Light Pollution and Astronomy

By far the biggest problem facing amateur and professional astronomers is excess light. The reason observatories are built in remote areas is to get away from obtrusive lighting, smog and other bad "seeing" conditions, astronomers are not anti-social. A lot of planning must go into site selection to take advantage of the clear steady air in unpopulated areas. It is useless to build a facility that costs millions of dollars only to have its useful life cut short by the growth of a new city.

For amateur astronomers the problem of light pollution becomes a nightmare. Light from shops, sports grounds and yard lighting limit, if not end totally, the usefulness of the "backyard observatory". Apart from the simple pleasure of looking at the night sky, the work of some amateurs supplements the work of professionals. These amateurs should be regarded as unpaid professional observers.

The main function of a telescope is to amplify light from distant objects, as these objects are very faint. Stray light has the effect of washing out the contrast and reducing the image quality. If you turn up the brightness on your TV you can simulate the effect. The higher the brightness the more the image deteriorates. For an astronomer, that light YOU leave on in the back yard, or those flood lights in the driveway, can mean the end to any chance of using a telescope on all but the brightest of objects.

The big problem with most lighting is poor design or bad layout. Most domestic lighting is improperly shielded and spreads light in all directions, casts shadows, makes blind spots and puts very little illumination where it is needed. For example, in the case of a path, if you use a torch you shine it on the ground to see where you are walking. So why put in lights that light up the trees and half the street to find the front door? "Well lit streets, parking lots, and walkways are in everyone's best interest. Common sense argues, however, that the best way to achieve good lighting is by directing light toward the ground and not toward the sky." (Sky & Telescope - August 1995)

Lower voltage lights with full cut-off shields are less likely to dazzle you and most importantly they use less power and this saves energy and money. The fight against light pollution is not designed to put you "in the dark" it is not aimed at disadvantaging anyone. It is important to understand the difference between good visibility and more light. The International Dark Sky Association provides comprehensive information about the fight against light pollution.

For information about other forms of pollution and the environment in general, click here.

Canberra Astronomical Society
PO Box 1338
Woden ACT 2606

Last updated: 2005-09-06

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