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Best Light pollution map?

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#1 Aquarius Of The Night

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Posted 15 November 2017 - 05:13 PM

Anyone know what the most accurate map is? 



#2 jklein

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Posted 15 November 2017 - 05:31 PM

A lot of folks use this one - https://www.lightpollutionmap.info

Click on the red Atlas in the menu in the upper right. Then when you click on various spots, it will give Bortle rating as well as the one I don't understand as much.


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#3 kellyvictoria

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Posted 15 November 2017 - 05:58 PM

A lot of folks use this one - https://www.lightpollutionmap.info

Click on the red Atlas in the menu in the upper right. Then when you click on various spots, it will give Bortle rating as well as the one I don't understand as much.

This is Fabulous... thank you..

I clicked on the VIIR2017 and thought it was even better than the Atlas...

although the Bortle rating was helpful the Constellation star map counter was good too... 


Edited by kellyvictoria, 15 November 2017 - 06:14 PM.

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#4 Muddman97

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Posted 15 November 2017 - 06:05 PM

A lot of folks use this one - https://www.lightpollutionmap.info

Click on the red Atlas in the menu in the upper right. Then when you click on various spots, it will give Bortle rating as well as the one I don't understand as much.

I like that map as well, Jim.

 

I had class 2 skies in my backyard back home, now I live under class 5 and best I can do within an hours drive is class 4.  bawling.gif



#5 jklein

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Posted 15 November 2017 - 06:06 PM

 

A lot of folks use this one - https://www.lightpollutionmap.info

Click on the red Atlas in the menu in the upper right. Then when you click on various spots, it will give Bortle rating as well as the one I don't understand as much.

This is Fabulous... thank you...

 

You are welcome. I have been using this and Google Earth to find some dark skies "near" my house. It can be a real time sink, but dark skies are worth it!


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#6 jklein

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Posted 15 November 2017 - 06:11 PM

 

A lot of folks use this one - https://www.lightpollutionmap.info

Click on the red Atlas in the menu in the upper right. Then when you click on various spots, it will give Bortle rating as well as the one I don't understand as much.

I like that map as well, Jim.

 

I had class 2 skies in my backyard back home, now I live under class 5 and best I can do within an hours drive is class 4.  bawling.gif

 

Alan - you are pretty far from where they hold the Okie-Tex Star party? I was going to check that out after I moved to Fort Worth, but it is really far - seems like 400 miles - we tend to forget distances involved with the panhandles of our states.

I'm going to join the TAS out of Dallas - their dark site is near Atoka. Much closer for me and I think it is a class 3.


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#7 Muddman97

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Posted 15 November 2017 - 06:53 PM

Yeah, its just over 400 miles for me as well but might be worth the trip next year.



#8 BrooksObs

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Posted 15 November 2017 - 09:05 PM

A lot of folks use this one - https://www.lightpollutionmap.info

Click on the red Atlas in the menu in the upper right. Then when you click on various spots, it will give Bortle rating as well as the one I don't understand as much.

 

Unfortunately, this map system is quite inaccurate. I find that for New York and New England locations it typically provides values significantly too low on the Bortle scale for even modestly populated areas, while at the same time rating darker semi-rural locations as far too bright.

 

BrooksObs


Edited by BrooksObs, 15 November 2017 - 09:07 PM.

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#9 csa/montana

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Posted 15 November 2017 - 09:17 PM

Seems like many members like this map; it's pretty accurate for my location; however I'm not in a populated area.


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#10 jklein

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Posted 15 November 2017 - 09:54 PM

I don't have a dark sky meter (yet) to verify my location readings. I do know for Houston it seems to reflect what we have. I was in an IDA dark site last weekend which showed as Bortle 2/3 on the map and it was DARK and seemed to match the descriptions in the Bortle chart. I just look for anything better than a class 9 sky where I live and figure it can get me close to 3 and lower classes. I'm probably going to be happy with a 4/5, but a 1 or 2 in reach via RV would be great. If a 2 is really a 1, then I have won a bonus.



#11 krneki

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Posted 16 November 2017 - 02:16 AM

If you don't agree with World Atlast 2015 prediction about a certain place, you can always submit your SQM measurement using tools on the map and it may be eventually used for calibration in the next generation of the World Atlas. In the meantime anyone can see your measurement and see the real situation. The Bortle scale on the map is just an estimation because not only it is a subjective scale but also it's calculated only from the zenith sky brightness parameter (taken from https://www.handprin...TRO/bortle.html) which may be not enough for accurate results.


