As the United States experiences a powerful cold front, many southern states are beginning to experience a phenomenon they've never seen before. When looking at the sky at night, there is a large ring around the moon, somewhat like the corona around the sun during a solar eclipse.
In addition to the ring itself, many people experience specific colors in or around the halo. Generally, the light closest to the ring has a reddish tint, while the outside of the ring might have more blue coloring. The inside of the ring is often slightly darker than the sky beyond it as well.
The popular term for this is "moon halo," but it is scientifically known as a 22° halo. For those who have never seen it before, it can be beautiful and shocking. Those who live farther north have probably experienced this phenomenon before, but what is causing it?
What causes a moon halo?
Technically speaking, a moon halo is an optical illusion. There is no ring at all, and it is only visible to the particular viewer because of a very specific combination of atmospheric conditions. Even so, the science behind it shows that moon halos are remarkable because of how hard it is to get precisely the right conditions to see them.
The reason so many people have never seen a moon halo before is that they usually only occur in very cold environments. Scientists have found that the phenomenon occurs when there are ice crystals in the atmosphere, which interact with the latent light. The light from the moon bounces off of these crystals to make a distinct ring, usually with a radius of 22 degrees.
According to Atmospheric Optics, it all comes down to how light refracts. Most of the time, the light hits ice crystals at angles that make a negligible difference in how we experience it. However, when the light hits ice crystals perpendicularly, the light refracts at an angle of 22º to 50º. This causes the inner section of the ring to be brighter than the outer portion.
In most cases, these will only be seen around full moons, because they tend to provide the most light. They may be more common on cloudy nights as well because cirrus cloud forms make it ideal for light to hit the ice crystals correctly. In perfect conditions, there may even be multiple visible rings.
In addition to the light, the ice crystals have to fit the right circumstances. According to Space.com, the ice should be between 20,000 and 40,000 feet (6,000 to 12,000 meters) above the observer. As ice frequently forms hexagons, 22 degrees is the minimum angle needed for the light to be affected. If the ice crystals form other shapes, they may either make no effect or a very different one.
If all these conditions are met, the light reflecting off the moon will essentially be projected farther away from the object itself. This is what causes the appearance of a ring or circle, with the moon precisely at the center.
Because so much of this comes down to angles and distance, the particular moon halo a person encounters can be very different from the one others around them perceive. There may actually be a halo on most cold nights, but only a few lucky people are at the right location to see it.
While this kind of halo can actually happen around the sun as well, it's more common around the moon because the night sky makes it easier to see variations of light. However, solar halos often have more noticeable colors, thanks to the strength of the light.
What does a moon halo mean spiritually?
Moon halos have a long history within folklore, supposedly providing information about incoming weather and even personal fortune.
The most common interpretation of moon halos has to do with weather patterns. The Farmer's Almanac notes that a moon halo is an omen for imminent storms. This actually has some scientific grounding, as the cirrus clouds that help form moon halos are often signs of changing weather fronts.
Valentin Komarovskiy documented some different historical interpretations of the moon halo on LinkedIn. In Hinduism, the moon halo was a sign of good fortune in general, while the Ojibwe people saw the halo as a sign of personal good luck. Ancient Egypt believed it meant that the God of writing and magic was watching over them.
Overall, the moon halo has had a generally favorable reputation throughout history. While it might mean storms were on the horizon, it was generally known to mean good times were on the way. Even if it didn't foretell specific events, it was often a sign that God was watching over you.
However, some cultures saw it as a sign of change, which may not be a good thing. Spiritual Unite claims that the Chinese saw it as an omen of danger, while some African and Native American cultures saw it as an omen of death.
Taking it all into account, those who want to understand a moon halo as an omen should understand that it means some form of divinity is watching you. This often means that change is on the way, though whether that change is good or not depends on the culture.
Got questions about history, trivia, or anything else? Send an email to email@example.com we might answer here on the site!