An amazing display: the science behind rare multiple sun halos
Friday, January 16, 2015, 9:58 AM - An image of multiple simultaneous sun halos over New Mexico captured the collective imagination of the Internet this week. We delve into the science behind this rare, amazing display.
If your first thought upon seeing the image above was "That can't possibly be real," you're not alone. But we're here to assure you it is real and not a composite image or the result of some clever Photoshop trickery.
First, some background: the image was shot by an American, Joshua Thomas, in Red River, New Mexico on the morning of January 9th and uploaded to his personal Facebook page. The U.S. National Weather Service in Amarillo, Texas discovered the image and, with help from sun halo expert Les Crowley, labeled the different phenomena visible in the photo.
The image has since been shared more than 19,000 times from NWS Amarillo's Facebook page.
So, what's going on in this picture? Chances are, if you've ever been outside on a clear, cold winter day, you've seen at least a partial halo around the sun, like the one below captured by viewer Rob Klassen of Winnipeg, MB. The bright, rainbow-like spots on either side of the sun are often called "sun dogs" or "phantom suns" (scientific name parhelia) and are caused by the refraction of light through hexagonal ice crystals drifting in the air at low altitudes.
Sun dogs often appear as part of a 22° halo encircling the sun, as can be faintly seen in the example below photographed by viewer Joe D. in Etobicoke, ON. 22° halos form when the sunlight is refracted through millions of randomly-oriented hexagonal ice crystals in the atmosphere. Depending on the time of day and the sun's position in the sky, the entire halo may be visible.
22° halos can also appear around the moon, occur at any time of year and are the most common type of optical phenomenon.
Obviously, there's a lot more happening in Joshua Thomas's image.
The outer rainbow ring is comprised of very rare supralateral and infralateral arcs. These form when sunlight enters horizontally-oriented, rod-shaped hexagonal ice crystals through a hexagonal base and exits through one of the prism sides. These often appear together with an upper tangent arc - the bright spot at the apex of the 22° halo stretching its "wings" out towards the supralateral and infralateral arcs.
Also appearing in Thomas's image are two Parry arcs curving toward and away from the sun above the upper tangent arc, a light pillar above the sun, and faint heliac arcs extending outward and upward from the sun.
To see all these different optical phenomena together at the same time is so rare precisely because the ice crystals in the atmosphere must be oriented a certain way to produce the different effects; however, a similar image was captured on January 14th in Park City, Utah. Here's that image with all the different visible phenomena labeled by Weather Network meteorologist Scott Sutherland:
And, just in case you needed further proof that it is possible for these phenomena to occur at the same time, here's a video of a multiple halo setup over Oshawa, Ontario in December 2012, captured by Weather Network viewer Shane Macaulay.