Moonbows
which are rather different from rainbows are also known as lunar rainbows. They
differ from the average rainbow that we know and are created by the shimmers of
the moon rays instead of the sun rays.
Image
source: Stefan Lee Goodwin – A
10pm blood red night rainbow over Scotland
Its
formation is no different apart from the light source. Similar to the
occurrence of a rainbow, the moonbow is also created by the reflection of light
in water droplets present in the air, but in the presence of moonlight.
However, these moonbows are usually positioned opposite from the Moon relative
to the observer.
Details
of moonbows have been mentioned in Aristotle’s Meteorology (circa 350 BC) too.
The moonbows are much fainter than the rainbows that occur during the daytime
as the moon only reflects a smaller amount of light. Therefore, it's quite
difficult to discern the colors in a moonbow for a human. The light reflected
is too dim to activate the color receptors in our eyes. Thus, the moonbows
appear to be white. But still, we'd be able to see its colors in long exposure
photographs.
Image
source: Arne-kaiser – Lunar
rainbow over Kihei, Maui, Hawaii, US
Moonbows
are best visible when there's a full moon. The moon should be in one of its
brightest phases and should not be obscured by clouds for the best view. And
also, the moon must be low in the sky at an elevation of less than 42 degrees
at least. Plus, the night sky should be completely dark. Even though the sky is
not at all dark during a full moon; the moonbows can be observed for two or
three hours after the sunset.
These
requirements are those that make moonbows quite rarer than rainbows. The
possibility for the occurrence of a moonbow is less than 10% as often as
rainbows. In some instances, moonbows can be observed during full moonrise
during the months of winter when rain falls at extreme latitudes. However, the
definition of the colors depend on the size of the water drops. The smaller the
moisture drops are the less vivid the colors will be.
Image
source: Garry – A night
rainbow on Fraser Island, Queensland, Australia
Moonbows
are often induced by fog, spray and mist apart from rain. Such bows can be
noticed around various waterfalls in the USA including Niagara Falls, New York,
Yosemite National Park, California, or Cumberland Falls, near Corbin, Kentucky.
Moreover, Victoria Falls, on the border between Zimbabwe and Zambia is also
well-known for spray moonbows.
Image
source: CalvinBradshaw – A
spray-induced moonbow (lunar rainbow) at Victoria Falls (Zambia side)
As
mentioned earlier, moonbows can be seen for only about 3 hours around the full
moon during the end of evening twilight or before sunrise. Summer can be
identified as the best time for long lasting moonbows as the moon spends more
time in the lower sky. Moonbows may last only up to a maximum of one hour
during other seasons.
You
can also try to find a quite pale moonbow in showery weather. Though you won't
see many colors in it with your naked eye, you'd definitely be able to witness
the colors if you capture it by mounting a camera on a tripod.
Image
source: Terje Nesthus
So,
make sure to try to capture a Moonbow. Stay tuned for more interesting stuff!
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