Earth and sky
seen either side of the Moon during a lunar halo, they are known as
Moon dogs (paraselenae).
Rainbow
This is a commonly seen phenomenon caused by droplets
of moisture in the Earth’s atmosphere refracting (bending)
different wavelengths of light by different amounts, smearing the
wavelengths out into a spectrum of colours. Rainbows always
appear in the section of sky opposite the Sun, and often indicate
that rain is on the way or has just passed through. In a so-called
primary rainbow, the effect is caused by light being refracted once in
the droplets of water. In a double rainbow a second arc may be seen
above the primary arc. This secondary rainbow is caused by light
being refracted twice inside the water droplets. The sky in between
the bows is darker and is called the Alexander dark band. At night-
time, the Moon can also produce rainbows, though they are very
much fainter than solar rainbows.
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