On December 1 2021, the Facebook page “Vellum and Vinyl” shared a screenshot of the following Tumblr post, discussing “albedo” — a measurement of reflectivity and the “bright darkness” caused by snowfall after dark:
In the post, Tumblr user reputayswift shared images of an uncharacteristically bright night sky, illuminated by a blanket of snow. Initially, they asked:
Is there a word for that like, “bright darkness” you get in winter?? When it’s been snowing or it’s supposed to snow past sunset and the sky isn’t Dark Enough. One of my favorite things
In a follow up post, u/reputayswift added:
Thanks to @raindropwindow and a handful of articles, it’s called snow albedo, skyglow, snowglow, or just light scattering! It’s the result of moon- or artificial light reflecting off ground snow, low clouds, or ice crystals.
As of December 2 2021, the post received more than 65,000 “notes” (Tumblr comment engagements) since its publication on November 30 2021. Google Trends data showed searches for “albedo” began steadily registering prior to the post’s appearance, with an initial spike on November 26 2021.
Related searches included “albedo,” “snowglow,” and “skyglow.” According to Brittanica.com, “albedo” was a slightly more generalized term:
… [a] fraction of light that is reflected by a body or surface. It is commonly used in astronomy to describe the reflective properties of planets, satellites, and asteroids. It is an important consideration in climatology since recent albedo decreases in the Arctic have increased heat absorption at the surface.
Albedo is usually differentiated into two general types: normal albedo and Bond albedo. The former, also called normal reflectance, is a measure of a surface’s relative brightness when illuminated and observed vertically. The normal albedo of snow, for example, is nearly 1.0, whereas that of charcoal is about 0.04.
The National Snow and Ice Data Center’s “albedo” entry mentioned snow, explaining:
Albedo is a non-dimensional, unitless quantity that indicates how well a surface reflects solar energy. Albedo varies between 0 and 1. Albedo commonly refers to the “whiteness” of a surface, with 0 meaning black and 1 meaning white. A value of 0 means the surface is a “perfect absorber” that absorbs all incoming energy. Absorbed solar energy can be used to heat the surface or, when sea ice is present, melt the surface. A value of 1 means the surface is a “perfect reflector” that reflects all incoming energy.
Snow has an even higher albedo than sea ice, and so thick sea ice covered with snow reflects as much as 90 percent of the incoming solar radiation. This serves to insulate the sea ice, maintaining cold temperatures and delaying ice melt in the summer. After the snow does begin to melt, and because shallow melt ponds have an albedo of approximately 0.4 to 0.5, the surface albedo drops to about 0.75. Albedo drops further as melt ponds grow and deepen.
Although the post and interactions with it generally viewed light conditions of the night sky influenced by snow in a positive light, an August 2019 Atlas Obscura piece about it described some downsides. NewScientist.com published a similar article about the same research in August 2019:
In 2017, a multi-institute team of researchers, including Jechow, reported that our planet brightened by roughly two percent annually between 2012 and 2016. Artificial light has been found to deter pollinators from making pit stops at the plants they typically visit, lead birds toward fatal collisions with buildings, and throw off animals’ migration patterns and meals. And whether they’re washed out by moonlight or artificial light, bright skies can snuff out stargazers’ dreams, making it harder to glimpse meteor showers and other celestial shows. Now, in a new paper in the Journal of Imaging, Jechow and his collaborator Franz Hölker suggest that skyglow is amplified by snow—an effect they dub “snowglow.”
Their analysis suggested that, at the suburban site, fresh snow could make the sky 33 times brighter on a clear night, and 200 times brighter on a cloudy one—enough to eclipse the brightness of the Moon. That much light can be dangerous: “The high nocturnal light levels we measured are so high that they potentially affect animals and could also disturb sleep of very sensitive humans,” Jechow says. The darkness-drenched Latvian village wasn’t immune from light pollution, either. When Jechow returned to the main road, a 15-minute walk from the lonely beach where he collected measurements, he spied the distant glow of a city nearly 50 miles away.
A popular Tumblr post about “snow albedo” was shared to Facebook, initially describing the unusual brightness of the night sky during or after snowfall; a follow-up post by the same user described the phenomenon as “snow albedo” or “snowglow.” Snow was frequently used as an example in broader definitions of “albedo,” a measure of relative reflectiveness. The condition was more commonly described as “snowglow,” and in 2019, researchers observed that it could cause the night sky to become “200 times brighter” on a cloudy night.