For decades, the images used by Walt Whitman to evoke a meteor storm were deemed to be the fruit of the great American poet's imagination. He wrote: "Nor the comet that came unannounced out of the north flaring in heaven/Nor the strange huge meteor-procession dazzling and clear shooting over our heads."
Despite the vividness and rich detail of Whitman's verse, scholars have long been puzzled by the apparent absence of any real astronomical event that could have inspired his poem Year of Meteors, written between 1859 and 1860 while he was living under the skies of New York.
Now a team of "forensic astronomers" have solved the riddle of whether Whitman was dreaming or reporting by rediscovering the real-life source of the poet's "dazzling and clear" meteor procession.
Astronomers and literature researchers at Texas State University have connected the poem to a rare celestial event, known as an Earth-grazing meteor procession, which was widely reported across America in July 1860 but later forgotten.
The discovery was made by Donald Olson, a physicist who has become the world's leading expert on linking celestial events – from the dust cloud caused by the eruption of Mount Krakatoa to a moonrise in Provence in 1889 – to works of art and historical accounts that refer to astronomical or sky-bound phenomena, such as Julius Caesar's invasion of Britain or the paintings of Munch.
His previous studies have ranged from the writings of Chaucer to the canvases of Van Gogh. Professor Olson's latest breakthrough came when he remembered seeing a catalogue of work by a little-known American painter, Frederic Church, a contemporary of Whitman, admired for the accuracy of his skies.
On the back cover of the catalogue was a picture, entitled The Meteor of 1860, showing a meteor travelling across the night sky which had broken up into a succession of blazing fragments; it was painted by Church at his home near New York.
Professor Olson, who published his results in an American journal, Sky & Telescope, said: "This is the 150th anniversary of the event that inspired both Whitman and Church. It was an Earth-grazing meteor procession. Meteor processions are so rare most people have never heard of them. There was one in 1783 and a Canadian fireball procession in 1913. Those were all the meteor processions we knew of."
Unlike most meteors, which flare in the sky for a just a few moments before they burn up in the Earth's atmosphere, the type seen by Whitman and Church enter and exit the atmosphere without crashing to the ground. A procession takes place when these meteors break up on entry into a series of burning objects streaking horizontally across the sky for up to a minute.
Whitman's work was unusually rich in specific references to the sky. Alongside his description of the comet and meteor procession, he wrote: "A moment, a moment long it sail'd its balls of unearthly light over our heads/ Then departed, dropt in the night, and was gone."
The comet he referred to was identified as the "Great Comet" of 1860, which followed the northern path described by the poet and would have been seen around the world.
But the separate meteor procession was far more difficult to pinpoint, having previously been ascribed to the famous 1833 Leonid meteor storm and a fireball seen in 1859. Despite falling into the timeframe of Whitman's poem, the 1859 sighting was problematic because it happened during the day, and Whitman described a night-time event.
Professor Olson traced Church's observation to 20 July 1860 and found from diaries of a friend of the artist that he had been honeymooning in New York state that summer – under the same skies as Whitman.
When the date was cross-referenced with newspapers and periodicals of the time, the researchers found that, far from passing unnoticed by all but a few canny observers, the meteor procession had created a sensation as it crossed from the Great Lakes to New York.
Professor Olson said: "We have hundreds of eyewitness accounts. From all the observations in towns up and down the Hudson River Valley, we're able to determine the meteor's appearance down to the hour and minute. Church observed it at 9.49pm when the meteor passed overhead, and Walt Whitman would've seen it at the same time, give or take one minute."
The Olson team's case files
Battle of Marathon
Legend has it that a lone runner collapsed and died after announcing to Athens victory in the Battle of Marathon. Olson's team found the battle took place in August, not September, suggesting the messenger had died from heat exhaustion.
With its dramatic red sky, Edvard Munch's The Scream is renowned as a depiction of despair. Less well known is the fact that the Norwegian artist was merely recreating what he saw in Oslo in 1883. Professor Olson's team found that the eruption of Mount Krakatoa in Indonesia led to a series of sunsets in Norway which made the sky seem ablaze.
The Canterbury Tales
When a colleague of Professor Olson complained of being unable to decipher a passage in Chaucer's Canterbury Tales referring to a strange high tide, he decided to run a computer simulation recreating medieval tidal positions. He found that there had indeed been extremely high tides in 1340. Professor Olson said: "Most people see liberal arts on one side and sciences on the other, but I get to break those barriers down."
Frederic Church in Catskill, New York
Earth-grazing meteor processions are an extremely rare phenomenon. Until now, astronomers believed there were just two in the last 220 years. But the discovery of this painting by Frederic Church, and its link to Walt Whitman's Year of Meteors poem, has led to the re-discovery of another example of the event, witnessed by both men in 1860.
Van Gogh in Provence
Art historians once believed that the canvas below depicted a setting sun in Saint-Remy-de-Provence, painted by Vincent Van Gogh in 1889. But astronomers led by Professor Olson travelled to the French town and pinpointed the exact location of the painting. Using maps and records, they calculated it actually showed the moon rising at 9.08pm on 13 July 1889.
Caesar invades Britain, 55BC
Historians have long argued over the date of Julius Caesar's invasion of Britain in 55BC, finally settling on 26-27 August. But in 2007 the American researchers visited the English Channel and, after recreating the precise tidal conditions, announced that the invasion of 100 Roman warships must have taken place on 22-23 August.