Robert Burns was not alone as a hearer of auroral hiss. As we noted yesterday in Weather Eye, Burns mentions in one of his verses a strange aspect of the aurora borealis that has puzzled scientists for centuries - that among northerners in Europe, Asia and America there is a persistent tradition that the aurora is sometimes accompanied by a distinctive crackling or hissing sound. Physicists have found no explanation, yet popular references to this mysterious noise are legion.
Robert Service, the creator of those unforgettable characters Sam McGee and Dangerous Dan McGrew, has it in his Ballad of the Northern Lights. He first describes the aurora with his typical evocative hyperbole:
The skies of night were alive with light, with a throbbing, thrilling flame;
Amber and rose and violet, opal and gold it came.
It swept the sky like a giant scythe, it quivered back to a wedge;
Argently bright, it cleft the night with a wavy golden edge. And later comes the hiss:
They writhed like a brood of angry snakes, hissing and sulphur pale;
Then swift they changed to a dragon vast, lashing a cloven tale.
Lesser poets also mention the phenomenon. Sir Charles Robert, for example, describes the noise in a poem called The Iceberg:
And close ranked spears of gold and blue,
Thin scarlet and thin green,
Hurtled and crashed across the sphere
And hissed in sibilant whisperings,
And died.
And one T.A. Robertson, in Northern Lights, calls up a metaphor in idiom:
You tink you hear da skruffel
O der lang, green goons o sylk.
Besides being likened to angry snakes and a silken gown, the sound of the northern lights has also been variously compared to the noise made by a radio tuned to a station that has gone off the air, to cellophane paper being crinkled near the ear and, perhaps most evocatively, to a "low, slow, wubble-wrangwubble-wubble". But despite the many plausible reports of its existence, no one really knows what causes the auroral hiss.
Perhaps the nicest explanation is that offered by the ancient Norsemen. They identified the northern lights with "the ride of the Valkyries", the warlike maidens who were "the choosers of the slain", and who rushed into the melee of battle and selected those whose destiny it was to die: the northern lights were seen as the Valkyries setting forth in splendour on their macabre errand. The Song of the Valkyries in Norse mythology was the auroral hiss.