Bundle of rays

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Cloud rays caused by Saharan dust in the atmosphere

Clusters of rays or light clusters are a phenomenon of atmospheric optics that is caused by the obscuration of the sun by atmospheric cloudiness. In most cases, the phenomenon is observed in clouds , which is why one speaks of cloud rays. If the sun is very low, the effect can also extend over the entire sky, which is then referred to as twilight rays . These should not be confused with pillars of light . If you have the sun behind you, then under favorable circumstances you can see the counter-dawn rays at the opposite point of the sun .

Origin

Beams of rays as seen from the ISS. The almost parallel lines can be seen, in contrast to the distortion effect that is visible on the earth's surface.

The direct solar radiation is blocked by the clouds and seems to appear at their edges. Water and dust particles in the air - the aerosols - scatter these rays at a small angle and thereby direct them into the observer's eye. The rays stand out from the cloud shadow and only then emerge visibly, which is also known as the Tyndall effect .

The same effect can be seen, for example, with a film projector, which makes the dust particles in a room visible, or with car headlights when driving through fog . It is therefore particularly evident when the sun is low, because the aerosol concentration is then highest, and the brightness contrasts are also most evident at dusk .

Due to the effect of the falling lines , one perceives the actually parallel sun rays in a distorted manner. It appears as if these are spreading radially around the sun. Iridescence often occurs at the edges of the clouds .

Another effect occurs when the light penetrates through small gaps in the cloud. The sun's rays now seem to spread conically upwards or downwards, as the pictures below illustrate.

gallery

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  Beams of rays in Taipei , Taiwan (2018).

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  Rays of clouds over a fjord in Norway

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  Fog bank with bundles of rays

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  Clusters of rays at hot spring in Yellowstone National Park

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  Beams of rays at sunset on the Waterberg plateau

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  Twilight rays at the edge of a sea of ​​fog off San Francisco

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  Sunrise in the Namib near Sossusvlei (2017)

Individual evidence

1. ^ John A. Day: The Book of Clouds . Sterling, 2005, ISBN 978-1-4027-2813-6 , pp. 124–127 ( limited preview in Google Book Search [accessed October 9, 2010]).
2. ^ Crepuscular Rays, India . In: Earth Observatory . NASA. Retrieved May 7, 2018.
3. ↑ Crepuscular Rays . In: Weather World 2010 . University of Illinois, Champaign-Urbana.,
   Vincent J. Schaefer, John A. Day, Jay Pasachoff: A Field Guide to the Atmosphere . Houghton Mifflin Harcourt, 1998, p. 169. ,
   Crepuscular Rays, India . In: Earth Observatory . NASA. Retrieved May 7, 2018.

Web links

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