2017 December 30
Light pollution – penetrating the veil
As we move through the twenty-first century, the twentieth-century phenomena of light pollution and light nuisance have gained an increasingly high profile in the environmental debate. The growth of towns, rural urbanisation, the 24-hour lifestyle and fear of crime have all led to a rapid expansion of uncontrolled exterior lighting. Newcomers to astronomy in urban areas might well decide that it is a pursuit more easily followed in an armchair or at a computer keyboard – what is there to see outdoors at night, beneath what the Royal Commission on Environmental Pollution compared in 2010 to ‘a cloud of visually impenetrable, artificial vapour’?
Three types of light-related problems concern the amateur astronomer and the responsible citizen.
Skyglow is caused by wasted light escaping upwards from wasteful and unshielded fittings, scattered by atmospheric aerosols to create the familiar glow hanging above every town (and many villages) in the UK. Skyglow has veiled the starry sky for more than 90% of Britons, according to surveys by the BAA’s Commission for Dark Skies (CfDS), and recent national star counting projects organised jointly by the Campaign to Protect Rural England (CPRE) and the CfDS.
Glare is the most safety-related aspect of light pollution, and is the typical result of the ubiquitous home ‘security’ lamp, usually angled outwards in the vain hope that its excessive dazzle may deter burglars (it does not). The rapid worldwide switch to LED lighting has led to the appearance of poorly designed, cheap lights on outside walls and masts all over the UK, almost all too bright for their purpose and spraying light not only onto the premises to be lit, but outwards and upwards into the eyes of pedestrians and drivers. While road lighting shows a trend nationally towards better, downward direction, the lack of regulation of private lighting means that poorly aimed domestic, commercial and sports lights continue to steal the stars from most residents of the British Isles.
Light intrusion, the spilling of light into neighbouring houses and gardens, is increasingly a matter of concern to environmentalists. Local authorities, and retailers of the offending lamps, react to that concern in a variety of ways, some seeking to alleviate the problem, others showing little interest. Even thick bedroom curtains may not give relief to victims of excessive lighting, and anyone advised by councils and judges to seek such a solution should firmly reject the advice: would councils and courts tell victims of noxious smells to wear pegs on their noses? In law, the polluter must solve the problem.
The answers to the problem of wasted light seem self-evident: simply aim lights properly, with appropriate shielding, and use only the amount of light needed. In these energy-conscious days, why isn’t everyone using economical, environmentally sensitive lighting? The answer lies largely in the fact that it is not easy to find. Whole generations have now grown up knowing only poor-quality lighting, and they think it is normal. Lighting practice in the UK is often subject only to guidelines rather than regulations, and guidelines can be ignored with impunity. Other contributory factors include the fostering by manufacturers of the myth that bright lights deter crime, and the fact that retailers still offer lights that are not designed for the task in hand. Most electrical devices are carefully designed to perform their stated functions, but lights are usually allowed to shine not only where their emissions are needed, but also where they manifestly are not. Government, manufacturers and retailers have sometimes responded sympathetically to calls for improvements, but they are slow in coming.
Environmental Health Officers have powers to deal with light-nuisance offenders under the Clean Neighbourhoods Act of 2005, but many local councils seem strangely reluctant to pursue complaints. Victims sometimes resort to expensive litigation. Planning laws and advertising regulations may also be invoked against intrusive lighting, especially from commercial premises. Illogically, transport hubs such as bus stations and docks are exempt from legislation, and can pollute at will, an anomaly currently being addressed by the CfDS in consultations with DEFRA.
Bodies such as the BAA and the CPRE have taken the lead in urging the government to ‘get lighting right’, but the night sky is still without protection in law. It seems perverse that those who dump rubbish in fields and spoil our countryside can be fined thousands of pounds and even go to prison, but the night sky can be despoiled, and its beauty veiled with wasted light, without fear of penalty.
Humans are not the only species whose lives are disrupted by spilled light. Nocturnal insects, birds, fish, reptiles and mammals have no curtains to pull. Millions of our fellow creatures on this planet are disturbed, and even die, because we do not aim lights properly or use reasonable wattages. The health implications of living with artificial light at night, and not sleeping in darkness as we have for countless thousands of years, are only beginning to be realised. The current biodiversity crisis may owe as much to the loss of the night as it does to pesticides, urban growth and other factors. Most of the world’s species are nocturnal. Anyone seeking more information on what has become known as the ‘LAN (light-at-night) debate’ should refer to the CfDS website.
Can the enthusiastic newcomer to astronomy do some real observing beneath tainted skies? Apart from the Moon and planets, there are many night-sky objects that can be found and studied in light-polluted areas, if the observer is not standing directly beneath a streetlight or a few metres from a ‘Rottweiler’ light. Here is a small selection of five assorted targets, near brighter objects that help to locate them, arranged by season of culmination (when at their highest point in the sky).
Galaxy NGC 3992, RA 11h 57m, Dec. +53° 22′
This tenth-magnitude barred spiral galaxy is part of the group of galaxies strewn across Ursa Major. It is in the same low-power field as Gamma UMa (Phad). Sometimes referred to by Owen Gingerich’s 1960 appellation M109, it is a beautiful object in photos, shaped like a slewed Greek letter Theta. I first observed it at a magnification of 108 times on a clear spring night in 1992, when it was almost at the zenith, in a moderately light-polluted sky. I noted a large inner area of brightness, bulging slightly northwards to give the nucleus a bean-shaped appearance; a fainter oval glow surrounds this. Distance 60 million light years.
