© 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.10U.3

Image I.D.: 5578

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  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.10U.3
  Image I.D.: 5578
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  Noctilucent cloud

  Noctilucent clouds (NLC) are usually only visible to observers in mid to high latitudes (roughly 50°N to 65°N or 50°S to 65°S) and in the twilight or night sky for a few months in summertime, when temperatures in the mesosphere are the coldest. This photograph was taken in late June, during summer in the northern hemisphere, from a location 55.78°N.

  Noctilucent clouds are generally observed during the twilight periods when the Sun is between 6° and 16° below the observer's horizon. It is during this period that the background sky is dark enough for the cloud to be seen, yet the high-altitude clouds are still illuminated by sunlight.

  Typically what sets noctilucent clouds visually apart from tropospheric clouds is their visibility in the night and their obvious, and sometimes bright, blue-white colour. The low-level tropospheric clouds at 2 and 3 are within the Earth's shadow and they stand out as dark silhouettes against the relatively brighter background sky. In contrast, noctilucent clouds are always brighter than the twilight sky. Near the horizon, they may have a reddish tint. Two main types of NLC are shown here: bands (type II) – these are long streaks – and billows (type III), seen at 7 and 8 – these are closely spaced, roughly parallel streaks.

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

  © Ewan Kane
  East Kilbride, Scotland, United Kingdom of Great Britain and Northern Ireland
  Latitude: 55° 46' 49'' N
  Longitude: 4° 8' 48'' W
  23 June 2015 2247 (Local Time)
  
  
  Camera direction: towards NW
  Image P/S code: P.10
  Image I.D.: 5581
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  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.10
  Image I.D.: 5879
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  Noctilucent cloud type IIb – bands with sharply defined edges

  The principal noctilucent type in this picture is type IIb – bands with sharply defined edges (seen at 1, 2 and 3). The brightest band across the centre of the picture appears twisted or braided.  

  The short, straight and narrow streaks just above the centre of the image are type IIIa – billows.

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

  © Mark Zalcik
  Namao, Alberta, Canada
  Latitude: 53° 42' 58'' N
  Longitude: 113° 29' 32'' W
  28 June 2014 0243 (Local Time)
  
  
  Camera direction: towards N
  Image P/S code: P.10
  Image I.D.: 5691
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  Noctilucent cloud type IIIb – billows: wave-like structure with undulations

  Type III – billows: these are arrangements of closely spaced, roughly parallel short streaks. There are two types:

  – Type IIIa: comprised of short, straight and narrow streaks

  – Type IIIb: exhibiting a wave-like structure with undulations

  The billow type shown in this picture is type IIIb – a wave-like structure with undulations.

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

  © Mark Zalcik
  Namao, Alberta, Canada
  Latitude: 53° 42' 58'' N
  Longitude: 113° 29' 32'' W
  09 July 2014 0031 (Local Time)
  
  
  Camera direction: towards NW
  Image P/S code: P.10
  Image I.D.: 5690
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  Noctilucent cloud: type IVc

  The main type of noctilucent cloud in this picture is type IVc – whirls: a large-scale ring structure. In the upper left there are diffuse billows of type IIIb. In the upper right there is a complex structure of type O. There are also tropospheric clouds in the foreground.

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

  © Pekka Parviainen
  Kustavi, Finland
  Latitude: 60° 32' 42'' N
  Longitude: 21° 21' 19'' E
  10 August 1988 0043 (Local Time)
  
  
  Image P/S code: P.10
  Image I.D.: 5795
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  Noctilucent cloud: complex structure

  Often in displays of noctilucent cloud, several forms may be seen simultaneously. It is not unusual, therefore, for two or more intersecting or overlapping groups to give rise to complex structures such as bright knots or net-like structures, or types that do not fit the standard classifications. This picture, taken just before midnight from the Edmonton area of Alberta, Canada, shows one such complex display of noctilucent cloud. The central part of the display had a peculiar billow-like appearance with a number of lacunosus holes.

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

  © Mark Zalcik
  Namao, Alberta, Canada
  Latitude: 53° 43' 2'' N
  Longitude: 113° 29' 39'' W
  26 June 2014 2343 (Local Time)
  
  
  Camera direction: towards NW
  Image P/S code: P.10
  Image I.D.: 5687