People in New York City and across the northeastern United States woke up Tuesday morning to an unusual sight. Depending on the time, early risers reported witnessing either the moon or the sun bearing a reddish glow. It was not the first time in recent months that both the sun and the moon have turned red in skies over various parts of the Northeast and the Pacific Northwest, as wildfires burning in eastern and western Canada continue to send smoke down the border.

Canada is experiencing one of its worst wildfire seasons on record, with close to 11 million hectares, or about 27 million acres, of land already burned since the beginning of the year, according to the Canadian Interagency Forest Fire Centre. Wildfires are burning from coast to coast, and more than 900 were active at once on Tuesday. The total area burned in 2023 is roughly the size of Indiana, and it has grown tremendously since just last month, when smoke plumes traveling south into the U.S. turned attention to the fires on a large scale. 

In early June, officials said wildfires had scorched 6.7 million acres of land since the beginning of the year. The blazes were especially severe at the time in the country's eastern provinces, with wildfires raging in Quebec and Nova Scotia that forced roughly 14,000 people to evacuate, CBC News reported. The fires spread as weeks passed, and Canadian officials on Tuesday reported 391 active fires in British Columbia, along the west coast, 125 active fires in Alberta to the east and 107 active fires in Quebec, which borders New England.

Wildfire smoke from Canada helped give the sun and moon a red-orange tint overnight into Tuesday, Mike Bettes, a Weather Channel meteorologist, told CBS News, noting that they appeared red in skies over most of the Northeast while "many other locations around the Great Lakes and Southeast also experienced smoke and vivid sunrises and sunsets." 

The phenomenon corresponds with a series of air quality alerts that are cropping up again across large sections of the country, which Bettes said are a direct result of northern and northwestern winds blowing smoke from Canadian wildfires into the U.S. As the country's wildfire season continues into the summer and fall, "the U.S. is likely to see intermittent periods of smoke and hence reddish glows to the gun and moon," Bettes said.

Earlier this summer, winds rotating around a stationary, low-pressure system hovering over the eastern provinces of New Brunswick, Nova Scotia and Prince Edward Island, known as the Canadian Maritimes, were directing smoke from the wildfires toward the northeastern U.S., Matt Sitkowski, the science editor in chief at The Weather Channel, told CBS News in June.

The smoke has caused the sun and the moon to appear red behind grey, hazy skies, said Sitkowski. Because the color of the sky is determined based on how sunlight interacts with the number and size of particles in the air, it changes with the infiltration of smoke, which introduces more particulate matter into the atmosphere.

"The sky is blue, for example, because small particles in the atmosphere scatter short wavelengths of the visible light spectrum more strongly than long wavelengths," Sitkowski said, noting that blue-colored light has shorter wavelengths while red-colored light has longer ones.

"When smoke is in the atmosphere, it not only makes the sun dimmer, it increases the amount and size of particulate matter in the atmosphere that absorbs more of the shorter wavelengths, leaving longer wavelengths to reach our eyes," he explained.

Why is there an air quality alert?

The red sun and moon over northeastern U.S. states this week came with a series of air quality alerts that impacted millions of people over the weekend and into Tuesday, some living as far west as Minnesota, Montana and Nebraska. The alerts stretched across to the east coast as hazy skies settled over places like Boston.

An air quality health advisory was in effect for most of New York State, according to the New York State Department of Environmental Conservation, which said affected regions included the Upper Hudson Valley, Adirondacks, Eastern Lake Ontario and Central Regions. Alerts were also in effect in parts of Massachusetts, Pennsylvania, Virginia, Georgia and the Carolinas, according to AirNow, a site that tracks air quality nationally and is operated by the U.S. Environmental Protection Agency.

Officials said air quality was considered "unhealthy for sensitive groups" in places where alerts were issued, but likely would not harm the general public. Sensitive groups, including older adults and children, as well as people with asthma and other preexisting respiratory conditions, are encouraged to limit strenuous outdoor activity for long periods while the health advisory is active. 

In general, the air quality index measures pollution by the amount of solid and liquid fine particles found in a given airspace, and weather authorities have recognized that the pollution happening Tuesday was linked to smoke plumes from at least 100 wildfires burning across the border in Quebec and Ottawa.

"Air quality has plummeted across much of the northeast as smoke from wildfires in Canada moves south," the National Weather Service wrote in a tweet last month. "Poor air quality can be hazardous. Before spending time outdoors, check the air quality forecast. Make sure you aren't doing yourself more harm than good."

Officials expect that winds will continue to blow smoke from the Canadian wildfires toward the Northeast until Wednesday at the earliest. The Midwest experienced similar consequences of wildfires across the border earlier in the week, with the Minnesota Pollution Control Agency saying in a tweet on Monday that "a band of smoke from wildfires in Quebec will continue to linger across east central and southeast Minnesota today due to very light winds." 

What's causing the fires in Canada?

As hundreds of fires burned across Canada in June, CBC News reported that federal officers like Michael Norton, an official with Canada's Natural Resources ministry, had said it was unusual for the country to see such a large coast-to-coast spread of wildfires at that time of year. Wildfires in Canada are typically sparked by lightning strikes, although human-caused fires have erupted into more significant blazes as well, Norton said. 

"Wildfire smoke can travel thousands of miles and linger in the air for days," Sitkowski said. "How the smoke is dispersed is a function of the larger weather pattern," like the direction of the wind and its strength. "Smoke also exists at different levels of the atmosphere, with the most hazardous to our health being when it is closer to the ground." 

In:
• National Weather Service
• Wildfire
• Smoke Advisory
• Wildfire Smoke
• Canada