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New 2020 Global Light Pollution Atlas

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#26 vsteblina

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Posted 11 October 2021 - 08:06 PM

Several comments....

 

I live 7 km up Burch Mountain.  The measurements were taken at 13.3 km.

 

1)  I did take meter reading with a SQL meter during the transition period.  My meter readings were taken at N45, S45, W45, E45, and overhead.  They all showed a slight decrease in light pollution during the transition.  Unfortunately, I only took meter reading during clear nights and from Thanksgiving through President's Day Wenatchee weather is just as awful as Seattle's.

 

2)  The DOT streetlights are VERY BRIGHT and at 4000K.  I was coming home last weekend and noticed the significant difference between the county streetlights and WA Department of Transportation streetlights.  There are lots of DOT streetlights along the three interchanges and two highways in the immediate vicinity seen directly from Burch Mountain.

 

3) There has been significant "subdivision" growth up Burch Mt.  The county does not have any streetlights, but all my new neighbors from  Seattle think ONE porch light is not enough and have taken to stringing up 40 plus lights in from of their homes.  That is a significant increase in light since ALL are unshielded.

 

4)  My sky to the east was pretty dark and then suddenly new businesses opened along Highway 97 to the east of me.  Now that sky is pretty bright in spite of the fact I am 500 feet above and blocked by a ridge.

 

5)  Wenatchee has lots of ball fields that "spray" and unbelievable amount of light up Burch Mountain.  There is a chance that the 2018 reading, the ball field lights were off and on for 2019.  That would account for the increase just by itself.  Not sure if there is a way to check this at this point.

 

There is a problem with just ONE observation.  I would have given the PUD permission to set up a monitoring station at my house.  I do give them credit for attempting the measure the effect of LED streetlights on the night sky.

 

My take, streetlights are not the problem.  It is the private lighting practices that are degrading the night sky, much more than streetlights.



#27 DaveL

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Posted 11 October 2021 - 09:44 PM

My take, streetlights are not the problem.  It is the private lighting practices that are degrading the night sky, much more than streetlights.

Probably similar in the rural areas I observe (southwest Wisconsin). A significant fraction of farmhouses have huge unshielded light fixtures on all night. Unfortunately for the light pollution atlases, these farmhouse lights are isolated and "relatively dim" enough that these sources are not detected by the satellite. This likely leads to a bias in rural areas with lots of farms.

 

-Dave



#28 BPO

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Posted 12 October 2021 - 01:53 AM

Aerosols can play a big role. There are settlements (a town and two or three small villages) not far from my observatory which is sited atop a mountain plateau at around 1900 meters asl, but the two SQM-LEs I operate routinely read 22.0x on clear moonless nights. The site is above two usually active inversions which keep any dust and smoke well below the mountain top, so local artificial skyglow is effectively nonexistent. The small mountain range rises near vertically from the flat terrain about 1500 meters below, and it's not unlike being on the roof of a tall building in the middle of nowhere. If the terrain and conditions were different I'm sure my sky would be a little brighter.



#29 ar-pharazon

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Posted 12 October 2021 - 06:13 AM

Congratulations and thank you, Dave.

I think this video may be useful for this topic:

https://youtu.be/z67k0VCijik

https://www.mdpi.com...4292/13/16/3311

Edited by ar-pharazon, 12 October 2021 - 07:30 AM.


#30 Ron359

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Posted 12 October 2021 - 11:16 PM

Perhaps an inflection point in bad LED city lighting?

 

https://skyandtelesc...-begin-a-trend/



#31 DaveL

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Posted 12 October 2021 - 11:56 PM

For fans of the Bortle Scale, see this rather obscure paper, not peer reviewed .

https://artificialli...2015_bortle.pdf

Especially pages 18-22 which show that Borle Class correlates pretty well with NELM and the BRIGHTEST part of the sky (which is always near the horizon), and quite poorly with Zenith Sky Brightness, especially in classes 1-4 where the curve is almost flat.

....

Dan

Very interesting results, I've been looking at similar plots and they are consistent with what you find. One little nitpick, you say that "Only 8 Class 1 nights observed (very rare), and 7 had outstanding extinction < 0.15". Actually half have 0.15 or worse extinction. The two Bottle 1's with the worse extinction (obviously night dependent) are Capitol Reef (0.23) and Glen Canyon (0.22):

 

http://www.sierranig...CARE070617.html

http://www.sierranig...GLCA070614.html

 

These are still good extinction values, but still, based on scatter plots I have looked at, extinction doesn't seem to help distinguish Bortle numbers. Also, some sort of "expert assessment" should be used to exclude certain sites. For example, the Bottle 1 Denali case (http://www.sierranig...DENA100915.html) has an aurora present which makes the brightest part of sky measurement way off.

