The Green Flash Effect
The green flash effect is a rare sunset phenomenon. The last shard of the setting Sun turns green for a second or less, due to optical effects of our atmosphere.
Photo by Aymen Ibrahem, Senior Astronomy Specialist

On 13 November 2007, shortly before sunset, there were scattered clouds in the sky of Alexandria, Egypt, but the western horizon was fairly clear. BA Senior Astronomy Specialist Aymen Ibrahem imaged rare optical atmospheric phenomena through his observation of the fascinating sunset and evening twilight of that day.

"During sunset, the western horizon was glowing in bright golden hues," said Ibrahem. "I observed two dazzling Suns, merging just above the sea, due to the sunset mirage. The merging Suns gradually sank in the sea. The last shard of the setting Sun glimmered in green for a second or less, due to optical effect of our atmosphere, known as the green flash effect."

Our atmosphere acts like a gigantic prism. Due to refraction in our atmosphere, sunlight is bent and separated into different colors. Short-wavelength lights (blue and green) are bent more strongly than red light. The atmosphere also enhances the dispersion of colors. Due to contamination in the atmosphere, blue light is scattered and mostly removed. More green light passes through, and therefore is observable more clearly. In exceptional conditions, a "blue" flash might be seen. "I observed two blue flashes in autumn 2005, using a 5-inch telephoto lens," added Ibrahem.

A green flash may also be visible during sunrise, but the observer should determine precisely the position and time of sunrise to capture the brief, rare glimmer.

Shortly after sunset, the BA sky observer imaged green clouds, hovering over the position of sunset. "I believe the green hues of these clouds were similar in nature to the green flash effect," remarked Ibrahem. "Through evening twilight, the western horizon glowed in spectacular hues of orange and yellow, and the blue sky was gradually dimming. This was one of the most beautiful sunsets I have ever observed."

Ibrahem took numerous images, recording these celestial wonders. He named his series of images "A Green Sunset". Some of the images are presented in the picture gallery below.

Picture Gallery

Fig (1)
Development of Sunset Mirage
This sunset sequence shows the earliest stages of the sunset mirage.
As the Sun is just about to set, an image of the Sun rises from the sea, and merges with the real Sun.
Photo by Aymen Ibrahem, Senior Astronomy Specialist

Fig (2)
Omega Sun
In this image, the Sun resembles the Greek letter omega, due to the sunset mirage effect.
Photo by Aymen Ibrahem, Senior Astronomy Specialist

Fig (3)
Evening Twilight
Green-tinged clouds are visible over the location of sunset.
Photo by Aymen Ibrahem, Senior Astronomy Specialist

Further Reading

A Banded Star
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Merging Suns
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A Spectacular Sunset Wows Sky Observer
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Aymen Mohamed Ibrahem
Senior Astronomy Specialist