In the course of the total solar eclipse of 8 July 1842, observers throughout Europe recorded a wierd impact within the closing moments earlier than totality: faint, wavering bands of sunshine and shadow shifting quickly throughout the bottom, a phenomenon now referred to as shadow bands. In keeping with the astronomer and author George F. Chambers, whose 1902 ebook The Story of Eclipses is among the earliest detailed compilations of eclipse observations, England’s Astronomer Royal, George Biddell Ethereal, famous “undulations” alongside the thinning crescent of the Solar roughly six minutes earlier than totality that yr. The 1842 eclipse is usually cited as one of many earliest well-documented sightings of the impact, although because the astronomy author Joe Rao has identified, “no person can state with certainty as to when shadow bands have been first famous.”
The eclipse itself is properly established. Its path of totality crossed Spain, France, Italy, Austria and central Europe earlier than reaching into Russia and Central Asia, with totality lasting barely over 4 minutes close to the centre of the trail. It was additionally notable for early scientific observations of the photo voltaic corona and prominences, which is a part of why detailed written accounts from a number of observers survive.
Older studies, more durable to confirm
Some secondary sources push the document again additional, citing a report from the German astronomer Hermann Goldschmidt describing an analogous impact as early as 1820, and a few retellings of Ethereal’s 1842 account add vivid element, describing “a wierd fluctuation of sunshine” so pronounced that kids reportedly ran after it and tried to catch it with their arms. These particular particulars couldn’t be confirmed in opposition to a main supply for this piece, and they need to be handled as unverified color somewhat than established reality. The extra solidly documented reference stays Chambers’ 1902 account of Ethereal’s “undulations,” itself a secondhand compilation written six many years after the eclipse it describes.
The reason most textbooks give
Shadow bands have a typical clarification, and it’s not appropriate to say, as is typically claimed, that no person has ever proposed why they occur. The dominant account, formalised by the physicist J.L. Codona in 1986, treats shadow bands as a scintillation impact: because the Solar narrows to a skinny crescent within the final seconds earlier than totality, its gentle passes by way of the ambiance as an more and more slim supply, and odd atmospheric turbulence, the identical turbulence that makes stars twinkle, refracts that slim band of sunshine erratically because it travels to the bottom. The result’s the flickering, shifting sample of sunshine and darkish bands that observers have reported for hundreds of years.
That is the reason normal references like Wikipedia give in the present day, and it accounts for the fundamental character of the phenomenon properly: bands that seem solely within the minutes surrounding totality, transfer with variable velocity and route, and are extra pronounced on some eclipses than others relying on native atmospheric circumstances.
What the usual mannequin doesn’t totally account for
The place issues get much less settled is within the particulars, and that’s the place energetic analysis has continued. A group from the College of Pittsburgh, calling themselves the “Shadow Bandits” and led by David Turnshek with Jeffrey Peterson of Carnegie Mellon College, has flown high-altitude balloon payloads throughout two latest eclipses, in 2017 and once more on 8 April 2024, particularly to check the place within the ambiance the bands really originate. Their 2017 flight returned a sign according to bands forming above the planetary boundary layer, increased within the ambiance than the straightforward ground-level turbulence mannequin assumes. The 2024 flight, at two websites in Texas and Vermont and utilizing improved devices, detected no such sign above the boundary layer. Within the resulting paper, the group says the mismatch means both that shadow bands weren’t current at their 2024 websites or that the 2017 measurement wants re-examining, leaving open the likelihood that the bands are, in any case, primarily a ground-level turbulence impact.
A 2026 paper on the preprint server arXiv, “The Optics of Shadow Bands” by Sretenović, goes additional, arguing that “regardless of centuries of studies, their bodily origin has remained unresolved” and that present turbulence-based fashions can not quantitatively predict a number of noticed options of the bands, together with their typical spacing and their obvious movement, drawing as an alternative on an analogy to Younger’s double-slit experiment for an alternate geometric-optical mannequin. It has not but been by way of peer overview. For now it’s best learn as one researcher’s case for reopening a query many textbooks deal with as closed, a speculation nonetheless awaiting impartial testing.
Why the excellence issues
Neither excessive captures the state of affairs: shadow bands do have an evidence, and that clarification shouldn’t be the ultimate phrase. There’s a well-established normal mechanism, atmospheric scintillation of a narrowing gentle supply, that explains why shadow bands occur in any respect. What present variations of that mannequin don’t predict properly are particular, measurable options of the bands: their typical spacing and their obvious movement. The phenomenon’s existence shouldn’t be in query; its finer mechanics are what stay unresolved.
Its geometric-optical different has not but been examined in opposition to impartial balloon and ground-based knowledge. The balloon programme and the Sretenović preprint don’t, the truth is, level the identical means: the Pittsburgh and Carnegie Mellon group’s personal 2024 flight undercut, somewhat than confirmed, their 2017 suggestion of a higher-altitude origin, and the preprint’s spacing-and-motion critique doesn’t depend upon the altitude query in any respect. What the 2 share is just that each deal with the usual turbulence account as incomplete, not that their proof converges.
The following alternative to collect extra knowledge will include future complete eclipses, when additional balloon flights or ground-based photometry may also help settle whether or not the 2017 or the 2024 consequence was the outlier. Till an impartial group resolves that discrepancy, and till a peer-reviewed mannequin might be checked in opposition to actual spacing and movement knowledge, shadow bands stay a case the place the framework is known in define however the particulars, the components that may let anybody predict a given eclipse’s bands upfront, usually are not.
