CPRE Star Count 2019

Forums General Discussion CPRE Star Count 2019

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    Bill Barton

    This February the Campaign to Protect Rural England is running a light pollution survey. The survey opens on February 2 2019 and closes on February 23 2019.

    To take part simply count the number of naked eye stars you can see inside the rectangle formed by Betelgeuse, Bellatrix, Rigel and Saiph (that is the four main stars in the constellation Orion). Do not include these stars though, just the ones inside the rectangle.

    The recommended period to use would be from the 2nd to the 9th to coincide with the dark of the moon and from 7pm.

    For further information and to upload your results go to:-


    Peter Anderson

    Just a few comments from the ‘peanut gallery’ as it were.

    In 1978 our Association (Astronomical Association of Queensland) in Brisbane, Queensland Australia (27.5 deg south 153 deg east) conducted a light pollution survey which we repeated in 2018 forty year later.

    Needless to say, the membership was generally lethargic, even for something as simple as this involving simple naked eye observing, but we got enough results to show that as the city grew skies deteriorated. The mean limiting magnitude in 1978 was 5.5 and in 2018 it was 4.6. My personal site deteriorated from 5.8 to 5.4. By this statement you will see that it was not a simple ‘star count’ which provides limited information, and in a large area like Orion there can be miscounts and double ups. Besides spanning (from the UK) over 15 degrees in altitude, extinction will play a factor. (See later comments).

    However I would like to make my point that we tried to do this as scientifically as we could.  The ideal would be to have a scientific device to properly measure it, and the next best would be to have a roving team who would first meet and test their eyes so that they could add a ‘correction factor’.  Then they would visit key sites and take the readings.  However this sort of exercise is costly and you have to operate with those funds and volunteers that you have.

    Anyway, what we did was publish a map of Scorpius with the brightness of the stars marked.  This was to be our reference.

    The sightings were to take place within one half hour of 9pm during a specified moonless week in July when Scorpius would be nearly overhead. This way we avoided contamination from shopping centres and stuff near the horizon as well as  extinction at lower altitudes.

    The instructions were to get dark adapted, and first identifying stars that were easy to see, then moving to ever fainter ones until they were no longer visible. A bit of ‘averted vision’ might be used but not ‘wishful thinking’. I remember reporting 5.3 okay and 5.4 with a ‘following breeze’.

    Now people’s eyes change with age. There is a grey/green cast which develops and reduces contrast and changes the colour balance. (Fixed by cataract surgery.) So without cross-checking, which in an amateur society is probably difficult, you will have to take the results on faith. There is also the factor that some people like to ‘talk up’ how good their site happens to be, but though you know who they are, you can’t reasonably address this.

    I just supply all of this for interest. Orion is easy to identify. It straddles the celestial equator so from your locations would at best be under 40 degrees altitude on average and at a reasonably altitude would be in the South East- South- South West quadrant. If sites had bright developments in that direction, it would badly skew results.

    For near overhead at your latitude in early evening, at present there is Capella, but the surrounding star patterns are not distinctive.  Might I suggest using Ursa Major in April-May. Nearly overhead early/mid evening and very distinctive. Just print and distribute a map with magnitudes marked, say in your Journal/Newsletter.

    I hope my thoughts are helpful.

    Peter Anderson


    Robin Leadbeater

    Yes possibly of  not much scientific value unless you can get a large enough number of observers in a given location and over a reasonable length time to beat down the variability (The key to success in citizen science projects) but I suspect this project by CPRE is more about public awareness of the issue and to get a conversation going than the actual quality of the measurement. Hence the use of an instantly recognisable constellation.   Interestingly I met a casual observer from a nearby village the other day who had been lent a sky quality meter to monitor their skies by the Friends of the Lake District.


    Neil Morrison

    Any thing that gets  folk out looking at the Stars cant be  bad  shurely. Youngsters are particularly good at developing enthusiasm and  persuading their parents  to come outside and look up.  The count may not be truly scientific  but  it will reap dividends in the future if only to make people aware of the  poor skies we endure. In contacts during  outreach events many  people  have commented on the difference  between U.K. conditions and their  camping  holidays abroad when  the constellation patterns  were lost  amongst the  multitude of stars  visible there. 

    Callum Potter

    Thanks for alerting us Bill – actually the CPRE got a little ahead of us, as this is a joint BAA / CPRE project that we have been working on for the past couple of months. Helpfully the CPRE kindly offered to host the website submission forms and process the results.

    I hope members will take part, and spread the word to their local societies, forums, and encourage friends and families to take part too.

    Clear skies


    Robin Leadbeater


    Robin Leadbeater

    I see this website which plots the VIIRS satellite data also accepts SQM readings, though they are rather sparse


    The string of readings up the M6/A74 is interesting. Perhaps I should mount a one on the roof of the car, coupled with a GPS logger.



    I did the star count last night and could count 12 stars from my back garden; 10 were easy to see, 2 were with averted vision. Will be interested to see the final national results.


    Tim Haymes

    On this subject I use:    https://www.lightpollutionmap.info/#zoom=9&lat=6724317&lon=-84999&layers=B0FFFFTFFFT
    I have compared my measured SQM-L readings at places in Berks/Bucks and Oxon and find a reasonable good correlation with the map in the range 20.2 to 20.9.  I use the LP map to spec out places to observe from. Ive not done an Orion count from the 20.8 locations, but i hope to do this.

    Bill Barton
    Dr Paul Leyland

    La Palma is famous for its dark skies, right? Not last night. There was a brilliant moonlit Calima. I didn’t even bother counting stars because a single glance showed that I’ve had much better skies from central Oxford or Cambridge.

    It didn’t stop me observing variables but the limiting magnitude was markedly poorer than usual.

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