Solar Halos: What Are They, and How Do They Appear?
Key Takeaways
- Solar halos form when sunlight is refracted, reflected, and dispersed by ice crystals in high, thin clouds.
- The most common solar halo is the 22° halo, a faint circular ring that appears around the Sun.
- Sun dogs, light pillars, eclipse halos, and lunar halos are related sky phenomena with different causes and appearances.
- You should never look directly at the Sun while observing a solar halo or eclipse-related phenomenon.
Have you ever looked at the sky and noticed that there is a faint rainbow wrapped around the Sun? This is an optical phenomenon known as a solar halo, and it can be a marvelous sight to behold! But did you know that there are several different types of these halos, and each one has its own unique characteristics and causes?
Let’s take a look at what causes these halos in the first place, the different types of halos that occur, and explore ways you can study these amazing events even further.
What Causes Solar Halos?
So, what causes solar halos? You may be surprised to learn that the answer is ice crystals! When the weather conditions are just right, ice crystals become suspended in the upper atmosphere, typically within cirrus, or wispy, clouds.
When sunlight hits these ice crystals, light is reflected, refracted, and dispersed through the prism of the crystal, where it is bent at a 22° angle. This separates the light into its individual colors of the spectrum, the same principles of light behavior that cause traditional rainbows to occur after a rain shower.
As with rainbows, these halos are all about the position of the observer (you) to the light source. That is why two people in different locations may notice the same halo at slightly different angles or levels of brightness.
Before modern meteorology, these halos were considered leading indicators of an impending rainfall. The cirrus and cirrostratus clouds, which cause the halos, often signal a frontal system on the horizon. Today, solar halos are still a useful reminder to look at cloud conditions, but they should be treated as one visual clue rather than a guaranteed forecast.
Before modern meteorology, these halos were considered leading indicators of an impending rainfall; the cirrus and cirrostratus clouds which cause the halos often signal a frontal system on the horizon.
What are the Different Types of Halos?
There are a few different types of solar halos that you can observe, but let’s take a look at some of the most common. In addition to the standard circular halo (known as the 22° halo), there are also sun dogs and light pillars.
Sun Dogs are bright spots that occur on either side of the Sun: to the left, right, or both. These are most commonly observed when the Sun is close to setting along the horizon and when ice crystals are closer to the ground rather than floating in the upper atmosphere. In this instance, the ice crystals are referred to as ‘diamond dust’.
Sun dogs can be especially noticeable in colder weather because low-angle sunlight makes the bright patches easier to see.
Light pillars are another type of optical phenomenon that produces a vertical beam of light near the Sun. These are typically caused by flat, hexagonal ice crystals that fall through the sky like flakes. As those flat crystals fall, sunlight is reflected vertically through them, thus creating the telltale ‘pillar’.
Light pillars are often easiest to spot near sunrise or sunset, when the Sun is low on the horizon.
Solar Halos During an Eclipse
There is another type of solar halo that occurs during an eclipse, one which has to do with the Sun’s corona. The corona, which is Latin for ‘crown’, is the gaseous outer atmosphere of the Sun. Although it is always hanging around the surface of the Sun, we normally cannot see it due to the brightness of the Sun’s light.
A solar eclipse halo occurs during a total solar eclipse, during the moments when the Moon passes in front of the Sun. When the Moon blocks the Sun, thus blocking out the light being emitted by the Sun, the corona becomes visible. This halo appears as a hazy white cloud surrounding the blacked-out Sun.
During any partial phase of an eclipse, proper solar viewing protection is still required.
Scientists use total solar eclipses as an opportunity to study the Sun’s atmosphere, from the temperature of the surrounding atmosphere to the intensity of the radiation it produces. These observations can help us gain a better understanding of the Sun’s behavior, including its impact on space travel and communication systems here on Earth.
What Causes Lunar Halos?
The Sun isn’t the only celestial body that gets to have all the fun. The Moon is capable of producing a lunar halo, too!
The basic principles involved are the same: ice crystals trapped in high altitude cirrus clouds reflect, refract, and disperse the light coming off of the Moon. That is why you are more likely to observe a lunar halo during colder months and around the time of a full moon, when the light being reflected by the Moon is brightest.
Because moonlight is much dimmer than sunlight, lunar halos often appear softer and less colorful than daytime solar halos.
Continue Your Study of Halos
If solar halos have piqued your interest, and you would like to continue your study of light, refraction, and rainbows, consider picking up a pair of diffraction glasses. Our plastic diffraction glasses are an affordable way to continue your exploration of light, halos, and rainbows, and can help bring your lesson plan to life in a way that students will never forget.
If you’re planning on experiencing a total solar eclipse in the near future to catch a glimpse of a solar eclipse halo for yourself, you’ll want to be prepared. We have a wide selection of eclipse viewing equipment, including a variety of solar eclipse glasses, solar eclipse viewers, and solar filters for cameras and telescopes.
All of our eclipse gear is "CE" Certified, meeting standards for transmission Module B EU Type-Examination Certificate for the requirements of Personal Protective Equipment Regulation (EU) 2016/425 and EU Type Examination by CCQS Certification Services Limited, EU Notified Body, Number 2834 www.CCQS.com.
They’re also certified to meet the requirements for ISO 12312-2:2015 (EN ISO 12312-2:2015). They meet the 2012 Transmission Requirements of EN 1836:2005 and AS/NZS 1338.1:1992 for eclipse filters (Queensland Directive).
Our “Silver/Black Polymer” lenses block out 99.999% of intense visible light, 100% of IR, and 100% of ultraviolet light.
Discover the Wonder
Discover the wonder of solar halos for yourself, from circular halos and sun dogs to light pillars and solar eclipse halos.
If you have any questions about the diffraction glasses or the eclipse gear you need to further your education, don’t hesitate to get in touch. Rainbow Symphony can help you choose approachable tools for light, color, and solar astronomy lessons. Contact Rainbow Symphony by phone at (800) 821-5122, or by email at support@rainbowsymphony.com.
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