The refraction of sunlight in the atmosphere gives rise to many optical illusions that can be observed from Earth with the naked eye. One of the most spectacular phenomena of this kind is the solar halo. This phenomenon has many varieties, each of which is beautiful in its own way. But for the appearance of any kind of this optical illusion, a certain set of conditions is required.
The causes of the solar halo
So what is a solar halo and why does it appear? First, let's answer the first question. Essentially, a halo is a rainbow around the sun. However, it differs from the usual rainbow both in appearance and in its characteristics.
A halo appears in the sky when several factors combine. It is most often observed in frosty weather in conditions of high humidity. There are a lot of ice crystals in the air. Passing through them, sunlight is refracted in a special way, forming an arc around the Sun.
Halos should not be confused with "sun crowns". The latter are areas of hazy glow located around the sun, moon, or other bright light sources such as street lamps and spotlights.
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The difference between a solar halo and a rainbow
Despite some external resemblance to the rainbow, the solar halo has a number of differences from it. The first of these is that a rainbow is usually observed with its back to the luminary. And the halo occurs only around the Sun, with the exception of a few extremely rare varieties.
In a rainbow, most often you can see the entire spectrum of colors, from red to purple. The solar halo is usually colored only in red and orange tones. The rest of the spectrum colors are mixed with each other and therefore appear white. However, it is very rare to observe a halo in which all the colors of the spectrum differ. This is a very spectacular sight.
In the rainbow, the red spectrum is located on the outside (far from the horizon). In the halo, it is located as close as possible to the center, that is, to the Sun.
The main difference between a rainbow and a halo is that we see a rainbow as a result of light refraction in water droplets. These droplets always look and behave the same in the atmosphere; only their sizes can differ. Ice crystals, in which the light of the Sun is refracted during the observation of the halo, is a completely different matter. They come in many different shapes and sizes. And crystals can move in completely different ways - soar calmly, fall down, rotate, etc. The result is a variety of solar halo types.
Varieties of the solar halo
So, we learned what a solar halo is, and what are the reasons for its appearance. Now let's look at its main types.
The solar halo differs in its position in the sky relative to the Sun. Most often, you can observe halos located close to the luminary - the so-called 22-degree halos. Less common are halos located at an angle of 46 degrees or more in relation to the Sun, and the rarest are its varieties, which occupy the entire sky.
According to their color, halos are divided into white (light, colorless), red-orange and full spectrum. The most common 22-degree halos are usually only red, orange, and white. Halos can be located not only vertically, but also horizontally. They are called subhalos.
People's attitude to halos
In the past, this phenomenon has sown fear and panic among people. Due to the insufficient development of science, people did not know that an optical illusion was opening up to their eyes, and they considered the halo an unkind sign, especially if it was accompanied by parhelia (light spots that outwardly resemble the Sun and are located next to it).
Sometimes the appearance of a halo became the reason for making important political decisions. One of the most striking examples is the refusal of Emperor Charles V from the siege of Magdeburg in 1551. Seeing a halo with false suns over the city, he considered it a symbol of the heavenly protection of the besieged.
How to look at the solar halo correctly
Halo is an unusual optical phenomenon that always attracts people's attention. But in order to enjoy its beauty without unpleasant consequences, you need not only to know what a solar halo is, but also to understand what danger it poses to the organs of vision. Sunlight refracted in ice crystals is too bright for our eyes. Therefore, it is best to watch the halo in sunglasses. It is wiser to use for this (as well as for being in the sun in any other conditions) high-quality glasses with a high level of protection against UV radiation. Looking at the halo, it is best to cover the sun with an object or, for example, a palm. The same should be done when photographing this phenomenon. Otherwise, the image may not be clear enough.