Maunder's "Strange Celestial Visitor": the auroral torpedo of 17 November 1882

November 1882. One of the great geomagnetic storms of the nineteenth century was under way. From 11 to 26 November, telegraph and telephone systems were widely disrupted. Between 17 and 20 November the aa index averaged 214.25 nT, the highest four-day disturbance since the index began in 1868. An aurora was expected.

Friday, 17 November. About 6 p.m. At Guildown Observatory near Guildford, the amateur spectroscopist J. Rand Capron watched the aurora "fitfully blazing in the north, north-east, and north-western sky." Then, in the east, "there rose from the horizon a long beam of detached bright light, which, apparently lengthening as it advanced, crossed rapidly the southern horizon in front of or near the moon, and then sank in the west, shortening in length as it did so."

At the Royal Observatory, Greenwich, Edward Walter Maunder saw it too. The object was pearly white to pale green, sharp-edged, roughly 30 degrees long and 3 degrees wide. It moved "as the Sun, Moon, stars and planets move but nearly a thousand times as quickly." Horizon to horizon in about two minutes. No sound was reported.

"This 'torpedo-shaped' beam of light was quite unlike any other celestial object that I have ever seen," Maunder wrote. It "differed very widely in appearance from any other aurora."

Capron collected twenty-six separate accounts, mostly from the UK, including letters to The Times. People reached for whatever they knew. A beam. A spindle. A definite body. One saw something "well-defined and shaped like a fish... extraordinary and alarming." Another saw "a most magnificent luminous mass, shaped somewhat like a torpedo." Some described a dark nucleus. In the Netherlands, a schoolboy named Pieter Zeeman, a future Nobel laureate in physics, observed from Zonnemaire. Observers in Laon and Brussels reported it as well.

Five students of auroral spectra, Capron among them, independently turned their spectroscopes on it. All seemed to agree. The light showed the characteristic green auroral line, and the Fraunhofer dark lines were absent, so this was not reflected sunlight. Most of the lower-latitude observations put it at 100 miles or more.

Capron published the main study in the Philosophical Magazine in 1883. He and Maunder concluded it was a transient illumination of an otherwise invisible auroral arc. In Nature, the Dutch analyst H. J. H. Groneman went another way. He treated it as an "auroral meteoroid" and calculated its "true orbit", leaning on the sightings from Laon and Brussels.

Some correspondents suggested a meteor. The spectrum and the roughly two-minute crossing count against it. Noctilucent cloud and an upper tangent arc have been raised too, but the rapid horizon-to-horizon motion rules both out. Most scientific discussion favored an extremely unusual auroral phenomenon, though its precise mechanism remained uncertain. Even so, one modern retelling ends simply: "What was it? No one knows."

Charles Fort gathered the case into The Book of the Damned in 1919. In 1953 Donald H. Menzel gave it a chapter in Flying Saucers, "The great saucer of 1882", calling it "the best-observed flying saucer in history and one of the most difficult to explain." Menzel argued that foreshortening made the auroral beam look like a disk low in the sky and a cigar at its highest point. Scientists had watched a famous saucer, he said, and found nature behind it. In 1916 Maunder looked back on that evening for the 500th number of The Observatory. He never saw anything like it again.