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Shadow bands

Shadow bands are thin, wavy lines of alternating light and dark that appear to flicker and move rapidly across plain-colored surfaces, such as white sheets or pavement, in the final moments before and immediately after the totality of a total solar eclipse. These elusive phenomena, typically 3 to 8 centimeters wide and separated by similar distances, are caused by the refraction of the Sun's narrowing crescent of light through turbulent eddies in Earth's atmosphere, particularly in the planetary boundary layer of the troposphere, which distorts the light into rippling patterns projected onto the ground. The bands' motion, often several meters per second, results from shifting air currents at various altitudes combined with the Sun's angular movement during the eclipse. First reliably documented in the , shadow bands have been reported in observations dating back nearly 1,000 years, though their intermittent visibility—dependent on clear skies, low atmospheric , and observer positioning—has made them a subject of ongoing scientific intrigue. Not all s produce observable bands; for instance, during the 1970 along the U.S. East Coast, numerous sightings were recorded, while others, like certain modern events, yield none due to unfavorable conditions. Scientific efforts to study them have included , balloon-borne instruments, and detector arrays, revealing light intensity variations in frequencies from 1 to 500 Hz, yet the precise mechanisms remain partially unexplained, with hypotheses focusing on the 's reduction of the to a point-like source akin to a . These bands, visible only under the unique low-light conditions of totality's approach, highlight the interplay between celestial geometry and terrestrial atmosphere, captivating astronomers and enthusiasts alike.

Description and Observation

Appearance and Characteristics

Shadow bands manifest as thin, wavy lines of alternating and that sweep rapidly across flat, plain surfaces such as the ground, walls, or white sheets during eclipses. These patterns appear as faint, undulating ripples or elongated shadows, often described by observers as flickering, rippling effects resembling "dancing " or "wavy lines" due to their , low-contrast form. The bands are typically grayish in tone against a brighter background, with parallel rows that can become more organized and vivid as totality approaches. In terms of physical dimensions, the bands generally measure a few centimeters to about 30 cm in width, with separations between them ranging from 3 to 8 cm, and can extend up to several meters in length along their elongated axis. They move at speeds of 1 to 3 m/s in random, often parallel directions, creating a dynamic, flowing motion that blurs slightly to the . These characteristics arise from atmospheric effects that distort the narrow crescent of sunlight just before and after totality. Shadow bands are visible only in the final 10 to 30 seconds before second contact (the onset of totality) and the first 10 to 30 seconds after third contact (the end of totality), typically resulting in a total duration of approximately 20 to 60 seconds, though some observations extend to 90 seconds. During the April 8, 2024, total solar eclipse, shadow bands were widely reported and captured on video in regions like and , highlighting their visibility on surfaces like under clear conditions. Not everyone perceives them clearly, as their faintness and rapid motion can make them elusive, particularly under suboptimal conditions. Visibility is enhanced on light-colored, smooth surfaces like pavement, , or laid-out white fabrics, where the contrast against the uniform backdrop highlights the moving patterns.

Optimal Viewing Conditions

Shadow bands are best observed during total solar eclipses under clear skies with minimal low-level wind to minimize ground-level disturbances, though moderate turbulence in the upper atmosphere can enhance their visibility. Calm ground conditions are crucial, as excessive local wind can blur the effect, while high-altitude winds contribute to the necessary without directly interfering at the observer's level. Shadow bands occur during total and annular solar eclipses when narrows to a thin , but not in non-central partial eclipses. Heavy obscures them entirely. For optimal location, select open areas free from trees, buildings, or other obstructions that could cast interfering shadows or block the view of the ground. Light-colored, flat surfaces such as white sheets, , or projection screens provide the necessary to detect the faint, wavy lines of alternating and . These surfaces should be oriented to the incoming for maximum backscattering and clarity. Preparation involves lying flat on the ground or positioning low to scan the surface with , avoiding direct gaze at to prevent eye damage—use safe indirect methods like pinhole projections if needed. Spread a large white cloth or sheet on the ground in advance, and consider video recording with a tripod-mounted camera at high frame rates (e.g., 60 or higher) to capture and analyze the rapid motion, as often fails due to low contrast and speed. Visibility depends on atmospheric seeing, where excessive stability reduces the effect, but favorable conditions with some yield success in many cases, though the bands remain elusive and not universally observed even in ideal setups. Additional tips include aligning observation areas perpendicular to the prevailing wind direction to stabilize the view and employing multiple observers for confirmation and broader coverage of the site.

