green spot where the last ray of the upper rim of the sun hung on the skyline. It lasted an appreciable length of time, several seconds at least, and no sooner disappeared than it flashed forth again. Altogether it remained on the horizon with short interruptions for thirty-five minutes. When it disappeared momentarily it seemed to have been shut off by a tiny spurt, an inequality in the skyline caused by the barrier surface. Even by moving the head up a few inches it would disappear and reappear again and after it had finally disappeared from view it could be recaptured by climbing up the first few steps of the antennae.
Scientists report that a “blue flash”, although very rare, is also possible.