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#12 caveman_astronomer

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Posted 16 November 2017 - 07:10 AM

Despite any flaws, these maps still give you an idea of where to start looking look for dark(er) skies and where not to expect them.


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#13 Aquarius Of The Night

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Posted 16 November 2017 - 08:17 AM

The reason I was asking is for that reason.  They seemed to show different results. Some said I was in a yellow zone while some said I was in a light green light blue area which is a big difference. 


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#14 kellyvictoria

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Posted 16 November 2017 - 09:34 AM

It helps if you zoom down on your street, and I clicked on VIIR2017 ... it seems clearer...

 

Regardless of Bortle, I do know my immediate horizon and where we have dark sites w/others for viewing ... 

For now I like it... to get any darker here I would have to be in the FL Everglades...and even then the lights of Miami & Naples might have to be contended with...  Eyecrazy.gif



#15 BrooksObs

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Posted 16 November 2017 - 09:39 AM

If you don't agree with World Atlast 2015 prediction about a certain place, you can always submit your SQM measurement using tools on the map and it may be eventually used for calibration in the next generation of the World Atlas. In the meantime anyone can see your measurement and see the real situation. The Bortle scale on the map is just an estimation because not only it is a subjective scale but also it's calculated only from the zenith sky brightness parameter (taken from https://www.handprin...TRO/bortle.html) which may be not enough for accurate results.

Unfortunately, this so-called formula cited for use in converting the Bortle Dark Sky Scale to a simple numerical calculation will do nothing of the sort. The Bortle Scale classifications are based on the observer's evaluation of the appearance of much of, if not the entire, appearance of sky features. The author of the formula linked to above is a numerical interpretation based on just the observer's limiting magnitude, which is very far from the Bortle Scale  and is certainly no worthy substitute.

 

BrooksObs   


Edited by BrooksObs, 16 November 2017 - 12:19 PM.

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#16 csa/montana

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Posted 16 November 2017 - 09:56 AM

Whether one considers any LP maps "not worthy substitutes", or not;  if they help someone, no need to disregard them as a "mistaken numerical interpretation"!  For my site, I never use the Bortle, rather using my SQM meter.  

 

I think the members are well served with the different links being posted, and thanks to those posting the links.


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#17 BrooksObs

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Posted 16 November 2017 - 12:26 PM

Whether one considers any LP maps "not worthy substitutes", or not;  if they help someone, no need to disregard them as a "mistaken numerical interpretation"!  For my site, I never use the Bortle, rather using my SQM meter.  

 

I think the members are well served with the different links being posted, and thanks to those posting the links.

 

Inaccuracy does not help anyone, it simply leads and misinforms them, Mr. Moderator. As I pointed out up-stream, the map cited is incorrect on both the bright and faint end of the colored regions, so just what can be gained from that as an observer?

 

BrooksObs



#18 jdupton

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Posted 16 November 2017 - 01:19 PM

BrooksObs,

 

   Exactly to which maps are you referring? There are two styles of maps at the Website  https://www.lightpollutionmap.info/ that give different and sometimes confusing information.

 

   If you are referring to the VIIRS maps, be reminded that they do not represent sky brightness at all. They are maps showing upward radiance information ie the brightness of light emanating from each point on the ground. The color coding of that data bears no direct relationship to the more commonly used Bortle scale of estimating a combination of sky brightness at the zenith and the extent of light domes near the horizon.

 

   If you are referring to the World Atlas 2015 map at the same Website, it is based on a best case calculated estimate of sky brightness at the zenith (without an actual separate inclusion of light dome visibility -- to the best of my understanding). In addition, the World Atlas 2015 map is based on data gathered in late 2014 with some data dating back to 2013 for selected areas. That is the latest data which has undergone the complex integration process used to generate the map.

 

   Local "temporary" changes in sky brightness can occur due to forest fires, gas well flaring, construction projects, ground snow cover, and so forth. Some of these are accounted for by selective inclusion of data from the range of dates used as mapping data. Of course, any changes after 2014 will not be reflected in the maps until someone undertakes a new integration project using the latest data. 

 

   As you have pointed out, I think the Bortle scale was intended to account for overall sky conditions including both sky brightness at the zenith and extent and visibility of light domes at the horizon. To the best of my knowledge, no one has ever created a map that combines both pieces of information for a more accurate way to predict overall sky conditions at any given site.

