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Dear BAA members –
I hope you are well?
I am a journalist with NBC News in London currently looking into a piece about London’s night sky. I’ve lived in the city for 13 years and back in February it struck me and a few other friends that the sky appeared much more starry than we could ever remember it here. Presumably some of this is down to the weather but I still don’t remember being able to see so many stars during similar periods of clear, cold nights in previous years.
I would be interested in exploring this idea, potentially for a written story on NBCNews.com, so I am trying to canvass some expert opinion. To that end, I wondered whether you or any of your members had thoughts on this? Is this something you have experienced yourself? If so, what are the possible explanations? Could the drop in NO2 over London reported by City Hall last month be a factor?
I would be fascinated to hear any thoughts you might have for the story I hope to write for NBCNews.com. Any help at all would be very much appreciated. How does that sound? Any questions please let me know.
A bit about us: NBCNews.com and NBC News Digital reach more than 58 million unique visitors, generating more than 1.2 billion page views each month. I am the lead enterprise reporter on the London team, which covers international stories. You can see some of my previous work here: http://www.alexander-smith.com
Thanks and all the best –
Alex
I wonder whether the impression of the sky looking more start was a consequence of three bright planets being on view during the evenings? My initial impression of the night sky being clear is always stronger when I am looking towards Orion and Sirius than when I am looking towards blander constellations such as Cetus or Hydra.
Over the years, my impression has been that daytime blue skies have more milky, presumably due to an increase in aircraft contrails that gradually spread out. A notable exception being in the early weeks of lockdown in 2020 when there were few aircraft flying.
In contrast, during runs of clear nights, haze seems to be less of a problem than it was 40 years ago. Then, I could get a couple of useable nights before the haze became too bad. Nowadays, this happens much less often. Maybe due to a reduction in air pollution?I would also add in the period when the Eyjafjallajokull volcano in Iceland saw aircraft grounded too – that saw an unusually long run of blue skies too.
It might take some of the fun out of the discussion for the journalist, but by looking at VIIRs imagery for London over (say) the last 10 years you should be able to see what has happened in recent years as the measured upwelling radiance would need to be constant before you could safely attribute more stars to NO2 levels and the ULEZ.
Something like…
The website now actually offers the option for trend analysis on the light pollution levels. Impressive how dark some of the Motorways have become.
Perhaps upwelling blue light is scattered more strongly and never reaches space and so gives a false impression.
By comparison my home location has seen a small rise in light pollution as new house builds seem occupied by people afraid of the dark (despite every phone having a torch inbuilt) – even out here in the boonies where a crime is a major event!
I had people commenting on the recent nice line of three bright stars – aka Mars, Pollux, Castor.
As for folk afraid of the dark, the attached image shows my neighbours are recreating Chevy Chase’s Christmas Vacation lights. They have every light on in the house, intensely bright through paper-thin blinds or none at all, and floodlight their garden in multi-colours.
Apologies if I’m not monitoring mag 16 29P/SW1 for outbursts, etc.Thankfully, this ‘spectacle’ isn’t on display all night, every night. Perhaps a la Chevy, the National Grid has asked them to reduce the loading on the local electricity network?
Alex.
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I suggest that this version of VIIRS mapping is correctly correlated and validated. https://pmisson.users.earthengine.app/view/trends
It is slightly more difficult to use than the one published by https://www.lightpollutionmap.info/ but is better once the transparency of the layers are adjusted. A useful exercise is to click randomly over the London area and note the great variability in year by year trends depending upon location.
It is very difficult to draw overall conclusions about trends. The consensus within CfDS is that levels of sky brightness are either unchanged or continue to rise in suburban/urban areas, while some rural locations, in reserves for example, are getting darker, which is good news.
There are fundamental flaws with the satellite method of assessment and continuous ground based monitoring using qualified photometry is probably the most believable way of assessing trends. Are any London based observatories monitoring zenith SQM levels on a continuous basis (with offset to miss the Milky Way)? Of the two rural observatories I am familiar with, one is showing no change at zenith but great increase at lower elevations over a long period, while the other is recently starting to record an increase in sky darkness at zenith (good news but more analysis needed). My own SQM observations from a suburban area are just spot checks and so invalid for true trend analysis.
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