Astronomers pinpoint an opportunity to relive a scene documented by one of the 20th century's greatest photographers
YOSEMITE NATIONAL PARK—Ansel Adams, the venerated photographer, was notably scrupulous about recording the details of his craft — camera apertures, shutter speeds, film type — as he documented the Western outback in monochrome.
But he also was notoriously poor at writing down dates.
Now a team of Texas astronomers has found that one of Adams' photos of the Yosemite backcountry, a solitary shot from Glacier Point of the moon rising over saw-toothed peaks beside a pillow of clouds, was misdated by four years.
The Texas State University astronomers, who have built a reputation for pinpointing historical dates and events, also determined that the celestial clock is ticking toward a rare encore performance early on Thursday evening, re-creating the same dance of moon and mountains Adams captured on the same date more than half a century ago.
An obscure color print of Autumn Moon helped the researchers' investigation.
That cycle repeats itself only once every 19 years, so folks in Yosemite are expecting a crowd of amateur photographers, astronomers and Adams aficionados atop Glacier Point, eager for a brief chance to relive a scene documented by one of the 20th century's greatest photographers.
Matthew Adams, the photographer's grandson and president of the Ansel Adams Gallery in Yosemite, considers it a fitting tribute to the lifelong environmentalist, who died on Earth Day 1984.
"It's wonderful," he said. "It's interesting [that] astronomy can do this. And it's great [that] there's this ongoing interest in Ansel. We're planning to go out and see it for curiosity's sake."
The photograph in question, "Autumn Moon: the High Sierra From Glacier Point," is not among Adams' best-known, but has appeared in half a dozen books and magazines over the years. It long was believed to have been shot in 1944.
But the Texas State astronomers sleuthed through celestial history, plotted lunar phases, crafted a special computer program and calculated angles of shadows cast by the setting sun to determine the exact time, date and spot where the photography legend snapped the shutter on his bulky view camera.
It actually was Sept. 15, 1948, at 7:03 p.m. Pacific Daylight Time. Give or take a few seconds.
"Ansel Adams' genius was in getting there at the right time and the right day," said Donald Olson, the Texas State astrophysicist who led the study, detailed in the October issue of Sky & Telescope magazine. But, Olson adds, the photographer was actually there four years later than everyone believed.
Such acts of cosmic detective work have become a scholarly mission for Olson and his collaborator, physicist Russell Doescher of Texas State. "Forensic astronomy," it's called, and the astrophysicists have conducted more than two dozen studies of suspect dates in history, literature and the arts.
They theorized that Confederate Gen. Stonewall Jackson fell to friendly fire because his own troops failed to recognize their general's silhouette against a full moon. They ferreted out why Marine Corps landing craft unexpectedly ran aground short of the beach at Tarawa in the South Pacific during World War II (a rare lunar cycle caused an extremely low tide).
The Texas astronomers, whose exploits have earned them a bit of fame, also determined where and when Vincent van Gogh set up his easel to paint some of his most famous portraits of the heavens.
"They have a very good track record," said Owen Gingerich, a Harvard University professor and emeritus astronomer at the Smithsonian Astrophysical Observatory. To the common man or scientist, Gingerich added, "it's fascinating" to precisely pin down a great moment in time — and see it reprised.
"This is a slightly different kind of anniversary — and in some ways more meaningful than those we arbitrarily pick," Gingerich said. "There's something exact involved here that isn't repeated often."
Drew Johnson, curator of photography at the Oakland Museum of California, said Adams' foibles with the calendar weren't unusual among photographers of his day.
Dorothea Lange, the great Depression photographer, "wasn't so great about recordkeeping," Johnson said, noting how a Lange photo for years thought shot in Alabama was later determined to have been taken two states away in North Carolina.
The date correction for "Autumn Moon" "is a footnote," Johnson said. "In a sense, you could say it misses the point, which is art. But I totally respect people who take on a project like this. Footnotes can cumulatively add up to something big."
Olson, a Renaissance man at heart who received his doctorate at UC Berkeley, said the fusion of astronomy with art, literature and history has "made my study of science richer."
A decade ago, he and Doescher dabbled for the first time into Ansel Adams and the photographer's habit of recording incomplete or contradictory data about the location, time and place he shot those famous black-and-white negatives.
