Claude Monet's masterpiece The Cliff, Atretat: Sunset.

Afternoon delight: The Cliff, Etretat, Sunset is the only Etretat painting by Claude Monet that includes the disc of the sun. Photo: Supplied

London: If someone asked you what artist Claude Monet was doing at 4.53pm on February 5, 1883, you might struggle to answer, but a group of academics believe they could now tell you.

The French impressionist was standing at his easel, overlooking cliffs at Atretat in Normandy, capturing the watery winter rays of the fading sunset.

For the past 131 years his work The Cliff, Atretat, Sunset has held a secret that has now been unlocked by a group of research astronomers and physicists.

Claude Monet

Claude Monet. Photo: Supplied

The Texas State University team applied a practice known as forensic astronomy to the painting, studying the tides and alignment of the sun to pinpoint the exact moment Monet was trying to capture. Astronomer and physics professor Donald Olson said: "We like to use astronomy to show students how science can solve real-world puzzles.

"We asked, 'Could we use the dramatic rocks in the landscape and the position of the setting sun to determine where and when, specifically, Monet created this beautiful masterpiece?'"

Monet made a series of paintings featuring the same stretch of the Normandy coast during his three-week visit to the area during the winter of 1883.

With The Cliff, Atretat: Sunset, the artist painted a rock formation known as the Falaise d'Aval, together with the arch Porte d'Aval, overlapping a tall rock spire known as the Aiguille that stands just offshore. Of all the paintings Monet painted at Atretat, it is the only canvas that includes the disc of the sun. To determine on which days in February the sun would have set in the correct location for Monet to capture in his painting, the team of researchers travelled from Texas to France.

They made extensive topographic measurements of the terrain at Atretat to determine the exact locations where Monet stood.

The team found that the view matched the scene depicted in Atretat: Sunset at only one location - a spot 390 metres from the Porte d'Amont on a rocky beach under an overhanging cliff.

The Texas State researchers then used planetarium software to compare the modern sky with that of the 19th century and calculated that the sun would have set along that path on February 5, 1883.

They then combed through letters written by Monet from Atretat during his stay, along with weather records and tide tables from February 1883 to confirm the date.

The team discovered that on February 3 Monet was working on nearby Jambourg Beach and that the artist spent all of the following day entertaining his visiting brother. The tides of February 6 did not match the painting, and Monet's letters show that he paid close attention to the tides. On February 7, cloudy weather and rain storms began.

Through the process of elimination, the calculated date of February 5 is the only one remaining that matches the sun's position, the weather and the tide level in the painting.

Armed with that knowledge, the Texas State team used the height of the Aiguille formation to calculate the exact time from the altitude of the sun above the horizon.

"We were able to determine the month, day, hour and precise minute - accurate to plus or minus one minute - when Monet was inspired by that beautiful scene," Professor Olson said.

"Monet observed this sunset on February 5, 1883 at 4.53pm local mean time."

Telegraph, London