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

Ursa Astronomical Association

Active aurora band - 26.3.2022 at 21.26 - 26.3.2022 at 21.44 Valtimo Observation number 110113

Visibility III / V


Ragda? #sarg



More similar observations
Additional information
  • Aurora brightness
    • Bright auroras
  • Observed aurora forms
    • STEVE-arc info

      STEVE (Strong Thermal Emission Velocity Enhancement) is an aurora-like phenomenon that can be observed in middle latitudes. STEVE does not belong to traditional auroras as a phenomenon, but may appear at the same time with them.

      STEVE looks like a narrow, white or mauve arc that is clearly separate from the rest of the aurora oval in the pole-ward side of the sky. In Northern Europe, STEVE can sometimes be seen quite far from the oval and be visible across the southern half of the sky.

      STEVE, Keijo Lehtimäki
      A mauve STEVE with a clear gap to the oval. Image: Keijo Lehtimäki

      It forms a long and narrow east-west aligned dim line that goes across the night sky. The length of the arc can be over 2 000 km and it is located at altitudes of 110-300 kilometers.

      The best time for observing STEVE is when the active aurora of a substrom have subsided.

      The arc is white, grey or light purple in color, but the appearance of the arc may vary slightly. In more colorful versions, the bottom edge of the arc shows while/grey color, whereas the upper part has more purple shade. These colorful versions are called Double-Layer STEVE.

      Double layer STEVE, Eero Karvinen
      Double-Layer STEVE. Image: Eero Karvinen

      STEVE's appearance can resemble single, detached rays or there can be rays within the arc itself.

      Riku Talvio, STEVE
      A ray-like STEVE. Photo by: Riku Talvio

      Quite often purple rays within the aurora oval itself get mistakenly identified as STEVE. While within the aurora oval the purple rays tend to disappear relatively fast, STEVE-events can last from ten minutes to hours.

      STEVE very rarely shows green color, whereas lower edges oval's traveling rays tend to be clearly green. However, occasionally there may also be a green, "toothed" band called ”picket fence” below and aligned with the STEVE arc.

      Sirpa Pursiainen, STEVE picket fence
      STEVE with picket fence. Image: Sirpa Pursiainen

      SAR arcs are a different phenomenon happening in the same region that sometimes gets mixed up with STEVE. SAR-arcs, however, are more diffuse, dimmer or fainter, purely red, and lasts longer than STEVE, even days.

      Atacan Ergin, STEVE SAR
      This rare image shows a red SAR-arc with a white STEVE arc. There is an area without aurora light around STEVE. Image: Atacan Ergin

      When photographing a suspected STEVE, it is important to try capturing both the arc form and the arc's location in relation to the rest of the oval.

      In some cases, fine westward-moving structures can be observed within the arc. These can be captured by taking videos of the event or capturing short-exposure animations.

    • 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

       

  • Colors with unaided eye and other features
    • Green auroras info

      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.

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