Did you notice the stunning, colorful sight in the sky Monday morning? It wasn’t a rainbow.
It’s called a sundog, a weather phenomenon that only happens when the conditions are just right.
But what exactly is it and how is it formed? Here’s an explainer:
What is a sundog?
According to the National Weather Service, “sundogs are colored spots of light that develop due to the refraction of light through ice crystals.”
The refractions are located about 22 degrees to the right, left, or on both sides of the sun and can appear rainbow-like, with red seen closest to the sun and blue to the outside. Some, however, may simply appear white.
“Sundogs are also known as mock suns or parhelia, which means ‘with the sun,’” the NWS reports.
The phenomenon is similar to sun halos or pillars, which are also considered “atmospheric optical effects.”
The Farmer’s Almanac notes the phenomenon can also be called a “parhelion” and is often rainbow-colored.
“A sun dog is similar to a rainbow and is more common,” the Almanac stated. “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.”
How do sundogs form?
“In the atmosphere, under certain conditions, water drops and ice crystals can act as a prism, allowing us to see the various colors that make up visible light,” the NWS reports.
According to the Almanac, sundogs appear when sunlight passes through a thin veil of ice crystal clouds, which acts as a prism and refracts the light.
Not to be confused with a rainbow, which forms when “drops of rain act as prisms, breaking sunlight into a multitude of colors.”
What else to know
According to Space.com, certain conditions make sundogs more likely.
They most often appear near sunrise or sunset, as the sun is closer to the horizon.
“When the sun is high in the sky sunlight can’t pass through ice crystals as easily,” the publication reports.
Winter is also more likely to see sundogs, since ice crystals are needed.
The Chicago area was under a cold weather advisory Monday morning, with wind chills as low as -25 degrees expected.
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