Active aurora band - 7.3.2017 at 22.20 - 7.3.2017 at 22.50 Kuusamo Observation number 61808

• Aurora brightness
• • Bright auroras
• Observed aurora forms
• • 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.

  • 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.

• Colors with unaided eye and other features
• • Red coloration of the shapes lower edge

    Red lower edge visible with the naked eye. The bands which are starting to level up their activity and are green colored have quite often a narrow red lower edge. This is the most common form of red color which is derived from molecular nitrogen.

    Aurora band with purple lower edge. Photo by Ilmo Kemppainen.

    The low hanging brightest aurora band is colored red at the lower edge. Photo by Tero Ohranen.

    Narrow purple reddish tones at the lower part of this aurora band. Photo by Merja Ruotsalainen.

    Purple band at the bottom. Photo by Panu Lahtinen.

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