Shadow bands are thin, wavy lines of alternating light and dark that can be seen moving and undulating in parallel on plain-coloured surfaces immediately before and after a

total solar eclipse A solar eclipse occurs when the Moon passes between Earth and the Sun, thereby obscuring the view of the Sun from a small part of the Earth, totally or partially. Such an alignment occurs during an eclipse season, approximately every six month ...

. They are caused by the refraction by Earth's atmospheric turbulence of the solar crescent as it thins to a narrow slit, which increasingly collimates the light reaching Earth in the minute just before and after totality. The shadows' detailed structure is due to random patterns of fine air

turbulence In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...

that refract the collimated sunlight arriving from the narrow eclipse crescent. The bands' rapid sliding motion is due to shifting air currents combined with the angular motion of the sun projecting through higher altitudes. The degree of collimation in the light gradually increases as the crescent thins, until the solar disk is completely covered and the eclipse is total. Stars twinkle for the same reason. They are so far from Earth that they appear as point sources of light easily disturbed by Earth's atmospheric turbulence which acts like lenses and prisms diverting the light's path. Viewed toward the collimated light of a star, the shadows bands from atmospheric refraction pass over the eye.

History

* In the 9th century CE, shadow bands during a total solar eclipse were described for the first time – in the

Völuspá ''Vǫluspá'' (also ''Völuspá'', ''Vǫlospá'' or ''Vǫluspǫ́''; Old Norse: 'Prophecy of the völva, a seeress'; reconstructed Old Norse: ) is the best known poem of the ''Poetic Edda''. It tells the story of the creation of the world and ...

, part of the old Icelandic

poetic edda The ''Poetic Edda'' is the modern name for an untitled collection of Old Norse anonymous narrative poems, which is distinct from the ''Prose Edda'' written by Snorri Sturluson. Several versions exist, all primarily of text from the Icelandic med ...

. * In 1820,

Hermann Goldschmidt Hermann Mayer Salomon Goldschmidt (June 17, 1802 – August 30 or September 10 1866) was a German-French astronomer and painter who spent much of his life in France. He started out as a painter, but after attending a lecture by the famous Fren ...

of Germany noted shadow bands visible just before and after totality at some eclipses. * In 1842, George B. Airy, the English astronomer royal, saw his first

total eclipse of the sun ''Total Eclipse of the Sun'' is a 1999 EP released by the German experimental/industrial band Einstürzende Neubauten. It was their first release recorded with their new line-up featuring Jochen Arbeit and Rudi Moser (formerly of Die Haut) and w ...

. He recalled shadow bands as one of the highlights: "As the totality approached, a strange fluctuation of light was seen upon the walls and the ground, so striking that in some places children ran after it and tried to catch it with their hands." * In 1905, Catherine Octavia Stevens observed shadow bands at the start of the total eclipse of August 30 at Cas Català,

Majorca Mallorca, or Majorca, is the largest island in the Balearic Islands, which are part of Spain and located in the Mediterranean. The capital of the island, Palma, is also the capital of the autonomous community of the Balearic Islands. The Bale ...

. "As to the character of their appearance and mode of progression, it was observed that they swept along with a flight that was at once rapid and orderly, there was no confusion of the wavy lines with one another, but all bore along in one and the same direction in parallel formation, traversing the ground as water-wave reflections may be seen to do on the under surface of a boat, only that there seemed in the case of the shadow-bands to be a more distinct expression of a forward movement." Clouds prevent observations after totality. * In 2008, British astrophysicist Stuart Eves speculated that shadow bands might be an effect of

infrasound Infrasound, sometimes referred to as low status sound, describes sound waves with a frequency below the lower limit of human audibility (generally 20 Hz). Hearing becomes gradually less sensitive as frequency decreases, so for humans to perce ...

, which involves the shadow of the moon travelling at supersonic speed and inducing an atmospheric shock wave. However, astronomy professor Barrie Jones, an expert on shadow bands, stated, "The cceptedtheory works; there's no need to seek an alternative."

References

{{reflist Light Solar eclipses