Light Pollution: Chapter Three

An article on Light Pollution experiments in and around the St Austell area, by Tara Hill

Results of Observing Session

Initial Analysis

View a full screen size image of this Chart

At first glance it was obvious the limiting magnitude was severely depleted, ranging from 0.7 to 2 magnitudes. Further study of the results showed a discrepancy. The constellation at 40 degrees had lost more magnitudes than the constellation of 20 degrees, this was the opposite of what should have been seen, as the higher up a person looks from the horizon the clearer and darker the sky should get (see diagram 4a).

It was thought the problem had probably been generated by the use of the chart at 40 degrees.

The chart for Ursa Minor has a large gap between the limiting magnitudes of 3.9 and 5.2, whereas the the chart for Orion has four measurements between these figures making it a lot more accurate. These charts were designed to discover the limiting magnitude of a persons observing site using just one constellation at an optimum angle of 45 degrees and not for a survey such as this. However, they did do the job which was required of them and that was to determine whether light pollution existed in the St Austell area.

Another factor which should be taken into account, two of the stars on the Orion chart were very hard to see and at times almost impossible but they were included in the results as they had been glimpsed, this could also account for the discrepancy.

4.2 Altitude at 20 Degrees

As expected the magnitudes lost at 20 degrees appear high. If they were less an explanation could usually be found. For example at Site D, the observation at 20 degrees shows less magnitudes lost than at 60 degrees. This was probably due to the later observation facing seawards and sea mist needs to be taken into consideration for this observation.

4.3 Altitude at 40 Degrees

After producing Map Three it could be seen that seven of the northerly observations would have been affected by light pollution of some sort. The observation North of Site C is of special interest. From this site only 0.65 magnitudes were lost, coincidentally North of Site C there is no major source of light pollution. However, looking South (at 20 degrees) of Site C, 1.25 magnitudes were lost. This observation was in the direction of Par and Par Harbour, nearly doubling the Northern observation. Looking at the result for 40 degrees and considering the presence of light sources, my initial statement about a discrepancy in the results may in fact be due to the light pollution present.

4.4 Altitude at 60 Degrees

All observations were as expected at 60 degrees. There was some loss of magnitude suggesting that even though light pollution is reduced at this altitude it still has some detrimental effects on astronomical observations.

4.5 Difference Between the Four mile and Two mile Sites

The sites at two miles distance from St Austell railway station have similar light pollution results to the island settlements in the china clay area. This suggests that both areas have a similar affect on the rate of light pollution.

4.6 Light Pollution in St Austell and Surrounding Area.

The results of this study show light pollution is a problem in the St Austell area. It would be very hard to find a truly dark site for astronomical observations.

Conclusion

It is a fact that to escape light pollution in Cornwall would be very difficult, in St Austell it would be impossible, look at the satellite picture on the title page (Ref: Starry, Starry Night handout), the St Austell area seems to glow. No site on this survey was clear of light pollution. However, if I were to build an observatory , Hewaswater would be my choice but even here the magnitudes were depleted.

The reason for this is the direction in which light leaves the various luminaires. An unshielded or even partially shielded light will cause skyglow. Therefore, if more of the Full Cut Off Shielded lights were used less electricity would be produced which would eventually result in the reduction of greenhouse gases and extended use of fossil fuels. This would not only help the environment as a whole but also give back the dark skies which Man has used as a recreational activity for thousands of years. If we lose the night sky to pollution then we lose the stories of the ancients.

There is hope however, as large organisations such as Cornwall County Council are well aware of the issues concerning light pollution. There replacement of the older SCO luminaires with the newer FCO designs will greatly reduce light pollution, however this is going to be a gradual process taking many years to complete. The more pressing problem now is the increased use of the unshielded domestic security light, which can be bought cheaply from DIY shops with no instruction on reducing light pollution.

To increase the awareness of the problem the Campaign for Dark Skies (CfDS), are producing leaflets and have a website with example of light pollution. There officers campaign in their own locality, there are over 100 local officers spread around Great Britain. The CfDS campaign is not to turn the lights off altogether as this would be unacceptable. Careful use of light is their advice, this will not only benefit astronomers, but anyone who is concerned about the nocturnal environment.

There have been a few people I have spoken to who seem aware of the problem, including some specialist lighting contractors. Generally though, there is a lack of awareness. I think if more publicity were given to the affects of nature, such as bird collisions with lit up buildings, more people would take notice.

Evaluation

The investigation was successful as it did show that light pollution was a problem in the St Austell area. This result was expected due to the industrial nature of the area. It would be interesting to carry out the survey over a longer period of time. This would provide information from all directions and eventually a more detailed version of Map Three could be produced.

If I were to carry out the investigations again, I would want to use more sites than were surveyed in this instance. Instead of dividing the circle into six, I would like to divide the are into sixteen squares. From each these squares I would like to choose one area to observe from, they would need to be high up and away from any type of lighting, as I found this was a problem when surveying. This would give a more widespread view and I would probably be able to pinpoint which lights were causing the pollution.

With respect to Aim 6, on the project proposal form regarding awareness of light pollution. A letter was sent to the Cornish Guardian Opinion Page but unfortunately was not printed before the closing date of this project. It would have been more productive to have included a questionnaire in the investigation. I would however, like to produce a questionnaire for the astronomy groups of Cornwall, with questions and a small survey perhaps of two or three constellations to complete.

Finally, as a result of this investigation and my contacts with Campaign for Dark Skies, I am now on their records as a local officer (correspondent only). As time goes on I would like to become more involved in their campaign and help to stop the growth of excessive lighting.

Bibliography

Books

Foster Ian & Matthews Hugh; Geographical Data - Sources, Presentation and Analysis; (1992); Oxford University Press; ISBN 0 19 913328 X.

Mizon Bob; Light Pollution - Responses and Remedies; (2001); Springer-Verlag London Ltd; ISBN 1 85233 4975

Moore Patrick; The Amateur Astronomer; (1964); No ISBN due to age.

Moore Patrick; Guide to Stars & Planets; (1998) Reed International Books Ltd; ISBN 0 540 07261 3.

Moore Patrick; Atlas of the Universe; (1998); Reed Consumer Books Ltd; ISBN 0 540 07261 3.

Ridpath Ian; Oxford Dictionary of Astronomy; (1997); Oxford University Press; ISBN 0 19 211596 0.

Websites

www.buildinggreen.com ; 13.03.02; Light Pollution Efforts to Bring Back the Night Sky.

http://www.darksky.org/ida/infoshts/is109.html ; 09.01.02; Kenneth D Frank; Impact of Outdoor Lighting on Moths July 1996.

www.ile.co.uk ; 22.02.02; Frequently Asked Questions - Drafts for Discussion; (Institute of Lighting Engineers)

http://members.aol.com/ctstarwchr/ ; 16.01.02; Light Pollution Awareness Site.

www.weather.co.uk/weather/local/ukxx1502 ; 15.02.02 and 16.02.02; The Weather Channel.

http://www.dark-skies.org : Campaign for dark Skies

CDROM Redshift 4; Focus Multimedia Ltd; 2000.

MAP Ordnance Survey; Touring Map of Cornwall; ISBN 0 319 25031 8