Quiet aurora arc - 13.9.2018 at 21.30 Akaa Observation number 77606

Visibility II / V

Markku Ruonala

For three hours, the repo arc remained low in the northern sky. Green did not separate

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Additional information

Aurora brightness
- Very dim 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.

Colors with unaided eye and other features
- White auroras
  
  Paljain silmin valkoinen väri näkyy useimmiten himmeissä näytelmissä, kun silmä ei kykene erottamaan mitään varsinaista väriä. Harvoin kirkkaissa näytelmissä valkoinen väri voi myös syntyä sopivista vihreän, punaisen ja sinisen yhdistelmistä.

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Quiet aurora arc - 13.9.2018 at 21.30 Akaa Observation number 77606