On numerous occasions, scientists have had great difficulty in explaining some meteorological phenomena that take place on our planet. Either according to its strange frequency or because of its operation. In this case we are going to talk about a phenomenon whose origin was slow to be explained by meteorological physicists. It is about the solar halo.
The solar halo is a luminous circle that sometimes forms around the Sun and can be seen from the Earth's surface. But how is it formed and in what situations? If you want to know more, keep reading.
How is a solar halo formed?
This phenomenon, which consists of a bright circle around the Sun, is known as a halo or anthelion . It mainly occurs in colder places like Russia, Antarctica, or northern Scandinavia. However, provided the right conditions for its formation are present, it can occur in other locations.
This halo is formed by ice particles suspended in the upper troposphere. When sunlight strikes these ice particles, it refracts the light , causing the entire spectrum of colors (similar to a rainbow) to be visible around the sun. We could call it a circular rainbow, characterized primarily by its iridescence.
For this phenomenon to occur in areas with typically lower temperatures, there must be a significant contrast between surface and high-altitude temperatures. A solar halo requires a sufficient number of ice crystals at higher altitudes to refract enough light to create a complete halo. This phenomenon will not be visible in areas with higher temperatures.
High temperature contrasts tend to occur in the early hours of the morning, where the air is colder as it has not had the Sun's heat source throughout the night. Therefore, this halo is most frequently seen in the early hours of the morning.
It is also necessary that the type of cloud present in the sky at that moment be cirrus clouds. These clouds are formed by small ice crystals that can cause the reflection and refraction of sunlight. To better understand the formation of a solar halo, you can consult the article on cirrus clouds.
High in the troposphere, sunlight strikes suspended ice crystals and fragments as they pass through. The hot air that rises from the earth's surface makes the humidity rise, giving rise to the formation of clouds. When the clouds reach the highest part of the troposphere, it converts that humidity into water crystals that, when receiving direct sunlight, decompose it to create the solar halo.
Features
Solar halos typically have an angle of approximately 22 degrees . When a solar halo occurs, if a person points their hand towards the sun, regardless of the angle from which they point, the halo will form an angle of 22 degrees.
Its inner edge tends to have the reddest color in the spectrum and its most common shape is that of a ring of light that borders the Sun. On some occasions you can see another halo that is caused by the ice crystals that are suspended around the sun. main halo with an angle of 46 degrees from the center of the Sun. There are also other types of light formations that resemble the solar halo. These are the so-called false suns or parahelios and can also be seen at 22 degrees with respect to the sun, both vertically and horizontally. These false suns are luminous images whose shape is very similar to the disk of the Sun.
Confusions when seeing a solar halo
Sometimes a solar halo can be confused with coronas that form on hazy days. Coronas, visible when thin clouds cover the sky, are caused by the diffraction of light as it passes through particles suspended in the atmosphere . In terms of their formation, these coronas are similar to rainbows and arcs of white or yellowish light. These arcs of white light form when there is fog. Sunlight strikes the fog bank, producing a luminous arc at an angle of 40 degrees from the center of the sun.
How can it be visualized?
The most common halo is formed by refraction processes in hexagonal ice . This shape allows more colors of the spectrum to be refracted.
As mentioned in other articles, such as the one on the Layers of the Atmosphere , as we increase altitude in the troposphere, the temperature decreases. Thus, in the upper part of the troposphere, temperatures are lower. So much so, that at almost 10 km altitude, the ambient temperature is -60 degrees Celsius. At these very low temperatures, the suspended water droplets are ice crystals that can refract sunlight and form a halo.
To properly view a solar halo and enjoy this unusual phenomenon, it's essential to avoid looking directly at the sun. Remember that looking directly at the sun can cause serious corneal damage and vision loss due to the high levels of solar radiation and UV rays that damage eye tissue. The best way to view this type of halo is to use a circular object to block the sun and allow you to fully appreciate the halo. You can also use eclipse glasses.
As you can see, numerous meteorological phenomena take place on our planet that, until not long ago, the reason for their formation was unknown. However, thanks to the discoveries granted by the scientific community, today we can enjoy meteorological phenomena such as the solar halo, knowing their origin and formation characteristics.
And you, have you ever seen a solar halo?
