Moonstars

Moonstars refers to a phenomenon observed in the night sky where the Moon appears to be surrounded by a faint, luminous ring or halo. This optical effect occurs due to the refraction of moonlight through ice crystals in high-altitude cirrostratus clouds. The crystals typically form hexagonal shapes, bending the light and creating a circular appearance around the Moon.

Moonstars are similar to sun halos but occur at night when the Moon is visible. The effect is most noticeable when the Moon is near its full phase, as its brightness enhances the visibility of the surrounding ring. Unlike sun halos, which can sometimes be accompanied by other optical effects like parhelia (mock suns), Moonstars are generally simpler in appearance, consisting primarily of a single ring.

This atmospheric phenomenon is not rare and can be observed in various parts of the world, particularly in regions with cold, stable air masses that favor the formation of cirrostratus clouds. While Moonstars are a natural occurrence, they can also be mistaken for other celestial phenomena, such as the faint glow of the zodiacal light or atmospheric refraction near the horizon. Unlike auroras or meteors, Moonstars are purely a result of light refraction and do not involve charged particles or debris entering Earth’s atmosphere.

The study of Moonstars and similar optical effects falls under the broader field of atmospheric optics, which examines how light interacts with particles in the atmosphere. While they lack the dramatic visual impact of phenomena like rainbows or coronas, Moonstars remain a subtle yet fascinating aspect of natural light phenomena.