A combination of thick smoke, fog, and heavy cloud cover caused darkness to fall on parts of Canada and the New England area of the United States by noon.

New England's Dark Day occurred on May 19, 1780, when an unusual darkening of the daytime sky was observed over the New England states and parts of eastern Canada. The primary cause of the event is believed to have been a combination of smoke from forest fires, a thick fog, and cloud cover. The darkness was so complete that candles were required from noon on. It did not disperse until the middle of the next night.

New England is a region consisting of six states in the Northeastern United States: Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont. It is bordered by the state of New York to the west and by the Canadian provinces of New Brunswick to the northeast and Quebec to the north. The Gulf of Maine and Atlantic Ocean are to the east and southeast, and Long Island Sound is to the southwest. Boston is New England's largest city and the capital of Massachusetts. Greater Boston, comprising the Boston–Worcester–Providence Combined Statistical Area, houses more than half of New England's population; this area includes Worcester, Massachusetts, the second-largest city in New England; Manchester, New Hampshire, the largest city in New Hampshire; and Providence, Rhode Island, the capital of and largest city in Rhode Island.