Buzz
A circumhorizontal arc occurs when sunlight bends through ice crystals within cirrus clouds, producing these captivating atmospheric phenomena. (HeatherNemec/GettyImages)Key Insights
- Known as 'fire rainbows,' or circumhorizontal arcs, these stunning displays form when sunlight bends through ice crystals in cirrus clouds, usually seen in summer at mid-latitudes, creating vivid rainbow-like effects in the sky.
- The proliferation of smartphone cameras has made it easier than ever for people to capture and share pictures of atmospheric events such as circumhorizontal arcs and 'sun dogs,' sparking widespread interest in atmospheric optics across social media.
- Despite the frequent sharing of these visuals, confusion remains about their nature, with some mistaking circumhorizontal arcs for sun dogs, underscoring the need for more educational resources on atmospheric phenomena.
If you're a regular user of social media, you may recall the recent surge of Instagram posts showcasing 'fire rainbows' — a breathtaking collection of images, with thousands posted at last count. These were ethereal, iridescent clouds of red and gold that seemed to form a delicate V-shape in the sky, as if angelic wings had appeared. Here's one particularly striking photograph of this phenomenon captured in the sky above South Carolina.
In May, a number of smartphone photographers captured nearly identical images of the sky in Wisconsin, as reported by the local TV news station WATE on its website.
Many news outlets quickly explained that the term “fire rainbow” is somewhat misleading, as the images captured by amateur photographers were not actually rainbows, nor did they involve fire. Instead, they were witnessing a phenomenon known as a circumhorizontal arc, which occurs when sunlight bends through ice crystals in cirrus clouds. This differs from rainbows, which typically appear after rain when the sun is lower in the sky.
“There are numerous types of arcs formed by the refraction of sunlight through flat ice crystals,” explains meteorologist Chris Robbins, a private consultant and the founder of iWeatherNet, in an email. “The angle at which the sun interacts with the arc determines the type of arc. A circumhorizontal arc is always 46 degrees below the sun, and the sun must be very high in the sky—at an angle of 58 degrees or greater. That’s why these arcs are more common in the summer in mid-latitudes, and are rarely seen farther north where the sun is lower.”
The “fire rainbow” photo craze is just part of a larger trend: more and more people are using their smartphone cameras’ increasingly sharp optics to capture atmospheric phenomena and share them on social media platforms. The popularity of this trend has even led NOAA’s Weather in Focus photo contest to include an “In the iMoment” category, dedicated to images taken with smartphones and mobile devices. This year’s winner: a stunning shot of altocumulus clouds above the Great Smoky Mountains.
Although the sharing of sky images on social media has become widespread, it doesn’t necessarily mean that we fully understand the phenomena we're capturing. For example, Robbins points out that some people who posted images of what they thought were “fire rainbows” were actually photographing a different type of arc called a “sun dog,” which appears on either side of a rising or setting sun. However, Robbins believes it’s a step forward in education. “I think it’s fantastic that people are sharing their observations of atmospheric optics,” he says.
Capturing Your Own Weather Shotss
If you’re keen on snapping beautiful cloud photos, iPhone Photography School has a helpful article titled “How to Capture Dramatic Skies.” One particularly effective piece of advice is to use the HDR (High Dynamic Range) setting on your smartphone camera. This feature allows you to preserve the intricate details and highlights in both the clouds and the ground, preventing any overexposure in either area.
Another excellent tool is Clouds-online.com, an online resource offering a comprehensive cloud atlas that showcases the diverse variations in cloud formations, complete with photos. For those seeking a more straightforward approach, you can explore NOAA’s “Ten Basic Cloud Types.” online guide.
In June 2015, smartphone users across the United States flooded social media with images of a strange dark orange-red sun. It was later revealed that this peculiar hue was caused by smoke drifting from Canadian wildfires.
