This includes some pictures showing nacreous clouds, and experiments with filters suitable for photography in areas with low pressure sodium lighting.
These are small images of Cygnus rising over my northern horizon where the city lights of Middlesborough make the sky very bright. Even on the clearest nights there is obvious light pollution near the horizon, if there is the slightest haze over the city the sky is visibly yellow on the Northern horizon.
|Unfiltered showing strong Na-D light||Filtered with NoNad neodymium glass|
The limitations of the digitised image make it a little hard to appreciate how effective this filter is against low pressure sodium lamps. The weaker filter attenuates the yellow sodium D-line by a factor of 100, whilst transmitting most of the continuum (adds about 1/2 a stop to exposures).
The stronger filter (which is too strong for most decent astronomy sites) but may be of interest to city dwellers cuts the D-line by about 10000. This is sufficient to look up at the inside of a street lamp and see no yellow light!
More information and sample shots of constellations and comparison shots of Comet Hale Bopp with and without the photographic Nonad filter
My personal views on light pollution as submitted to the UK select Science and Technology Committee report on Light Pollution and Astronomy.