Fogbows And Glories Delight The Eye From Lake Superior To Mars

A striking fogbow arcs over Lake Superior near Silver Bay, Minn. earlier this month. At its center is the shadow of my head surrounded by a glory. Credit: Bob King

Two weeks ago I went for a boat ride on Lake Superior out of Silver Bay, Minn. The reporter and I were doing a story on a new tour operation. Fog is common on the lake even during summer as warm, humid air blows across the 40-degree waters, gets chilled and condenses into low clouds.

We board the Wenonah to begin our tour of the Lake Superior shoreline and visual treats hidden within the fog. Credit: Bob King

This was a partly-foggy day with occasional clearings that brought welcome sunshine. While standing on the prow of the boat with the sun at my back, I soon became aware of a ghostly double-bow of light arcing from the water’s surface up and over the horizon. A fogbow!

Even though the fog between the prow and water’s surface was barely noticeable it was enough to create a gorgeous, color-fringed bow. That’s not all. Further down on the water directly opposite the sun I could make out my shadowed head surrounded by a multi-ringed halo of colored circles called a glory. It’s as close to angelic as I’ll ever be.

Raindrops act as tiny prisms that bend or “refract” light into separate colors. Credit: University of Wisconsin-Stout

Like rainbows, fogbows are opposite the sun. To see one, the sun must be at your back and less than 30-40 degrees high (10 degrees is one fist held at arm’s length). Since I was standing on the front of the boat some 20 feet above the water, I could look down on the bow and see it below the horizon. On flat ground it would have never showed until later in the day when the sun’s altitude dropped to 40 degrees or less.

Unlike rainbows, which are formed by nice big raindrops and produce spectacular colors through reflection and refraction, fogbows are created by extremely tiny water droplets (0.0020 inches / 0.05 mm) that diffract sunlight.  Sunlight enters the fog droplet and reflects off its backside just as it does in a rainbow, but instead of emerging as a neat spread of colors from red to violet, diffraction smears everything together to produce a diffuse, white band.

Want to make your own fogbow? I made this one using one car headlight (I covered the other with a blanket) to illuminate the scene on a foggy night. With camera on tripod and time exposure underway, I stuck my arms out to add a bit of alien flare. The bow-shadow combo has a special name: the Specter of Brocken, after similar natural scenes witnessed in sunlight and fog near Brocken peak in the Harz Mountains in Germany. Click for more on the Specter. Credit: Bob King

You do sometimes see a bit of color – a red outer edge and blue inner – but very rarely. The photo also shows a second bow below the primary fogbow called a supernumerary bow.

Supernumeraries form when light rays in the droplets overlap and interfere with each other. Imagine simultaneously dropping two stones a few feet apart in a still pond. When the waves meet, some will overlap and intensify (grow taller) while others cancel each other out. The same happens with light. Where wave crest meets crest, light’s intensified; where crest meets trough, the two cancel each other other and there’s darkness. The overall pattern looks something like a bullseye or series of bright and dark rings. The dual bows show the bullseye pattern well.

A colorful glory rings an airplane’s shadow seen from inside the plane. Credit: Wikipedia

What about my (less than) glorious head? Glory formation is still not completely understood. Diffraction, reflection and backscattering of light by tiny droplets toward the light source (sun) all appear to be involved. Whatever the exact process, a glory is as beautiful as its name. If you’ve ever flown in a plane, you may have already seen one surrounding the plane’s shadow on the clouds. If not, watch for it on your next trip. And keep an eye out for fogbows on these cooler mornings as we transition from summer to fall.

A canyon in Valles Marineris on Mars filled with dense ground fog photographed from orbit by Mars Express. Click for a large version. Credit: ESA/DLR/FU Berlin

Glories and fogbows can form anywhere there’s fog. That includes places like Mars, where water vapor occasionally condense as ground fog over low regions of the planet like the grand canyons of Valles Marineris. Just think of it – a future astronaut looks up from sample collecting to see a Martian fogbow and his helmeted head fringed by glorious rings of color!

11 Responses

  1. Edward M. Boll

    Glorious rainbow the other night. I believe that the north shore of Superior is as scenic as I have ever seen.

  2. Suzanne

    I saw a fogbow on a boat tour in the Apostle
    Islands about 2 weeks ago as well! It was eerily cool!
    Thanks for the info!

  3. Edward M. Boll

    One of my favorite times of the evening is from about 30 minutes before sunset till about 45 minutes after. To see the sky turning darker as the west Horizon changes colors. To see Venus come out, the brightest stars and then Saturn makes a discouraging day seem encouraging.

  4. Edward M. Boll

    Only from Earth can this be seen. I stepped out at 10 PM, and saw 2 jets or aircraft with vapor trails hanging over where the Moon was located in the sky. The first time I noted this was on the evening of January 13, 1986. I was new in Astronomy then and I thought and hoped what I saw was the tail of Halley’s Comet. I told Pastor Pete Helland about that 3 days later. He had first seen the comet 3 months earlier with his 6 inch reflector telescope. He told me what I saw was not the comet.

  5. Giorgio Rizzarelli

    Congrats Bob for the fog photos

    I’v seen a glory from airplane for the first time this summer. Too bad I didn’t make in time to catch it in photo, also because of the small window. I asked them if they could open it for me a minute, but they didn’t want to.

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