Physical Explanation

Atmospheric Turbulence Mechanism

The primary cause of shadow bands is the of by eddies in Earth's atmosphere, which distort the incoming wavefronts and produce irregular patterns projected onto the ground as moving bands of and . These eddies arise from variations in air and , creating localized regions with differing refractive indices that act like tiny prisms, bending rays in unpredictable ways. As the passes through multiple such layers, the cumulative shifts lead to constructive and destructive , manifesting as the observed wavy patterns. This phenomenon is analogous to the that causes stars to twinkle, where atmospheric similarly modulates intensity, but shadow bands are more pronounced during an because the Sun's image is reduced to a narrow , effectively collimating the rays like light passing through a slit and amplifying the spatial variations in illumination. In everyday conditions, the full solar disk averages out these distortions, but near totality, the crescent's geometry heightens the effect, turning subtle refractive perturbations into visible, dynamic shadows. The relevant turbulence occurs primarily in the , the lowest 1-2 km of the , where small-scale eddies of 10-100 cm in size are driven by temperature gradients near the surface and aloft. These eddies induce variations on the order of Δn ≈ 10^{-6}, sufficient to diverge nearly parallel rays from the Sun's thinning crescent, which narrows to about 1 arcminute in angular width just before totality. The resulting projections at ground level form interference fringes due to phase differences in the refracted light, with the bands' motion driven by the eddies' by prevailing winds.

Relation to Eclipse Phases

Shadow bands are exclusively observed during total solar eclipses, manifesting in the final 10-20 seconds leading up to second contact—the onset of totality—and reappearing for a similar duration immediately following third contact, when the Moon begins to uncover . This precise timing aligns with the 's progression toward and away from complete obscuration, where the phenomenon is absent at maximum during partial phases due to the lack of dynamic transition to totality. The underlying geometry involves the Sun's disk being narrowed to a thin with an angular width of less than 1-2 degrees, functioning as an extended but slit-like light source. As this thins rapidly near totality—at rates around 0.5 arcseconds per second—the refracted from its edges produces the characteristic linear, undulating patterns rather than the point-source seen under normal conditions. Atmospheric enhances these patterns by distorting the incoming rays, but the geometry is essential for their formation. In contrast, shadow bands do not occur during partial eclipses because the broader Sun disk diffuses the refractive effects, preventing distinct linear features. Similarly, annular eclipses lack the due to the uniform ring of , which fails to create the necessary thin-crescent collimation. The duration and intensity of the bands are thus closely tied to the eclipse magnitude, with sharper thinning amplifying the slit-like projection of through the atmosphere.

Historical Observations

Early Sightings

The earliest verified scientific observation of shadow bands dates to 1820, when German astronomer Hermann Goldschmidt reported seeing fleeting wavy lines moving across the ground just before totality during a total . A notable account followed during the total solar eclipse of July 8, 1842, visible across parts of including , where described the bands as rapidly moving shadows on walls and the ground, so vivid that children chased after them in attempts to catch the fleeting patterns. In 1905, British astronomer Catherine Octavia Stevens provided one of the clearest early descriptions while observing the total of August 30 from Cas Català in Majorca, Spain; she noted the bands' distinct wavy, undulating motion sweeping across white surfaces like the ground and walls, lasting about 30 seconds before and after totality. Pre-19th-century eclipse records from ancient civilizations may allude to similar phenomena but remain unconfirmed and lack specific details matching shadow bands; although there are reports dating back nearly 1,000 years, documented sightings are confined to 19th-century observations. These initial reports were frequently met with skepticism, with some astronomers attributing the bands to optical illusions, retinal fatigue, or subjective visual artifacts rather than objective atmospheric effects, a view that persisted until photographic and cinematographic evidence in the early 20th century substantiated their existence.

