Eclipse & Corona

The January 4, 2011 eclipsed sun surrounded by a water droplet diffraction corona.

Imaged by Tamás Ladányi (site, TWAN) at Kab Mountain, Hungary.
  ©Tamás Ladányi, shown with permission.


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Tamás’s corona is serene, pearly smooth and of subtle colours merging imperceptibly into one another. It is produced by diffraction from individual small water droplets in thin cloud.

The shape of the sun's eclipsed disk has almost no material effect on the corona's shape.

But its composed appearance belies its makeup. The subtle colours are all mixtures from the superimposed coronae from each sunlight colour. Shorter wavelength coronae are smaller than those of redder light and a ring of one colour can fill a gap in the rings of another.

Dig deeper and the ring intensities themselves fluctuate in apparent disorder as the light wavelength changes.

At left and lower left are exact Mie theory simulations for coronae of a few precise individual wavelengths. The calculations were made by IRIS.

The strange intensity fluctuations arise physically from higher order interference between wave diffraction in different modes. Most wave scattering is at the droplet rim but a small but important component is from light passing within the drops.

Rainbows also show apparent disorder from higher order interference. But at our macro level of existence flooded with wideband sunlight all seems smooth.