BY THE OPTIMIST DAILY EDITORIAL TEAM
The ring around the moon, also known as the lunar halo, is a breathtaking yet surprisingly common sight in the night sky. Unlike other unusual lunar phenomena, a moon halo can happen at any time of year, but it is most often in the winter. So, if you’ve seen a ring around the moon, you’ve probably experienced a wonderful phenomenon that combines beauty and science.
In this article, we’ll look at the science behind the lunar halo, discuss the best conditions for detecting one, and highlight some other celestial wonders you might see.
What causes the lunar halo?
When moonlight penetrates through thin ice crystal clouds at high altitudes, it creates a lunar halo. Cirrus and cirrostratus clouds, which normally float more than 20,000 feet above the Earth’s surface, contain ice crystals. In very cold temperatures, water vapor condenses into tiny hexagonal ice crystals that bend, or refract, light as it travels through them.
These crystals are necessary to create a lunar halo. Moonlight penetrates one side of a hexagonal ice crystal and emerges out the other, bending at an exact 22-degree angle. This is why lunar halos are known as “22-degree halos.” The refraction forms a ring of light around the moon, with each tiny ice crystal throwing moonlight outward in a circular pattern.
Unlike the vibrant hues of a rainbow, lunar halos are primarily white because moonlight is approximately 400,000 times less luminous than sunshine. This weak light is often insufficient to activate our eyes’ color-detecting cells, resulting in a soft, milky halo. However, in certain situations, small indications of color may occur on the inner edge of the halo.
How to see a moon halo: ideal conditions
If you want to catch a lunar halo, search for nights with generally clear skies but a thin coating of cirrus clouds. When there are lower-level clouds, it is more difficult to see a halo because thick clouds tend to hide moonlight. These high, thin clouds allow enough moonlight to flow through while acting as an ideal scattering medium for the light.
Because cirrus clouds are more abundant in winter, the colder months are the greatest time to see a moon halo. Cirrus clouds, on the other hand, can appear throughout the year, so you can look for them at any time. Just remember that, unlike other stargazing activities, an overcast sky (at least partially) is required.
Why does everyone see their own halo?
The moon halo you see, like a rainbow, is dependent on your viewing angle and position. For the halo to emerge, the ice crystals in the clouds must align in a specific pattern to focus light at precisely 22 degrees toward your eyes. This orientation makes each lunar halo a unique experience, since the exact appearance of the halo varies somewhat from one viewer to the next, depending on personal height, elevation, and perspective point.
Are there any other rings around the moon?
Lunar halos aren’t the only rings of light you can see around the moon. Here are several other moon-centric occurrences and how to tell them apart from a lunar halo:
1. Lunar Coronas
Moonlight diffracting through water droplets rather than ice crystals creates lunar coronas, which are often confused with halos. Coronas appear as rainbow-like discs that revolve closer to the moon, with an average radius of 10 degrees, as opposed to the 22-degree halo. Their small size and bright colors make them easy to identify when they appear.
2. Fogbows
Fogbows, with their pale color, resemble moon halos. They form near the ground rather than high in the sky. These “ghost rainbows” are whitish and are frequently visible in fine fog or misty conditions, caused by moonlight (or sunlight) passing through small water droplets in mist or fog.
Can the sun also create a halo?
Yes! A halo can form around the sun when light interacts with cirrus clouds in a similar manner. Solar halos are more common during daylight and have a mild red tint on the inner edge and a blue one on the outer edge. Because sunlight is so brilliant, solar halos are frequently more colorful than their lunar counterparts.
Rare and unique moon ring sightings
The most intriguing lunar halos are often accompanied by other unique atmospheric optics. During the winter of 2020, for example, residents of Manitoba, Canada, saw a moon surrounded by a spectacular ring, as well as other phenomena such as a corona, “moon dogs,” and tangent arcs—a spectacular sight not commonly seen. These types of spectacles, with numerous light effects surrounding the moon, provide remarkable stargazing experiences that surpass even the most famed “blood moons.”
So, the next time you see clouds floating in front of the moon, don’t stay indoors. Take a glance at the sky and see if you can identify a halo or one of its stunning replicas. Lunar halos are abundant, yet each one feels like a small miracle of light, clouds, and ice in perfect harmony.
