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Earth Notes: The Mirage Phenomenon

Brocken Imaglory

Southwest deserts are a good place to see atmospheric phenomena called mirages. They occur where distinct layers of warm and cooler air form. When hot air is trapped below cooler air, entering light is inverted and bent upwards – forming an inferior mirage below the real object.

While a mirage looks like shimmering water, it’s actually an image of the sky. But the shallow refraction angle means you see it only from a distance, and it seems to recede at the same speed as your vehicle.

But when cold air gets trapped beneath warmer air, light rays are bent so the image appears above the true object, forming a superior mirage. Distant cliffs or shorelines seem to tower above their true height.

If that air becomes turbulent, a special type of superior mirage may form. They’re called Fata Morgana, after the Arthurian sorceress Morgan le Fay, believed to be caused by witchcraft designed to lure sailors to their death. Fata Morgana are rapidly changing, compressed and stretched optical illusions. Stacked up, they can look like a dancing city in the sky.

If conditions are right, you might have a chance to view one from Mars Hill in Flagstaff. Looking east, you’ll see what look like quivering layers of cinder cones.  

No wonder the word mirage comes from the Latin mirari — which means “to look and to wonder at”!

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