What is this phenomenon
The bright glowing ring that forms around the night luminary, or a lunar halo (from the Greek «halos»: circle, aureole) – is an incredibly beautiful sight. To see this natural phenomenon with your own eyes – is a great stroke of luck, since it happens infrequently. A halo can be observed in the sky for anywhere from a few minutes to hours. But most often it lasts a very short time.
Wonders or the laws of physics?
In ancient times the halo, like everything inexplicable, filled people with awe, and many superstitions and myths are associated with it. In reality, the causes of this colorful phenomenon are quite simple. Like a rainbow, it forms as a result of the interaction of light with water.
Moonbeams penetrate cirrus clouds located at an altitude of about 6 km. The air there is very cold, and the water droplets freeze, turning into ice crystals. Striking them, the light is reflected and changes its direction. Each crystal – is a tiny six-sided prism. In a lunar halo, all of them have a slightly elongated shape resembling a pencil and are oriented in the air in a chaotic manner.
A ray enters through one face of the prism, is refracted, and exits through another. As a result, in each crystal a small ray is formed that is deflected by 22 degrees from the direction of the light source. To the human eye, the totality of such rays looks like a white glowing circle, at the center of which is the Moon.
Depending on the number of crystals and on their arrangement in the cloud, the aureole can become brighter or paler. Like a rainbow, it shines with different colors, but because of the dim lunar light and the features of our vision, we do not notice this.
When and where you can see a lunar halo
Rings around the Moon can appear in any part of the planet and at any time of year, if the right conditions are created. Some Russian cities where this phenomenon has recently been observed: St. Petersburg, Anapa, Yekaterinburg, Samara.
It can most often be observed during:
- Severe frost
- Increased humidity
- During a full moon
The essential conditions, without which a halo will not appear:
- The presence of a thin, semi-transparent layer of cirrus clouds at an altitude of 5 to 10 km above the ground
- A clear sky (since dense clouds located at lower levels would simply hide all the beauty)
The halo phenomenon can occur around the Moon, the Sun, and even near such bright light sources as street lamps or lighthouses – in low air temperatures and the appearance of fog consisting of tiny ice needles. Sometimes, with a lunar halo, not only circles form but also glowing spots, light pillars, diamond dust (the tiniest ice crystals floating in the air close to the Earth’s surface), and many other varieties of this amazing natural phenomenon.
Folk omens
In ancient times people feared the halo as a harbinger of great calamities and troubles: earthquakes, floods, bloody wars. And the weather was also predicted by it: it was believed that if you saw a lunar aureole – you should expect imminent snow or rain. These forecasts often came true, for cirrus clouds, without which a halo does not occur, really are the first sign of an approaching warm front. And precipitation may fall within 24 hours after the glowing rings appear. But one should not put too much faith in ancient superstitions. Above all, a halo – is yet another of the wondrous phenomena with which our mysterious universe never ceases to amaze.
