RAS PN09/22 (NAM09): Restoring our view of the stars in rural Britain
Rural areas in Britain could see a return to dark skies if the UK lighting industry adopts the results of a seven-year study by Dr Chris Baddiley, the Scientific Advisor to the BAA Campaign for Dark Skies. Dr Baddiley will present his research at the European Week of Astronomy and Space Science in Hatfield on Tuesday 21st April.
Dr Baddiley has developed a comprehensive mathematical model that calculates how light emitted by street-lamps is reflected by surrounding surfaces, such as roads, grass, walls and trees, and then scattered through the atmosphere back down to the ground. He has found that in rural areas, improved street-lamp design could cut sky-glow by a factor of three to five, depending on the lamp’s elevation and distance of view.
"In the UK, glow from towns illuminates the sky even in rural areas and the majority of young people have never seen the Milky Way. The research shows that they are being deprived needlessly of this inspiring sight and, as part of International Year of Astronomy, we should try to restore our view of the stars. With changes to street-lamp design, we can not only reduce sky-glow significantly, but also save energy in lighting our streets roughly equal to the continuous output of two power stations," said Dr Baddiley.
Dr Baddiley’s model tracks how the scattering of light is affected by atmospheric conditions, such as cloud cover, the concentration of dust and water droplets and the variation in density with altitude. It also takes into account the angle and the wavelength of light emitted and the viewing distance, allowing him comparisons of the contribution to sky-glow by different, commonly found designs of street-lamps.
The research shows that close to towns, sky-glow is dominated by reflections from surrounding surfaces to the roads, such as grass in suburban areas. At a distance from towns, direct radiance from lighting above the horizontal is the main cause of sky-glow.
Full cut-off lights (FCOs), where the light is only emitted downwards through a flat glass panel and no light escapes above the horizontal, can cut sky-glow by a factor of eight compared to traditional low-pressure sodium lights. The FCOs produce around 15-30% less sky-glow than lamps with shallow bowls. A light with a polycarbonate bowl will cause about 15% more sky-glow than the same light fitted with a glass cover.
The study also shows that the trend towards white light sources is increasing the reflections off the vegetation and scattering in the atmosphere substantially. "Shorter wavelengths, towards the blue end of the spectrum, are scattered more than longer wavelengths which is why we see the sky as blue during the day. White lights emit across the visible spectrum and the blue and green components are adding significantly to light pollution, compared to yellow or orange light. This is something that most lighting engineers have never thought about," said Dr Baddiley.
Dr Baddiley’s work has been published by the Institution of Lighting Engineers and the UK Highways Agency has incorporated his findings into their new standards.
"The findings have been accepted by our national organisations, but we need to ensure that the message reaches the people that are designing and commissioning light fittings. We are currently working to produce some educational tools based for use in professional lighting engineer qualification courses."
"Modelling light pollution for sky-luminance reduction based lighting standards" – Dr Chris Baddiley, Scientific Advisor to the British Astronomical Association Campaign for Dark Skies.
For images, see the British Astronomical Association Campaign for Dark Skies image library http://www.star.le.ac.uk/~dbl/cfdsdisk/cfdsdisk
Light pollution simulator by Dan Nixon
NOTES FOR EDITORS
BRITISH ASTRONOMICAL ASSOCIATION’S CAMPAIGN FOR DARK SKIES The British Astronomical Association (BAA) is the UK's largest body representing the interests of all those - astronomers and non-astronomers - who appreciate the beauty of the night sky and value it as a natural resource. The Campaign for Dark Skies (CfDS) was set up by concerned members of the BAA in 1989, to counter the ever-growing tide of sky-glow which has tainted the night sky over Britain since the 1950s. CfDS has grown into a network of over 120 volunteer local officers, and several hundred committed supporters, who work to persuade their local councils and organisations of the benefits of well directed lighting, the motto being: the right amount of light, and only where needed.
THE EUROPEAN WEEK OF ASTRONOMY AND SPACE SCIENCE More than 1000 astronomers and space scientists will gather at the University of Hertfordshire for the European Week of Astronomy and Space Science (EWASS), incorporating the 2009 Royal Astronomical Society National Astronomy Meeting (RAS NAM 2009) and the European Astronomical Society Joint Meeting (JENAM 2009). The meeting runs from 20th to 23rd April 2009.
EWASS is held in conjunction with the UK Solar Physics (UKSP) and Magnetosphere Ionosphere and Solar-Terrestrial Physics (MIST) meetings. The conference includes scientific sessions organised by the European Organisation for Astronomical Research in the Southern Hemisphere (ESO) and the European Space Agency (ESA).
EWASS is principally sponsored by the Royal Astronomical Society (RAS), the Science and Technology Facilities Council (STFC) and the University of Hertfordshire, Hatfield.
THE ROYAL ASTRONOMICAL SOCIETY
The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.
Dr Christopher J Baddiley
1 Kingshill Close
Tel: +44 (0) 1684 566205
Mob: +44 (0) 7956449233