Author Topic: Introducing DarkSiteFinder.com  (Read 345 times)

John Wilson

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Re: Introducing DarkSiteFinder.com
« Reply #15 on: January 13, 2018, 02:05:02 AM »
Kevin, have you discussed using Dave Lorenz' maps with him?

omunsopoo

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Re: Introducing DarkSiteFinder.com
« Reply #16 on: January 13, 2018, 05:37:37 AM »
The original "World Atlas" map ranges are ratios between the artificial sky brightness and an average reference natural sky brightness  (corresponding approximately to 21.6V mag/arcsec, although the authors go to pains to point out that the natural sky brightness varies considerably based on several factors, and this scale is best seen as a relative scale).The map level ratios are:0.00 (black)0.01-0.11 (gray)0.11–0.33 (blue)0.33–1.00 (green)1–3 (yellow)3–9 (orange)9–27 (red)>27 (white)I'm wondering, based on the many discussions of sky brightness v. extended object contrast, if this is the most helpful way to segment the light pollution ranges? We need not be limited to the same factor of 3x nor the same number of levels.In fact, it might be good to intentionally use a number of levels that clearly distinguishes this from the Bortle scale, to prevent further confusion.

Dan Perez

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Re: Introducing DarkSiteFinder.com
« Reply #17 on: January 13, 2018, 11:13:11 PM »
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In fact, it might be good to intentionally use a number of levels that clearly distinguishes this from the Bortle scale, to prevent further confusion.

Attempting to mimic the Bortle scale would simply increase confusion. The color zones based on satellite measurements and the Bortle scale are fundamentally different; there's no way that they can ever correlate with each other.

I deeply regret the original publication of the correlation by the North Virginia Astronomy Club, although their intentions were entirely legitimate. And its propagation through Wikipedia is even more unfortunate. However, the cat's out of the bag now; the harm cannot be undone.

Aside from problems with the underlying data and the fact that it's now more than a decade old, the color zones can at best represent either average skyglow or possibly skyglow under ideal conditions. They don't change from night to night; that's both a good and a bad point.

The Bortle scale represents a subjective evaluation of the sky at one particular time. Despite attempts to smooth it out by using multiple criteria, the assessment is bound to differ from one person to another, and it most certainly varies from one night to another. That's particularly true in the best (lowest) classes. It also inherently factors in transparency as well as artificial skyglow.

SQM measurements are yet another thing. Like the Bortle assessment they vary from night to night -- often by a fair amount. But unlike the Bortle classes they don't take transparency into account. And the SQM measurements are inherently inaccurate at the dark end of the scale due to "contamination" by the Milky Way and zodiacal light.

I use the color zones for two different purposes: to communicate sky conditions between people at different locations and to figure out where to travel to find relatively dark locations. For the former purpose, the current number of levels is probably about right. Any more would give a false sense of precision. For the latter purpose, the more the better.

swittetsakee

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Re: Introducing DarkSiteFinder.com
« Reply #18 on: January 14, 2018, 03:55:16 AM »
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Kevin, have you discussed using Dave Lorenz' maps with him?
I have attempted to but I got no reply. But since he has the PNG images available for download on his website, I don't think he would have a problem with it. I made sure to give him credit.

Michael Shen

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Re: Introducing DarkSiteFinder.com
« Reply #19 on: January 16, 2018, 11:14:14 PM »
I tried to avoid defining exactly what the color zones mean, since I know there has been some confusion with the Bortle scale. The color maps are really just a starting point anyway. They don't take into effect elevation, clouds on the horizon reflecting more light, or distant light domes. The only way to see how dark a site truly is, is to visit there on a good night.

loraderclot

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Re: Introducing DarkSiteFinder.com
« Reply #20 on: January 18, 2018, 08:35:20 AM »
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The only way to see how dark a site truly is, is to visit there on a good night.

Amen. The maps are tremendously useful, but at best they can only be approximations of reality.

ivirlocri

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Re: Introducing DarkSiteFinder.com
« Reply #21 on: January 23, 2018, 03:28:30 AM »
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<p class="citation">QuoteKevin, have you discussed using Dave Lorenz' maps with him?
I have attempted to but I got no reply. But since he has the PNG images available for download on his website, I don't think he would have a problem with it. I made sure to give him credit. [/quote]
Alternate e-mail address for Dave sent via PM.
Lee

jumphindnore

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Re: Introducing DarkSiteFinder.com
« Reply #22 on: January 23, 2018, 03:42:50 AM »
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<p class="citation">QuoteIn fact, it might be good to intentionally use a number of levels that clearly distinguishes this from the Bortle scale, to prevent further confusion.

Attempting to mimic the Bortle scale would simply increase confusion.[/quote]

aththrilnalo

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Re: Introducing DarkSiteFinder.com
« Reply #23 on: January 23, 2018, 01:13:43 PM »
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I deeply regret the original publication of the correlation by the North Virginia Astronomy Club, although their intentions were entirely legitimate. And its propagation through Wikipedia is even more unfortunate. However, the cat's out of the bag now; the harm cannot be undone.
The Wikipedia entry for "Bortle Scale" is now fixed.

Nathan Harper

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Re: Introducing DarkSiteFinder.com
« Reply #24 on: January 25, 2018, 10:13:41 PM »
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Would their be any reason why the light pollution map wouldn't show up on an IPad? I can get the map ( underlay) to show up fine but no light pollution map.

