Watch That Mirage!

The final predictor of the most common variety of green flash is when an inferior mirage image of the Sun itself — sometimes called the “countersun” — seems to peek up above the horizon just as the true Sun’s bottom edge is about to touch the horizon.

In a matter of seconds, the countersun merges with the real Sun, creating something that looks a little like the Greek letter Omega. When the last piece of the merged pair is left on the horizon, it’s an enlarged combination of the green edges of the Sun and countersun. It’s easily large enough for your eye to detect, and it appears green — for just one or two breathtaking seconds.

To see the green flash caused by an inferior mirage you must usually be standing on a wide expanse of flat ground. There’s another kind of mirage that can produce an enhanced green flash if you are higher above ground level, perhaps on a mountain or in a building. That one requires a temperature inversion (when warm air lies over cold air). If you see a pair of spikes sticking out of the sides of the Sun and these drift up the Sun’s disk, get ready for them to detach from the top of the Sun and vanish in a last-second gleam of green.

Catching your first strong green flash may take considerable patience, but it will be worth it. And along the way you’ll see many otherwise spectacular sunsets and wonders of the sky. Everyone loves beautiful sunsets — why not become a knowledgeable connoisseur of them? One of your rewards will be the emerald or blue-green solar flame whose sight is more wondrous than even Jules Verne could ever hope to convey.
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Fred Schaaf is the author of A Year of the Stars: A Month-by-Month Journey of Skywatching (Prometheus Books, 2003) and many other books about observing the sky.

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