According to Mr. van Tilborgh, it was painted on the same type of canvas with the same type of underpainting van Gogh used for at least one other painting of the same area, “The Rocks.” The work was also listed as part of Theo van Gogh’s collection in 1890. It has “180” painted on the back, which corresponds to the number in the collection inventory. “That was the clincher,” he said.

Mr. Rüger added: “This time, we have topographical information, plus a number of other factors that have helped us to establish authenticity. Research is so much more advanced now, so we could come to a very different conclusion.” The last major van Gogh brought to light, the museum said, was the 1888 painting “Tarascon Stage Coach,” in the 1930s. The date of “Sunset at Montmajour” has been identified as July 4, 1888. In a letter van Gogh wrote to his brother the next day, he seemed to have described the scene:

“Yesterday, at sunset, I was on a stony heath, where very small, twisted oaks grow, in the background a ruin on the hill, and wheat fields in the valley. It was romantic, it couldn’t be more so, à la Monticelli, the sun was pouring its very yellow rays over the bushes and the ground, absolutely a shower of gold. And all the lines were beautiful; the whole scene had charming nobility.” (He was referring to the works of Adolphe Monticelli, one of the first painters van Gogh admired when he moved to Paris in 1886, and who played a role in van Gogh’s decision to move to Provence.)

“Sunset at Montmajour” is comparable in size to “Sunflowers,” which was painted the same year and sold for $39.9 million in 1987 at an auction at Christie’s in London.

Van Gogh moved to Arles in February 1888 and spent time exploring the landscapes in Provence, and doing work “en plein air,” or in nature. He was particularly fascinated by the flat landscape around the hill of Montmajour, with its rocky outcroppings and hay-colored fields.

In a letter dated July 1888, he said that he had been to Montmajour at least 50 times “to see the view over the plain.”

Mr. Leeman, the historian, said that “in hindsight, many pointers in his letters and entries in catalogs of the 1900s have been linked to other paintings or misidentified,” adding, “Here, we see a painting that fits those descriptions exactly.”

The painting will be on view at the museum for one year, starting on Sept. 24, as part of the current exhibition, “Van Gogh at Work,” which focuses on other new discoveries about the painter’s artistic development. Mr. Rüger said the current owners have not indicated what they intend to do with it after that.