Fogbow & Moon, Poland

Tomasz Adam of Staszów, Poland imaged this early morning fogbow. Its huge dimensions are evidenced by the diminutive waning moon at upper left.

Inside the bow there is a dark space and then a faint and broad supernumerary bow.

© Tomasz Adam , shown with permission.

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Fog droplets are sufficiently small that light interacting with them reveals its wave nature. Light is no longer simply refracted or reflected as when a rainbow is formed. Instead, light waves are scattered, diffracted, in all directions to produce a wildly oscillating and complex ringed pattern around the sky.

The finite size of the sun and variations in droplet size blur out the very closely spaced oscillations and background skylight conspires to obscures more. But the brightest survive; a coloured corona around the sun, a ringed glory directly opposite and a large and ghostly fogbow.

Raindrops are 10-1000X larger than fog droplets and their diffraction effects are consequently small. The corona and glory shrink to insignificance and instead of a diffuse fogbow we see a rainbow. Yet the latter retains echoes of waves in its supernumeraries.