Why do ancient observers often report seeing three suns in the sky at once?

Nature · Published 3 October 2026 Swipe more like this →

In short: Known as sun dogs or parhelia, these bright, colorful patches of light flanking the sun have puzzled humanity for millennia. Far from being supernatural omens, these optical illusions are the result of sunlight refracting through high-altitude ice crystals, turning the atmosphere into a massive, shimmering natural prism.

Sun dogs occur when sunlight passes through plate-shaped hexagonal ice crystals suspended in cirrus clouds or drifting as diamond dust. As these crystals float with their large faces oriented horizontally, they act as prisms, bending light rays with a minimum deflection of 22 degrees. This creates a pair of subtly colored patches at the same altitude as the sun. Because these crystals are often responsible for other halo phenomena, sun dogs frequently appear alongside 22-degree halos or circumzenithal arcs.

Historically, these displays were often interpreted as divine portents. In 1461, the Yorkist commander Edward IV used the appearance of three suns before the Battle of Mortimer's Cross to boost his troops' morale, claiming the images represented his own family. Similarly, in 1535, a display over Stockholm sparked rumors of God's vengeance against King Gustav Vasa. The king, however, viewed the 'fake' suns as a political conspiracy against his rule, leading to the trial of his advisors, Olaus Petri and Laurentius Andreae.

Scientific understanding of these phenomena evolved slowly. While Aristotle and Roman authors like Cicero and Pliny the Elder documented the sightings, it was not until 1629 that Pierre Gassendi correctly attributed them to the reflection of light by ice crystals. Today, we know that sun dogs are not unique to Earth; similar displays can occur on Mars, and the giant planets—Jupiter, Saturn, Uranus, and Neptune—can produce complex halos featuring four or more sun dogs due to clouds of ammonia and methane crystals.

The term 'sun dog' remains etymologically obscure, though theories range from the Scandinavian myth of wolves hunting the sun to the English verb 'dog,' meaning to track or follow. Regardless of the name, these phenomena serve as a reminder of the complex physics occurring in our atmosphere, transforming simple sunlight into a fleeting, multi-sun spectacle that has captivated observers from ancient Rome to modern Inner Mongolia.

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