Halo and corona
We would like to turn our attention to two interesting types of light apparitions around the Moon: halos and coronas. Both are optical phenomena in the atmosphere that, if looked at from a physical point of view, come about in different ways and also look dissimilar.
A halo (left picture) develops through refracting ice crystals and creates a clearly defined light ring around the Sun or the Moon, whereas the surface between the celestial body and the ring, almost appears to be empty. Light spots, light arches and pillars can also emerge.
The rings have mostly a size of 22° or 46°, which correlates with the hexagonal shape of ice crystals. The ice crystals are located in high levels of the atmosphere, hence are always present. In winter and with snowy and icy surroundings, the probability of halos being formed is reinforced.
A corona (right picture) however, is created when the light of the Sun or the Moon, is diffracted on small drops of water in the clouds, so by diffraction of the light and not refraction. A whitish disc with a coloured rim becomes visible. The corona is often interpreted as harbinger of bad weather (which can be correct in connection with the present clouds). Coronas are always affiliated with clouds that can only be as dense as to allow the light to shine through them.
As well coronas as halos can be better observed at the full moon than at any other lunar phases, due to the larger amount of light, which does not mean that they only develop or can only be seen at the full moon.
The light apparitions around the Moon are always fascinating to watch for people. Especially in the dark, a halo looks almost like a nimbus and therefore appears particularly sublime.