What is a halo? The easy answer – rainbow around the sun. Rainbow, which creators are not drops of water (as usual rainbow), and the rainbow that is created by ice kristalikami. Watch this halo in the sky at any time of year, night and day. You need only a little care and a little luck. The nature of this phenomenon – the dispersion of light in ice crystals, in some cases together with the reflection (s) on the boundary of the crystals. But why is this happening? White sunlight (or light from a lamp) is composed of many colors (a rainbow is there to remember). And each color is refracted differently in the crystal, since for every color (and its corresponding wavelength) index refractive index is different. The scientific name for this phenomenon variance.
The textbooks of physics there is a picture where the Newton divided the beam of light at the rainbow – it’s the same phenomenon. When a ray of light passes through the ice crystal, it deviates from its initial direction by about 22 degrees. More specifically the red beam is deflected by 22 percent, and orange, yellow, green and blue a little further. Calculate the deviation can any student who knows the law Sneliusa (Act refraction, which tells how are the angles of incidence and refraction angles). Pass from one crystallite to the cloud. How is a circle in the sky? After all nemogut same crystals, which is in the clouds, hang and hang in a strictly certain position! In the clouds are so many small crystals, much smaller than snowflakes, about 0.1 mm.
Crystals floating, spinning, spinning. And at every moment some of them will be of the name as you would need to deflection of 22 degrees. Crystals are much more at this point so that deflect light at a greater angle. But at 22 degrees angle can deviate only red, but on the other hand, greater angle deflected all colors at once and again form white light. It turns out that a distance greater than 22 degrees from the sun the eye sees more light, and this whole area seems to be more vibrant. Therefore, only clearly visible red and orange color, and the rest as it blurred by haze, almost imperceptible. On the same diagram shows how the circle is formed. Light rays from the sun are parallel, meet on the way crystals and rejected. Interested? Read the theory of other halo here, and if you have any pictures – send them to me for publication on the blog, there by the way, a lot of pictures halo.