Half-sky auroras - 25.1.2022 at 18.00 - 26.1.2022 at 00.00 Liminka Observation number 104292

ARC The arcs are wider than the bands and do not fold as strongly. The arcs are normally neither very bright nor active.

The arc is probably the most common form of aurora. When aurora show is a calm arc in the low northern sky it often doesn’t evolve to anything more during night. In more active shows the arc is often the first form to appear and the last to disappear.

The lower edge of the arc is usually sharp but the upper edge can gradually blend into the background sky. As activity increases rays and folds normally develop, and the arcs turn gradually into bands.

An aurora arc runs across the picture. Vertical shapes are rays. Photo by Atacan Ergin.

Aurora Arc. Photo by Mauri Korpi.

Aurora Arc. Photo by Anna-Liisa Sarajärvi.

Aurora Arc. Photo by Matti Asumalahti.

The raysare parallel to the lines of force of the magnetic field, i.e. quite vertical, usually less than one degree thick light streaks. The rays can occur alone or in connection with other shapes, mainly with arcs and bands. Short rays are usually brightest at the bottom but dim quickly. The longest rays, even extending almost from the horizon to the zenith, are usually uniformly bright and quite calm, and unlike the shorter rays, most often occur in groups of a few rays or alone. Rays, like bands, are a very typical form of aurora.

Artificial light pillars, which are a halo phenomenon visible in ice mist, can sometimes be very similar to the rays of aurora. Confusion is possible especially when the lamps that cause the artificial light pillars are far away and not visible behind buildings or the forest. The nature of the phenomenon is clear at least from the photographs.

Rays. Picture of Tom Eklund.

Rays. Photo by Mika Puurula.

Two beams rise from the aurora veil. Photo by Anssi Mäntylä.

Two radial bands. Show Jani Lauanne.

Radial band and veil. Photo by Jussi Alanenpää.

Two rays. Photo by Aki Taavitsainen.

It may be possible to confuse such rays with artificial light columns. Compare the image below. Picture of Tom Eklund.

There is no aurora in this image, but all the light poles - including the wide and diffuse bar seen at the top left - are artificial light pillars born of ice mist. Photo by Sami Jumppanen.

Aurora and artificial light pillars. All the radial shapes in the picture above are probably artificial light pillars that coincide appropriately with the aurora band. In the image below, the aurora band has shifted and does not overlap with the pillars produced by the orange bulbs. There is no orange in auroras. Photo by Katariina Roiha

Dunes

The dunes are a dim and very rare shape that has so far been associated with the aurora visible in early evening.

Aurora dunes can be most easily confused to ribbons on lower clouds. In order to fill in the description of the phenomenon, a striped pattern formed by parallel lines must also appear in the aurora. The stripes are most easily recognizable right at the front edge of the aurora but they may also occur among the rest of the aurora.

The dune auroras are visible as a parallel striped float. Photo by Tapio Terenius

Raidallisen dyynilautan reunassa voi toisinaan olla voimakastakin aaltoilua.

There can sometimes be strong ripples at the edge of a striped dune float. The rippling of the edge of the dune float can vary from minor to large (pictured). Photo by Pirjo Koski

Green, seen with the naked eye, is one the most common colors of the aurora. The green color is derived from atomic oxygen.

Green auroras. Lea Rahtu-Korpela.

Green auroras. Photo by Juha Ojanperä.

Auroras which have red top part that can be seen with naked eye are most often observed in the bands and long rays. In this case the lower parts are usually green. If the upper parts are in sunlight, red may be stronger than green. This shade of red is due to the discharge of the excitation state of the atomic oxygen.

Aurora that shift to reddish towards the top. Photo by Karri Pasanen. 

Red top in a aurora band. Photo by Simo Aikioniemi.

Red at the top of the aurora. Picture of Tom Eklund.

Clearly blue auroras can be seen only during the best aurora displays close to the maximum phase or soon after it. Sometimes blue auroras can be seen shortly after the sunset at the top part of the auroral shapes, specially rays. It is created by the mission of the ionized nitrogen molecules created by the suns radiation.

Strongly colored blue auroras. Photo by Jorma Mäntylä.

Blue top parts of the aurora. Image by Tom Eklund. 

Blue top parts of the aurora. Image by Jaakko Hatanpää.

Partly blue corona. Photo by Tapio Koski.

Faintly blue top parts of an aurora veil. Photo by Jaakko Hatanpää.

Usually in Lapland or even in the south you can see purple auroras in stronger aurora shows. The most common color in auroras along with green and red.