Under certain conditions, observers will notice what seems to be a hazy-looking ring around the Moon in the evening. We take a closer look at this phenomenon, better known as a lunar or 22-degree halo.

Although there are many theories and folklore surrounding this “supernatural” occurrence, very few people really know what exactly these rings (or halos) are or how they are formed. 

In this article, we take a look at what these rings are and how they are created. We also address a few common assumptions and look at some folklore surrounding these mystical objects in the sky.

During the introduction, a brief description of what these sometimes mysterious-looking rings around the Moon are has already been provided. To better understand their formation, though, one needs a more elaborate and detailed definition.

Lunar Halo Definition​​​​​​​​​

​A Lunar halo, or 22-degree halo, is defined as a hazy ring that occurs around the moon at a radius of approximately 22 degrees. It results from the moon’s light being refracted by ice crystals in Cirrus clouds in the upper troposphere at an altitude of approximately 6000 meters or 20 000 feet.

A few conditions need to be in place, though, to observe these rings around the moon clearly..

1. 1. The presence of a full moon is ideal for the best viewing conditions.
   2. Secondly, a clear sky with only a thin layer of cirrus clouds high up in the atmosphere is essential. (The presence of thicker clouds lower down in the atmosphere will obscure or eliminate the effect.)
   3. As the light from the Moon (or Sun) hits the cirrus cloud, it gets refracted or “bent” by the ice crystals, redirecting the light towards the observer.
   4. If the light is refracted or “bent” at a certain angle, specifically 22 degrees, the rings will become visible to the observer. (This also means the rings have a radius of about 22 degrees around the moon or sun.) That is why this occurrence is also referred to as a 22-degree halo by scientists and meteorologists.
   5. The observer also needs to be in the right position for the refracted light to reach them and make the halo visible.

A notable feature of the halo surrounding the moon is that its inner edge is usually more clearly defined than its outer edge. The outer edge appears hazier as the refracted light gradually fades away.

Although the ring around the moon has a mostly hazy white color, other colors can also be observed. This is a direct result of the hexagon shape of the ice crystals.

Much like raindrops separate sunlight into the colours of a rainbow, the faceted, hexagonal shape of ice crystals not only refracts moonlight but also separates it into its different colours.

This is why you will occasionally notice some rings around the moon or sun that have a red tint on the inside and a blue tint on the outside.

Since the moon isn’t as bright as the sun, the rings around the moon mostly appear white, while the rings around the much brighter sun more often display these rainbow colors.

Another interesting fact about the rings surrounding the moon is that the sky inside the ring/halo appears darker than the rest of the night sky.

Finally, if you are lucky, you may catch a very rare glimpse of not one but a double halo surrounding the moon. 

For centuries, many cultures around the world have regarded a ring around the moon as a clear sign that rainy weather is on the way.

And to be honest, this is neither a myth nor a superstition. The presence of high cirrus clouds is very often an indication of wet and stormy weather on the way.

Cirrus clouds normally precede low-pressure systems by a day or two, and as many of you may already know, low-pressure systems are normally at the heart of stormy wet weather. (You can read more about low-pressure systems and cold fronts in this article.)

The most noteworthy aspect of the folklore surrounding rings around the Moon is the surprising lack of any specific beliefs about them.

Different cultures and religions often attach significant meaning to changes in the appearance of the Sun and Moon.

Significant events like the Full Moon and New Moon, and especially rare events like solar eclipses and lunar eclipses, have held special meaning in many cultures and have often been marked by religious ceremonies and rituals.

The worship of the Sun (and events surrounding the Sun) is probably the oldest religion in the world and predates any recorded history. The worship of the sun god Ra and the later combined deity Amun-Ra is well documented in ancient Egyptian history.

Celebrations of the winter solstice, often symbolising the victory of light over darkness, also predated Christmas celebrations marking the birth of Christ.

Yet, despite all the importance given to events surrounding the sun and moon by various religions and cultures over the centuries, there is no evidence of any particular attention being given to halos surrounding the Moon.

The biggest irony is that the only folklore surrounding the rings around the moon is based on actual science. And that is the belief that the hazy ring we see at night surrounding the moon symbolizes rainy weather. As it turns out, this belief is actually scientifically correct.

As you can clearly see, the visible ring/aura around the moon that sometimes occurs under ideal conditions is not nearly as mystical as one might think.

There is a very simple scientific explanation for it, which has everything to do with what is going on in our atmosphere, and nothing to do with what is happening in space around the moon itself.

The multicolored rings we sometimes see around the sun are also exactly the phenomenon that occurs around the moon.

Until next time, keep your eye on the weather!