Sundogs, Sun Dogs, Parhelia, Mock Suns

Last updated on September 16, 2023

Sundogs, Sun Dogs, Parhelia, Mock Suns: A Phenomenon of Ice Halos

Sundogs, also known as Sun Dogs, Parhelia, or Mock Suns, are a fascinating atmospheric optical phenomenon that often accompanies the 22º halo. They are most commonly observed when the sun is low in the sky. To spot sundogs, simply extend your arm and locate them approximately 22° to the left and right of the sun, at the same height. As the sun rises higher, the sundogs appear farther away. These celestial companions exhibit a striking red coloration towards the sun, sometimes accompanied by hues of green and blue in the outer regions.

Sundogs can vary in intensity, ranging from blindingly bright to a mere smudge of color in the sky. Despite their varying appearances, they can be observed all around the world and at any time of the year, regardless of ground-level temperature. If you actively search for them, you can expect to encounter sundogs on average twice a week in Europe and North America.

The scientific explanation behind the formation of sundogs lies in the interaction of sunlight with ice crystals suspended in the atmosphere. These crystals typically take on the form of hexagonal plates or columns. When sunlight passes through these ice crystals, it undergoes refraction and dispersion, resulting in the formation of a sundog on either side of the sun. The specific angles at which the light is bent within the crystals contribute to the distinct position of the sundogs relative to the sun.

While sundogs are commonly associated with the 22º halo, they are not always present simultaneously. The 22º halo itself is a circular halo that forms when light is refracted by ice crystals at a specific angle of 22 degrees. This halo encircles the sun and is often accompanied by sundogs on either side. However, it is important to note that sundogs can occur independently of the 22º halo as well.

In addition to their scientific significance, sundogs have also captivated the imaginations of cultures throughout history. They have been the subject of various mythologies and folklore, often associated with mystical or divine interpretations. Ancient civilizations saw them as omens or signs of impending change. In Norse mythology, for instance, sundogs were believed to be the companions of sun goddesses, representing their radiant power.

To fully appreciate the beauty and intricacy of sundogs, it is worth noting that they are just one of many ice halos that can occur in the atmosphere. Other notable examples include the circumzenithal arc, the circumhorizontal arc, and the upper tangent arc. Each of these phenomena arises from different combinations of ice crystal shapes and orientations, leading to a diverse array of optical displays in the sky.

In conclusion, sundogs are a captivating atmospheric phenomenon that adds a touch of wonder to our skies. Their vibrant colors and distinct positioning make them easily distinguishable, especially when the sun is low. Remember to keep an eye out for these celestial companions during your strolls or outdoor adventures, as they can offer a glimpse into the fascinating interplay between sunlight and ice crystals suspended in the atmosphere.

Red hued sundogs flank the sun's left and right. Wide angle image by Mark Trusz ( Photography site, Flikr) from Toronto Islands, Canada. The circular halo is the 22° halo. Image ©Mark Trusz , shown with permission.

Sundogs, sometimes called Sun Dogs, Parhelia or Mock Suns, are with the 22º halo, the most frequent of the ice halos. They are most easily seen when the sun is low. Look about 22° (outstretched hand at arm's length) to its left and right and at the same height. When the sun is higher they are further away. Each 'dog' is red coloured towards the sun and sometimes has greens and blues beyond. Sundogs can be blindingly bright, at other times they are a mere coloured smudge on the sky. They are visible all over the world and at any time of year regardless of the ground level temperature. In Europe and North America one will be seen on average twice a week if searched for.

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Reference Atmospheric Optics

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