 

   The best we can do today is look to the zenithal brightness maps like the World Atlas 2015 map to get an overhead sky brightness estimate and then estimate light domes by referring to the VIIRS maps to show where most of the light will be coming from. I had attempted to do such a merging of data via a method I used when searching for a personal dark sky property a few years back. Using Google Earth, I was able to combine both forms of data using a methodology that included some calibration by taking panoramic photos at night from prospective sites. Unfortunately, Google moved the Google Earth program to the newer Web-App-based Google Earth Pro and my methodology quit working the same. I have not had time to try making things work reliably again in the new Google Earth Pro.

 

 

John


Edited by jdupton, 16 November 2017 - 01:43 PM.

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#19 jklein

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Posted 16 November 2017 - 02:01 PM

 

A lot of folks use this one - https://www.lightpollutionmap.info

Click on the red Atlas in the menu in the upper right. Then when you click on various spots, it will give Bortle rating as well as the one I don't understand as much.

 

Unfortunately, this map system is quite inaccurate. I find that for New York and New England locations it typically provides values significantly too low on the Bortle scale for even modestly populated areas, while at the same time rating darker semi-rural locations as far too bright.

 

BrooksObs

 

 

 

A lot of folks use this one - https://www.lightpollutionmap.info

Click on the red Atlas in the menu in the upper right. Then when you click on various spots, it will give Bortle rating as well as the one I don't understand as much.

 

Unfortunately, this map system is quite inaccurate. I find that for New York and New England locations it typically provides values significantly too low on the Bortle scale for even modestly populated areas, while at the same time rating darker semi-rural locations as far too bright.

 

BrooksObs

 

Which map do you recommend?


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#20 JayinUT

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Posted 16 November 2017 - 02:12 PM

I like the GlobeatNight map, if we are looking at SQM readings over time. Here is a LINK to it. I'll probably add my historical data from Unihedron's website for my SQM-L model. My home is getting worse, and sites closer to home are getting worse. My personal favorite dark sites in Utah's West Desert are holding for now, but I expect over the next twenty years for those to begin to decrease as to maintain the SQM rate in the 21.8 range will require a longer drive out west.  My favorite site I don't post is about 3 hours away in eastern Nevada. Darker than dark there still.  



#21 csa/montana

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Posted 16 November 2017 - 03:26 PM

 

Mr. Moderator

Actually, I'm not a Mr. and I was not posting as a Moderator, rather as a member that observes, and for my purposes, uses the SQM meter.  For anyone that thinks the sites are not accurate, they don't have to use them; but those that like & appreciate the sites, it probably suits their needs.  We all have our opinion as to what is "accurate", when it comes to dark sky readings.smile.gif


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#22 BrooksObs

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Posted 18 November 2017 - 09:54 AM

 

 

A lot of folks use this one - https://www.lightpollutionmap.info

Click on the red Atlas in the menu in the upper right. Then when you click on various spots, it will give Bortle rating as well as the one I don't understand as much.

 

Unfortunately, this map system is quite inaccurate. I find that for New York and New England locations it typically provides values significantly too low on the Bortle scale for even modestly populated areas, while at the same time rating darker semi-rural locations as far too bright.

 

BrooksObs

 

 

 

A lot of folks use this one - https://www.lightpollutionmap.info

Click on the red Atlas in the menu in the upper right. Then when you click on various spots, it will give Bortle rating as well as the one I don't understand as much.

 

Unfortunately, this map system is quite inaccurate. I find that for New York and New England locations it typically provides values significantly too low on the Bortle scale for even modestly populated areas, while at the same time rating darker semi-rural locations as far too bright.

 

BrooksObs

 

Which map do you recommend?

 

In all honesty, I can not recommend any specific map as none that I've have seen truly reflect the ground conditions an observer encounters at a given site, at least not east of the Mississippi. Typically, light pollution maps depict intensities about one or  even two Bortle darkness classes too dark for specific locations in the eastern U.S., at the same time suggesting a more rapid drop-off in sky glow away from major cities than exists. The latter is particular true for any region that has a nearby significantly urbanized area, especially a large city. The glow of the New York Megalopolis is  detectable well beyond 100 miles from Manhattan and to a small degree will still impact the sky's darkness nearly up to the zenith! Thus, while light pollution maps may depict such a location 100 miles out from NYC as Bortle class 2, it will most likely be class 3 or worse in reality.

 

The ONLY way to know the darkness of a location is to visit it on a good night and evaluate it yourself. Often one finds a compact nearby light source that is not indicated on the maps at all that causes the location to be a write-off. Larger service stations, rest spots, high school sports fields, mini-malls and such that are illuminate most, or all, night are surprisingly common across much of our country even in otherwise rural areas and they can often be seen at a considerable distance. Don't forget winter sport trail locations either. I've noticed these in winter from scores of miles away.

