Moonbows, also known as lunar rainbows, are different from regular rainbows in that they are created by the shimmers of moon rays rather than the sun.
A moonbow (sometimes spelled moon rainbow or lunar rainbow) is a rainbow created by moonlight rather than direct sunlight. Apart from the light source, its production is identical to that of a solar rainbow: light is reflected in water droplets in the air as a result of rain or a waterfall, for example. They are always on the opposite side of the sky as the Moon in relation to the viewer.
Moonbows, which have been mentioned at least since Aristotle’s Meteorology (about 350 BC), are much fainter than daylight rainbows because the surface of the Moon reflects a lower quantity of light. As a result, the human eye has a considerably more difficult time distinguishing colors in a moonbow because the light is too faint to activate the color receptors in our eyes. As a result, moonbows are normally white, although their hues may be seen in long exposure images.
Moonbows are best seen at and around full moon, when the Moon is at or near its brightest phase and is not obstructed by clouds. The Moon must be low in the sky (at a height of less than 42 degrees, ideally lower) and the night sky must be very black for moonbows to emerge. However, because the sky is not fully black on a rising/setting full moon, moonbows may only be seen two to three hours before or after dawn or sunset. And, of course, water droplets (from rain or spray) must be present in the sky opposite the Moon.
Moonbows are extremely rarer than solar rainbows due to these conditions; they occur fewer than 10% as frequently as conventional rainbows. Moonbows can also be seen at full moonrise during the winter months, when the sky is darker and rain falls at high altitudes. Color definition is affected by the size of moisture drops in the air: the smaller they are, the less brilliant the colors will be.
Moonbows can be caused by spray, fog, or mist in addition to rain. Such bows may be observed surrounding many waterfalls in the United States, including Niagara Falls in New York, Yosemite National Park in California, and Cumberland Falls near Corbin, Kentucky. Victoria Falls, located on the border of Zambia and Zimbabwe, is also well-known for its spray moonbows.
How to spot a moonbow?
Moonbows, as previously said, are only visible for roughly 3 days around full moon when viewed against a black sky near the end of evening twilight or before daybreak. Summer full moons are the optimum period for moonbows in the middle latitudes since the Moon spends more time low in the sky. Moonbows may last barely 1 hour at other seasons.
When the Moon is low and brilliant, watch for a faint moonbow in showery weather. You won’t notice many colors, but if you set a camera on a tripod, you can easily catch them.