I was out cross-country skiing with Billy the dog yesterday, in the Cascades. I saw a most unusual rainbow. No humans nor camera to verify the event.
A brief tutorial on rainbows prior to describing what I saw.
The primary rainbow can be located in relation to the anti-solar point. The anti-solar point corresponds to the location of the shadow of your head. The primary rainbow forms a circle with the anti-solar point as its center. The points of the rainbow are 42 degrees from the anti-solar point. My fist subtends about 15 degrees when my arm is extended. Using this method of angular measurement the primary rainbow is 3 15 degree fists from the antisolar point. Good enough.
If you are traveling in an airplane you can locate the anti-solar point by the shadow of the plane on the clouds. You should be able to locate a circular rainbow below the plane at 42 degrees about that point.
The secondary bow is outside the primary bow at 51 degrees. The colors of the secondary bow are reversed from the colors of the primary bow.
Note that the sky between the two bows is darker than the sky outside them.
Another type of “rainbow” is the halo that can sometimes be observed around the sun. This is formed by ice crystals in the atmosphere instead of water drops. If conditions are right, haloes can be observed at 22 and 46 degrees around the sun.
Tutorial over.
Billy and I were traveling through snow covered terrain in the Washington Cascades. The sun was shining brightly, the sky was clear and blue. A few wispy high clouds were coming over one side of the valley. Upon the clouds was a portion of a circular rainbow. It was much farther from the anti-solar point than 51 degrees. (It was about 5 fists from the anti-solar point.) The sun was not at the center of the bow, like it would be for a halo. In fact, the sun was entirely outside the circle of the bow. The sun was 3 fists above the imaginary (I was in the mountains) horizon. The closest point of the rainbow was 4 fists from the sun along the same line.
My theory is that the snow was acting like a mirror for the bright sun. There was a virtual sun in the mirror (three fists below the ground), creating a virtual anti-solar point in the sky at 9 fists above the horizon. The rainbow was around this point. It was the same circular rainbow often seen from airplanes, but instead of being below me it was above me.
A halo was visible around the sun at the same time.
This really made my day.
Billy wasn’t impressed.