map of light pollution trends

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  • #612511
    Robin Leadbeater
    Participant

    Recently a map was posted on the Cloudy Nights forum showing a decrease in light pollution across the UK (and France) between 2014 and 2020, bucking an increasing trend across the rest of Europe, particularly in South East Europe
    http://djlorenz.github.io/astronomy/lp2020/overlay/dark.html
    (select the 2014-2020 trend from the drop down list)
    I voiced a certain scepticism of this satellite based assessment. A marked colour shift in public lighting here from predominantly sodium to (mostly blue white) LED lighting is very apparent in appearance of the light domes seen from my rural location and in the sky background spectrum. The blue white light scatters more in the atmosphere though which would make it less visible from satellites but would increase the sky brightness looking up from the ground.) Am I right to be sceptical? What does the (broad band, upward looking) sky brightness trend show?

    Cheers
    Robin

    #612523
    David Totney
    Participant

    Interesting. I was under the impression that most LED lights were deliberately designed to project the light more in a downwards direction, in contrast to the older sodium lamps which did allow a lot more light to escape upwards. Maybe this is a factor?

    Telescopes: One Newtonian, three Maksutov Cassegrains, seven refractors, and a large SCT.

    #612527
    Paul Leyland
    Participant

    Interesting. It seems to tally with my experience of the last four years in La Palma. Los Llanos is below my horizon, though still visible because I am at a significantly higher altitude, but has become markedly brighter. Everywhere else is much the same. I was mildly surprised to see a hint that my sky may have become slightly darker.

    A Major problem for me is the increased frequency of calimas, the local term for Saharan dust clogging the atmosphere.

    #612561
    Gianni
    Participant

    You are lucky, here in Italy the stars have practically disappeared from the sky. Today was a very clear day, this evening (21 UTC+2H) the sky is still without the Moon but very few stars can be seen (5 in all including Jupiter in the east). The sky in Italy is a real disaster. From the high plateau of Campo Imperatore (2100 m) there used to be clusters of stars with the Milky Way marvellous, so that the constellations could be spotted with great difficulty. Now, clear skies, glimpses of cities near and far, mists. The eyepiece field is white! Pollution would not exist if the air was not laden with aerosols from industrial waste and cars. Light is backscattered by molecules (Rayleigh scattering) and aerosols (Mie scattering) + various optical effects (reflection from particles much larger than the wavelength of light).

    Translated with http://www.DeepL.com/Translator (free version)

    #612562
    David Totney
    Participant

    On a good night I can see the Milky Way from my back garden. Although I do live in the greenbelt.

    Telescopes: One Newtonian, three Maksutov Cassegrains, seven refractors, and a large SCT.

    #612563
    Daryl Dobbs
    Participant

    Caerphilly County Bourgh Council decided over the past couple of years to replace the mercury and sodium streetlights with LED, I have found the skies are less transparent than they were, on a good night (don’t get many of those) I can just about see to mag 4.5 overhead, usually around mag 3.5. The LED streetlights seem to have a lot more glare which is annoying. The prevalence of security lights also is a factor, the light pollution from Cardiff, Newport, Cwmbran, Pontypool and across the stream Bristol seems to have changed from an orange colour to a light mush which I guess is due to LED’s.

    The results from the last Star Count do seem at odds with reality around here. 6 years ago, I did an experiment to see if in a pair of binoculars, I could see M82 and M81 from my garden, I could only just see M81 but traveling further into the valley away from the lights I could just about see M82 as well as M81. Earlier this year I did the same experiment with the same binoculars and from my garden couldn’t see M81 and at the same spot in the valley M81 was just visible and M82 I couldn’t see. I tried to pick a good night transparency wise.

    So in my opinion the skies around here have got slightly worse.

    #612564
    David Totney
    Participant

    I agree that the LED streetlights have a lot more glare.

    Telescopes: One Newtonian, three Maksutov Cassegrains, seven refractors, and a large SCT.

    #612565
    Robin Leadbeater
    Participant

    This is also my experience. I don’t think these satellite maps are showing the true picture. They are measuring the light escaping into space. (If all the light did that we would have dark skies!) What we need to know is the light which is scattered back which depends on the wavelength and the factors Gianni mentioned. A shift in the spectrum of the light pollution from a predominantly orange to blue at the same light intensity would increase the scattering reducing what the satellite sees but making the skies brighter when viewed from the ground.

