A moonbow, also referred to as a moon rainbow or lunar rainbow, is a rainbow that emerges from moonlight instead of direct sunlight. Its formation closely mirrors that of a solar rainbow, as it is engendered by light being refracted through airborne water droplets, often originating from rain or a cascading waterfall. These moonbows invariably manifest on the opposite side of the sky from the observer’s perspective, in relation to the Moon.
The concept of moonbows has even found mention in Aristotle’s Meteorology, believed to have been composed around 350 BC. Yet, moonbows exhibit a notably subtler appearance compared to their daytime counterparts, as the moon’s illumination is comparatively feeble. Consequently, discerning distinct colors within a moonbow is challenging for the human eye, since the dimness of the reflected light fails to activate our color receptors. As a result, moonbows tend to appear predominantly white. However, the vibrant colors of moonbows can be captured through extended exposure in photography.
Moonbows are most effectively observed during nights of a full moon, particularly when the moon is in its brightest phase and not concealed by cloud cover. Additionally, the moon should be situated low in the sky, with an elevation of at least 42 degrees. To optimize visibility, the night sky should remain shrouded in complete darkness. Although a full moon naturally imparts some illumination to the sky, moonbows can still be perceived for a period of two to three hours following sunset.