Quiet aurora arc - 24.9.2017 at 23.35 - 25.9.2017 at 00.05 Mäntsälä, Ohkola Observation number 67180

Visibility II / V

Teppo Laitinen, Keski-Uudenmaan Altair

The telescope photographed the subject on the edge of the field when I noticed inside the computer screen that a change was beginning to take place in the histochrome.

At first I thought the reason was fog, but I went to check it out and the reason was revealed by the northern lights.

This description has been automatically translated from Finnish. Click here to see the original text.

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Additional information

Aurora brightness
- Dim auroras
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.
- 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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Quiet aurora arc - 24.9.2017 at 23.35 - 25.9.2017 at 00.05 Mäntsälä, Ohkola Observation number 67180