Modern Research and Studies

In 1927, astronomer P. M. Ryves proposed that shadow bands arise from the refraction of light from a small segment of the Sun's disk by irregularities in the Earth's atmosphere, establishing an early connection to atmospheric turbulence. During the total solar eclipse of February 16, 1980, photoelectric observations using spatially separated detectors captured short-term light variations associated with shadow bands in a frequency bandpass of 1–500 Hz, occurring in the half-minutes before and after totality. of the data revealed a sharp drop-off in power above 50 Hz, consistent with spectra from stellar and supporting an atmospheric origin for the phenomenon. Cross-correlations between the detector outputs were low, indicating that the turbulent elements responsible for the patterns have a short persistence time on the order of milliseconds. Between 2001 and , researchers documented shadow band motion as occurring at speeds of a few meters per second, perpendicular to the bands' elongation and aligned parallel to the tangent of the 's center, with the direction rotating as the changed relative to the observer's position. In , Stuart Eves hypothesized that shadow bands result from generated by the rapid cooling of air along the supersonic-moving shadow, creating a shock front that refracts light into the observed patterns. This proposal suggested the bands' direction changes—with before totality and after—mimic wave patterns behind a moving object. However, Barrie W. Jones refuted the idea, noting that sound waves propagate at approximately 400 m/s, far exceeding the observed band speeds of 0 to a few m/s dictated by , and affirmed that by the thinning through turbulent air adequately explains the effect without invoking acoustics. In 2024, a team conducted experiments during the April 8 total solar eclipse to distinguish between atmospheric and "moon slit" theories for shadow band formation. The balloons, equipped with sensors, ascended above the to measure light fluctuations, confirming that in this lower atmospheric region—rather than higher-altitude effects or simple geometric slitting by the —dominates the production of the bands. Contemporary investigations employ high-speed imaging and numerical wave simulations to replicate shadow band patterns, modeling the of crescent-shaped sunlight through distributed screens in the lowest 2–3 km of the atmosphere. These approaches yield intensity fluctuations and temporal evolutions matching observational records, including wind-driven band motion, while quantifying indices from turbulent contributions. Challenges persist due to the phenomenon's rarity and brevity, limiting data collection; however, multi-site observations reveal site-specific variations in band movement and intensity, attributed to local atmospheric conditions such as and strength.