Variable star R Coronae Borealis, RA 15h 48m, Dec. +28° 09′
This reliable sixth-magnitude variable, easily studied through binoculars, lies within the distinctive and delicate arc of the Northern Crown (Corona Borealis), at its highest in May. R Coronae has an interesting habit of disappearing from time to time. It is a yellow supergiant, and fades at intervals varying from weeks to years, to magnitudes as faint as +14. This is due, it is thought, to a continual build-up of carbon dust in its atmosphere. It is intriguing to think that you might be the first person in the world to notice that R Coronae has disappeared again.
Gamma Andromedae (Almach), RA 02h 03m, Dec. +42° 20′
This bright naked-eye star is a fine double system for any size of telescope. The primary (magnitude +2.3) is golden yellow. The secondary (+5.1) is often listed in handbooks as blue, but it remains resolutely green whenever I look at it. Is this just an idée fixe, a contrast effect, or a real colour? Try a moderate magnification. I see it well at x108.
h3945, RA 7h 17m, Dec. –23° 18′
In summer, telescopes at star parties often turn to Albireo (Beta Cygni), a double star with components of wonderfully contrasting colours. In winter, however, they are rarely aimed at the finest coloured double star then available in the sky, h3945 in Canis Major. Look for this orange-red and electric blue pair, just east of Omicron2 CMa and north of Tau CMa. I found it by chance for the first time in 1971, low in the south through the light pollution of Poole, and was surprised that I had never heard of it before. The magnitudes are +4.8 and +6, and the separation 27 seconds of arc, so it is easily split with moderate power. This is an optical double, i.e. a line-of-sight effect; the brighter of the two stars is 2500 light years from us, while its ‘neighbour’ is only one-tenth of that distance away.
Cluster M35 (NGC 2168), RA 6h 09m, Dec. +24° 21′
This is a superb, tight cluster of hundreds of sparkling stars, with a pleasing curve of slightly brighter stars at its centre, at the ‘top right-hand corner’ of the box-shaped constellation of Gemini. Even low powers will give great views through the telescope; binoculars will show a fuzzy mass. American astronomer and writer Jeff Kanipe described it as resembling ‘a tangle of Christmas lights strewn across the floor’, and it is at its highest around the end of December.
Apart from observing only bright objects, are there other courses of action astronomers can undertake to counter light pollution?
Publicise the problem
Arm yourself with facts, and approach those with poor quality lighting. Talk to local media about problems caused by waste light in your area. Remember that not everybody thinks astronomy is important, but they all want to save money and energy, so stress these before mentioning the wonders of the night sky. If you give talks or hold star parties, or belong to a club or society, take the opportunity to mention light pollution as part of more general discussions.
Can darkness be measured? How much money and energy are being wasted? Can the lighting be better managed? The CfDS can provide plenty of supporting ‘ammunition’, much of which can be found on its website. Surveys have shown that most owners of offending lights will take action, and will be surprised that they were causing a problem – whole generations have grown up surrounded by indifferent lighting, and consider it normal.
The measurement of the amount of skyglow above a given location is not easy, depending as it does on many variables.
An instrument now well known to astronomers is the Sky Quality Meter, for example the Unihedron SQM designed by Dr Doug Welch and Anthony Tekatch. The meter is a small hand-held instrument, about the size of a TV remote control. It measures sky brightness. The instrument is aimed at the zenith, and ‘sees’ a cone of about 80° width of sky. The meter has a digital display showing a number, usually between 15 and 20 for most night-time observers. The larger the number, the darker the sky.
20 is a typical reading at a fairly dark site, while 15 represents a very light-polluted sky. For example, in 2009, in one of England’s darkest places, Exmoor in the south-west, David Brabban recorded a meter reading of 21.85 at Prayway Head, showing it to be one of the best observing sites in the country. See page 147 in the 2012 June Journal (JBAA, 122(3), 147) for a description of how North Norfolk AS used an SQM to find their darkest local observing sites.
Exmoor became the UK’s first Dark-Sky Reserve in 2010, joining Galloway Forest Park in south-west Scotland (a Dark-Sky Park) and Sark (Dark-Sky Community) as areas where stars are protected by local administrators and inhabitants.
The amount of energy and money wasted by poorly aimed lights – a very useful item of information to have when approaching their owners – can be calculated if the model and power of the lamp can be identified, and its mounting angle measured. Recently, a hospital in Dorset, whose new lighting scheme caused skyglow visible from many kilometres away in the New Forest, re-configured its lights to a more acceptable angle when local astronomers pointed out the correct mounting angle (available from the manufacturer) and informed the hospital how much energy it was wasting.
Join the CfDS
Most amateur astronomers take no action on light pollution, a fact that is a source of constant bafflement to dark-skies activists. To support the CfDS, you can subscribe to its twice-yearly newsletter (£3.00 for 4 issues) available from the BAA Office, donate to its fighting fund, or become one of its local representatives. CfDS officers are not expected to walk around waving banners and trying to extinguish lights – reasoned argument and a constant outflow of information are the aims, since we realise that to change attitudes, we need informed friends, be they our neighbours, local and national legislators, or lighting professionals. The aim of the CfDS is a gradual but sure evolution towards a well lit environment and the optimum night sky for all Britons, whether or not they are astronomers, and wherever they live. Be part of that evolution.
Bob Mizon MBE FRAS is co-ordinator of the BAA Commission for Dark Skies, and author of Light Pollution: Responses and Remedies (second edition) (Springer, 2012, ISBN 978-1461438212) and Finding a Million-Star Hotel (Springer, 2016, ISBN 978-3-319-33854-5).