The Mysterious Dark Day

For just one day during the American Revolution, everything went dark in the northeastern American colonies.

May 18, 1780

The sky was a strange yellow color, the sun a dull red. For General George Washington, camped out in New Jersey, the clouds were “dark,” “heavy & uncommon,” and mixed with “a bright and reddish kind of light.”

May 19, 1780

People in New England stared at the sky, amazed as the sun disappeared and a thick darkness gradually fell. By midday, the sky was black as night and raining a thick, sooty-smelling rain.

Birds stopped singing.

Flowers closed.

Cows headed for home.

And there was no light that night — the full moon was covered!

People panicked. Many rushed to churches. A lady in Boston sent her son to their minister to ask what was happening. “Tell your mother I am as much in the dark as she is,” he explained. 

Just the day before, there had been an eclipse of the moon. Did these two events mean the end of the world? Many were sure that doomsday had arrived.

Some recorded their fears in diaries and letters. A judge remarked that when he held “a sheet of white paper… within a few inches of the eyes,” the writing was not visible. One man wrote: “This day was the most Remarkable day that ever my eyes beheld.” An American soldier noted that the day was “terrible indeed to all the beholders.”

The year 1780 was already a bad-luck year. The American Revolution still dragged on after four years, and the British were winning. Just one week before the Dark Day, the British had taken Charleston, South Carolina. Washington’s friend General Benedict Arnold had turned traitor earlier in 1780. And Washington had few troops left.

Perhaps the Dark Day meant doom for the war. No wonder people worried! 

May 20, 1780

But the next morning, the sun came up. And people were talking. News about the Dark Day spread. Professors, amateur scientists, and the interested public suggested all kinds of reasons for the Dark Day.

Some believed the moon eclipse had caused it. Others said no — that kind of eclipse doesn’t cause days to go dark.

An eclipse of the sun, then? No, that wasn’t it, scientists replied.

Nor was the Dark Day caused by a comet or a planet passing between the Earth and the Sun, or a large mountain in space.  

But at Harvard College in Massachusetts, Professor Samuel Williams had a thought. He believed that the Dark Day was brought on by “vapours,” something that absorbed and weakened the sunlight. Nearby in Ipswich, Massachusetts, a man who called himself Viator (meaning “wayfarer” or “traveler”) saw “quick flashes” in the west, like northern lights, on May 19. By 3:00 p.m., he reported that the air smelled terribly sooty. One of his friends thought nearby chimneys caused the odor; others thought it was burning leaves. Viator bent over and sniffed some standing water — the same strong, sooty smell stung his nostrils. Between his fingers, he rubbed the scum from the top of the water. He pronounced that it was made of black ashes and burned leaves. He suggested that “smoke from the woods” caused the problem.

But the mystery of the Dark Day remained unsolved. 

June 2008

Until more than 200 years later!

In 2008, scientists at the University of Missouri announced that massive Canadian wildfires caused the mysterious Dark Day. Their study of tree rings in the mountains of southern Ontario and other places showed that a huge fire burned in the spring of 1780. Thick columns of smoke rose into the upper atmosphere and spread east.

The red sun and strange yellow sky reported by people like George Washington are typical of this condition. The smoke hung over the East Coast, shutting out the sun for many hours. (Today this is called an inversion and is common over major cities.) People had no way of knowing that the forests in Canada were burning so fiercely, but Professor Williams and Viator definitely had the right idea.