In 1994, they pinpointed the exact moment he shot his iconic photograph of the moon rising over Half Dome in Yosemite Valley, and alerted the curious about a rare return engagement that December. About 40 photographers braved Yosemite Valley's cold to walk in the steps of Adams.
The two professors teamed up this year with three honors students to tackle the truth about "Autumn Moon."
The shot depicts an ethereal mix of land and sky, looking away from Yosemite Valley southeast toward the jagged peaks of the Clark Range.
The scene is breathtaking, the darkroom work flawless. But there's no exact date in the record.
"Dates never meant much to Ansel," recalled Mary Street Alinder, for five years the photographer's assistant before his death and later the author of an Adams biography. "It meant something to the historian, but not the artist. It simply wasn't on his radar."
The university team, based in San Marcos, Texas, began its astronomical investigation by using topographic maps and sky photographs to triangulate the location of Adams' camera to a spot near the Geology Hut, a stone building halfway between Glacier Point's popular cliff-side railing and a parking lot.
Armed with that information, they could plot the moon's location in Adams' photo — between Mt. Starr King and Gray Peak — to narrow the list of possible evenings.
From there, the lunar face helped pin it down further. "Autumn Moon" is of such rich detail that the moon's lava-strewn seas and rimmed craters were easily discernible as a point of reference. Given the moon's penchant for rocking and nodding ever so slightly as it cycles through the skies, the astronomers could toss out a third of the suspected dates.
The final clues, Olson said, were earthbound shadows.
A sharp triangular shadow cast on the distant ridge by the setting sun sent Olson and his team scurrying to their computer. Accounting for atmospheric refraction and the curvature of the Earth, they concluded that "Autumn Moon" was shot in mid-September 1948. A trip to Glacier Point by the team in June firmed up those findings.
"It was the only date that fit everything," Olson said.
Number crunching also revealed the upcoming anniversary. For only the third time since the shutter snapped on "Autumn Moon," a waxing gibbous moon and setting sun will conspire between 6:50 and 6:52 p.m. Thursday to reprise the same golden scene captured by Adams.
"It's like you're re-creating a moment in time," Olson said. "I can envision myself up there on Glacier Point with Ansel Adams."
Word is spreading among photography buffs. Reid Stott, an Atlanta photographer who has posted an article about "Autumn Moon" on his website, photodude.com, said he would "give almost anything" to be there Thursday.
Johnson, of the Oakland Museum, said it would seem fitting if a few contemporary big shots of photography — John Sexton, Ted Orland and Mark Klett, among others — find their way to Glacier Point.
"It's a great opportunity," he said, "to commune with the spirit of Ansel."
Alinder, the biographer, said Adams would be "tickled pink" by the whole thing. He was delighted, she recalled, years ago when another astronomer pinned down the date of his most famous photo, "Moonrise, Hernandez, New Mexico."
Adams had guessed it was shot in 1944. It was really 1941.
Before he died, Alinder remembered, Adams offered a wry comment: "I just wish the moon was in more of my pictures. Then we'd know when I made them."
Solving the puzzle
Two astronomers found that Ansel Adams took "Autumn Moon: the High Sierra From Glacier Point" on Sept. 15, 1948, and the moon will be there around sunset again Thursday. Here are some clues they used:
Shape of the moon
Photo shows a "waxing gibbous" moon, a phase between first quarter and full moon. This
narrows the range of dates. Planetarium software extracts 24 dates between 1941 and 1959.
Location of the moon
General calculations are made of the moon's height in the sky. They then study moonrises to the southeast from Glacier Point, between Gray Peak and Mt. Starr King.
Matching the moon's face
The print from an 8-by-10-inch negative clearly shows surface features near the moon's north pole. Since the moon rocks slightly as it orbits the Earth, matching up features helps to rule out some dates.
A shadow's direction and length helps determine the sun's relative position. The image was shot just before sunset.
Making sure it all lines up
A telescope is used at Glacier Point to confirm the camera's location by precisely aligning granite features in Mt. Starr King and the Clark Range beyond it.
Where in the High Sierra?
Early on, topographic and National Park Service maps point research-ers to the Clark Range area from Mt. Clark to Gray Peak. A ranger takes pictures from Glacier Point for comparison.
Sources: Texas State University, Sky & Telescope, National Park Service