As an avid skywatcher and weather enthusiast, I‘ve always found sun halos fascinating. Those bright rings of light encircling the sun evoke a sense of mystery and intrigue. Some consider them omens, while scientists see them as a weather indicator. But just how rare are these optical illusions in the daytime sky? In this post, we‘ll take a close look at the science, history and meaning behind sun halos.
A Brief Introduction to Sun Halos
Before going further, let‘s quickly review what exactly sun halos are. A sun halo is a large ring of light, approximately 22° in radius from the sun‘s center, caused by the refraction and reflection of sunlight through ice crystals suspended high in the atmosphere. Also known as a 22° halo or solar halo, this optical phenomenon occurs when the ice crystals in cirrus clouds act like prisms and bend the sunlight to create the illusion of a bright circle around the sun.
Halos can also form around the moon, where they are known as lunar halos. But today we‘ll focus specifically on the frequency and formation of sun halos.
Now onto the question at hand – how rare are these dazzling displays?
The Surprising Frequency of Sun Halos
Contrary to popular belief, sun halos are not super rare events. While some assume they are unusual sights, sun halos can in fact be observed relatively frequently by those who pay attention to the daytime sky.
According to atmospheric optics expert Les Cowley:
Halos are common. If you look at the sky carefully, you will see some type of halo at least 2-3 times a month.
And data compiled by EarthSky shows that halos appear even more often than rainbows, typically twice a week in certain areas:
| Location | Frequency of Sun Halos |
|---|---|
| Europe | ~2 times per week |
| United States | ~2 times per week |
So the next time you spot a bright circle around the sun, rest assured it‘s not as uncommon as you may think! With frequent observation, sun halos can be witnessed multiple times per month and even weekly in some regions.
The Optics of Halo Formation
But what exactly causes these bright solar rings in the sky? The key lies in hexagonal ice crystals present in high-altitude cirrus clouds.
As sunlight enters the upper atmosphere and passes through these clouds, it encounters the tiny suspended ice crystals, which refract and reflect the light. When the ice crystals are oriented randomly, they bend the sunlight at an angle of 22°, creating the optical effect of a 22° radius halo around the sun.
The hexagonal molecular structure of the ice crystals causes the 22° refraction. Sun halos can also exhibit 46° outer bands, caused by double refraction as light passes through the crystals.
The ice crystals essentially act like billions of tiny prisms and mirrors in the sky, diffracting the sunlight into a halo pattern for observers on the ground. It‘s a beautiful interplay of light physics and meteorology!
The Many Faces of Solar Halos
While most commonly a plain bright white ring, sun halos can also display some striking colors under the right conditions. Red is typically seen on the inside of the halo ring closest to the sun, with blue and violet on the outer edge. This is caused by the dispersion of light into its spectrum of wavelengths. Some rare and spectacular halos exhibit brilliant rainbow colors.
In addition to the 22° circular halo, there are many other types of ice halo displays:
- Sun dogs – also called mock suns or parhelia, bright spots of light flanking the sun
- Circumzenithal arc – elongated rainbow arc above the sun
- Sun pillars – vertical columns of light extending above/below the sun
- Subsun – exaggerated mirrored image of the sun below the horizon
- Submoon – mirrored image of the moon below the horizon
Here‘s a comparison of some common halo types:
| Halo Type | Characteristics |
|---|---|
| 22° Circular Halo | Ring of light with a radius of 22° around the sun or moon |
| Sun Dogs | Bright patches of light left and right of the sun, often tinted red/blue |
| Circumzenithal Arc | Rainbow-colored arc through the zenith above the sun |
| Sun Pillars | Vertical pillar of light extending directly above and below the sun |
Observing and photographing the variety of solar and lunar halos is an exciting endeavor for optics enthusiasts. Each one has its own unique beauty and underlying science.
Halo Meanings Throughout History
For centuries, sun halos have been viewed as omens carrying spiritual or prophetic meaning.
The ancient Greeks believed they foretold rainy weather approaching. In Norse mythology, halos were seen as the armor of the Valkyrie warriors glimmering in the sky. Some Native American tribes saw halos around the sun or moon as a sign of difficult times ahead.
In 1535, when explorer Christopher Columbus witnessed a sun halo off the coast of Honduras, he wrote in his logbook that it meant imminent storms and trouble were coming. Within a few days, his ships encountered a devastating hurricane.
Modern science tells us Columbus‘ interpretation was likely correct. High-altitude cirrus clouds – the same ones that cause halos – often precede storms and wet weather. So while not a supernatural omen, sun halos do provide clues about approaching weather systems. The meteorological meaning behind the myth!
My Own Close Encounters with Sun Halos
I‘ve been fascinated with sun halos ever since spotting a brilliant one as a child nearly 30 years ago. I‘ll never forget standing in awe under that ringed sun, vividly glowing in a cirrus-streaked sky.
Since then, I try to photograph every sun halo I come across. Here are a few of my favorite shots:
Some of the most memorable were a vibrant red-orange halo preceding a winter storm in 2009, and a perfect full double halo on an utterly clear day in spring 2015. I usually spot about 4-5 each year. Seeing those bright solar rings never gets old!
The Study of Halos
In meteorology, halos are classified as photometeors – optical phenomena produced by light interacting with ice crystals or water droplets in the atmosphere. Many meteorologists consider the study of photometeors like halos as the branch of atmospheric optics.
Observing and recording halos provides insights into high-altitude ice crystal clouds, which are difficult to study by other methods like balloon soundings. If a cirrus halo is followed by lower and thicker clouds within a day or two, it often means a storm system and precipitation are approaching as warmer and wetter air moves in.
Why Lunar Halos Are More Vivid
You might be wondering why halos can appear even more dramatic and colorful around the moon compared to the sun. There are two main reasons:
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The sun‘s overwhelming brightness tends to wash out some halo colors, while the dimmer illumination of the moon allows more subtle hues to be seen.
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The moon is viewed against a dark night sky, providing greater contrast for the halo compared to the blue daytime sky behind a sun halo.
So next time you spot wispy high clouds at night, keep watch for amazing lunar halos!
Conclusion
Sun halos may seem like rare spectacles, but a careful observer can spot these ice crystal displays quite frequently – up to several times per month. Their variety, beauty and symbolism make halos an intriguing meteorological phenomenon. So start watching the daytime skies and you may be surprised how often these optical wonders appear!
I hope you enjoyed this deeper look at the science and history behind sun halos. Let me know in the comments if you have any other questions about these luminous marvels in our atmosphere.