Any thoughts? Or is this something you already are aware of? I would love to take a look at your maps!

Same here.   color doesn't come up??

Jose Lukeson

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Re: Introducing DarkSiteFinder.com
« Reply #25 on: January 26, 2018, 12:00:10 AM »
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<p class="citation">QuoteWould their be any reason why the light pollution map wouldn't show up on an IPad? I can get the map ( underlay) to show up fine but no light pollution map.

Any thoughts? Or is this something you already are aware of? I would love to take a look at your maps!
Sorry I didn't really optimize the website for mobile devices. I don't have an Ipad to test with either. Maybe someday I'll learn how to build an app though. [/quote]

retpoiwerround

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Re: Introducing DarkSiteFinder.com
« Reply #26 on: January 30, 2018, 01:20:35 AM »
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The Wikipedia entry for "Bortle Scale" is now fixed.

Wow, that's pretty drastic! I did add a caveat to that article, but I'm reluctant to remove information even if it's only approximately correct.

reapriavoland

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Re: Introducing DarkSiteFinder.com
« Reply #27 on: January 31, 2018, 03:22:58 AM »
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<p class="citation">Quote
The Wikipedia entry for "Bortle Scale" is now fixed.

Wow, that's pretty drastic! I did add a caveat to that article, but I'm reluctant to remove information even if it's only approximately correct. [/quote]

Given John Bortle's own statements that he was *not* involved, and that there would be considerable differences between the two, and that the Bortle Dark Sky Scale is intended for use for on-site evaluation, not for use in creating maps (and your own respected expression of deep regret), it seems perfectly appropriate to me.

It's a simple matter of respecting John Bortle's wishes. I think you said it was a shame it had happened, but could not be undone. I am willing to undo it where possible; it's a small effort made to show some respect and remove some of the confusion that we see often here on CN.

If you like, we can add a short summary of the other main LP measurement systems / night sky evaluation methods there and point to Wiki pages on them. That might be even more helpful - to remove the false connection, but to show the way to additional information. There is already a question in "talk", unanswered, about the relationship between the Bortle Scale and SQM readings.

Does that sound worthwhile to develop?

Lee

John Trujillo

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Re: Introducing DarkSiteFinder.com
« Reply #28 on: January 31, 2018, 03:23:45 AM »
Quote
<p class="citation">Quote<p class="citation">Quote
The Wikipedia entry for "Bortle Scale" is now fixed.

Wow, that's pretty drastic! I did add a caveat to that article, but I'm reluctant to remove information even if it's only approximately correct. [/quote]

Given John Bortle's own statements that he was *not* involved, and that there would be considerable differences between the two, and that the Bortle Dark Sky Scale is intended for use for on-site evaluation, not for use in creating maps (and your own respected expression of deep regret), it seems perfectly appropriate to me.[/quote]

You're probably right; I should have been more decisive when I edited that article some years ago. No matter how many caveats you add, people will take the chart as gospel.

I do have an article on the <em class="bbc">S&amp;T website discussing the relationships,  here.

litgeschsappa

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Re: Introducing DarkSiteFinder.com
« Reply #29 on: January 31, 2018, 11:45:15 AM »
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Please let me know how you like the website and if you have any suggestions to make it better.
Ken,First, let me get something out of the way. Your site is using Dave Lorenz' work. He programmed the algorithms from the research papers from scratch, a significant amount of work. I know he has them for download, but there is no statement of release for various uses, especially for web sites that may be considered partially commercial. I will feel a lot better talking about the site here (CN is quite sensitive about copyright) and encouraging others to use it once you have Dave's explicit permission.OK, now for the suggestion: I think the 8 colors can be improved on, to solve two problems. 1) Since the colors are solid and bright, people simply remember "green" is "green", when in fact there is a 3x difference in light pollution between the green/blue boundary and the green/yellow boundary, and this makes a very large difference in practice.2) The color ranges do not directly correspond to magnitudes. This is unfortunate since we have a meter, the SQM, and at least one app, that allows one to measure sky brightness in magsas directly. The natural sky brightness, without light pollution, varies by up to about one magnitude (not counting the effect of the moon) anyway due to several natural effects. So the map is relative to a baseline dark sky which varies, between perhaps 21 magsas and 22 magsas.My first suggestion is to use the 255 grayscale map to create a new color mapping. It uses 7 colors:clear - no light pollution, natural pristine skies (e.g. 22 magsas)gray - 0-1 magsas brighter than natural, pristine skies (21-22)blue - 1-2 magsas brighter (20-21)green - 2-3 magsas brighter (19-20)orange - 3-4 magsas brighter (18-19)yellow -  4-5 magsas brighter (17-18)white -  5+ magsas brighter (17+)My second suggestion is to help people intuitively and also quantitatively see a finer gradation of sky brightness. The 8-color scale is insufficient, the 16-color scale is better, I think this is much better still: For each of the 5 colors besides clear and white, draw a contour line at the boundary and for each .25 magsas, and label them with the magsas (e.g 21.25). This is exactly like the contour lines on a topo map. This gives 3 lines within each color. This is needed since there is a large difference in one whole magnitude, and it would be helpful to remind people and show people where the changes are, down to a quarter of a magnitude. Along with this, I would greatly reduce the saturation of the colors to make the map look more "smooth". I have an example of this last, if you PM me an e-mail address I will send it to you.Regards,Lee