(ORDO NEWS) — In February, according to forecasts of the Hydrometeorological Center, frosts await Central Russia. This means more chances to see such unusual atmospheric phenomena as halos, false suns and light pillars. When the air is saturated with ice crystals, they act like glasses, refracting or reflecting light on their facets. What happens from this depends on the shape of the crystals, their orientation in relation to the ground and the location of the light source.
Freezing, water droplets in the air turn into a crystalline form: the molecules line up in groups of six, so ice crystals are almost always hexagonal or hexagonal. The lower the thermometer, the larger the crystals. At minus 20, snowflakes-plates form in the clouds. If the temperature drops even lower, oblong pencil snowflakes are already flying in the air.
A bright halo around the sun, moon, as well as some stars, planets, lanterns and searchlights can be observed at any time of the day or night. To do this, there must be a layer of ice dust between the luminary and the observer. For example, when there are not very dense cirrus clouds in the sky (with dense ones we will see only a slight glow). Unlike cumulus clouds, which are saturated with water vapor, cirrus clouds are icy. The halo can be seen in summer, but in winter it looks spectacular.
For a halo to form, the water in the cloud must be in the form of a prism. Passing through each piece of ice, the light is refracted, that is, it goes on no longer straight, but at an angle. Because of this, it seems to us that there are others around the main light source. When there are a lot of crystals and they are arranged randomly, an even luminous circle is obtained. And sometimes not alone. In rare cases, complex patterns appear in the sky from circles strung on top of each other. But a single halo can also be mesmerizing, especially when it sparkles with different colors.
When a light beam passes through an ice crystal, the light is not only refracted, but also breaks up into different colors. The same thing happens with a drop of water – that’s why we see a rainbow after rain or near a waterfall. But ice crystals are a denser medium than drops of pure water. Because of this, most of the colors of the spectrum are absorbed, and we only see red and yellow. The larger the crystals, the more regular they are, the brighter the circle glows. When the crystals are small and randomly arranged, the colors mix and the circle turns white.
The conditions for the appearance of a halo often develop in winter during the transition from clear frosty weather to warmer and more humid. The air is still quite cold, but thin cirrus clouds are already covering the sky. Beyond the Arctic Circle, where “diamond” dust from ice crystals is constantly present in the air, the halo can be observed more often.
Parhelia or false suns
These are also members of the “halo family”, but they will have to be seriously hunted. They look like bright light spots on the sides of the sun, often uneven in shape. They can be seen at sunset or sunrise when the sun is still close to the ground. As ice crystals approach the surface, they tend to line up in the same direction—vertically down—to overcome air resistance. The thicker the cloud of crystals, the more powerful the flow of refracted light. This flow forms solar twins on the sides.
Why are parhelia rarer than halos? This is because the air is warmer closer to the ground. And for the formation of large crystals near the surface, tens of degrees of frost are needed. Such “gifts” usually bring with them anticyclones with cold frosty weather. More often they are observed in the North – in St. Petersburg, Petrozavodsk, Murmansk or Finland. Approximately once a year or several years, it may also appear to the south (for example, in Moscow or Tver). But there, as a rule, parhelia are more faded.
Often parhelia can be seen at the intersection of two halos – vertical and horizontal. The horizontal halo is called the parhelic circle. It is very rare to see it in its entirety. This phenomenon occurs when light bounces off the vertical edges of ice crystals, which are almost evenly distributed across the sky.
Sunlight is too bright for the eyes – although it seems to be softer in diffused form. Therefore, it is better to observe the halo in sunglasses. It is wiser to choose high-quality glasses with a high level of UV protection.
Looking at the halo, it is best to cover the sun with some object or, for example, with a palm. The same should be done when photographing this phenomenon. Otherwise, the image may not be clear enough.
At night during the full moon, you can observe false moons – parselens. They, too, are colored reddish, although it is difficult to see with the eye. The light of the moon is much dimmer – it is not enough to excite the cones – the cells of the retina that are sensitive to color. The ideal conditions for parselena are a clear and frosty night.
This is also a halo, but very unusual and not so widespread. It is formed when a light beam falls on the top or bottom of the crystal, and exits through one of the side faces. When refracted, the light is distributed into a spectrum, as in an ordinary rainbow – a bright multi-colored band is obtained. But in order to see it, several conditions must coincide at once.
Ice crystals should be relatively flat, not elongated, horizontal, and the sun should be high enough in the sky (at least 58 degrees above the horizon). North of 55 degrees north latitude (and this is, for example, Moscow) or south of 55 degrees south latitude you will not see it: the sun does not rise so high here.
For a fiery rainbow, it is better to go to the mountains. Due to the fact that the rays have to travel a fairly long path inside the ice, the dispersion very strongly separates the white beam into color components, and the clouds really begin to blaze with all the colors of the spectrum.
Sometimes at dawn or sunset you can see an elongated solar path above the horizon – as if the sky were the smooth surface of a transparent lake. When the sun is low, and flat ice crystals are slowly falling in the sky above the earth, light is reflected from them, as from the surface of the water. At sunset, the sun turns yellow, orange, or red, and the pole takes on the same hue.
The light column is best seen when the sun is slightly hidden behind the horizon, a house or a tree and does not illuminate the view. Sometimes at night in the city or near it, you can even observe a whole light forest – due to the fact that the light is reflected from the lanterns and other light sources. Such a “forest” is often multi-colored due to the different colors of the lamps – bluish from mercury, yellow from sodium and green from neon.
To see such a phenomenon, it is better to dress warmly – the temperature should not be higher than minus 20 degrees. Most often it is observed in the northern countries – Finland, Norway, Sweden – or in Siberia and the Far North.
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