At dawn on Friday, May 19, 1780, farmers in New England stopped to marvel at the ominous pink hue of the sun. By noon the sky had darkened to midnight blackness, causing Americans, still in the throes of a protracted war of independence, to light candles and tremble at thoughts of the Last Judgment. As the birds quieted and no storm accompanied the darkness, men and women crowded into churches, where one minister commented wryly that “The people were very attentive.” John Greenleaf Whittier later wrote that “Men prayed, and women wept; all ears grew sharp/ To hear the doom-blast of the trumpet shatter / The black sky . . .”

A recent study in the International Journal of Wildland Fire, the work of a team of researchers led by Richard Guyette from the University of Missouri’s Tree Ring Laboratory, has shown that vast forest fires in the Algonquin Highlands of southern Ontario and elsewhere in Canada brought this eerie event upon the Puritan lands. The scientists have discovered “fire scars” on the rings for that year, left when the heat of a wildfire has killed a part of a tree’s cambium. Dendrochronological evidence also points to a drought that year. An easterly wind and low barometric pressure helped force smoke into the upper atmosphere. “The record fits pretty close,” says Guyette. “We had the right fuel, the drought, the conditions were all there.”

Lacking the ability to communicate quickly over long distances, Americans in 1780 remained literally and figuratively in the dark about the event, which had dissipated by the next day. Over the next several months, the papers carried vigorous debates about the causes. Some were the voices of angry prophecy, such as one Massachusetts farmer who wrote, “Oh! Backsliding New-England, attend now to the things which belong to your peace before they are forever hid from your eyes.” Others wrestled for different answers, one postulating that a “blazing star” had passed between the earth and the sun, another attributing the dark day to the rise of “aqueous, sulphorous, bitimeneous, salineous, vitreous” particles into the atmosphere. Ash, argued another commentator. “Vast quantities of elastick, heterogeneous vapours, generated in consequence of the great body of snow which covered the earth so long the winter past, and exhaled during the warm dry weather,” stated another. The debate, carried on throughout New England, where there were no scientific journals or academies yet, reflected engagement with Enlightenment ideas and an unfolding culture of scientific inquiry already sweeping the Western world, a revolution nearly as potent as the war for independence from the English.

New Englanders would not soon forget that dark day; it lived on in folklore, poems, tracts, and sermons for generations.

— John Ross