A kind of optical phenomenon in nature, which is caused by the fact that the light of the sun or the moon passes through high and thin white clouds（Cirrus cloud, cirrostratus clouds or cirrocumulus clouds), which are refracted by ice crystals and form a colored aperture, and the color sequence is infrared purple.The aperture appearing around the sun is called the halo, and the aperture appearing around the moon is called the halo.The halo appears at night[1]。
The halo is the light passing through the skycirrostratusUnder the refraction of ice crystals, the seven color composite light is dispersed into an inner infrared purple halo or light arc, which generates an aperture around the moon, the same principle as the rainbow.These 'halos' are actually cirrostratus clouds, which means that when cold air meets warm wet air, it will form clouds that will rain. At this time, the sky is very cold, and water droplets have frozen into hexagonal ice crystals. When the moonlight shines on these ice crystals at night, it will form a halo.The moon halo was calledMao Moon, also known asWind circle。
Halo can be divided into "small halo" and "big halo", "small halo" means 22 degree halo, and "big halo" means 46 degree halo.Small halo is a kind of halo whose inner circle is light red and the outer circle is occasionally purple or white. The sky inside the halo is obviously darker than that outside the halo, while the big halo is a halo with an angle radius of 46 degrees, which is very rare and generally darker than the small halo.
The halo is usually circular or arc-shaped, with seven colors of red, orange, yellow, green, blue, indigo, and purple. The halo color is generally internal infrared purple, forming a color halo, and sometimes silver white halo.
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lunar halo
The appearance of the sun halo or the moon halo often indicates that the weather will change to a certain extent.Before the weather changed, we sometimes saw one or even more than two colored or white apertures around the moon, and the sun and moon seemed to dim a lot.Generally, the sun halo indicates that it is likely to rain, while the moon halo indicates that it will be windy. Sometimes the moon halo will have a gap, and the direction of the gap is the direction of the wind.Therefore, there are folk proverbs: "It rains at the third watch when the sun is shining, and the wind blows at noon when the moon is shining" and“The moon faints and the wind blows, the foundation is moist and the rain falls”。
The cirrostratus itself does not produce rain, but the middle and low clouds with a lot of water behind it may rain, so we can say that "it will rain at the third watch of the solar halo, and it will be windy at noon of the lunar halo". The appearance of "halo" indicates that it will be windy and rainy soon.Is it certain that it will be windy and rainy if 'dizzy' occurs?Not necessarily. Whether it's windy or rainy depends on how the middle and low level clouds behind the cirrus clouds develop[1]If they continue to develop,cloudinessIncrease,a bank of cloudsIf it thickens, it will be windy and rainy.Whether the 'halo' lasts for several days or a short-lived 'halo', we should see the development speed of medium and low clouds after the 'halo': medium and low clouds develop and move in quickly, and precipitation comes quickly;If the development and migration are slow, the precipitation will come too late;If it does not move in, there will be no precipitation.
