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How do you know what bortle you are in

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#1 grif 678

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Posted 22 November 2019 - 08:46 PM

I have no clue, but I see lots of peolpe describing their darkness or lack of darkness. measured in bortles. So how do you determine what is yours.



#2 AstroKerr

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Posted 22 November 2019 - 08:50 PM

Bortle


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#3 FLT-Astro

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Posted 22 November 2019 - 08:51 PM

https://astrobackyar...e-bortle-scale/


Edited by FLT-Astro, 22 November 2019 - 08:52 PM.

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#4 Nicole Sharp

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Posted 22 November 2019 - 08:53 PM

Better question is how do you determine what Bortle other places are (that you have never been to before)?  E.g. if you are scoping out new observing spots.


Edited by Nicole Sharp, 22 November 2019 - 08:53 PM.


#5 DLuders

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Posted 22 November 2019 - 09:01 PM

Better question is how do you determine what Bortle other places are (that you have never been to before)?  E.g. if you are scoping out new observing spots.

Using the LightPollutionMap.info graphic (for the Denver area, as an example     https://www.lightpol...0FFFFFTFFFFFFFF  ), one can click on a nearby town (say, Georgetown, CO to the west of Denver).  A popup window appears that says that the Bortle Index value there in Georgetown, CO is Class 4.   smile.gif     Pan and Zoom around the map to click on the area of interest, worldwide.  


Edited by DLuders, 22 November 2019 - 09:01 PM.

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#6 John Fitzgerald

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Posted 22 November 2019 - 09:01 PM

Better question is how do you determine what Bortle other places are (that you have never been to before)?  E.g. if you are scoping out new observing spots.

Cleardarksky.com is one site that gives it.


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#7 nicoledoula

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Posted 22 November 2019 - 09:03 PM

Look at the label. Oh, you said bortle. Nevermind. 


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#8 jaraxx

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Posted 22 November 2019 - 09:39 PM

It's pretty simple.

If I can't see my own galaxy, I'm in a bad Bortle.

if I can see my own galaxy, I'm in a fair Bortle.

If I can see another galaxy, I'm in a good Bortle.


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#9 Barlowbill

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Posted 22 November 2019 - 09:41 PM

I'm in a I can't see my own galaxy



#10 Jim Waters

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Posted 22 November 2019 - 09:49 PM

https://www.lightpol...0FFFFFTFFFFFFFF



#11 dalbaugh

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Posted 22 November 2019 - 10:32 PM

https://darksitefind...#4/39.00/-98.00

#12 GalaxyPiper

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Posted 22 November 2019 - 11:31 PM

I was wondering what a Bortle was too! 

But was a afraid of looking like too much of a Noob.

(You know, they eat Noob's alive I'm told, if you show it in Oga’s Cantina.)

 

https://thisfairytal...-drinks-ranked/

 

I do own a SQM meter, but I would be nice if I had one to display and shout, "MY EYE"S MY EYE"S!" if it's too bright, and "OH MY GOD, IT"S FULL OF STARS!" when it is dark enough...



#13 rk2k2

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Posted 22 November 2019 - 11:38 PM

Cleardarksky.com is one site that gives it.

DITTO

 

I don't know the accuracy or the update frequency, but besides the 'limited' site locations, this is the best I have found for (not literally) real time conditions (it provides forecast by hour).  I'm in Calif and there is quite a large list of sites, and I think I found one site representative of my location (Cool, CA).  If not, the site was Auburn (3 or 4 miles as the crow flies) but Auburn isn't really that representative as it has local light pollution and Cool doesn't, whereas the hills also lay between me and them (perhaps 500' above and between us)


Edited by rk2k2, 22 November 2019 - 11:51 PM.

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#14 GalaxyPiper

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Posted 22 November 2019 - 11:49 PM

DITTO

 

I don't know the accuracy or the update frequency, but besides the 'limited' site locations, this is the best I have found for real time conditions.  I'm in Calif and there is quite a large list of sites, and I think I found one site representative of my location (Cool, CA).  If not, the site was Auburn (3 or 4 miles as the crow flies) but Auburn isn't really that representative as it has local light pollution and Cool doesn't, whereas the hills also lay between me and them (perhaps 500' above and between us)

Blue Canyon, star party Saturday. Stop on by...might be the last one this year, as a Winter storm is brewing and snow is expected next week!

Kyack Airport!


Edited by GalaxyPiper, 22 November 2019 - 11:49 PM.

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#15 rk2k2

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Posted 22 November 2019 - 11:59 PM

Blue Canyon, star party Saturday. Stop on by...might be the last one this year, as a Winter storm is brewing and snow is expected next week!

