Brocken Spectre: An Erie Optical Phenomenon

In northern Germany, in the state of Saxony-Anhalt, between the rivers Weser and Elbe, stands a mountain that is home to mysterious legends and strange weather. For centuries, travellers have reported seeing giant shadowy figures looming in the mist, surrounded by glowing rings of light. These eerie apparitions were once attributed to witches, spirits, and supernatural forces. Today, science has explained the phenomenon, but the Brocken remains one of Europe's most atmospheric and intriguing mountains.

Credit: Wikimedia Commons

The Brocken is the highest peak in the Harz range, a mountainous region that straddles the German states of Saxony-Anhalt, Lower Saxony, and Thuringia. At an elevation of 1,141 meters, it is a modest mountain compared to the Alps. Yet, its exposed summit experiences remarkably harsh weather. Dense fog, strong winds, frequent rainfall, and winter snow are common throughout much of the year.

Due to its exposed location, the climate of Brocken resembles that of the alpine in the 1,600–2,200-metre elevation. The summers are short and the winters very long, with many months of continuous snow cover, strong storms and low temperatures even in summer. The mountain is also almost persistently covered in fog.

The mountain is most famous for a strange optical phenomenon known as the Brocken Spectre, named after the peak itself.

A Brocken Spectre occurs when a person stands on a mountain ridge with the sun low behind them and a bank of mist or cloud in front. The observer's shadow is projected onto the cloud, often appearing enormous and distorted. Because the cloud surface is much farther away than the observer expects, the shadow can seem gigantic, often many times larger than the person. The effect becomes even stranger because the cloud droplets are constantly moving. As a result, the shadow may appear to sway, stretch, or float.

Brocken mountain. Credit: Wikimedia Commons

Often accompanying the spectre is another optical effect known as a “glory”. Around the shadow's head appears one or more concentric rings of coloured light, resembling a halo.

The glory forms when sunlight is scattered backward by tiny water droplets in the cloud. Unlike a rainbow, which appears opposite the sun and is produced by refraction and reflection within raindrops, a glory results from complex interactions between light waves and microscopic cloud droplets. The combination of a towering shadow and a luminous halo can create an image that appears almost supernatural.

The phenomenon was first reported by Spanish Navy officer Antonio de Ulloa and French mathematician and astronomer Pierre Bouguer during the 18th century French Geodesic Mission to the Equator. While walking near the summit of the Pambamarca mountain, in the Ecuadorian Andes, they saw their shadows projected on a lower-lying cloud, with a circular "halo or glory" around the shadow of the observer's head. Ulloa noted:

The most surprising thing was that, of the six or seven people that were present, each one saw the phenomenon only around the shadow of his own head, and saw nothing around other people’s heads.

Credit: Wikimedia Commons

Ulloa reported that the glories were surrounded by a larger ring of white light, which would today be called a fog bow. On other occasions, he observed arches of white light formed by reflected moonlight, whose explanation is unknown but which may have been related to ice-crystal halos.

In German folklore, it was believed that witches gathered on the Brocken each year on the night of April 30, known as Walpurgis Night. They were said to fly to the summit to celebrate and dance before the arrival of spring. To ward off evil and protect themselves and their livestock, people would light fires on the hillsides, a tradition that continues in some regions today.

The Brocken became so closely associated with witchcraft that it appears in numerous German folk tales and literary works.

Walpurgis' Night, an illustration by Johann Heinrich Ramberg, 1829. Credit: Wikimedia Commons

The mountain achieved fame through the writings of Johann Wolfgang von Goethe. Goethe visited the Harz Mountains several times and incorporated the Brocken into his masterpiece, Faust. In the famous Walpurgis Night scene, Faust and Mephistopheles ascend the Brocken to witness a gathering of witches and supernatural creatures.

Now, to the Brocken, the witches ride;
The stubble is gold and the corn is green;
There is the carnival crew to be seen,
And Squire Urianus will come to preside.
So over the valleys, our company floats,
With witches a-farting on stinking old goats.

Reference to the Brocken spectre also appears in the Samuel Taylor Coleridge's poem "Constancy to an Ideal Object":

And art thou nothing? Such thou art, as when
The woodman winding westward up the glen
At wintry dawn, where o'er the sheep-track's maze
The viewless snow-mist weaves a glist'ning haze,
Sees full before him, gliding without tread,
An image with a glory round its head;
The enamoured rustic worships its fair hues,
Nor knows he makes the shadow he pursues!

The Brocken Spectre is not unique to the Brocken. It can occur anywhere suitable conditions exist. Similar sightings have been reported in the Alps, the Scottish Highlands, and even from aircraft flying above cloud layers. Yet the phenomenon will forever bear the mountain's name because it is observed there so frequently.

Credit: Wikimedia Commons