Quiet aurora arc - 4.9.2021 at 22.30 - 4.9.2021 at 23.10 Ulvila Observation number 101073

Visibility II / V

Juha Ojanperä, Porin Karhunvartijat

Very dim northern lights had been recorded in the Bear Camera on the night of 4/5/09/2021.

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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
- 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.

Technical information

Camera: ZWO ASI 120MC-S, wide-angle lens, Thomas Jacquin's Allsky Raspberry Pi 4 in Model B, automatic shooting and image processing

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Quiet aurora arc - 4.9.2021 at 22.30 - 4.9.2021 at 23.10 Ulvila Observation number 101073