The Green Flash
The green flash is a result of the atmosphere bending light so the top edge of the sun will momentarily turn green. The atmosphere acts like a weak prism, separating the light into different colors. It is a rare event. The observer must know what to look for. Despite the name, there is no "flash". The event only lasts from a fraction of a second to a few seconds.

The Omega Sunset
Omega sunset in the photo shows how the sun's shape is distorted as it touches the horizon. It has long been known that an Omega sunset will often end with an observable green flash. The comparison of the sun's shape to the capital Greek letter Omega was made by the Italian astronomer Annibale Ricco about a century ago. He was one of the first people to photograph the setting sun at the horizon. It seems that it was this Omega sunset that Jules Verne described in the final chapter of "Le Rayon vert."

What to Look For
The green flash is best observed when you have a clear view of the horizon and the line of sight is nearly parallel to the horizon. The best place to see a green flash is on the ocean horizon while standing on the beach. The atmospheric conditions which are most favorable for the green flash are a calm and stratified atmosphere. When the sun is a few degrees above the horizon, the ball appears distorted and flattened in the vertical direction (to the omega shape). The closer it gets to the horizon, the more flattened it gets. Finally, the top of the ball is pinched off the edge. This is the part that suddenly turns green. The intensity and hue of the color will vary between yellow, green, and blue depending on many factors.

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