Kyack Airport!

Darn, wish I had known sooner.  You guys ever go up to Cronan Ranch?  I hear some clubs occasionally use it.  Not the greatest as the Valley lights to the West effect seeing, but it's not too bad observing North and East.



#16 GalaxyPiper

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Posted 23 November 2019 - 12:06 AM

Darn, wish I had known sooner.  You guys ever go up to Cronan Ranch?  I hear some clubs occasionally use it.  Not the greatest as the Valley lights to the West effect seeing, but it's not too bad observing North and East.

Not familiar yet for that area. I just joined this group two months ago. And have only been to Blue Canyon once. Going again tomorrow.

Just keep in mind that there is usually a star party every month if the weather is good on the weekend closest to the new moon.

Or you can check the SVAS website.

 

https://www.svas.org/

 

P.S. the group has it's own observatory on the premises.

 

https://www.youtube....eature=youtu.be


Edited by GalaxyPiper, 23 November 2019 - 12:20 AM.

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#17 Tony Flanders

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Posted 23 November 2019 - 05:50 AM

John Bortle, one of the leading comet experts and variable-star observers, defined his Dark-Sky Scale in an article in the February 2001 issue of Sky & Telescope. You can find it online on the S&T website. Because the scale is based entirely on personal observations, the only way to truly find out how your sky rates on his scale is to step outside on a clear night and see for yourself. For instance, what does the Milky Way look like from your location? How easy is it to see M31 without optical aid? Answers to those and similar questions tell you where your skies fall on the scale.
 
A word of warning. Most people find that Bortle's criteria don't necessarily match all that well; your skies may be Bortle 5 by one criterion and Bortle 7 by another. Do your best! It isn't a precise scale.
 
Now in addition to that strict meaning, people also (more commonly, in fact) use Bortle classes to denote things shown by various light-pollution maps. Because these articles are well known, and most people are completely unaware of John Bortle and his S&T article, when people toss around terms like Bortle Class on the internet without saying what they mean, it's a fair bet that they're talking about how their location is ranked on one of these maps. My own favorite is David Lorenz's 2006 Light Pollution Atlas, which is also used as in the overwhelmingly popular Clear Sky Chart website. For instance, the CSC light-pollution map for Stellafane is here.

 

The correlation between what's shown on a map and how your skies actually rate by Bortle's criteria is weak, and the different maps don't necessarily agree with each other. Take any statement about somebody's Bortle classification with a shaker-full of salt.


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#18 Araguaia

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Posted 23 November 2019 - 08:59 AM

What matters is the ability to look up and compare the sky you have with others you have seen.  Knowing from the appearance - or non-appearance - of objects and features if that night is better or worse than others.

 

I went out last night for the first time in months because the skies appeared to have cleared.  Just binoculars and a chair, but willing to haul out the big gun if conditions were up to it.  Immediately I see the SMC low in the sky, way too faint, with 47 Tuc barely visible.  To the north, M31 was just some fuzz.  Through the binoculars, I could make out just one galaxy of the Grus Quartet, and the Sculptor galaxy, straight overhead, was indistinct and blurry.

 

A bad night, even if the sky was just as dark as ever.  Although the sky was clear, transparency was poor.  Darkness had nothing to do with it.  I went inside when the first mosquitoes found me.



#19 sg6

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Posted 23 November 2019 - 09:00 AM

Looked mine up on a few LP Maps and eventually gave up.

One gave everything as basically 4 or 3. Center of town B4, edge of town B4, 3 miles away B4.

If I deliberately tried a place where there was nothing (twice annual star party held there) it said B3.

I think the middle of the North Sea 50 miles from everything was B3 also.lol.gif lol.gif

 

One place I have seen the Milky Way at and quite strongly is again B4. It was dark enough that walking was a bit hazardous in the dark.

Another place that has no street lights and is dark, you need full headlights on in a car to be safe driving through it, is again B4.

 

Another site said how good the Bortle scale was and said it had a 9 digit scale. So having said how good it was they used a 15 digit scale bangbang.gif

So no longer Bortle.

 

Sometime around then I gave up, and developed my own scale: Dark enough or not dark enough.

Seems to be easier.

Certainly easier then the map that scaled the LP level by: (NanoWatts/cm2/sr) question.gif


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#20 j.gardavsky

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Posted 23 November 2019 - 11:30 AM

The Clear Outside web page tells me Bortle 4, and 20.57 mag, even if it is cloudy, hazy, and snowing.

