Quiet aurora arc - 1.9.2019 at 23.40 - 1.9.2019 at 23.55 Järvenpää Observation number 85372

• Aurora brightness
• • Dim auroras
• 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.

• Observed aurora forms
• • Veil

    Veil
    Veil is the most bland and very common form of aurora. It usually covers its homogeneous dim glow over a wide area of the sky at once. Most often, the veil is seen in the calmer and quiet phase of the night after the aurora maximum as a background for other forms. The veil can also occur alone and in that case it will be quite difficult to reliably identify as an aurora, especially at a observation site which has a lot of light pollution.

    A similar glow of light can also be caused by airborne moisture, smoke, or a very thin layer of clouds that reflects the light that hits them. However, clouds can also be used to identify veil, especially if the middle or upper cloud appears dark against a lighter background, then it is very likely to be aurora veil if the brightness of the background sky is not due to the rising or falling Moon or Sun. When photographing, very long exposure times usually reveal the green colour of the veil auroras.

    

    Veil and rays. Photo by Esa Palmi.
     

    

    Red aurora veil. Photo by Marko Mikkilä.

     

    

    Veil. Photo by Milla Myllymaa.

     

    

    Aurora veil that changes color from green at the lower edge through purple to blue at the top. Photo by Jaakko Hatanpää.

     

    

    Dim green veil. Photo by Jarmo Leskinen.

     

    

    Radial aurora band surrounded by veil. Photo by Jussi Alanenpää.

  • 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.

Nikon D3200 + Nikkor 18-55mm f / 3.5-5.6 @ 18mm F / 3.5, 30 s, ISO 800

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