All-sky aurora - 16.2.2015 at 23.00 Keitele Observation number 33658

• Aurora brightness
• • Very bright auroras
• Colors with unaided eye and other features
• • Streaming auroras

    Streaming. In streaming aurora fast irregular variations in brightness occur along the horizontal dimension of homogeneous shapes.

  • Flaming auroras

    Flaming. This rare subclass of aurora does not mean so much a single shape, but a large area in the sky. In the flaming aurora, bright waves that are sweeping upward towards the magnetic zenith emerge in the sky. Very rarely waves can wipe downwards. Bands are usually reported during flaming, less often spots.

  • Blue auroras

    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.

  • Fully red auroras

    Completely dark red aurora is a very rare and strikingly handsome revelation. This phenomenon is also due to the discharge of an excitation state of an atomic oxygen.

    Throughout red aurora. Photo by Tobias Billings.

  • Red coloration of the shapes top

    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.

  • Green auroras

    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.

• Observed aurora forms
• • Band

    Bands are usually narrower, more twisty at the bottom, brighter, and more active than arches. Bands usually develop from arches.

    Bands can form J and U shapes, sometimes even full spirals. The corona can also arise from bands. Bands are a fairly common form of aurora.

    Aurora band. Photo by Merja Ruotsalainen.

    Aurora band. Photo by Matias Takala.

    Aurora band. Photo by Lea Rahtu-Korpela.

    Aurora bands. Photo by Lauri Koivuluoma.

    Aurora band. Photo by Matias Takala.

  • Corona

    CoronaA corona is a hand fan shaped structure, it usually forms south of the observer's zenith, most commonly consisting of rays or bands. The corona is usually the most beautiful part of the aurora show. It is bright and active, but on the other hand also short-lived.

    Aurora corona. Photo by Anna-Liisa Sarajärvi.

    Aurora corona. Photo by Merja Ruotsalainen.

    Corona formed from bands. Photo by Markku Ruonala.

    Aurora corona. Photo by Tapio Koski.

  • Arc

    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.

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