 

So, while light pollution maps may give you some approximation of how conditions are trending in an area, they are far from real predictors of any sort.

 

BrooksObs


Edited by BrooksObs, 18 November 2017 - 09:57 AM.


#23 caveman_astronomer

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Posted 19 November 2017 - 06:45 AM

The reason I was asking is for that reason.  They seemed to show different results. Some said I was in a yellow zone while some said I was in a light green light blue area which is a big difference. 

If a green/blue zone is what you seek then concentrate on areas that show as green/blue on each or all of the maps.  You'll have to verify from the ground, in person, whether the zone is yellow, green or blue.  There is no rule that says that the LP maps must agree with each other.



#24 Tony Flanders

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Posted 19 November 2017 - 07:34 PM

A lot of folks use this one - https://www.lightpollutionmap.info
Click on the red Atlas in the menu in the upper right. Then when you click on various spots, it will give Bortle rating as well as the one I don't understand as much.


To which BrooksObs responded:
 

Unfortunately, this map system is quite inaccurate. I find that for New York and New England locations it typically provides values significantly too low on the Bortle scale for even modestly populated areas, while at the same time rating darker semi-rural locations as far too bright.
...
In all honesty, I can not recommend any specific map as none that I've have seen truly reflect the ground conditions an observer encounters at a given site, at least not east of the Mississippi. .


I agree that the map referred to above gives sky brightness readings that are consistently quite a bit darker than what I measure with my SQM.

However, I find that my SQM readings are very much in line with David Lorenz's 2006 Light Pollution Atlas. This is the map referenced by the Clear Sky Chart.

As for the correlation between SQM readings and Bortle classes, that's very problematic. I think that most of these are taken from the Wikipedia article on the Bortle scale, which I find quite clearly wrong on many fronts. Just to name one, putting all readings between 19.1 and 20.4 into a single Bortle Class (5) is lunatic. That's a huge range of different kinds of sky! SQM=19.1 is a poor suburban sky where the Milky Way is barely visible. At SQM=20.4, the Milky Way has considerable size and structure, and likely reaches from horizon to horizon unless it happens to hit the middle of one of the major light domes.
 

The ONLY way to know the darkness of a location is to visit it on a good night and evaluate it yourself. Often one finds a compact nearby light source that is not indicated on the maps at all that causes the location to be a write-off. Larger service stations, rest spots, high school sports fields, mini-malls and such that are illuminate most, or all, night are surprisingly common across much of our country even in otherwise rural areas and they can often be seen at a considerable distance. Don't forget winter sport trail locations either. I've noticed these in winter from scores of miles away.


All very true. Intermittent and seasonal light sources, such as playing fields and ski areas with night skiing, are particularly tricky, since an area that's fine when those lights are off can be unusable when the lights are on. Bright lights that are always on, such as truck stops, do in fact show up on the maps.

 

On the other hand, an area that's shown as unacceptably bright on any of the maps will almost certainly be unacceptably bright -- although there are highly localized sources of light, there's no such thing as a localized source of dark -- more's the pity.

 

My experience is that at least within any geographical area, such as the U.S. Northeast, the maps are pretty reliable for giving the relative brightness of different sites -- always assuming the absence of a local source that is too small or intermittent to be picked up by satellite. In other words, the red zone will always be brighter than the orange zone in any map using that color scheme, regardless of what absolute meanings you assign to red and orange. So when looking for a dark site near you, it makes sense to look first near the centers of areas that are shown as relatively dark on the maps.

 

Because of the proliferation of different maps using similar color schemes, it's getting almost meaningless to say "orange zone" without specifying which map you're using.


Edited by Tony Flanders, 19 November 2017 - 07:36 PM.

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#25 caveman_astronomer

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Posted 20 November 2017 - 02:32 AM

Forget all the LP maps for a moment and just look at the population densities of each county within about 200 miles of your prospective observing site.  Pick the least densely populated counties and then within those counties find the spots that are furthest from their respective cities, towns and major highways.  Then, weed out those with the worst potential sources of localized light pollution (not easy.)

 

Or just look for National Forests, mountain ranges, swamps or isolated seashores.  Then there's the weather prospects....

 

Cheap, low-maintenance, low-operating-cost LEDs will complicate matters and make long-term development of dark sites, if you can find them anywhere, problematic in the coming years.


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