Forensic astronomers have been able to pinpoint the exact day on which van Gogh's Moonrise was painted.
Credit: Stichting Kroller/Muller Museum; AFP
Myths and classical literature often refer to signs and omens in the sky. "These late eclipses in the Sun and Moon portend no good to us," says a character in Shakespeare's King Lear.
Modern readers tend to presume that these references are mere window dressing: like murder on a dark and stormy night or thunder in a B-grade horror movie. But recently, scientists have discovered that they can be used to resolve long-standing historical debates.
Scholars, for example, have never been sure when Shakespeare wrote King Lear. Estimates ranged from about 1604 to 1606. But in 2001, astronomer David Levy (co-discoverer of comet Shoemaker-Levy 9, which crashed into Jupiter in 1994) began a doctoral thesis on "The Sky in Early Modern Literature". In 1605, he determined, Londoners were witness to both a lunar eclipse and a near-total solar eclipse, one in late September and the other in October. Odds are that Shakespeare had these in mind when he wrote his play. If so, he was still working on it in late 1605.
Donald Olson, a physics professor at Texas State University in San Marcos, U.S., has used similar techniques to help art historians pin down details of famous paintings. In 2000, for example, he found the location at which Vincent van Gogh created one of his last paintings, The White House at Night.
Knowing that van Gogh painted it in mid-June, and the direction in which the house faced, Olson was able to determine that a bright star in the painting was mostly likely the planet Venus, which would have been prominent at the time.
Two years later, Olson used a similar process with another van Gogh painting, Moonrise. That painting depicts the full Moon rising behind an overhanging cliff in southern France. Historians knew the work was made sometime in 1889, and haystacks in the foreground indicate that the time of year is somewhere around harvest season.
Olson's team hunted down the location and, with a bit of astronomical detective work, determined that there was only one date on which the Moon rose in the right place: 13 July 1889. Since van Gogh once said he never worked from memory and always painted what he saw, this was probably the date on which he started painting Moonrise.
Scientists call this emerging field of research forensic astronomy. It's becoming popular, says Geza Gyuk of Adler Planetarium in Chicago, Illinois, because of the ready availability of off-the-shelf astronomical software such as Starry Night and RedShift. It means that anyone with a computer can see what the sky looked like from anywhere in the world, at any date in history. The programs are not only remarkably accurate, but they're also easy to use. "It's the work of an afternoon now to sort through all the autumn moonrises from a particular location on Earth during a particular span of years," says Gyuk.
Shakespeare and van Gogh are only starting points for forensic astronomers. More recently, they've been investigating Homer's Odyssey. Scholars have long debated the degree to which ancient Greek text, the Odyssey and its prequel, the Iliad, were inspired by actual events. Of particular interest is a passage in the Odyssey, shortly before Odysseus slaughters the suitors besieging his faithful wife, Penelope. The passage, an obvious prophesy of doom, asserts that the Sun has "perished out of heaven" and an "evil mist" has spread across the world.
Nearly 2,000 years ago, the Greek historian and philosopher Plutarch suggested that this might be a reference to an eclipse. By the 1920s, astronomers knew that a total eclipse had occurred in the region on 16 April 1178 BC. And they knew it occurred sometime around noon, as described in the poem.
But the idea that this was what Homer was describing was pooh-poohed by Homeric scholars. After all, Homer wrote his poem hundreds of years after the Trojan War. How could he possibly have known of the eclipse?
But it turns out the eclipse isn't the only astronomical event described in the Odyssey. In a June 2008 paper in the U.S. journal Proceedings of the National Academy of Sciences, Marcelo Magnasco, a physicist at Rockefeller University in New York City, and Constantino Baikouzis of the Astronomical Observatory in La Plata, Argentina, noted that the poem also sets the date of the slaughter on a new moon - a necessary condition for a solar eclipse.
Elsewhere, the poem describes Odysseus steering his boat by the positions of the constellations Boötes and the Pleiades, 29 days before the slaughter. That establishes the date as early spring. The poem also describes Venus as a morning star, high in the sky, and refers to the god Hermes (equivalent to the Roman god Mercury) taking a trip to the far west, then turning back, 34 days before the slaughter.
That, Magnasco and Baikouzis hypothesised, might be a description of the planet Mercury at the end of one of its retrograde cycles.
Any one of these events occurs fairly often, but they don't always occur in the order described in the poem, and particularly not with the timing assigned to each event in the poem. As Magnasco explains, "The Moon gets out of whack with the solar calendar. Mercury and Venus have yet again different periods."
So Magnasco and Baikouzis simulated the Greek skies, night-by-night for 135 years (49,000 nights), focussing on the date of the eclipse (see their reconstruction below). Even without adding the eclipse to their simulation, they found only one match for the sequence of events described in the poem: one that put the slaughter on precisely 16 April 1178 BC. Magnasco adds that he and Baikouzis were not "cherry picking" references in the Odyssey. "As far as we're aware, there are no other astronomical references," he says.
Did Homer really include an eclipse in his story? Who knows? What's certain is that it's one of the more controversial findings, to date, to come out of the infant field of forensic astronomy.
"The implication is that 'Homer' [who may have been many poets] was aware of astronomical events occurring four centuries before the poem was cast in its current form, and was interested enough in those events and knowledgeable enough about them to weave them into the narrative," Magnasco says.
Historians didn't think Greeks of the Trojan War era were interested in tracking the motions of the planets in such detail. If Magnasco and Baikouzis are right, it will force a reconsideration of what we thought we knew of early Greek astronomy. Their finding also heightens the debate over how much history is woven into the Odyssey and the Iliad. If the vanished Sun and evil mists are real, what else might also be real?
But not everything about the theory is perfect. "The astronomical reasoning seems fairly sound," says Jerry Oltion, a telescope-maker, amateur astronomer and award-winning science fiction writer from Eugene, Oregon. But he thinks that if the description really applies to the eclipse, it must have been added as an afterthought.
The problem, he says, is that the reference comes when the characters are indoors, at a banquet. "Any writer who has seen an eclipse - or even heard one described by someone who had seen one - would never put his characters indoors during the climactic moment," he suggests. "Nor would he miss the opportunity to use the eclipse's visual effects for dramatic purposes."
Eclipses, Oltion says, are accompanied by many phenomena not described in the poem. The dappled sunlight beneath trees, for example, changes to crescent-shaped shadows as totality nears. There's also the corona itself, "stretching away like fairy wings flying the Sun away." Oltion doesn't believe Homer could have ignored these dramatic, story-enhancing effects if he was indeed describing an eclipse.
Gyuk agrees that the evidence is tentative. "Does it convince me that a solar eclipse is referred to?" he asks. "No. Does it make it more plausible? Perhaps. We will probably never really know." But, he suggests, that may not really matter.
"It gives us a new lens through which to look at the Odyssey...How would contemporaneous listeners have heard it? Would the vastly greater familiarity with the sky that the early Greeks enjoyed lead them to understand the poem differently?" And, he notes, the dream of any author is to make the reader think about the story. "This celebrates Homer and pays homage to the Odyssey in the most sincere way."
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RICHARD A. LOVETT is a science writer in Portland, Oregon, USA.
