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Skywarden,
Ursa Astronomical Association
Kopernikuksentie 1
00130 Helsinki
taivaanvahti(at)ursa.fi

Ursa Astronomical Association

Quiet aurora arc - 7.10.2018 at 21.31 Kyyjärvi Observation number 78432

Visibility II / V


I just made it to the spot of observation when it started to happen! It was going quite a bit and the camera was exposing! The lights were green in the front, a little purple in the rays. Then I noticed the SAR arc and a small reposläkä while shooting to the south! That was the most interesting observation of the evening/night.

I added the picture with the dune effect in the lower left corner! #sarg



More similar observations
Additional information
  • Aurora brightness
    • Dim auroras
  • Observed aurora forms
    • Band info

      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.

    • Dunes info

      Dunes

      The dunes are a dim and very rare shape that has so far been associated with the aurora visible in early evening.

      Aurora dunes can be most easily confused to ribbons on lower clouds. In order to fill in the description of the phenomenon, a striped pattern formed by parallel lines must also appear in the aurora. The stripes are most easily recognizable right at the front edge of the aurora but they may also occur among the rest of the aurora.

      The dune auroras are visible as a parallel striped float. Photo by Tapio Terenius

      Raidallisen dyynilautan reunassa voi toisinaan olla voimakastakin aaltoilua.

      There can sometimes be strong ripples at the edge of a striped dune float. The rippling of the edge of the dune float can vary from minor to large (pictured). Photo by Pirjo Koski

    • Red Arc with Green Diffuse Aurora (RAGDA) info

      Red Arc with Green Diffuse Aurora (RAGDA), is a two-component form of northern lights that occurs south of the oval.

      Both parts of the aurora are formed when positive particles from the magnetosphere hit the Earth's upper atmosphere. The phenomenon occurs before magnetic midnight during large aurora substorms and is best distinguished when it deteches southward from the bright rays of the substorm aurora.

      The phenomenon consists of a faint red arc, which looks a lot like a Stable Auroral Red (SAR)-arc. The common factor for these two red arcs is the reaction of the ring current with the substorm.

      Antero Ohranen, RAGDA
      A Red Arc with Green Diffuse Aurora
      Photo: Antero Ohranen

       

      Below the red arc are green diffuse patches or sausage-like shapes. RAGDA's green aurora is essentially featureless and without any rays. It may appear slightly more bluish in camera images compared to the green aurora of the oval.

      Lasse Nurminen, RAGDA
      RAGDA's green has slightly more bluish shade than the rest of the oval.
      Photo: Lasse Nurminen

       

      Sometimes the red arc and the green patches are clearly separated from the aurora oval and sometimes almost in contact with the southward edge of the oval.

      During an active substorm, the green northern lights can sometimes be seen with red tops. These usually have rays that RAGDA's green aurora lacks.

      An emissionless gap without any aurora light can be observed between the red arc and green diffuse aurora. The two features don't seem to be connected. Of the two aligned structures, the red one is located ~ 100 kilometers higher than the green aurora.

      Markku Ruonala, RAGDA
      There seems to be an empty area without any aurora light between the red and green aurora.
      Photo: Markku Ruonala

       

      The event is dynamic. It sometimes starts with green blobs, then a red arc appears. These two can also appear in the sky at the same time. The shapes move often from east to west. Then the Red Arc with Green Diffuse Aurora fades away and only the red arc remains visible in the sky. The red arc is recognized as the SAR arc.

      Observing this phenomenon is easier when the night sky is clear and dark before magnetic midnight. When looking for the red arc with green diffuse aurora, the best results can be achieved by pointing the camera towards south or southwest of the brightest part of the oval.

      A wide-angle lens is recommended for photographing the shape of the red arc going over the sky, but a regular lens can also be used. The red arc is quite dim, so the exposure times needed are typically longer than the ones for northern lights.

      Pirjo Koski, RAGDA
      Two RAGDA-arcs
      Photo: Pirjo Koski

       

      If the red arc cannot be distinguished in the images, the phenomenon identification 'Diffuse green auroras' should be used for isolated hazy green blobs/arc.

      Matias Takala, RAGDA
      Dunes in RAGDA's green aurora
      Photo: Matias Takala

       

Comments: 2 pcs
Kari Rytilahti - 14.10.2018 at 17.15 Report this

Komea kuva SAR-kaaresta ja linnunradasta !

Antero Ohranen - 14.10.2018 at 19.58 Report this

Kiitos, Kari!

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