Light pollution or skyglow is caused by light scattered in the atmosphere by minute particles of dust or water. Light fittings which emit light above the horizontal are the main cause, although light reflected from illuminated objects and poorly directed floodlight do contribute to skyglow.
Below you can see how the use of inefficient streetlights can cause such a wide scale problem in the UK and Ireland. To see how light pollution is effecting Europe, visit the Light Pollution Science and Technology Institute web site. The maps below show the Artificial Night Sky Brightness in the British Isles.
Colours below correspond to ratios between the artificial sky brightness and the natural sky brightness of: <0.11 (black), 0.11-0.33 (blue), 0.33-1 (green), 1-3 (yellow), 3-9 (orange), >9 (red).
As you can see, Northern Ireland is badly affected, but it is not too late to reverse the trend towards a worsening skyglow. As the photographs below so aptly demonstrate, skyglow is a clear and present problem and hinders everyone’s view of the most spectacular and completely free light show in the universe!
These two photos should look the same, but one of them is taken from a light polluted urban setting.
Recent passing comets, Kudo-Fujikawa and NEAT, which were discovered by amateur astronomers in the Far East, were all but invisible to the naked eye in most parts of the UK and were only captured using long exposure photographs and broadband filters.
Shown below is a 360degree fish-eye view of the night sky during the 1997 passing of comet Hale Bopp. A 5 minute exposure was necessary to show the few stars which are visible in this image. Comet Hale Bopp, when captured was at magnitude -1.67 which is brighter than even Saturn and almost as bright as Jupiter. The bright star opposite the comet, just above the skyglow is Mars.