Ever seen a rainbow-colored patch of light on the side of the Sun? This is called a “sundog” (or “sun dog”). What does it mean when you see a sundog? Learn more!
What Are Sundogs?
A sundog is similar to a rainbow, and more common than rainbows. Sometimes they look like bright rainbows or colorful spots on either side of the Sun. Other times they are brighter and actually look like two extra Suns.
Sundogs are also known as “mock suns” or “parhelia,” which means “with the Sun”. The most common name, however, for these bright lights that faithfully follow the Sun is “sundogs.”
Both rainbows and sundogs are formed by moisture filtering the sunlight.
Rainbows form when drops of rain act as prisms, breaking sunlight into a multitude of colors. Sundogs appear when sunlight passes through a thin veil of ice crystal clouds (usually cirrus or cirrostratus) and the ice acts a prism, refracting the light.
A sundog is seen about 22° to the left or right of the Sun. Sundogs often form in pairs on either side of the Sun. Often they appear white but sometimes they are quite colorful, looking like patches of rainbow. The colors usually go from red on the side nearest to the Sun, shifting through orange out to blue on the outside of the sundog.
You may have heard of a related phenomenon called a “sun halo.” In this case, it’s an entire circle of light 22° wide around the Sun. Similar to sundogs, sunlight is refracts through ice crystals; these hexagonal ice crystals are suspended in cirrostratus clouds.
Viewing a Sundog
There are some differences between rainbows and sundogs, however.
You see rainbows when you look away from the Sun.
You see sundogs when you look toward the Sun. If the ice crystals are falling flat, then you see a bright point of light on either side of the Sun.
Look for sundogs when the Sun is rising or setting, so near the horizon. (Sun halos can appear anywhere, even when the Sun is high in the sky.)
What Does It Mean When You See a Sundog?
Probably the biggest difference between the two is that a rainbow usually signals an end to the rain, while a sundog often means that rain is on the way—often within the next 24 hours. Next time you see a sundog, look out for foul or wet weather!
Good luck? In medieval times, the three bright lights were sometimes interpreted as the sign of the trinity, a sign of great fortune. Nowadays, seeing a rainbow or a sundog is a sign of good luck (or, perhaps just being at the right place at the right time?).
How Did the Name “Sun Dogs” Come About?
According to Greek mythology, Zeus walked his dogs across the sky and those “false suns” in the sky on either side of the sun’s disk were his two dogs.
Now you get to see those faithful companions of our sun—the sundogs!