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This double rainbow behind Murriyang, CSIRO's Parkes radio telescope,
was captured by Maxim Voronkov on a visit several years ago. The
image also nicely illustrates how the sky inside a primary rainbow is
brighter than the sky outside of the bow. This arises as raindrops
are spheres and scatter light over a full circular disc in the sky.
Over most of the disc, scattered light at all wavelengths overlaps,
resulting in white light which makes the sky brighter. At the edge of
the disc, the wavelength dependence of the scattering gives rise to
the rainbow, with red light being scattered over a larger angle than
blue light and so red appearing on the outside of the bow.
(Image credit: Maxim Voronkov)
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