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Best dark Sky finder

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#1 André 123

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Posted 25 November 2021 - 10:25 PM

I know the maps just give us an idea about the light pollution, but which of them is better (generally)?
a) lightpollutionmap
b) darksitefinder

#2 DaveL

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Posted 25 November 2021 - 11:34 PM

Dark sky finder uses my 2006 light pollution atlas (with my permission). I've since updated it to 2020. According to my SQM measurements, my analysis of measurements by the National Park Service Night Sky Team, and various members on these forums lightpollutionmap.info has a systematic dark bias especially in rural areas away from cities. In other words, it's too optimistic.

 

lightpollutionmap.info also seems to be the most popular, maybe because it appears to give more information such as zenith brightness to the hundredths place (unrealistic precision) and the Bortle scale (even though the Bortle scale is not the same as zenith brightness). Maybe because it is more optimistic: it's nice to think you've found a good site to observe. Maybe because it is the only one linked in the "best of" section.

 

-Dave


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#3 paul

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Posted 26 November 2021 - 12:24 AM

A. lightpollutionmap 



#4 André 123

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Posted 26 November 2021 - 09:15 AM

Dark sky finder uses my 2006 light pollution atlas (with my permission). I've since updated it to 2020. According to my SQM measurements, my analysis of measurements by the National Park Service Night Sky Team, and various members on these forums lightpollutionmap.info has a systematic dark bias especially in rural areas away from cities. In other words, it's too optimistic.

lightpollutionmap.info also seems to be the most popular, maybe because it appears to give more information such as zenith brightness to the hundredths place (unrealistic precision) and the Bortle scale (even though the Bortle scale is not the same as zenith brightness). Maybe because it is more optimistic: it's nice to think you've found a good site to observe. Maybe because it is the only one linked in the "best of" section.

-Dave

https://darksitefind...4/31.60/-102.10
So this site is better, right?

#5 DaveL

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Posted 26 November 2021 - 10:21 AM

https://darksitefind...4/31.60/-102.10
So this site is better, right?

In my opinion it is better, yes. But it's older data. I linked to the newer 2020 one above. Here it is again:

 

https://djlorenz.git...erlay/dark.html

 

Sites that have the updated maps are Astrospheric and Clear Sky Clock.

 

As an example of the bias in lightpollutionmap.info, I have a site that is 50 minutes away from my house. Here are the stated and measure zenith sky brightness:

 

lightpollutionmap.info: 21.74

my 2020 maps: near edge of dark and light green: ~21.51 

measurements: the darkest I've consistently gotten with a SQM-L is 21.52. Typical good summer nights after midnight are around 21.48ish. 

 

lightpollutionmap.info is a 0.23 darker than anything I've ever gotten at that site. I've also gone to sites that actually are 21.74, and they are definitely better.

 

-Dave


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#6 DaveL

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Posted 26 November 2021 - 10:42 AM

Here's an example from the National Park Service Night Sky Team:

 

Hopewell Furnace National Historic Site, Pennsylvania

Longitude: -75.77, Latitude: 40.21

 

lightpollutionmap.info: 20.61

my 2020 map: 20.25

Zenith sky brightness (which is also darkest point) measured with CCD camera: 20.23

 

My atlas is well within the type of variability you expect in this measurement. lightpollutionmap.info is too dark by 0.38 mag/arcsec^2. 

 

I've looked at the systematic bias across all National Park Service sites brighter than 21.5 (darker than this, variability in airglow and extinction make comparisons with light pollution maps less meaningful). The mean bias in lightpollutionmap.info is 0.34 mag/arcsec^2. The bias in my maps is 0.08 mag/arcsec^2. This is using the darkest point in the sky rather than zenith because sometimes the Milky Way is overhead.

 

-Dave


Edited by DaveL, 26 November 2021 - 10:55 AM.

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#7 André 123

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Posted 26 November 2021 - 12:26 PM

Here's an example from the National Park Service Night Sky Team:

Hopewell Furnace National Historic Site, Pennsylvania
Longitude: -75.77, Latitude: 40.21

lightpollutionmap.info: 20.61
my 2020 map: 20.25
Zenith sky brightness (which is also darkest point) measured with CCD camera: 20.23

My atlas is well within the type of variability you expect in this measurement. lightpollutionmap.info is too dark by 0.38 mag/arcsec^2.

I've looked at the systematic bias across all National Park Service sites brighter than 21.5 (darker than this, variability in airglow and extinction make comparisons with light pollution maps less meaningful). The mean bias in lightpollutionmap.info is 0.34 mag/arcsec^2. The bias in my maps is 0.08 mag/arcsec^2. This is using the darkest point in the sky rather than zenith because sometimes the Milky Way is overhead.

-Dave

Thank you!

#8 André 123

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Posted 26 November 2021 - 12:39 PM

In my opinion it is better, yes. But it's older data. I linked to the newer 2020 one above. Here it is again:

https://djlorenz.git...erlay/dark.html

Sites that have the updated maps are Astrospheric and Clear Sky Clock.

As an example of the bias in lightpollutionmap.info, I have a site that is 50 minutes away from my house. Here are the stated and measure zenith sky brightness:

lightpollutionmap.info: 21.74
my 2020 maps: near edge of dark and light green: ~21.51
measurements: the darkest I've consistently gotten with a SQM-L is 21.52. Typical good summer nights after midnight are around 21.48ish.

lightpollutionmap.info is a 0.23 darker than anything I've ever gotten at that site. I've also gone to sites that actually are 21.74, and they are definitely better.

-Dave


How can I type the coordinates (2020)?

#9 DaveL

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Posted 26 November 2021 - 01:00 PM

Hi Andre,

 

My maps do not have this feature, sorry, but I might be able to add something. So do you want a "box" to add the longitude and latitude and then the map zooms to those coordinates?

 

-Dave


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#10 André 123

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Posted 26 November 2021 - 02:49 PM

Yes, it would be really useful, please!

#11 André 123

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Posted 26 November 2021 - 03:24 PM

Hi Andre,

My maps do not have this feature, sorry, but I might be able to add something. So do you want a "box" to add the longitude and latitude and then the map zooms to those coordinates?

-Dave

May you do it?

#12 DaveL

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Posted 26 November 2021 - 08:44 PM

I've added a search:

 

type latitude, longitude at the search icon and hit return.

 

Hopefully this works for all browsers.

 

-Dave


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#13 André 123

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Posted 27 November 2021 - 05:23 AM

Thank you! It will help a lot


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