It had been raining since the night before.

By the morning of October 13, 1917, the Cova da Iria—a hollow of pasture outside the village of Fátima, in rural Portugal—was mud. People had walked in for days, some barefoot, carrying umbrellas or nothing at all. Estimates of how many came run from 30,000 to 70,000. They stood in the downpour and waited for three children.

A miracle with a date on it

Lúcia dos Santos was ten. Her cousins Francisco and Jacinta Marto were nine and seven. Since May 13 of that year, they had said, a lady of light appeared to them over a small holm-oak tree in the Cova, on the 13th of every month.

In July, Lúcia later wrote, she'd asked the lady to perform a miracle so people would believe them. The answer: keep coming back each month, and in October there would be one.

Very few miracles come with an appointment. Word spread, and the crowds grew every month. Portugal at the time was governed by an anticlerical republic, and the newspapers were openly mocking. In August, the local administrator in Vila Nova de Ourém held the children for two days to stop them reaching the Cova on the 13th.

By October the whole country was watching. If nothing happened, the story would be finished.

Around noon

The children arrived. Lúcia called out to the crowd to shut their umbrellas. Then, by most accounts, the rain stopped and the clouds broke.

What happened next comes to us through witnesses, and they don't all agree.

Many said the sun appeared as a flat, pale disc they could look at directly without pain. Then it began to move. People described it spinning, throwing off colored light that tinted the faces and clothes around them, and then seeming to break loose from the sky and drop toward the crowd—before swinging back into place. Some people fell to their knees. Some screamed. Several witnesses reported that their soaked clothes were suddenly dry.

One account, often attributed to a Coimbra professor named Almeida Garrett (historians disagree over whether it was the professor or his son), reads: "The sun, whirling, seemed to loosen itself from the firmament and advance threateningly upon the earth as if to crush us with its huge fiery weight. The sensation during those moments was terrible."

The man who did the most to make it famous was not a believer. Avelino de Almeida was a reporter for O Século, Lisbon's big secular, anticlerical paper. He'd written a sneering preview of the gathering. Then he went, and his front-page report described the crowd watching the sun "dance," in the words of the people around him. His paper couldn't dismiss it, and neither could anyone else.

Not everyone saw it. Some people in the crowd reported nothing unusual. No observatory anywhere recorded anything strange about the sun that day—which, since the whole hemisphere was under the same sun, is the strongest point skeptics have.

Explanations

For believers, the answer is straightforward. In 1930, after a church investigation, Bishop José Alves Correia da Silva of Leiria declared the apparitions "worthy of belief." Fátima became one of the largest Catholic shrines in the world. Francisco and Jacinta both died in the 1918–1920 influenza pandemic, still children, and were canonized in 2017. Lúcia became a nun and lived until 2005.

Skeptics argue the sun didn't move—people's eyes did. The physicist Auguste Meessen argued that staring at or near the sun produces after-images on the retina that appear to spin and drift, and that bleaching of the eye's light-sensitive cells produces the color shifts. Science writer Benjamin Radford adds expectation and suggestion: tens of thousands of people told a miracle would appear in the sky looked at the sky until they saw one. Neither of them says the witnesses were lying.

Others have proposed an unusual atmospheric effect—a sun dog, or dust or ice crystals in the clouds after a storm—localized enough that nobody further away noticed.

Each explanation leaves something out. Retinal effects don't explain why so many people saw the same thing in the same few minutes. A weather effect doesn't explain why a sun that visibly "fell" didn't show up anywhere else. And a miracle, of course, can't be tested.

One more detail. A photograph of a dark sky and a bright sun breaking through clouds is often shared as a picture of the miracle. It isn't. That image was later shown to have been taken years afterward, somewhere else in Portugal.

What's settled, and what isn't

Documented: A huge crowd gathered on a date the children announced months ahead. Thousands—including a hostile secular journalist—reported the sun behaving impossibly for several minutes. Some saw nothing. No instrument recorded anything.

Disputed: Whether the clothes and ground really dried, how long it lasted, and what exactly was seen.

Unsettled: What made so many people at once see the sun fall.

Our Short below shows the scene in under a minute. Were they seeing a miracle, or their own eyes? Tell us in the comments.