S1.  Definition of ALCORs—Astronomical Lighting Control Regions for Optical Observatories

  These guidelines were described by Paul Murdin in the astronomy magazine Observatory (1997), and they are an adaptation for astronomy of a zoning system produced for the Institution of Lighting Engineers (by Nigel Pollard), based on environmental considerations. The proposal is that the defence against light pollution would be drawn up for each ALCOR, to progressively more stringent standards.

  ALCOR 0: No astronomical activity is practical from such a region. Examples: urban entertainment areas, motorways, industrial zones.

  ALCOR 1:  Casual sky viewing of planets and constellations is possible, including from public (city-centre) observatories, schools and colleges (with telescopes around 30 cm in diameter). Examples: suburban, residential districts in general, recreational (park) areas.

  ALCOR 2:  Special types of observing (avoiding light pollution) such as infrared observations, high-resolution spectroscopy of bright stars, and other observations are undertaken by undergraduates or "expert" amateur astronomers at university or "museum" equivalent sites (with telescopes around 50 cm to 1 metre). Examples: particular places in urban, suburban, town locations.

  ALCOR 3:  Photometry and intermediate-resolution spectroscopy, could be undertaken by professional or "expert" amateur astronomers to a high standard (with telescopes around 50 cm to 1 metre). Examples: selected near-rural or rural locations.

  ALCOR 4:  Narrow-band imaging, imaging in general, low-resolution spectroscopy, could be undertaken by professional astronomers for wide-ranging programmes to the highest professional standards. Examples: national parks, remote, selected rural locations, probably the darkest sites in the UK.

ALCOR 5:  Wide-field imaging, low-resolution spectroscopy of faint sources, professional work from a site with rare quality. Examples: very remote locations, of which there are very few in the world (this region is above the ILE system to protect natural habitats, and it is unlikely that there would be any regions designated as ALCOR 5 in the UK).

  The acronym ALCOR was selected because Alcor is the name of a faint star in the handle of the Plough, regarded as a test for good eyesight. Control of light pollution to appropriate standards for each ALCOR zone would expand what astronomers—amateurs and professionals, and the public at large—could see.

S2.  Definition of forms of light pollution

  Light trespass:  Light that shines from one property into another where it is not wanted.

  Glare: Light that shines into the eye, preventing the person from seeing the illuminated scene properly.

  Confusion:Too many bright lights (also flashing lights) competing for attention.

  Light waste: Lights left on (all night), too-bright light for the task in hand.

  Sky Glow: The bright sky over our towns and cities, caused by light shining up and not down.

  The brightness of stars is measured in magnitudes, a logarithmic scale reflecting the way the eye reacts to light. The scale runs from negative to positive, with the brightest stars having magnitude -1. The normal limit for observing stars with the naked eye (in a dark site) is sixth magnitude. The effect of Urban Sky Glow can be shown to have an effect equivalent to reducing the limit by 5 magnitudes (or more in extreme cases), so that only stars brighter than first magnitude are visible in the urban situation. (Taken from D Schneider in "The Vanishing Universe".) There are only 16 stars in the whole sky brighter than first magnitude.

S3.  Lighting options available

  The Institution of Lighting Engineers has produced guidance notes for the reduction of light pollution. The notes include several helpful suggestions, which are listed below, but they also list standards and limits for the level of illumination recommended.

  Direct light downwards onto the target (from above), rather than illuminating up from ground level.

  Use shields and baffles to eliminate light spill upwards.

Keep glare to a minimum by ensuring the main beam angle is below the horizontal.

Do not "over" light.

  For sport and area lighting, use floodlights with asymmetric beams, permitting the front glass to be horizontal.

  Lighting above the horizontal should be minimised for road lighting.

S4.  Guidelines for lighting to avoid light pollution

  Public and private lighting should be strictly limited in intensity and duration to the need of comfort and security of the population.

  All outside lighting should be equipped with efficient reflecting hoods so that only what should be seen is lit; no light should be directed towards the sky to prevent interference with vegetation, nocturnal animal life, astronomy, aviation.

  To avoid all waste of energy, the best energy efficient lamps should be chosen first and foremost, ie low-pressure sodium, or any other similar system developed in the future.

  Neon signs and floodlighting of monuments, buildings, outdoor sports facilities, or squares should be turned off at 11pm, apart from exceptional derogations for security reasons.

(Taken from J Kovalevsky in "the Vanishing Universe")

S5.  Summary of relevant IAU General Assembly and IAU/UN Symposium recommendations

  The International Astronomical Union (IAU) has expressed concern about future space projects seriously interfering with astronomical observations in the optical and radio domain:

—  protection of astronomically important radio frequencies,

—  vapour trails from aircraft affecting astronomical observations,

—  satellite-borne reflector and solar-reflector systems,

—  the contamination of space (with debris),

—  the protection of observing conditions at the remaining excellent sites on this planet,

and requests authorities to ensure the night sky receive no less protection than has been given to the world heritage sites on Earth.

  UN Member States should act to control pollution of the sky by light and other causes, for the benefit of energy conservation, the natural environment, night-time safety and comfort and the national economy, as well as science.

30 April 2003