What Is That White Thing In the Sky?

A fogbow is a very similar to a rainbow; however, as its name suggests, it appears as a bow in fog rather than rain.  It is also a rare phenomena too.  Small water droplets create a fogbow.  Very weak colors are seen in a fogbow.  It has a bluish inner edge and a reddish outer edge.

A sea dog fogbow over the south Oregon coast (Photo by JHL)
A sea dog fogbow over the south Oregon coast (Photo by JHL)

Since the water droplets are very small, the fogbow appears white, which is why it is sometimes white rainbows.  When the droplets forming it are almost all of the same size the fogbow can have multiple inner rings, or supernumeraries, that are more strongly colored than the main bow.  Unlike a rainbow, fogbows normally appear as a band of bright white, sometimes with hints of red or blue. Because of these differences, fog bows are often referred to by other names – cloud bows, white rainbows or ghost rainbows.

Mars & a Lunar Fog Bow
Mars & a Lunar Fog Bow Mars & a Lunar Fog Bow. Mars and a Colorful Lunar Fog Bow Credit & Copyright: Wally Pacholka (AstroPics.com, TWAN)

When viewing a fogbow from the air looking down, such as when you’re in an airplane, it is called a cloud bow.  Mariners sometimes called his phenomena sea dogs.  When a fogbow is seen at night, it is called a lunar fog bow.

The Mie scattering simulation used a mean droplet diameter of 60 micron with a lognormal distribution of diameters having a standard deviation 12% to match the width of the primary fogbow and the position of the two supernumerary arcs inside the main bow.

A fogbow has the same direction as a rainbow so that the sun would be behind the viewer and the direction would be into the bank of the fog.  Its outer radius is slightly less than that of a rainbow.

Fogbow in the Arctic
Fogbow in the Arctic

Your best chances of catching a fogbow are when the Sun is shining brightly and the fog is thin – they’ll appear as the sun breaks through the fog behind you. You’ll often find fogbows as the cool sea mists roll in over the ocean or as fog makes its way down a hillside or mountainside. And, if you happen to be in the middle of a fog or a cloud – say, in an airplane – you might see a full circle rather than an arch as seen below.

Full circle fogbow.
Full circle fogbow.

On rare occasions, you might see a solar glory or a Brocken spectre within a fog bow. Glories look just like halos, and they’re normally centered on a Brocken spectre or an object within the fog. These colorful rings are created by sunlight reflecting off water droplets in much the same way that rainbows and fogbows are created. A Brocken spectre is a spooky phenomenon that looks like a ghost within the fog. These shadowy shapes are named after a peak within Germany’s Hartz Mountains where Brocken spectres are commonly seen. Brocken spectres are caused by a shadow thrown on the fog – either your own, or that of a nearby object.

Brocken Spectre at Lough Corrib, a lake in the west of Ireland, near the city of Galway. Photo by Conor Ledwith Photography.
Brocken Spectre at Lough Corrib, a lake in the west of Ireland, near the city of Galway. Photo by Conor Ledwith Photography.

Till Next Time,

xo-heather

 

 

 

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