TNG & Fogbow ~ A fogbow arcs over the Italian 3.6m Telescopio Nazionale Galileo, TNG, on the Island of San Miguel de La Palma, Spanish Canary Islands. Imaged by Alex Tudorica.  ©Alex Tudorica, shown with permission.
Atmospheric
Optics

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The island of La Palma is home to several major observatories thanks to its good seeing. The latter is not too evident in this image.

TNG is used for research ranging from asteroid studies to galaxies.   It has an altazimuth mounting.   Active optics using an off-axis star compensate for deformations of the thin primary mirror and correct the positions of the Nasmyth secondary and tertiary mirrors.
Sunlight shining through mist or fog is needed to produce the fogbow. It is the small droplet counterpart of the rainbow. Diffraction by the droplets broadens the bow into a wide arc and at the same time smears the colours.

Rainbows produced by millimetre sized drops are actually also broadened and fringed by diffraction but the angular width of the sun and the range of drop sizes masks the effects.