INTRODUCTION

  My submission to the Committee describes the decline in night sky visibility over the last 30 years. Evidence is drawn from personal experiences over this period, initially as a boy active in a school astronomy society, to the present where travel to dark sites is the only way to continue my interest in practical astronomy.

  The evidence centres on the minimum stellar magnitude visibility over the period as recalled. This is directly related to the apparent background night sky brightness, and quantitatively indicates the number of stars visible, including the visibility of the milky way.

  The direct impact of the deterioration is considered in terms of the public awareness of the night sky and astronomy, especially with regard to younger people. This impact is measured through changes over the 30 year period plus differences observed in amateur astronomers as I travel to pursue my hobby.

  Much has been said and written as to the need or not for increased levels of lighting. This argument is not considered further in this submission.

EFFECTS OF INCREASING LIGHT POLLUTION

  The table below sets out the minimum stellar magnitude visibility for a variety of locations, both at the present, and as the author recalls it was 30 years ago.

  In the table U signifies a generally Uniform distribution of sky glow. I indicates an Irregular distribution caused by fairly large or close sources of light pollution visible in one or more compass directions. The figure given is for a typical area of interest situated halfway between horizon and zenith.

  The degradation in visible magnitude over the 30 year period seems to be maximum in the suburban and semi-rural districts. It would appear that the cities could not get any worse, and development of the deep rural UK countryside has remained low.

  The figure to the right shows the apparent zenith minimum stellar visibility, based on calculations from satellite measurements.[4] (not printed)

  Although the resolution is poor, the map indicates a difference between Camberley and Wellington of approximately 1.25 magnitudes. As this is a zenith figure, it can be expected to be worse nearer the horizon in light polluted areas. Thus the authors estimate based on practical measurements of between one and two magnitude dependent on viewing angle is not unreasonable.

  The map is informative as to the distribution across the UK, and in comparison with other European areas. Unpolluted night skies are now lost to all in the UK but the remote regions of Ireland & Scotland.

  This observed increase in light pollution over the 30 year period amounts to an average of around 5% per annum. This is broadly in line with estimates for other urban locations around the world.[5]

IMPACT

Naked Eye Visibility

  The empirical evidence presented above suggests that the main residential districts, and those areas easily accessible to the public in general (suburban and semi-rural), have suffered up to a two magnitude reduction in stellar visibility. More than 90% of our population are classified as living in "urbanised areas" and thus at least this number of people will be severely impacted now by light pollution.

  Let us consider what this drop in visibility means in practical terms. The following table[6] assumes one third of the total night sky (both hemispheres) can be seen.

  We can see therefore that at best (assuming a one magnitude drop in visibility), compared with 30 years ago only 1/3 as many stars can be seen with the naked eye, with some observers only seeing 1/10 as many stars (two magnitude drop). Below, six representations of the night sky are presented, showing a simulation of the number of stars visible for a given minimum stellar magnitude.

  The impact of the night sky on the casual observer will obviously be very much reduced today, and in most geographical areas the Milky Way has dropped below the threshold of visibility.

TELESCOPIC

  The impact over the 30 year period of light pollution on telescopic observations is for me more difficult to quantify. Details of observations were not kept from the 1970's by the author. Memory recalls that even from the suburbs of London (SE12), useful observations of deep sky objects were possible. One specific memorable fact was the seeing of the central star in M57. This is a classic test of the quality of seeing conditions and equipment.

  I can now report that deep sky observing is all but useless from suburban skies. Even in semi-rural areas observations have to be tailored to avoid local areas of light pollution from towns. I have not recently seen the central star in M57 from any but remote rural locations.

  Comparing the seeing between my two homes, I would estimate that the increase in light pollution in the suburbs over the last 30 years is equivalent to the difference seen today between semi-rural and suburban sites. This equates to the order of a two magnitude drop in visibility of telescopic objects.

OVERALL IMPACT

  If we consider that 90% of the UK population lives in "urbanised" areas[7]. It is clear that their casual view of the sky is not going to create any great impression or desire to know more. If anyone in these areas does look through or buy a telescope, then they are going to be disappointed, as they will only be able to observe bright objects.

  The better night skies are limited to those fortunate to live in rural areas, or those who are able to travel to them to observe.

  I have regularly attended astronomy observing camps, exhibitions and astronomy society meetings in the UK over the last five years, The absence of younger people at these events, and indeed the almost total absence of children is notable. Considering the popularity of TV programmes and books related to astronomy and cosmology, one might have expected a more general age distribution.

COMMENT ON PLANNING GUIDELINES AND THEIR IMPACT

  There is no doubt that full cut off lighting fixtures are being widely used in new installations and replacements. However against this potential reduction in stray light there are many other factors that serve to increase light pollution. Although cut-off fixtures are used, more areas are being lit and generally at higher levels. This light is reflected off the ground, buildings, etc and then adds to the light pollution.

  An example is a new all-weather pitch located some 800m from my home in Somerset. The lighting fixtures are well designed full cut-off units, but the intensity of the lighting and the reflectivity of the pitch creates a dome of light that obliterates the night sky completely. These lights are normally on most evenings until 11pm.

  Domestic "security" lights seem to be outside any planning guidelines, and they are being increasingly installed by residents around their homes. Their power levels, siting, and setting of time delays, all generally leave much to be desired. While they probably contribute very little to the general sky brightness levels, they can make many back gardens and public areas completely useless for observing because of the direct and indirect illumination into the garden

COMMENTS ON MEASURING LIGHT POLLUTION

  The work being led by Cinzano and others in Italy is producing maps of sky brightness for the whole world down to a resolution of 2-3km. Comparing his analysis with my observations, I would say that his maps are a good representation of what is observed in practice from the ground.

  Quantitative practical measurements from the ground in the UK would be difficult to make and use due to the variability in our weather. The approach used by Cinzano is much less dependent on such factors, and could be a very useful tool in the monitoring of changes in the UK levels over a period of time.

CONCLUSION

—  Over the last 30 years, light pollution has increased for the majority of the UK population, such that between only one third and one tenth of the stars are now visible to the naked eye.

—  The visual impact of the night sky has now been lost.

—  The Milky Way is no longer visible to anyone but those living in deep rural areas.

—  Most telescope users will have suffered a two magnitude drop in minimum stellar magnitude over the same period. This effectively prevents observations of deep sky objects.

—  Unaffected night skies can only be found in the furthest reaches of Scotland and Ireland.

—  Practical astronomy seems to be a dying interest, limited now to the true enthusiast or the wealthy.

—  Although full cut-off lighting fixtures are being more widely used, the overall increase in quantity of lights and in lighting levels is producing a net increase in light pollution.

—  Domestic security lights present a real obstacle to backyard observing.

25 April 2003

5   Cinzano, P, The growth of light pollution in North-Eastern Italy from 1960 to 1995. Back

6   Tycho Catalogue Back

7   http://www.planning.odpm.gov.uk/habitat/intro.htm Back