What Causes a Ring to Appear Around the Moon?

Although many lunar phenomena are only one night events, a ring around the moon is much less elusive. Also known as Halo Lunar, a shiny white light ring around the moon can appear at any time during the lunar calendar and at any time of the year, especially in winter.

But, if you hope to see a lunar halo, you will want to ignore the number one rule of star star who says that you should not suffocate in cloudy weather. The lunar halos are caused by thin, vaporous clouds, cirrus and cirrostratus and refraction and reflection of the moonlight by the ice crystals of the clouds.

Below, we explore the lunar spectacle of a ring around the moon and tell you how to find the best vision conditions.

Ideal sky conditions for the formation of rings

Like the rainbows, the lunar halos are formed when the light interacts with the water hanging in the air. This water is found frozen in the cirrus and cirrostratus clouds – standby clouds which float more than 20,000 feet (6 km) above our heads where temperatures are too gelid to remain liquid water.

To see as well as possible a lunar halo, the conditions of the sky must be clear with only a thin layer of cirrus clouds. If thicker clouds are present at lower levels, they will obscure the Halo effect.

While the moonlight shines through the cirrus clouds, it strikes the millions of tiny ice crystals and refracts, or folds and changes direction, as it enters each. The light then refracts again when it leaves the other side of a crystal.

How much the moon clear depends on the size and shape of the crystal. In the case of lunar halos, ice crystals are tiny (hexagonal) columns measuring less than 20 microns in diameter. And they all fold the light at an angle of 22 degrees compared to its original path (if you have already heard lunar halos called “22 degrees halos”, that’s why).

The light of the moon dispersed in all directions (above, below, next and diagonally) creates the characteristic circular shape of the lunar halo.

How and why we see a ring

Of course, to see the halo, the crystals must be oriented and positioned in a specific way to your eye. The light reflected on the ice crystals and that coming directly from the moon should cross in your eyes on angles of 22 degrees.

This is why, like the rainbows, the halos around the moon (or the sun) staff. Each observer sees his particular halo made by his orientation towards ice crystals. The view of the ring around the moon varies from person to person depending on the personal height, the elevation where you are and other factors.

The colors of a lunar halo tend to be dark because the sun is 400,000 times brighter than a full moon. They are so dark that light is often too low to be picked up by color detection cells in our eyes, which is why the lunar rings often appear in milky white – to be the combination of all visible colors of light.

As for the sky between the ring and the moon, it generally remains dark because none of the ice crystals reflect light to angles smaller than 22 degrees.

The ring will remain visible as long as the Cirrus clouds create a veil through the moon.

Lunar halo lookaller

The lunar halos are not the only rings you will find surrounding the moon. Halos are often confused with lunar coronas, but the latter are rainbow color discs that form when the moonlight (or sunlight) interacts with water droplets in the fog. Coronas also tend to tighten around the moon, creating a radius at 10 degrees rather than 22 degrees.

The fogs are white rings, similar to the lunar halos, forming low on the ground. They are also made up of water droplets – namely those of tiny size as in a fog or a fine mist.

During the winter of 2020, people saw the ring of all the rings on Manitoba, Canada. Not only was the moon crowned in white light, but the crown, moon dogs, and Tangent arcs have occurred alongside the Halo. Now it’s a show that beats a macabre blood moon every day.