The strange phenomenon seems to have stretched from Maine to as far south as New Jersey, where General George Washington wrote about the darkness in his diary while he fought the Revolutionary War against the British, according to ScienceDaily.
Darkness began to fall shortly after 10 a.m. and continued throughout the day. Eyewitnesses claimed it was as dark as midnight by noon, according to a study published in 2007 in the International Journal of Wildland Fire.
The study suggested that the incident was caused by distant wildfires near the Great Lakes. Smoke from these fires likely traveled hundreds of miles to blanket New England, obscuring the sun, according to the study.
How do they know? The researchers were studying trees in southeastern Ontario and discovered fire scars from the year 1780 (by counting the yearly tree rings back from the present day).
"Based on observation of wind direction and barometric readings on 19 May 1780, it seems most likely that a low pressure weather system carried dense smoke from the west or north to the New England region," the paper says. In addition to the wildfires in southeastern Ontario, widespread fires in Missouri and Arkansas may have added to the dense smoke.
Climate data suggests the fires were brought on by drought in the regions. Warfare between settlers and the British and Native Americans may have also played a role, in addition to intentional burning of tree debris from settlers clearing large swaths of forest.
The sun reportedly appeared dim and red before fast-moving red, yellow, and brown clouds rolled in. Rain falling from these clouds was dark and sooty, according to reports, corroborating the researchers' theory that there was dense smoke in the atmosphere from wildfires.
Of course, in 1780 the early American settlers could not understood this delicate interaction of climate forces. Worried villagers sheltered together at community centers and discussed what the phenomenon meant.
The Connecticut Legislature, in session during the darkness, debated whether to adjourn because of the possibility that the world was ending. "I am against adjournment. The day of judgment is either approaching, or it is not," said one legislator, Abraham Davenport, according to CNN's history of the incident. "If it is not, there is no cause for adjournment; if it is, I choose to be found doing my duty."
The 19th century poet John Greenleaf Whittier wrote this about the incident, according to CNN:
"Over the fresh earth and the heaven of noon,/ A horror of great darkness, like the night/ … The low-hung sky/ Was black with ominous clouds, save where its rim/ Was fringed with a dull glow, like that which climbs/ The crater's sides from the red hell below./ Birds ceased to sing, and all the barn-yard fowls/ Roosted; the cattle at the pasture bars/ Lowed, and looked homeward; bats on leathern wings/ Flitted abroad; the sounds of labor died;/Men prayed, and women wept; all ears grew sharp/ To hear the doom-blast of the trumpet shatter ...."