 

Otherwise, I am using an extended scheme to this one,

It's pretty simple.

If I can't see my own galaxy, I'm in a bad Bortle.

if I can see my own galaxy, I'm in a fair Bortle.

If I can see another galaxy, I'm in a good Bortle.

namely, writing in my observing report which DSOs I have seen with unaided eyes.

 

When wanting to hunt the galaxies, then I check out the visibility of the circumpolar M101 through the 10.5x70 binoculars.

When the M101 is just nothing, then I can stay at home and read the CN.

 

Best,

JG


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#21 rk2k2

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Posted 23 November 2019 - 01:20 PM

I have no clue, but I see lots of peolpe describing their darkness or lack of darkness. measured in bortles. So how do you determine what is yours.

OK, I'll admit, I'm a little slow sometimes and more often than that, don't fully understand a question before answering ...

 

How have I determined my Bortle? - googled it, found a 'map' that placed me in the transition of 3 and 4.  Another result, an article, had the Bortle descriptions and sample pics from each, and the pic for 4 could have been taken from my house.  Finally,  per the actual Bortle Scale Title for 4 "Rural/suburban transition" and it's following DESCRIPTION, as a general rule I say 4 because that is almost always how it is at my house.

 

Considering there have been a few times where viewing (high up and/or away from the light polluted suburban/ urban directions of south to northwest), the night sky is so crisp that everything seems to snap out at you  With that in mind, and maybe I'm wrong, but it seems if I were documenting a nights viewing session and wanted to be more accurate using my Bortle, I might want to use 3?

 

With all that said, and maybe someone has said something like this before:

 

I'd rather be at a Bortle 6 site on a clear night than a Bortle 1 site in the rain (if you think on that you should realize that the Bortle scale obviously refers to 'at the time you are observing', hence a Bortle 1 'site' is NOT Bortle 1 when it is raining).  So I use the Bortle scale in 2 ways, a general rule as to what I can expect, and literally as to what it is.

 

An addition- is it Bortle x per the Bortle Scale desrciptions if you're blind? wink.gif


Edited by rk2k2, 23 November 2019 - 01:41 PM.


#22 Tony Flanders

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Posted 23 November 2019 - 01:51 PM

It's pretty simple.

If I can't see my own galaxy, I'm in a bad Bortle.

if I can see my own galaxy, I'm in a fair Bortle.

If I can see another galaxy, I'm in a good Bortle.

Actually, I find M31 quite a bit easier to see than our own Milky Way. With a bit of effort, I can make out M31 naked-eye from my local city park, about 4 miles from the center of Boston, Massachusetts (USA). But I've never seen even a hint of the Milky Way there.

 

To get a rudimentary view of the Milky Way, I need to be about 10 miles from the center of Boston, by which point M31 is bold and bright. I would rate those sites somewhere between Bortle 5 and 6.

 

By Bortle's standard, any place where you cannot see the Milky Way in considerable detail, and where M31 isn't instantly obvious to the unaided eye, is very poor indeed. That cutoff is about Bortle 5, halfway in the Bortle Scale.


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#23 airbleeder

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Posted 23 November 2019 - 04:30 PM

   I am hardly ever able to see the MW or M31 from my yard, although the latter is sometimes a bit easier. One of the first things I noticed after getting into astronomy was how some of the DSO's jump out at you under a dark sky. One of my first trips to my younger brother's place, I went out to set up, looked up to find Polaris to align and although I had trouble picking it from all the stars M31, M33 and the Double Cluster stood out. 

    I have never had a reason to be concerned with the Bortle rating at home or there. I think I'm in an orange zone and my brother's home is in a dark green zone. I'm really not sure, but I do know there's a world of difference between the two.



#24 dr.who

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Posted 23 November 2019 - 06:59 PM

It's pretty simple.
If I can't see my own galaxy, I'm in a bad Bortle.
if I can see my own galaxy, I'm in a fair Bortle.
If I can see another galaxy, I'm in a good Bortle.


I can’t see it naked eye but I can see M51 and a very faint hint of the lane between the two galaxies on a night of good seeing in a 8” reflector from my house. And I can make out Andromeda as well as the Pleiades with averted vision naked eye. The former has to be very good seeing and the latter even down to below average to poor seeing. I am in a Bortle 7 18.49 SQM zone. Which was nice because I thought I was in an 8. I used the above mentioned LP map. So not sure this is a good way to say what kind of a zone you are in...

#25 dr.who

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Posted 23 November 2019 - 07:10 PM

My dark sky site is 21.68 SQM but a Bortle class 4...
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