An Old Superstition Explained

Legend records an incident that happened when a climber was scaling Mount Brockenthe highest peak in the Harz Mountains of what is now East Germany. At a particularly precipitous pointhe glanced up and sawin the haze before hima human figure with a halo surrounding its head. Understandably startled by this apparitionhe lost his hold and fell to his death.

If truethe unfortunate climber had jumped to a conclusion (pun intended). Glenn Shaw of the Geophysical Institute points out that what he saw had little to do with the sanctity of the beholderor that of whatever being he thought he saw.

Because of the notoriety of the account and the frequency with which the phenomenon can be observed on that mountainthe spectacle has been accorded the various names of Brocken BowBrocken Spectreormore simplyGlory (the latter because of the halo around the figure). It is now known that what is actually seen is merely a shadow of the mountain climber surrounded by a series of alternating dark and colored rings that are distantly related to rainbows.

Most air travelers have noticedat one time or anotherthe spectacle of the shadow of their airplane surrounded by a colored halo as it races along the clouds below. Obviouslythe shadow (and its accompanying halo) must be on the opposite side of the viewer from the sun. Each spectator at every window of the plane would see the halo as if it were centered around his or her own vantage point--that isas if each observer's head were at the center of the halo.

At northern latitudesthe Glory can often be seen (without the benefit of airplanes) from high vantage points when the sun is low behind the observer and there is a cloud or light mist in a low area ahead. These must have been the conditions that led to the demise of the unfortunate mountaineer in the Harz Mountains.

When sunlight penetrates water dropletssome is transmittedbut some is reflected backward from the rear side of the droplet. In the reflected sunlightsimilar wavelengths of light can get together and "enhance" each otherlike a chorus line kicking together. This will create a ring of particular color around a shadow object. But in a very long chorus linethe dancers can lag more and more behind the leader until the timing of the dancers at the end would be such that they would in effect be kicking the ones at the beginning in the shinseach nullifying the other's efforts (in the vernacular of physicsthis is called destructive interferenceor being 180 degrees out of phase). When this happens with light waveswe see the dark bands in the glory rings.

The phenomenon can happen over a wide range of distancesbut the illusion is nearly always the sameregardless of scale. Often there is more than one concentric circle of rainbow colors with red always being on the outside. There will be a ratio of about 3 to 1 between the diameters of the first and second dark ringsregardless of distance. That isif you can see two circles with repeating rainbow colorsthe outer circle of red (and an outlying dark line) will be about three times as far across as the inner circle.

The bottom line is: If you are camping in the high mountains when the sun is behind youthere is a mist or cloud in front of youand you see a ghostly figure with a halo approachingdon't panic. It's only you.