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Feature

Losing the Stars

If light pollution trends continue, New Zealanders may never see the Southern Cross again.

Dennis Rogers

Urban sky glow -- light pollution caused by poorly designed street lighting, security lighting, neon signs, car sales yards, billboards -- is dimming our view of the stars at night and threatening astronomical research.

New Zealand cities and cities around the world suffer from stray light shining upwards which lights up dust and water particles in the sky, causing the sky to glow. Astronomers, both professional and amateur, are fighting against this and are using concerns about energy efficiency to back up their campaigns.

Only about 20 years ago you could clearly see the Milky Way and Magellanic Clouds in your back yard at night from most New Zealand cities. Today, most of the Milky Way cannot be seen at all, and many stars have also been "lost" from city locations.

Lost Light, Wasted Energy

Most modern street lamp fittings used in New Zealand waste 22% of the light, which goes outwards and upwards. Older street light fittings waste much more than this; even industrial and commercial lighting has a very high percentage of light wasted each year.

There have been recent advances in lamp efficiency, but little has been done to improve the fittings, or shields, surrounding these lamps. Overseas experience has shown that light pollution can be reduced by 75%, which saves ratepayers' money and millions of dollars in electricity generation. One might think that a single lamp wastes very little electricity, but when you consider that 20% of New Zealand's electricity generation goes into lighting, then proper lamp fittings mean that a great deal of energy can be saved each year.

High-pressure sodium lamps, with which most of our street lights are fitted, produce a continuous spectrum that blocks astronomers' views of the night sky. Astronomers would prefer the use of low-pressure sodium lamps for street lighting, because these lamps emit much of their light in two yellow emission lines, which are close together in the spectrum and can be filtered out.

Another problem that light pollution causes is "light trespass". When stray light from a poor light fitting shines directly into people's homes, it invades their privacy and can cause stress. Birds nesting in trees can also be affected by stray light, causing them to leave their nests and sleeping sites.

Light Pollution Campaign

The Royal Astronomical Society of New Zealand has set up a subcommittee on light pollution, offering suggestions to astronomical societies throughout New Zealand, keeping in touch with overseas initiatives, and providing information on light pollution, its spread and causes to astronomical societies throughout the country.

The aim is to encourage local astronomical societies to work against light pollution in their areas -- this sort of campaign has gone nation-wide in Britain. The first effort towards a national effort here was the production of the Light Pollution Guide, sponsored by Mobil.

This guide has been designed to raise people's awareness of the problem of rapidly increasing light pollution in New Zealand, and to indicate some possible ways of addressing the problem. It is intended primarily to help astronomical societies in undertaking these two tasks, but may be used by other groups concerned about the waste of electricity and money.

Astronomers are not against outdoor lighting, but are in a position to be able to observe how poor lighting affects our night sky and wastes money. One of the worst forms of outdoor light is security lighting. Much of this form of lighting is poorly designed and fitted, causing glare and harsh shadows. This glare causes the pupils of the eye to close down, actually making it harder to see any intruders. A well-designed fitting does not cause such glare.

General Electric, which produces street lighting equipment here in New Zealand, has come out in favour of efforts against light pollution. It agrees that light pollution creates loss of performance and wastes money, and that light trespass can cause problems.

Because of modern crime levels, many people are calling for more lighting. However, there has been little research done on the relationship between outdoor lighting and crime. Over the last few decades, crime has increased along with an increase in outdoor lighting.

One way to encourage the use of good lighting is for local bodies to enforce an outdoor lighting code, which sets guidelines on the type of lighting to be used. Such codes have been adopted by Golden Bay near Nelson. In the US, the Arizona city of Tucson, with twice the population of Christchurch, has far less light pollution than Dunedin due to its tight lighting codes. This may be related to the fact that Tucson is the headquarters of the International Dark-Sky Association (IDA), an organisation devoted to helping spread the word about light pollution.

Dr David Crawford, head of the IDA, provided the Christchurch City Council with advice on outdoor lighting codes for Christchurch while attending an international astronomical meeting in the city.

There is one site in New Zealand which has had strong lighting codes in place for the last ten years or so, modified from the Tucson codes. The Mackenzie Basin in and around the settlement at Tekapo is the site of the Mt John University Observatory operated by the University of Canterbury. Ordinances under the Town and Country Planning Act have protected the observatory from light pollution.

No floodlighting is permitted in the area after 11pm, and illuminated advertising and lights are shielded. The university's Physics Department provided shields for the low-pressure sodium lights in use in Tekapo Village. Local regional bodies, such as the Mackenzie District Council, the South Canterbury Electric Power Board and even the New Zealand Army (who operate a large camp near Tekapo) cooperated in setting up the light controls.

Recently astronomers there checked the area's sky brightness and found no change over the village compared to the uninhabited areas around Mt John. The figures were excellent by international standards, ensuring that the work done at the observatory remains significant.

The Royal Astronomical Society of New Zealand would like to see a nationwide Skywatch program established to monitor sky brightness. This program involves observing well-known constellations, such as the Southern Cross, checking the visibility of the stars involved. This would provide an indication of how much light pollution is increasing throughout New Zealand each year.

There are plans to combine this information with that produced by Australia's light pollution organisation, the Association Against Obtrusive Lighting. Such data, ultimately handed on to the IDA, will provide information on light pollution trends in the Southern Hemisphere. Little is currently known about these trends, but it is possible that light pollution may well wipe the Southern Cross from the skies.

Dennis Rogers is a member of the RASNZ Subcommittee on Light Pollution, and Light Pollution Officer of the Canterbury Astronomical Society Inc.