In Alfred Eisenstaedt’s famous photograph “V-J Day in Times Square,” an American sailor kisses a nurse amid a crowd of revelers in New York City on August 14, 1945–the day President Harry S. Truman announced Japan’s surrender in World War II. More popularly known as “The Kiss,” the image ranks as one of the most recognizable in history, yet both the sailor’s and the nurse’s faces are obscured, and Eisenstaedt never asked for their names. In the seven decades since V-J Day, the question of the couple’s identity remained a mystery, as did the exact time the photo was taken. Now, however, physicist Donald Olson and his colleagues have managed to solve the latter mystery, using scientific analysis to determine—down to the minute—exactly when Eisenstaedt captured one of history’s most famous kisses.

Immediately after Truman made the announcement of Japan’s surrender in World War II, at 7:03 p.m. on August 14, 1945, an American sailor walking through Times Square grabbed a nearby nurse and bent her over backwards in a passionate-seeming kiss amid the cheering crowds celebrating victory. Or at least that’s how the story went.

V-J Day
Alfred Eisenstaedt’s iconic photo. (Credit: Alfred Eisenstaedt/Time & Life Pictures/Getty Images)

In fact, as reported by the New York Times in 2010, near the 65th anniversary of V-J Day, “The Kiss” might have taken place hours earlier, before Truman made his announcement. Nursing student Gloria Bullard was in Times Square that day and witnessed the kiss; she appears in the background of another, less iconic but still famous photo of the moment snapped by Navy photographer Victor Jorgensen. By then in her 80s, Bullard told the Times that she returned home by train to New Canaan, Connecticut, on the evening of August 14 by dusk—making it impossible for her to have witnessed the kiss as late as 7 p.m.

Commenters on the article when it was published online pointed out something interesting—a distinctive shadow that appears on one of the buildings near the upper right-hand corner, cast by another building. After reading the article, physics professor Donald Olson from Texas State University and his colleagues Steven Kawaler (an astrophysicist) and Russell Doescher (an astronomer) set out to determine the time of the photo based on the length and direction of that shadow. Over almost four years, they pored over vintage maps, aerial photos and blueprints and used the information to build a scale model of the buildings featured in Eisenstaedt’s photo.

As reported by Wired, Olson realized that a sign mounted atop the Hotel Astor had cast the uniquely shaped shadow on the building behind it. According to his team’s findings, published in next month’s issue of Sky & Telescope, in order to have created such a shadow, the sun would have had to be “at azimuth 270 degrees (exactly due west) and at an altitude of +22.7 degrees.” What’s more, it could only have achieved that position that day at 5:51 p.m. Eastern War Time. (Congress passed the War Time Act in early 1942 as an energy-saving measure, reinstating year-long Daylight Savings Time; Eastern War Time would have been the equivalent of Eastern Daylight Time.)

V-J Day
Another view of the famous kiss, taken by U.S. Navy photographer Victor Jorgensen. (Credit: U.S. Navy)

Olson, Kawaler and Doescher have been doing similar work together for some 25 years, thanks to Olson’s passion for pinpointing key moments in works of art and literature as well as history. Previously, Olson has determined the exact times when and locations where Claude Monet painted some of his masterworks and Ansel Adams shot such striking photographs as “Autumn Moon, The High Sierra From Glacier Point.”

The scientists’ detective work doesn’t completely solve the lingering mystery of the kissers’ identity, although it could serve to eliminate people who claim to have been on the scene in Times Square before or after 5:51 p.m. on V-J Day. Over the years since Eisenstaedt’s photo was published by LIFE magazine, becoming one of the most iconic images of the century, dozens of people have come forward claiming to be the sailor or the nurse.

To name only several of the more recent claims, Lawrence Verria and George Galdorisi argued in their book “The Kissing Sailor” (2012) that experts had used forensic analysis to conclude that the two people in the photo were George Mendonsa, a Navy quartermaster on leave from the Pacific theater at the time, and Gretta Zimmer (now Friedman), a dental assistant from Queens who had emigrated from Austria in 1939. Glenn McDuffie, a U.S. Navy vet who passed away in 2014, reportedly got backing for his claim to be the sailor from a forensic artist at the Houston Police Department, who concluded that McDuffie’s facial bone structure exactly matched the man in the photograph.