    Also some LED lights which look like they are full cut off are just flat LED panels with a very wide pattern and no attempt to contain the beam. I have a neighbour a couple of hundred metres away with a very bright one of these. It is directed almost straight down so should be ok but it still overspills into my garden.

    Robin

    #612566
    Peter Anderson
    Participant

    The light pollution map is a worldwide one but we each have our own parochial area that we worry about. Mine is Brisbane Australia where I live. The population is now 2 million.

    In 1978 when I arranged the first light pollution survey I decided to plan it carefully. The idea was to conduct the research over a short period of time in the mid evening between a short range of dates in the dark of the Moon and distribute charts of Scorpius marked with stellar magnitudes. Scorpius, easily recognisable, was near overhead at the time in July and so the problem of a bright horizon in one direction or the other was avoided. Also the zenith was ‘as good as it gets.’ Instructions about dark adaption were provided.

    This exercise was conducted by the Astronomical Association of Queensland in 1978 and repeated in 2018. Though the number of participants is limited, the deterioration in the intervening years is obvious.

    A few points about the attached image. Results below mv 4.0 are shown in red. There were only a few participants who contributed to both surveys, myself being one of them, where my results deteriorated from mv5.8 to mv5.4. Observations from near the centre of the city achieved mv4.8 in 1978, but only mv3,2 forty years later. Now of course, though I have tried to approach this scientifically, the big variable in such surveys remains the variability (acuity) of the eyesight of individual observers, plus the tendency to ‘talk up’ your own pet observing site.

    #612568
    Peter Anderson
    Participant

    Regarding the previous post, I am sorry for the error but results on the charts below mv5.0 (not mv4.0) appear in red.

    #612575
    Daryl Dobbs
    Participant

    I too think the satellites don’t portray the true picture, I live in a valley in Wales halfway up one side overlooking a small town Risca, when out walking one night looking from the ridgeline down into Risca the LED streetlights aren’t that obvious. However, when you are on a more level plane the glare from them is very obvious. From Risca itself there is marked difference in the number of naked eye stars you can see compared with 200mtrs higher on the ridgeline, as for seeing the Milky Way, the only chance of that around here is the confectionary counter of Tesco.

    In 2016 we went to Tivoli a small town in the hills 25km outside of Rome, looking up into the night sky I could only see 4 or 5 stars, the light pollution was horrendous.

    #612586
    Gianni
    Participant

    Yes, Daryl, I live in Abruzzo in L’Aquila, a small mountain town at the foot of the Gran Sasso d’Italia at an altitude of 700 m. Tivoli is not far away. The 2009 earthquake destroyed L’Aquila, the (very slow) reconstruction is turning the town into a beam of lights shot everywhere and at random. Especially since LEDs consume less electricity. Even in the countryside, you need at least binoculars to spot the Pleiades clusters and Perseus, M42 and M31 can barely be discerned through a telescope, while the Lyre ring nebula has disappeared completely. Only the Sun, Moon and the shining planets remain.
    In this hateful and hellish environment, I almost had to give up the telescope. For the past three years, I have been devoting myself to the study of twilight phenomena. At sunset, when the sky is clear, I take a photograph of the anti-solar sky. Then, from these photographs I determine the level of transparency of the local atmosphere.
    At first I thought it was a sad fallback. Now, I have an archive indicative of air pollution and the level of ozone in the local stratosphere.
    The photograph shows the beautiful view from my home, which shows the respect we have for the natural environment.

    Ciao

    Translated with http://www.DeepL.com/Translator (free version)

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    #612594
    Daryl Dobbs
    Participant

    Hi Gianni,
    Tivoli is a beautiful town we enjoyed our stay there, during the day looking down across the countryside towards Rome was usually very hazy, I remember the earthquake which was sad for such a picturesque town. Rome even back in 2016 was very bright on the horizon, above I could only see 4 or 5 stars, in Rome none, the air pollution in Rome seemed very bad. From our hotel balcony we could see several towns all was very bright and it seemed no light pollution control.

    #612618
    Gianni
    Participant

    I live in L’Aquila, a city 100 km from Rome, at the foot of the highest mountains on the Italian peninsula The peaks of Gran Sasso d’Italia are between 2400 and 2912 m (Corno Grande) above sea level. Snow abounds and 6 months of the year you can ski. An old saying is: on our snow, the sun never sets. And indeed here is the city at night. Take a look at the photograph.
    In the evening, three floodlights were turned on, shooting light straight up into the sky. Who is to be told? Here, no one seems to understand.

    Translated with http://www.DeepL.com/Translator (free version)

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