What causes halos?
We get many messages all year long from individuals who’ve simply noticed a big ring or circle of sunshine across the sun or moon. Scientists name them 22-degree halos. They bear this title as a result of the radius of the circle across the sun or moon is roughly 22 degrees.
There’s an outdated climate saying: ring across the moon means rain quickly. There’s reality to this saying, as a result of excessive cirrus clouds usually come earlier than a storm. Discover in these photographs that the sky appears pretty clear. In spite of everything, you may see the sun or moon. And but halos are an indication of excessive, skinny cirrus clouds drifting 20,000 ft (6 km) or extra above our heads.
These clouds comprise tens of millions of tiny ice crystals. The halos you see are brought on by each refraction, or splitting of sunshine, and likewise by reflection, or glints of sunshine from these ice crystals. The crystals should be oriented and positioned simply so with respect to your eye, for the halo to look.
That’s why, like rainbows, halos across the sun – or moon – are private. Everybody sees their very own distinctive halo, made by the ice crystals from their viewpoint. So they’re completely different from the ice crystals making the halo of an individual standing subsequent to you.
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A phrase of warning when taking solar halos
Take care when photographing solar halos. Pointing a digital camera immediately on the unobscured sun can harm it. By no means look immediately on the sun, even when it’s seen by means of clouds.
Are halos extra frequent at excessive latitudes?
We requested Les Cowley of the web site Atmospheric Optics if halos across the sun and moon are extra ceaselessly seen at excessive latitudes and fewer generally seen nearer to the equator. He mentioned:
That’s a superb query that isn’t straightforward to reply precisely as a result of no halo frequency statistics are collected besides in a single or two mid-latitude European international locations.
We have to distinguish between (a) halos shaped by low degree diamond dust throughout very chilly climate and (b) halos shaped by ice crystals in excessive cirrus cloud.
Clearly (a) halos solely happen in polar areas or international locations with very chilly winters (Canada for instance shouldn’t be excessive latitude).
(b) Halos can happen anyplace on the planet throughout winter or summer time. Their frequency is dependent upon the frequency of cirrus protection and whether or not it has had a historical past such that it accommodates halo forming crystals. The latter is tough to foretell. For instance, there are main variations in halo frequencies and kinds of halos throughout even 200 miles [300 km] within the U.Ok.
When you see a halo, discover this!
As a result of moonlight isn’t very shiny, lunar halos are largely colorless. Nevertheless, you may discover purple on the within and blue on the skin of the halo. These colours are extra noticeable in halos across the sun. When you do see a halo across the moon or sun, discover that the internal edge is sharp, whereas the periphery is extra diffuse. Additionally, discover that the sky surrounding the halo is darker than the remainder of the sky.
Some halo photographs
And extra halo photographs
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Backside line: Excessive, skinny cirrus clouds drifting excessive above your head create the halos you see across the sun or moon. The halos are from tiny ice crystals in Earth’s environment. They do it by refracting and reflecting the sunshine. Lunar halos are indicators that storms are close by.