References

  1. [1]
    Shadow bands are a solar eclipse mystery (and not everyone sees ...
    Jan 17, 2024 · Shadow bands are perhaps the most unusual. These mysterious gray ripples are sometimes seen flitting over the ground within several minutes of totality.
  2. [2]
    Research During Solar Eclipse Could Shed Light on Shadow Bands
    Apr 15, 2024 · The leading hypothesis is that shadow bands occur when sunlight travels through turbulence in the planetary boundary level in the troposphere.
  3. [3]
    Ask Astro: What causes shadow bands during a solar eclipse?
    Apr 19, 2023 · Scientists believe shadow bands arise because of the turbulent nature of Earth's atmosphere. As the Moon moves to fully cover the Sun or just ...
  4. [4]
    Shadow Bands in Solar Eclipses - Physics Van
    Oct 22, 2007 · It shows how observant people are during solar eclipses. Shadow bands are not spooky at all. The "atmospheric irregularity" explanation makes ...
  5. [5]
    Research During Solar Eclipse Could Shed Light on Shadow Bands
    Apr 15, 2024 · "Shadow bands been known about since the 1800s, and there are reports of them being observed nearly 1,000 years ago, but they haven't been ...Missing: history | Show results with:history<|control11|><|separator|>
  6. [6]
    Observation of eclipse shadow bands using high altitude balloon ...
    During the few minutes before and after totality of a solar eclipse, indistinct bands of light and dark, known as shadow bands, appear to sometimes chaotically ...
  7. [7]
    Observations of shadow bands at the total solar eclipse of 16 ...
    Dec 1, 1984 · Light variations in a bandpass of 1-500 Hz were detected during the half-minutes preceding and following the total phase.Missing: history | Show results with:history
  8. [8]
    2024 Total Eclipse: What to Expect - NASA Science
    Shadow bands are rapidly moving, long, dark bands separated by white spaces that can be seen on the sides of buildings or the ground just before and after ...Missing: appearance characteristics
  9. [9]
    [PDF] the shadow band phenomenon
    Two distinct types of shadow bands quite different in width, separation, and velocity were simultaneously visible at the site: (1) Width of bands: 1 foot ...
  10. [10]
    [PDF] Observations of shadow bands at the total solar eclipse of 16 ...
    Feb 16, 1980 · liferation of exotic proposals to explain the shadow- band phenomenon. In the simplest picture, the for- mation of shadow bands involves the ...
  11. [11]
    Qualitative Shadow Band Observations from Three Sites in the ...
    Shadow bands are not always visible at an observing location and even when present they can be missed by observers who are concentrating on other things at this.
  12. [12]
    The Solar Eclipse Experience
    Shadow Bands Very dim, undulating ripples of dark and light might appear, flowing across the ground or the side of a white building. These elusive features are ...Missing: characteristics | Show results with:characteristics
  13. [13]
    Shadow Bands - Total Solar Eclipse - Xavier Jubier - Free
    Start shooting 5 minutes before totality and stop the recording 5 minutes after. Usually shadow bands will show up during about one minute around totality. For ...
  14. [14]
    Qualitative Shadow Band Observations from Three Sites in the ...
    We theorize that the cause of the different movement of the parallel lines of shadow bands at each site is due to variations introduced by atmospheric effects ...Missing: scientific | Show results with:scientific
  15. [15]
    [PDF] Optical scintillation; a survey of the literature - GovInfo
    (1948), On Shadow Bands at Total Eclipses of theSun, Pop. Astron. _56,. 353 ... of Atmospheric Turbulence, Proc. IRE 43, 1391-1401, October. Herbstreit ...
  16. [16]
    [PDF] Measurement of variations in atmospheric refractive index with an ...
    As in this work D.n is of the order of 10- 6, it is con- venient to introduce a quanti ty D.N defincd by. D.N= D.n X 106, where N is called an IV-unit. D.j ...Missing: Δn shadow
  17. [17]
    What Can You See during a Total Solar Eclipse? - Time and Date
    Shadow bands. Faint waves of light—the result of turbulence in Earth's atmosphere—may be seen moving across the ground and walls. ~20 seconds before totality.
  18. [18]
    Shadow bands observed during the total solar eclipse of 4 ...
    It has been observed that shadow band spacing decreases and their contrast increases as totality approaches (Codona, 1986). ... The scintillation theory of ...
  19. [19]
    [PDF] Total Solar Eclipse of 1999 August 11
    Aug 11, 1999 · lies near path center for 2 minutes 17 seconds of totality. At 10:35 ... Moon's angular velocity with respect to the Sun is 0.379 arc-seconds per ...Missing: thinning | Show results with:thinning
  20. [20]
    Pitt students chase shadows in Texas to solve eclipse mystery
    Apr 8, 2024 · (During an annular eclipse, shadow bands are unlikely to appear because the moon is too far from the Earth to completely block out the sun.).
  21. [21]
    Scientists get another chance to study a solar eclipse mystery - NPR
    Apr 6, 2024 · BODEN: Shadow bands are thin, wavy lines of alternating light and dark that seem to race across the ground right before and right after the moon ...Missing: characteristics | Show results with:characteristics
  22. [22]
    [PDF] SOLAR ECLIPSE NEWSLETTER
    May 2, 2004 · ... shadow bands have been reported for the first time by H. Goldschmidt in 1820. ... -First observation of magnetic field before and after a flare.
  23. [23]
    4 Surprising Facts About the Total Solar Eclipse - Time Magazine
    Aug 21, 2017 · Renowned English astronomer George Airy wrote about shadow bands ... children ran after it and tried to catch it with their hands,” Airy ...
  24. [24]
    7 Para-reflections: Shadowgrams and the Black Drop
    Airy recalled seeing his first shadow bands in 1843: “As totality approached ... upon the walls and ground, so striking that in some places children ...
  25. [25]
    [PDF] OBITUARY CATHERINE OCTAVIA STEVENS In 1864, the year ...
    Majorca in 1905, and Quebec Province in 1932, with interest mainly centred on the shadow bands of eclipse. Her conclusions on this subject can be seen ...
  26. [26]
    https://britastro.org/sites/default/files/C.O.Stevens.pdf
  27. [27]
    Newly Deciphered, 4,000-Year-Old Cuneiform Tablets Used Lunar ...
    Aug 9, 2024 · Newly Deciphered, 4,000-Year-Old Cuneiform Tablets Used Lunar Eclipses to Predict Major Events · Ancient Babylonians linked astronomical ...
  28. [28]
    https://opg.optica.org/ao/abstract.cfm?uri=ao-23-23-4390
  29. [29]
    Science/Nature | Sound 'cause of shadow spectacle' - BBC News
    May 21, 2008 · Stuart Eves thinks that demonstrating a role for infrasound might explain some other puzzling phenomena associated with eclipses. For ...Missing: 2001-2008 | Show results with:2001-2008
  30. [30]
    High-Altitude Studies of Shadow Bands During the 8 April 2024 ...
    Radiosonde measurements indicated that all high-altitude light sensor observations were above the turbulent planetary boundary layer. But none of our five high- ...
  31. [31]
    Modeling solar eclipse shadow bands using wave optics simulation through distributed turbulence
    ### Summary of Research on High-Speed Imaging and Simulations for Modeling Shadow Bands Patterns