Among the more spectacular visual phenomena in the sky are undoubtedly halos and the polar_lights. Polar lights are formed at great heights in the atmosphere, up to 1000 kilometers.
They can be mainly seen over the polar region in the northern and southern hemisphere. They occur in the form of flames, clouds, threads, arcs or bands. Their colors vary a great deal. The intensity and brightness of the polar lights are dependent on the level of solar activity ( sunspot_cycle ).
The cause of the polar lights is energy-rich solar radiation, which occurs especially during solar eruptions. Electrically charged particles are carried by the solar_wind into theVan-Allen-Belt, where there is an overflow of charge.
The particles are discharged into the atmosphere and there, collide with gas molecules, which are then stimulated into emitting light. Polar lights are concomitant with strong variations in the terrestrial magnetic_field. They may cause interference in radio and telephone transmissions.
A halo is formed when the light is refracted by ice crystals in the atmosphere. The crystals must then be located between the Sun or the Moon and the observer. The halo usually appears as a ring that surrounds the Sun or Moon in colored light.
This light, which originates from the Sun or the Moon, is refracted at an angle of exactly 22 degrees to the observer. Sometimes a second halo is also displayed next to the first. Sometimes, there are also phenomena that appear like a second solar disc. Halos are dissimilar to coronas, which are the result of the dispersion of light in water particles in the atmosphere. They look more like rainbows.
