© Pekka Parviainen

Turku, Finland

Latitude: 60° 27' 6'' N

Longitude: 22° 15' 60'' E

21 July 2005 2146 (Local Time)

Image P/S code: P.10U.3.1

Image I.D.: 5879

• Images & related info Other Images Images of 1987 edition
• 

  Noctilucent cloud: type I – veils

  At the top centre of this picture, there is noctilucent cloud that is tenuous and lacking in any well-defined structure. This is type I – veils. On the left side, there are some bands of type IIa with diffuse, blurred edges and one band of type IIb that has sharply defined edges. At the top right of the picture, the structure is complex.

  Links in the image description will highlight features on the image. Mouse over the features for more detail.

  © Pekka Parviainen
  Turku, Finland
  Latitude: 60° 27' 6'' N
  Longitude: 22° 15' 60'' E
  21 July 2005 2146 (Local Time)
  
  
  Image P/S code: P.10U.3.1
  Image I.D.: 5879
• 

  Noctilucent cloud

  Noctilucent clouds (NLC) are high-altitude, “night-shining” clouds that are generally only visible to observers in mid to high latitudes (approximately 50°N to 65°N or 50°S to 65°S) for a few months in summer. They occur higher than all other clouds, near the altitude of the mesopause, and are seen against the background of a dark sky when the Sun is well below the horizon, but while the clouds themselves are still illuminated by the Sun. 

  Several types of NLC appear in this picture. There is a very tenuous background veil (type I), which is faint and lacks any well-defined structure. There are also bands or streaks of cloud (type II), some of which have diffuse, blurred edges (type IIa) and some of which have sharply defined edges (type IIb). Short, straight and narrow billows (type IIIa) cross a band, which together is known as a complex structure of type P. One band is a curved whirl (type IV) and there is a bright area with a complex structure.  

  Tropospheric clouds in the Earth's shadow appear as dark silhouettes against the background sky. Noctilucent clouds, in contrast, appear brighter than the twilight sky as they are still illuminated at high altitude. A clear identifying feature of noctilucent clouds is their distinctive bluish-white colour.  

  Generally, noctilucent clouds will be seen close to the horizon. For this early morning view (in the northern hemisphere), the photographer is facing towards the north-east.

  Links in the image description will highlight features on the image. Mouse over the features for more detail.

  © Nicky Mack
  Lossiemouth, Scotland, United Kingdom of Great Britain and Northern Ireland
  Latitude: 57° 43' 12'' N
  Longitude: 3° 17' 52'' W
  18 October 2014 0315 (Local Time)
  
  
  Camera direction: towards NE
  Image P/S code: S.10
  Image I.D.: 5578
• 

  Noctilucent cloud

  This image shows several of the main types of noctilucent cloud: veil, bands, billows and whirls. The sky was clear with good visibility, but also with some low-level tropospheric cloud.

  Links in the image description will highlight features on the image. Mouse over the features for more detail.

  © Alan C. Tough
  Hopeman, Elgin, Scotland, United Kingdom of Great Britain and Northern Ireland
  Latitude: 57° 42' 38'' N
  Longitude: 3° 25' 38'' W
  09 June 2013 0023 (Local Time)
  
  
  Camera direction: towards NE
  Image P/S code: S.10
  Image I.D.: 5580