 

Overall, a very nice analysis.

 

-Dave


Edited by DaveL, 12 October 2021 - 11:57 PM.


#32 ghayduke

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Posted 13 October 2021 - 07:10 PM

reply to vsteblina from Dr. Li-Wei Hung:

Hi Dan,

Thank you for forwarding the message. Please feel free to share my following response with him or post it on the board.

He (vsteblina) raised many good points. We have no way to track the private lighting, so it definitely introduces some uncertainties to this case study. Also as he pointed out, our ground-based observations are limited, and the potential drawback from the small sampling is discussed in the paper as well. That being said, here are some points I can clarify:
1. Ground based data are taken only one year apart, immediately before and after the retrofit. This short separation gave us the best chance to minimize the effects from long-term population growth and changes in private lighting.
2. The observations were taken at roughly same time of the year and same time of the night. High albedo of the snow is not a concern because these observations were outside of the winter months. Atmospheric conditions (extinction coefficients) are also similar. These were the best scenarios that one can hope for keeping all these variables under 'control.'  
3. Our data show the image of the entire night sky, offering more dimension than SQM measurements. The images not only show the zenith is brighter, but they also show size and brightness of the light dome are increased.
4. We have checked with the county officials. They said the ballfield lights were off by 10 or 11 pm in general, even if there were games earlier in the evening. Both of our observations were taken around midnight so the ballfield lights should not be a concern.
It was nice to hear from people living in that area and their personal observations. Thank you for sharing and I am looking forward to see his SQM observational report if he is plan to publish it in the future. 

Thank you,

Li-Wei



#33 ghayduke

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Posted 13 October 2021 - 08:02 PM

reply to Dave,

Aurora (and bright meteors) were always masked out by hand in the all sky data sets before analysis, treated the same as horizon obstructions. 

I have always had a little trouble distinguishing between Class 1 and 2. Since in the original S&T article both 1 and 2 are described to have essentially no visible artificial sky glow anywhere in the hemisphere, with the differences being mainly related to atmospheric transparency, I approached this in the field looking for faint stars near the horizon and subtle details in the Milky Way, as well as NELM well below 7. In that regard, the finest sky I have ever seen was at the summit of Mauna Kea, but because of lack of oxygen to my brain I was only able to reach 7.1 visually. V band extinction came out 0.10 mag/airmass. Also, the light dome from Honolulu, 300 km away, way barely seen to extend above 0 altitude, and easily seen below the level line. Does this make it Class 2 or 3? Absolutely not. Yet at less than 500 m elevation sitting in a hot tub at Saline Valley hot springs and dark adapting for 3 hours, I was able to get an NELM of 7.6, with V band extinction at 0.18 mag/airmass, even though "faint light domes from L.A. area, Las Vegas, and Fresno extend to no more than 10 degrees altitude."  I gave it Borle Class 2, but if you take the original manuscript's narrative literally, it should be Class 3 since light domes of distant cities were definitely visible to 10 degrees above the level. I just couldn't say it was Class 3 where the faintest star I ever detected with the unaided eye was seen The point of Chad's paper is that splitting hairs on the finer points is a somewhat inexact science, and a suite of all sky measurements calibrated in some system or other along with a measure of atmospheric clarity may arrive at a reproducible scale. We tried this with the 0-100 Sky Quality Index, but it never caught on, probably because few measures are all sky and include atmospheric extinction, other than the NPS method and ASTMON. SQI for Mauna Kea came out 99.8  and Saline Valley 97.6.  I personally like the ALR, or ratio of artificial to natural sky brightness averaged over the entire visible sky, but this is even more complicated, requiring a model of the natural sky for pixel-by-pixel subtraction. See: https://www.scienced...022407317308749 ; https://arxiv.org/ftp/arxiv/papers/1907/1907.02891.pdf 

The two finest skies I've ever seen.

http://www.sierranig...res_3_HA180.jpg

http://www.sierranig...res_2_HA180.jpg

Incidentally, the domain sierranights.com is my wife Cindy's, she has been paying yearly fees to keep it going for nearly 15 years primarily to keep these data publicly available.


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#34 BPO

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Posted 14 October 2021 - 02:44 AM

I live 7 km up Burch Mountain.

That's a big mountain!

 

xD



#35 DaveL

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Posted 14 October 2021 - 10:48 AM

reply to Dave,

Aurora (and bright meteors) were always masked out by hand in the all sky data sets before analysis, treated the same as horizon obstructions. 

Oh now I get it, I see the artificial sky mosaic has the aurora masked out. The problem I was running into is that the values in the "Photometric Indicators" table do not have the aurora masked out. So, for example, the brightest part of the sky is 20.57 in this Denali case. I have been using these sorts of values when I looking for relationships between Bortle and photometry. Do the SQI indices have things like aurora filtered out?

