Have you noticed something unusual about the sky lately? Here in Maine, it’s hazy rather than clear blue skies. Sunrises and sunsets seem more vivid, especially in yellow and orange colorations. What’s causing this mysterious layer of haze?
Not so mysterious, actually. The culprit ultimately is due to wildfires in the west.
The dust and other particles go up into the atmosphere and can progress across the globe in high-level winds at altitudes of from 10,000 to 20,000 feet, and it’s something that can happen at any time when a large wildfire is burning.
September 1950 – “An Eerie Twilight”
Some may remember an even thicker blanket of smoke that also originated from forest fires in northern Alberta in late September 1950 and swept across the northern U.S. The Sun was reported to be tinted with varying shades; the most frequently mentioned were violet, lavender, and blue.
In a story appearing in the September 25th edition of the New York Times, the resultant smoke “plunged New York City into an eerie twilight in the early afternoon while it swept south from the Canadian border like a great shroud.” One woman was quoted about how her rooster was so confused it crowed at 4 p.m., thinking it was dawn.
Accompanying the Times article was a photograph taken from Main Street in Buffalo, New York at 2:50 in the afternoon. The sky became so dark that streetlights were turned on.
The “Dark Day”
But perhaps the most amazing example of how airborne smoke can affect the appearance of the sky occurred over New England on May 19th, 1780, recorded for posterity in a poem by John Greenleaf Whittier titled Abraham Davenport. This poem vividly describes the celebrated “Dark Day of New England,” a day so dark that:
Birds ceased to sing, and all the barnyard fowls
Roosted; the cattle at the pasture bars
Lowed and looked homeward.
It was later suggested by several “scientific gentlemen” that forest fires burning in the interior of the continent might put such a mass of incompletely combusted material in the air so as to refract incoming light rays. Circumstantial evidence to support this theory came in the form of rainwater that had a black, sooty appearance and upon analysis was found to contain the residue of burned leaves. The maximum darkness moved southeastward during the day from Vermont to Cape Cod. The landscape and all objects took on a yellowish-green hue and caused “great consternation” among the general populace.
Some even believed that doomsday was at hand.
Pain in the Ash!
In addition to the yellows and orange colors caused by forest fire smoke, you can also add purple, thanks to . . . a volcano! According to SpaceWeather.com, almost 3 months after the Kirul Islands’ Raikoke volcano blasted a plume of sulfurous gas into the stratosphere last summer, sunsets around the northern hemisphere were turning purple.
Why purple? Fine volcanic aerosols in the stratosphere scatter blue light which, when mixed with ordinary sunset red, produce a purple hue.
The effect is going strong so long after the eruption because Raikoke had help: On August 3rd, New Guinea’s Ulawun volcano also punched through to the stratosphere, adding its own emissions to that of Raikoke.
Purple isn’t the only thing to look for, says atmospheric optics expert Les Cowley. In addition, he advises, skywatchers should “be alert for a very bright yellow twilight arch, fine cloud structure in the arch seen through binoculars, and long diffuse rays and shadows.”
Purple Clouds in Florida
Likely this purplish coloration was responsible for the unusual purple hue that was cast on clouds in Florida after the offshore passage of Hurricane Dorian, not the storm itself as some were led to believe. Instead of the more typical orange and yellow hues being reflected off the clouds, the purple colors caused by sunlight strained through volcanic aerosols and then reflected onto the clouds.
If you’ve made any unusual sightings of sky colors caused by these recent volcanic eruptions, we would lava to hear them!
Joe Rao is an astronomer and contributes regularly to the Farmers' Almanac.