The phenomenon of a false sun, also known as a sun dog or parhelion (plural: parhelia), is an atmospheric occurrence characterized by bright spots often seen on the edges of a halo surrounding the sun.
A false sun can appear as a colored spot of light to the left or right of the sun, at a position of 22° and at the same horizontal level as the sun on the horizon, within a halo of ice crystals. They can be observed anywhere in the world during any season, although they are not always distinct or bright. False suns are most visible when the sun is low in the sky.
A brilliant false sun over Fargo, North Dakota, USA. Note that the sun halo has a bright spot, which is the false sun.
The phenomenon of a false sun occurs when high-altitude sunlight passes through ice crystals in the atmosphere. In addition to the real sun positioned at the center, observers also see reflections on either side.
This phenomenon typically occurs when temperatures drop below -30 degrees Celsius, with moist air and abundant ice crystals.
Crystal halos are seen when the sun is near the horizon, in the same horizontal plane as the observer and the ice crystals. As light passes through the ice crystals, it is bent at an angle of approximately 22 degrees before reflecting into the observer’s eyes.
Simulation of the light reflection process creating the illusion of three suns appearing before the observer. (Image: Telegraph).
False suns are formed when hexagonal ice crystals in high, cold cirrus clouds exist under very cold weather conditions, as ice crystals drift within the low-altitude atmosphere. These crystals act as prisms, bending the rays of sunlight passing through them. As the crystals fall through the air, they align vertically, refracting sunlight horizontally, leading to the appearance of the false sun.
A false sun at the South Pole. (Image: Deven Stross / NSF).
False suns often appear with a slightly reddish hue on the side opposite the sun and may extend additional white-blue tails stretching outward. The tails of the false sun form when light passes through the crystals at angles different from the optimal deviation angle.
Just because they are formed from ice crystals does not mean false suns can only appear in cold weather. They can occur year-round and anywhere, although they are most visible when the sun is low on the horizon in January, April, August, and October. They also appear when ice crystals in the atmosphere are abundant, but they can be seen anywhere and at any time, as long as there are cirrus clouds present.
The phenomenon of three suns appearing in Russia.
As the sun rises higher, the false sun can drift away from the 22-degree point. Eventually, when the sun reaches a sufficiently high point, the false sun completely disappears.
Ancient Greeks recognized that the false sun was a fairly accurate omen of rain. The ice crystals that create halos and false suns also form cirrus clouds, which are typical clouds indicating the condensation of warm water.
In addition to the phenomenon of the false sun, there is also the false moon phenomenon that appears alongside the moon and forms due to sunlight passing through ice crystals. The false moon, or paraselenae, does not occur as frequently as the false sun because they are only visible when the moon is illuminated and appear at night.