 

I agree that Bortle 1 and 2 both seem to be for the same sort of light pollution "free" sites, and that distinguishing them comes down to meteorology and airglow. Also, I'm not sure what to do with this Bortle 1 statement: "If you are observing on a grass-covered field bordered by trees, your telescope, companions, and vehicle are almost totally invisible." The clear night sky always seems bright enough for me to see the stuff around me even when I'm at the darkest sites out west.

 

Also it seems like NELM has too much influence on the Bortle scale, even though in the introduction to the Bortle scale, John explicitly mentions the issues with NELM.

 

-Dave



#36 Tony Flanders

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Posted 14 October 2021 - 07:23 PM

I'm not sure what to do with this Bortle 1 statement: "If you are observing on a grass-covered field bordered by trees, your telescope, companions, and vehicle are almost totally invisible." The clear night sky always seems bright enough for me to see the stuff around me even when I'm at the darkest sites out west.


Just about everyone objects to that clause in the Bortle definitions. In fairness to John Bortle, it's actually much easier to see stuff on the observing field in the desert West than in the East, even though the West is for the most part much darker than the East. The key phrase here is "a grass-covered field bordered by trees." In the East we're talking lush, deep-green grass in a clearing that's probably smaller than the surrounding trees are high. That can make for a pretty low level of illumination on the ground. In the desert West you're typically talking about scrubby, sandy grass in larger natural clearings, often surrounded by less dense trees.
 

Also it seems like NELM has too much influence on the Bortle scale, even though in the introduction to the Bortle scale, John explicitly mentions the issues with NELM.


For what it's worth, my NELM seems fairly independent of skyglow. Once the sky gets darker than about 20.5 mpss, I can see some but not all stars of magnitude 6.0. That continues true even in the darkest skies.



#37 vsteblina

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Posted 14 October 2021 - 09:35 PM

reply to vsteblina from Dr. Li-Wei Hung:

Hi Dan,

Thank you for forwarding the message. Please feel free to share my following response with him or post it on the board.

He (vsteblina) raised many good points. We have no way to track the private lighting, so it definitely introduces some uncertainties to this case study. Also as he pointed out, our ground-based observations are limited, and the potential drawback from the small sampling is discussed in the paper as well. That being said, here are some points I can clarify:
1. Ground based data are taken only one year apart, immediately before and after the retrofit. This short separation gave us the best chance to minimize the effects from long-term population growth and changes in private lighting.
2. The observations were taken at roughly same time of the year and same time of the night. High albedo of the snow is not a concern because these observations were outside of the winter months. Atmospheric conditions (extinction coefficients) are also similar. These were the best scenarios that one can hope for keeping all these variables under 'control.'  
3. Our data show the image of the entire night sky, offering more dimension than SQM measurements. The images not only show the zenith is brighter, but they also show size and brightness of the light dome are increased.
4. We have checked with the county officials. They said the ballfield lights were off by 10 or 11 pm in general, even if there were games earlier in the evening. Both of our observations were taken around midnight so the ballfield lights should not be a concern.
It was nice to hear from people living in that area and their personal observations. Thank you for sharing and I am looking forward to see his SQM observational report if he is plan to publish it in the future. 

Thank you,

Li-Wei

My back deck looks right down into downtown Wenatchee. 

 

I did think about taking a series of photo's from the deck as the lighting turnover continued.  Wenatchee DOES look dimmer from my house.  The street pattern grid that was easily visible has totally disappeared.  Miller Street was a "feature" of the view, and is not visible since the turnover.

 

Unfortunately, I did not get serious about collecting data.  It was an after thought as I was using the observatory at night.  No chance of publishing!!!  But it does bring up the possibility of using local amateurs in future projects. Given the limited time and money by Feds and the PUD using local collection of data would help validate the limited observations made by the team.

 

I would have to go find my notes, but I believe the sky on average went from 20.3 to 20.4 at my house as the transition was completed.  It also "felt" darker, by the shadows cast on my house from the lights of Wenatchee.

 

One thing that I did try to do, but failed, was to use the photo's taken at Burch Mountain and correlate them with the azimuth bearing to the light areas on the horizon.  That would highlight the increase in sky glow to specific areas in the Wenatchee Valley.  That might be enough to isolate the DOT lighting or the growth along Highway 97A just to the east of me.

 

Can you reconstruct the azimuth bearings for the photograph??

 

Just a observation, but the deterioration of the sky has continued if not intensified in the last two years.  That seems to indicate that the streetlights are not the problem.

 

I do appreciate the PUD taking the time and effort to quantity the effects of LED streetlights on the night sky.

 

Vladimir




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