Friday is here again, and with it the weekly "A Taste of Physics" column — number 49.
This week: halos, light refraction angles, and their connection to honeycombs.
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The video was filmed in Sweden and captures a fascinating natural phenomenon of multiple light halos.
A halo is a ring of light around a light source such as the Sun or the Moon, and it typically appears as a single ring.
In exceptional cases, different refraction angles of light produce a combination of additional optical effects, like the one shown in the video.
How does it work?
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Halos tend to form in cold regions such as northern countries, when cirrus clouds (feather clouds) drift across the sky.
These clouds are made of hexagonally shaped ice crystals, and when light rays pass through them, an interesting process takes place.
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When light passes through a material, it changes direction slightly — a phenomenon familiar to all of us from the appearance of a spoon submerged in a glass of water.
As light passes through hexagonal ice crystals, it can enter and exit through one of the six side faces, in which case the refraction angle is 22°, or it can exit through the top or bottom face, in which case the refraction angle is 46°.
Since a hexagon has 6 side faces but only 2 base faces, statistically most refractions within the crystals occur at an angle of 22° through the side faces.
When we look toward the Sun on such a day, all the crystals positioned in a circle 22° relative to the Sun deflect light toward our eyes equally, which is why we see the halo as a perfect circle.
A 46° halo may appear alongside the primary halo, but because the probability of 46° refraction is lower, this halo will be less pronounced than the primary one.
Different weather conditions scatter light in different ways, giving rise to other optical phenomena such as sun dogs or rainbows.
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Hexagons are a fascinating subject in their own right.
In this case we dealt with light refraction through hexagons, but the reason water molecules in clouds crystallize specifically into hexagonal shapes is that this arrangement is a particularly efficient way to organize matter.
Honeycombs, for example, are arranged in hexagons because space utilization is maximized, and the absence of straight edges — as found in squares — means that each hexagon is held in place by its neighbors.
Shabbat Shalom 😊
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