Mirage of astronomical objects

A mirage of an astronomical object is a naturally occurring optical phenomenon, in which light rays are bent to produce distorted or multiple images of an astronomical object. The mirages might be observed for such astronomical objects as the Sun, the Moon, the planets, bright stars and very bright comets. The most commonly observed are sunset and sunrise mirages.

Mirages are distinguished from other refraction phenomena. One of the most prominent features of mirages is that a mirage might only produce images vertically, not sideways, while a simple refraction might distort and bend the images in any way. The distortion in both images displayed in this section was caused by refraction, but while the image on the left, which is a mirage, demonstrates only vertical distortion, the image on the right demonstrates distortion in all the ways possible. It is easier to see the vertical direction of the mirage not even at the mirage of the Sun itself, but rather at the mirage of a sunspot. As a matter of fact it is at least a three-image mirage of a sunspot, and all these images show a clear vertical direction.

Inferior mirage of astronomical objects is the most common mirage. Inferior mirage occurs when the surface of the Earth or the oceans produces a layer of hot air of lower density, just at the surface. There are two images, the inverted one and the erect one, in inferior mirage.They both are displaced from the geometric direction to the actual object. While the erect image is setting, the inverted image appears to be rising from the surface.

The shapes of inferior mirage sunsets and sunrises stay the same for all inferior mirage sunsets and sunrises. One well-known shape, the Etruscan vase, was named by Jules Verne. As the sunset progresses the shape of Etruscan vase slowly changes; the stem of the vase gets shorter until the real and the miraged Suns create a new shape – Greek letter omega Ω. The inferior mirage got its name because the inverted image appears below the erect one.

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Wikipedia