Violet and Green Flashes at Sunset

April 13, 2022

Blue-violet-flash_3000_95 Sole a Omega e Raggio verde sequenza orizzontale


Photographers: Salvatore Cerruto (Left Photo), Emanuele Nifosì (Right Photo)

Summary Authors: Salvatore Cerruto; Cadan Cummings

These two photo sequences feature an atmospheric optical phenomenon that produces colored flashes when the Sun sets below the horizon. The left photo series taken on December 31, 2021 near Marina di Modica, Sicily, Italy shows a violet flash, while the right photo series taken on January 15, 2022 shows a green flash visible on the horizon over the Riserva Naturale foce del Fiume Irminio in Ragusa, Italy. Colored flashes occur occasionally at sunset or sunrise when the upper rim of the Sun is visible slightly above the horizon. The flashes are the result of atmospheric dispersion, which causes the incoming light to refract differently depending on the wavelength.

In the images above, atmospheric dispersion unequally refracted shorter violet / blue spectra light in the first set of photos and green in the second photo set. Both events require good timing as well as suitable conditions to capture. Although clear conditions produce the clearest flashes, it is also possible to see the flash in cloudy weather. Purple colored flashes are overall more rare to see, especially at sea level. Most likely this event was due to a temperature inversion caused by the abnormal heat conditions at the end of the year on the Mediterranean Sea. Remember to always practice caution when viewing the Sun.

Photo details: (Left Photo) Nikon D800 + Tamron 100-400 f/4.5-6.3 @400mm, f/25, ISO-200, 1/100 second exposure; (Right Photo) Nikon D700, Skywatcher ED 50, Hyperion 17mm, ISO 1000, f / 4.8, exp 1/640 second exposure