Help figuring out my bortle level?

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realflow100 United States of America
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Help figuring out my bortle level?

#1

Post by realflow100 »


When I check my exact location on a map it says bortle 6 but that was a measurement taken in 2015 so I dont know how accurate that is

When I actually look up at the night sky I barely see any stars at all. Like just a few. Doesnt matter if theres a full moon. or no moon at all really. looks about the same.
Even if I get up in the middle of the night with maximum dark adaptation. Not turning on any lights at all. and looking out an open window. crouching underneath it so I dont get any streetlight glare in my eyes. and look up at the stars
I barely see any stars at all
orions belt is bare. I just see maybe 1 faint star near where orion nebula is located. but I dont see orion nebula itself at all. Even with 7x50 binoculars theres only a few more stars. and I do not see any nebula either.

Using stellarium I see approximately these stars in and around orions belt naked eye (I circled the ones I can see including faintest ones with averted vision circled)
I dont see any stars fainter than these ones i circled with or without averted vision.
Would this help to be able to figure out what my bortle level is for me
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realflow100 United States of America
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Re: Help figuring out my bortle level?

#2

Post by realflow100 »


Anyone? help?
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Re: Help figuring out my bortle level?

#3

Post by Lady Fraktor »


According to this the local bortle scale is 6
https://clearoutside.com/forecast/33.49/-80.86
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Re: Help figuring out my bortle level?

#4

Post by realflow100 »


I thought its more accurate to figure out bortle level by figuring out the faintest star i can see. since my local area could be much worse than bortle 6?

What about my picture example? How does that calculate into bortle level? (Faintest stars circled in that picture?)
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Re: Help figuring out my bortle level?

#5

Post by carastro »


There are a couple of ways of doing this:

You can use this LP map, find your location and click on the map and it should tell you your Bortle scale in a pop up box:
https://www.lightpollutionmap.info/#zoo ... 0FFFFTFFFF

The second way is to get yourself an SQM meter and measure the darkness of the sky, and then compare it to a Bortle Scale chart. There are also free phone apps that will do this too.

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Re: Help figuring out my bortle level?

#6

Post by pakarinen »


carastro wrote: Wed May 05, 2021 9:44 am The second way is to get yourself an SQM meter and measure the darkness of the sky, and then compare it to a Bortle Scale chart. There are also free phone apps that will do this too.
I use the Dark Sky Meter app on my phone. It last gave me a reading of 19.62 while my LP map shows 18.48 as of 2015. Or use this:
sky-brightness-nomogram.gif
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Re: Help figuring out my bortle level?

#7

Post by kt4hx »


The problem here is that the Bortle scale has nothing to do with the colored maps, phone apps, etc. Here is the original article from Sky & Telescope back in 2001 where John released his scale.

https://skyandtelescope.org/wp-content/ ... yScale.pdf

If you look at the criteria in the article you should be able to accurately determine your Bortle level, at least at the time you are observing and as you see it. This can change because it is meant as an in the moment assessment with the naked eye. As you will note, John includes an NELM for each level. So you are on the right track there, However, those estimates should be made at the zenith and by employing averted vision to gain the most accurate perspective. The main problem with NELM estimates is that they are very personal. You could line up ten people side by side at the same location and ask them to do an NELM estimate. While you may not come up with ten different estimates, they certainly would not agree because of personal optical differences and visual observing experience. So your estimation of the NELM there applied to the Bortle scale has a personal sense to it. That then leads us to the most often cited criticism of the Bortle scale - individuality. Because we are optically different and of varying experience levels and abilities, how we interpret our sky based on the Bortle scale may show some variation as well. I think John tried to get around that by using multiple criteria under each category.

Further, while the maps, apps and SQM meters have their place, they look at things a little differently than does the Bortle scale. As I mentioned above, John devised the scale as an in the moment naked eye visual method to assess one's sky based on a set of criteria. It is a sliding scale that can change from night to night or even hour to hour as conditions change. I have seen this particularly at our dark site house, but also under our suburban sky at home. Our sky at home used to be typically a Bortle 5, but over the years it has moved closer to a Bortle 6 unfortunately. A fate many folks are experiencing as suburban/urban sprawl continue.

The LP maps are based on satellite imagery with an algorithm applied to estimate the spread of light glow over terrain. By their nature they are static with somewhat defined borders. Of course LP does not adhere to borders, and the maps do not take into account small localized aspects that may make a specific site less usable than what one may expect based on the maps alone.

The apps and SQM calculate the sky quality based on its ability to detect sky glow. While these readings can and do vary night to night and even hour to hour, they still are not a reliable fit to the Bortle scale because they are using a different methodology.

All three ways are attempting to do the same thing, to help you determine the quality of your skies. But they do so in different ways and any correlation between them is purely coincidental and not wholly reliable. That doesn't make one method unreliable, simply that they aren't intuitively linked.

As an aside, I can tell you that John particularly dislikes all the attempts to draw a direct link from his scale to maps or devices. Those attempts were done by others, not him. As you can see in the article there are no "colors" associated with the different zones because that thinking was not part of the equation, and the SQM and apps were not around yet. All attempts to correlate any of those things to the Bortle scale were done by others in an attempt to link the scale to their methodology, and presumably make things easier.

I've had exchanges with John and I can tell you he bristles at any comparison between the methods. He is quite protective of his scale and still believes it is the best method to employ, and mostly eschews the maps and devices. I utilize the scale myself, but I also utilize an SQM-L from time to time. I don't wholly rely on it, rather I rely on my own eyes most of the time. I find they are the best method.

I have employed the maps from time to time to try to find locations that might be suitable, but of course each site must be vetted. I have found seemingly useful locations that had very localized issues such as pole lights, or vehicle traffic driving by frequently or even very small bodies of water that increase fog conditions under certain circumstances. So the maps do not tell the whole story. Nor do the apps, and some would argue nor does the Bortle scale.

So I believe you are on the right track here by using your eyes to gain a better understanding of your localized conditions. In the end they are the most reliable tool you have.
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Re: Help figuring out my bortle level?

#8

Post by realflow100 »


I discovered I can somehow just barely/vaguely see the milkyway with averted vision. but I have to look quite far away from it for it to even be noticable. like 30 to 45 degrees away from my center of vision.
I woke up around 4 AM and went straight outside without turning on any lights. and using my hands as "shields" to block any streetlight glare from directly getting to my eyes.

Its like barely even a tiny hint brighter than the background sky. absolutely no detail at all. its just more like a faint glowy vertical band going from the horizon to the zenith. Sorta like a fog or haze glowing in the sky.
Theres very few stars around or in it visible though. approximately what bortle 9 charts show (a little worse than the bortle 9 level in stellarium actually)
I somehow don't see andromeda galaxy at all not even the tiniest bit naked eye.

Pleiades is brighter with averted vision. and very fuzzy looking. faint with direct vision. barely able to discern any stars within it.
orion nebula is also not visible either naked eye unless I use fairly high magnification with my 4" reflector telescope. (40x to 80x magnification is in the right ballpark)
Svbony SV503 70mm ED F6 420mm FL refractor telescope (New)
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Tamron 18-200mm F3.5-F6.3 II VC lens
canon 50mm STM F1.8
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svbony goldline 66 degree 9mm and 6mm + 40mm plossl + 2x barlow.
svbony UHC 1.25 filter + astromania 1.25" O-3 filter + also an svbony H-B filter.
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Re: Help figuring out my bortle level?

#9

Post by Bigzmey »


I use this table to estimate Bortle level

https://en.wikipedia.org/wiki/Bortle_scale

From what you describe 6 is about right.
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