"The Cliff, Etretat: Sunset," which was painted during the early years of the French impressionist period, shows a distant orange sun fading into the horizon, overlooking the cliffs at Etretat in Normandy. (And, in case you're wondering: No, you can't buy this particular work of art on Amazon.)
Using a bit of math and detective work, researchers were able to figure out when Monet (ostensibly) took in the sunset, which historians had already narrowed to sometime in 1882 or 1883. The next step for researchers, led by Texas State University physics professor Donald Olson, was to use planetarium software to calculate the alignment of the sun relative to the painting's tidal patterns. With a handful of potential February dates in hand, they cross-referenced their guesses with handwritten letters Monet had sent to friends and relatives to figure out when the painter was actually in the area. Using the process of elimination, the team zeroed in on a date.
With a day all set, Olson and his team used the alignment of the pictured Aiguille rock formation and the sun's relative distance above the horizon to discern an exact time...
4:53 p.m. on Feb. 5, 1883.