18.02.11.Ustanovivshiesya in St. Petersburg frosts have enabled citizens to witness the rare atmospheric phenomena. On Thursday, the sky could be seen the so-called halo.
Halo — an optical phenomenon, illuminated ring around the light source (the sun, the moon, street lights). Ice crystals in cirrus clouds in the lower atmosphere at an altitude of 5-10 km reflect and refract light, which causes the appearance of atmospheric phenomena. Sometimes in cold weather halos formed crystals is very close to the surface. In this case, the crystals resemble sparkling gemstones.
These phenomena are not rare, so on Wednesday morning, residents of the Moscow region saw a rainbow, and a day — "mock sun". "Mock sun", or sun dog — is a special case of the halo phenomenon, which is not seen full or bright rainbow ring around the sun or moon, and a vertical rainbow (or light) pole on the light level.
"The advent of optical phenomena, first of all, depends on the state of the atmosphere: its density, temperature, and humidity as well as the position of the sun and the location of the observer. Some combination of these factors gives a beautiful optical phenomena. Any changes to these settings can strengthen or weaken the effect, "- said the weatherman.