Rengasmaisuus

Rengasmaisuus is a term originating from Finnish that describes a specific type of atmospheric optical phenomenon. It translates roughly to "ring-like appearance" or "annularity." This phenomenon is characterized by the appearance of a circular or ring-like halo around a celestial object, most commonly the sun or moon. While it can refer to various atmospheric effects, it is most frequently associated with the appearance of a solar eclipse in its annular phase.

During an annular solar eclipse, the Moon passes directly between the Sun and Earth, but is too far away from Earth to completely block the Sun's view. This results in the Moon appearing smaller than the Sun, creating a bright ring of sunlight around the dark silhouette of the Moon. This distinct ring of light is the primary visual characteristic of rengasmaisuus in this context.

The term can also be used more broadly to describe other visual effects where a circular halo is observed. For example, certain types of halos or arcs formed by ice crystals in the atmosphere, such as circumzenithal or circumhorizontal arcs, might be referred to as rengasmaisuus if they create a prominent ring shape. However, its most precise and widely understood application pertains to the annular phase of solar eclipses. The observation of rengasmaisuus therefore offers a visual cue for specific astronomical events or atmospheric conditions.