Every so often, a photo goes viral claiming to show two suns in the sky. It is usually paired with a dramatic explanation. “a rare Hunter’s Moon event”, “a shift in Earth’s orbit”, or even “the end days are coming”, or something like that.
Are the images with two suns in the sky real?
Yes, the photos are often real. The specific story attached to those viral photos, however, is almost always fabricated. Hunter’s Moon is nothing more than the name of the full moon right after Harvest Moon. It comes every year around October. And there are definitely never two suns in the sky.
The photos that look like two suns are actually an optical illusion. They’re called sun dogs, and the actual explanation is real atmospheric science.
What is a sun dog?
A sun dog (technically called a parhelion) is a bright spot of light that appears beside the actual sun. Sometimes on one side, sometimes on both.
Image source: US National Weather Service Goodland Kansas
It’s caused by refraction. The sunlight hits hexagonal ice crystals high up in cirrus clouds, about 6 km above the ground. The light then bends at a consistent angle, concentrating light into a bright patch positioned almost exactly 22 degrees to the left or right of the sun.
The science behind sun dogs
Unlike illusions caused by your brain misinterpreting information, sun dogs are a physical illusion. The “trick” happens in the air itself, through refraction, before the light even reaches your eyes. Everyone looking at the same sky would see the same effect, from their own angle, like you would see a rainbow or a mirage.
Just like with rainbows, sun dogs are mostly visible when the sun is low on the horizon, and the rays are nearly horizontal with the earth’s surface. Instead of raindrops in the sky to form a rainbow, cirrus clouds need to be present to form the right kind of ice crystals. This is more common in cold climates and winter months, but can technically happen anywhere in the world, at any time of year, given the right atmospheric conditions.
The ice crystals responsible are shaped like thin hexagonal plates, and as they drift and fall through the air, most of them settle into a roughly horizontal orientation. Light entering one face and exiting another consistently bends by about 22 degrees. This is why sun dogs reliably show up at that same distance from the sun, rather than randomly scattered around the sky.
