The Brocken at 1,142 m (3,747 ft) is the highest point in the Harz Mountains in Germany. A huge granite dome, it has magnificent views in all directions and can be reached without expenditure of energy as the summit is served by a mountain railway. When conditions are right shadows cast from the peak onto banks of cloud or mist are seen as gigantic silhouettes. This is the famous Brocken Spectre known locally as the Brockengespenst.

Long after the introduction of Christianity pagan rites continued to be enacted on the mountain on the eve of 1st May — Walpurgis Nacht — when witches were believed to gather on the Brocken to meet with the devil and celebrate their Sabbath, an event vividly described in Goethe‘s Faust. St Walpurgis, also known as Walburga, lived in the eight century and together with her brother St Winebald played an important part in St Boniface’s organisation of the Frankish church. She was a Benedictine nun at Wimborne in England when asked by Winebald to take charge of the nuns at Heidenheim. This was an unusual foundation in that it consisted of both of monks and nuns. On the death of Winebald in 761, following the practice of the English church (and that of the Irish church) of keeping the abbacy in the founder’s family, St Walpurgis took complete charge of the institution. Soon after she died in 777, memory of her became confused with that of Waldborg, a pre-Christian fertility goddess. Those of you versed in Irish history will recognise the parallels between the lives of St Walpurgis and St Brigid. Both are the Christian personification of pagan fertility goddesses and both presided over monasteries made up of monks and nuns.

The technical term for the Brocken Spectre is the anticorona. The apparent magnification of the size of the shadow created by the Spectre is an optical illusion, the observer judging his shadow on the cloud bank to be at the same distance as faraway land objects. The shadow is often surrounded by coloured bands or rings caused by diffraction of sunlight by the water droplets in the cloud. If the observer stretches out his arms the rings expand correspondingly. Even when climbers are standing side by side each can see only his own shadow. In Whymper’s account of the Matterhorn disaster he records seeing a mighty arch rising high in the sky. “Pale, colourless, and noiseless, but perfectly sharp and defined [it] seemed like a vision from another world; and almost appalled, we watched in amazement the gradual development of two vast crosses.” It was probably a manifestation of the Brocken Spectre with Whymper exaggerating the detail for dramatic effect.

Brocken Spectres are not confined to the Harz Mountains, they occur elsewhere including Ireland. It is frequently seen on Haleakala, a volcanic mountain in Maui Island, Hawaii, where the trade-wind clouds drift in over the volcano’s low eastern rim and accumulate in the centre of the crater which covers nearly 50 square km. This leaves the higher northern rim above the clouds, making it an ideal location for seeing the Spectre.

A somewhat similar solar phenomenon is Cellini’s Halo, known in Germany as Heiligenschein, a bright white ring surrounding the shadow of the observer’s head on dew covered grass. This may be seen in early morning when the low angle of the sun casts the shadow of the head far from the observer and the halo is caused by light reflected from the dewdrops. I saw the halo once when as a child we went on an early morning mushroom-picking on the Curragh Plain.

Three times in the course of my climbing career I have seen the Brocken Spectre. Once going up Snowdon, once on Galtymore and a very brief glimpse on Cloghernagh on my way up Lugnaquilla. The Brocken Spectre is rarely observed in these islands, my sightings averaging one every fifteen years. Curious as to how often the Spectre manifested itself in these islands I e-mailed the members asking if they had seen the phenomenon. I received 12 replies giving accounts of 20 sightings: Ben Nevis 2, Brandon 3, Camara Hill 1, Carrauntoohil 2, Galtymore 1, Little Sugarloaf 1, Lugnaquilla 4, Maam Turks 1, Skye 1, Snowdon 2, The Reeks 2. My thanks to those who replied to my enquiry.