On 16th February 1996 we in Britain were treated to a spectacular display of nacreous clouds - sufficiently attention grabbing to make the national news. They were seen over a wide area from Edinburgh in Scotland right down to Cambridge and London in the south of England. I saw them for about an hour after local sunset, waiting for it to go dark (latitude 54 N), but it proved too windy for astronomy.
They were truly amazing with strong iridescent bright colours and looked very eye catching. Like having opals in the sky. The clouds showing these colours were mostly lenticular in form and the thickest ones appeared bright white but with red and green parallel fringes on the edge facing the sunset. The best ones showed a range of really strong saturated colours and bright illumination. My video camera was unable to capture the colours, but some of the slides came out reasonably. I know these JPG images do not do the phenomena justice, but is the best I can manage. The cloud colours are not artefacts they really did look very bright and strongly coloured!
A couple manage to show some of the features I described despite the amazing level of contrast between the cloud and the sky. Venus is also visible in some of the frames, two shots give a very good impression of the main display I saw. The behaviour when I think of it is so reminiscent of Newton's rings seen between almost plane parallel glass that I wonder if the effect is due to many identical shape and size ice crystals in the cloud all aligned in the same orientation. You can see the same sorts of colours by looking obliquely at a shallow angle through any double glazed window!
The evening blue sky appears darker on slide film/prints than in real life. The JPG compression is seriously struggling with the enormous range of contrast in these images, and the original slides show quite a lot more detail in both cloud colours and extent.
Slide reference details
Date: 16th Feb 1996
Film: Fujichrome Sensia100
Camera: Pentax MESuperA f1.7 50mm lens
Location: East Rounton, Northallerton, North Yorkshire, UK
All views are essentially due West Kodak PCD scans from slides exposed for cloud detail. The small black features are crows returning to roost in a nearby wood in inconveniently large numbers.
|22- 17:25 first sighting - very bright pastel red/green in high cloud, some cyan and yellow in lower (very bright cloud). Automatic exposure (f2 1/30) Venus just visible on top edge of slide (cropped of print)|
|24 - 17:28 vertical format to frame high cloud edge
detail and Venus (70mm from left, 45mm from top margin) exposed for
colour in lower bright cloud now with cyan/purple and red/yellow on the
slide the cloud edge touches Venus, but the print cannot handle the huge
range of contrast. Auto exposure -1 stop (f2 1/60) Moved to pretty sight
(about 400yds) with better views across fields.
|25 - 17:33 good horizon, but very windy. Clouds now very highly coloured fringes to top, rhs and bottom show strong bright colours. Some shadowing of one cloud by another changing patterns, fast moving low dark cloud visible. Auto exposure -1 stop (f2 1/60)|
|26 - 17:34 good horizon, vertical to show Venus and
high clouds (Venus is 70mm from left, 33mm from top border) much easier
to see on slide. Colours now highly developed and starting to show
oranges and greens in bulk cloud. Cloud looks sculpted by the strong
wind (which was very cold) Auto exposure -2 stop (f2 1/60) -my favourite
of the sequence.
#26 larger image
|27 - 17:37 good horizon, to show cloud details and periodic structure in the cloud behind the bright colourful one. Colours are still highly developed, but hard to see on the print. The blue/purple leading edge spike of the main cloud sticks out a long way. Auto exposure -1 stop (f2 1/30)|
|28 - 17:38 (not printed) - superficially very similar
to #27 BUT - a new small bright cloud has appeared at rhs A faint trace
of the new proto cloud is visible in #27 (20mm from rhs, 60mm from top)
in some ways it looks like the spike off the top of the other cloud.
Surprising it switched on in a couple of minutes. Auto exposure -1 stop
#28 larger image
There was also a very large brilliant white cloud of the same type directly overhead, but it was far too big to photograph sensibly. The edge of the biggest cloud (which just had pretty fringes) but was overpoweringly bright is visible on the top left corner. I have some continued observation on video, but it is very poor as the camera interprets bright colours in the contrasty sky as white. The increasing amount of low dark cloud, and failing light together with high winds meant that I stopped taking slides when exposures increased beyond 1/30s (this may have been a mistake) The video covers a range of 17:40-18:20, but much of the interesting detail is lost behind foreground cloud. The final salmon pink cloud showed quite well on the video, but I didn't take a slide. If I had realised how rare this event was at the time I would probably have taken many more slides!
I have recently found the video tape and have transferred a few still frames from my Nacreous cloud video.
There have been two more separate displays of nacreous clouds over the UK in the winter of 1999/2000.