Cornish Skies V Hertfordshire Skies

Here's a set of images comparing light pollution between Crowdy Reservoir on Bodmin Moor, Cornwall, and south-east Hertfordshire, about a mile north-east of the town of Ware.

Crowdy Reservoir East

SE Herts East - the curved trail is a plane on approach to Stanstead Airport

Crowdy Reservoir South

SE Herts South - this view is particularly bad as London is in the distance

Crowdy Reservoir West

SE Herts West

Crowdy Reservoir North

Crowdy Reservoir Zenith

SE Herts North - the best views are in this direction

SE Herts Zenith

The same camera, lens, exposure settings and processing were used for both sets - Samyang 14mm lens at f2.8, Canon 700d (unmodded), 30 seconds at ISO 800 (with a +0.67 brightness adjustment in the Canon DPP software, making them roughly equivalent to ISO 1,300) - to make the comparison as fair as possible. They aren't quite right, the horizons between the two sets don't match up, but they show the stark difference in the levels of light pollution. It would be interesting to see similar shots from around the UK, I expect that most people who live in or around urban centres would experience something similar.

Despite appearances, the out-of-town Hertfordshire site can still be enjoyed for stargazing - a 30 second exposure with a fast lens exaggerates the light pollution somewhat. On a good night it's possible to pick out the Milky Way and Andromeda galaxy with the naked eye, and while the views towards the horizon are restricted - especially to the south - there is still a fair slice of sky available. If you live in a light polluted area here are a few tips to enhance your viewing:

• Light pollution maps can help you find more suitable local sites.
• A light pollution filter works by suppressing specific colours produced by common artificial lights, such as orange sodium and blue mercury street-lights. However, they are not very effective on modern LED lighting, which emit light across all wavelengths rather than a specific colour. 
• Narrowband filters are very effective at suppressing LP but are only suitable for viewing emission nebulae rather than galaxies or star clusters. For visual use a UHC or Hydrogen-beta filter may be the most effective, while Hydrogen-alpha (Ha), Oxygen (OIII) and Silicon (SII) are most commonly used for imaging.
• Choosing suitable targets can help. Lunar and planetary view are barely affected by LP (after all, they are lit directly by the Sun so it's daytime up there). Targets with high surface brightness (rather than magnitude) are easier to see, such as open and globular star clusters. Galaxies can be difficult to view under LP but some are brighter than others, especially starburst galaxies with a high rate of star formation such as M51, M81 and M82. Face-on spirals are also generally more difficult to view than inclined ones, as their light is spread out over a greater area.

For visual observations, a dark site can be thought of as an aperture multiplier - better views can be obtained with a small telescope at a dark site than a large one under light polluted skies, as greater contrast is delivered at the eyepiece.