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#1 stargazer32864

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Posted 18 June 2020 - 10:15 PM

Ok. I've been reading about Bortle scale in different areas. Where do I find the Bortle scale for my city? I know when we lived in town you could only see, maybe, a few hundred stars if that, in the night sky. But when we moved on my mom's new farm next to the county line, it was almost a religious experience. It went from a few hundred to a few thousand. And I could see the Milky Way. Yes, I could see the faint glow from Owensboro and a few security lights from the neighbors but that's about it. And I have a clear sky chart bookmarked on my computer, Yeah, I know that's totally different, but I can't seem to pull up any data from it. What is going on?

 

~Robin



#2 bobzeq25

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Posted 18 June 2020 - 10:46 PM

Find your location and click on it.

 

https://www.lightpol...FFFFFTFFFFFFFFF


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#3 stargazer32864

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Posted 18 June 2020 - 11:07 PM

Find your location and click on it.

 

https://www.lightpol...FFFFFTFFFFFFFFF

Thanks for the link. I live in Bortle 5. bangbang.gif  I miss living in the country.bawling.gif 



#4 bobzeq25

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Posted 19 June 2020 - 01:33 AM

Bortle 5?  I'm jealous.  <smile>

 

Bortle 7.


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#5 Tony Flanders

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Posted 19 June 2020 - 04:39 AM



Ok. I've been reading about Bortle scale in different areas. Where do I find the Bortle scale for my city? I know when we lived in town you could only see, maybe, a few hundred stars if that, in the night sky. But when we moved on my mom's new farm next to the county line, it was almost a religious experience. It went from a few hundred to a few thousand. And I could see the Milky Way. Yes, I could see the faint glow from Owensboro and a few security lights from the neighbors but that's about it. And I have a clear sky chart bookmarked on my computer, Yeah, I know that's totally different, but I can't seem to pull up any data from it. What is going on?

 

~Robin


When John Bortle first introduced his Dark-Sky Scale in the February 2001 issue of Sky & Telescope, it was reasonably well defined. It is based entirely on subjective criteria, designed to allow you to evaluate your own skies without using anything but your own eyes. Be aware, however, that different people may arrive at different Bortle estimates for the same site due to differences in eyesight and experience. Also, as Bortle originally introduced it, the Bortle Class was a property of a particular site. He has later clarified that he really meant it to apply to a particular night at a particular site -- in other words, the Bortle classification can vary depending on the conditions.

 

The original article is posted online here.

 

Since then, things have been somewhat muddied by the introduction of the various light-pollution maps that purport to predict the Bortle level for your site based on satellite data. The maps do not necessarily match reality perfectly, nor do they necessarily match each other. So when specifying your Bortle Class, it is useful to say where you got that number from.

 

Note that the maps are based entirely on skyglow from distant light sources. They do not and cannot take glare from nearby lights into account. If you are standing under the only streetlight in the middle of the Gobi Desert, your Bortle Class will be closer to 9 than to 1 -- as it would be if you were to walk a half mile away from that light.

 

To get from a Clear Sky Chart to a light-pollution map, click on Light Pollution map under Nifty Links directly below the colored bars.


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#6 stargazer32864

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Posted 19 June 2020 - 08:50 PM

Bortle 5?  I'm jealous.  <smile>

 

Bortle 7.

Ouch!!



#7 stargazer32864

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Posted 19 June 2020 - 08:59 PM

When John Bortle first introduced his Dark-Sky Scale in the February 2001 issue of Sky & Telescope, it was reasonably well defined. It is based entirely on subjective criteria, designed to allow you to evaluate your own skies without using anything but your own eyes. Be aware, however, that different people may arrive at different Bortle estimates for the same site due to differences in eyesight and experience. Also, as Bortle originally introduced it, the Bortle Class was a property of a particular site. He has later clarified that he really meant it to apply to a particular night at a particular site -- in other words, the Bortle classification can vary depending on the conditions.

 

The original article is posted online here.

 

Since then, things have been somewhat muddied by the introduction of the various light-pollution maps that purport to predict the Bortle level for your site based on satellite data. The maps do not necessarily match reality perfectly, nor do they necessarily match each other. So when specifying your Bortle Class, it is useful to say where you got that number from.

 

Note that the maps are based entirely on skyglow from distant light sources. They do not and cannot take glare from nearby lights into account. If you are standing under the only streetlight in the middle of the Gobi Desert, your Bortle Class will be closer to 9 than to 1 -- as it would be if you were to walk a half mile away from that light.

 

To get from a Clear Sky Chart to a light-pollution map, click on Light Pollution map under Nifty Links directly below the colored bars.

I got my Bortle classification from the map that was listed. Except I zoomed in on my neighborhood and then held the cursor over the area the house is located to get the number. But I noticed that the map hasn't been updated because the streets that were added in the past 2 years weren't on there.



#8 sunnyday

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Posted 19 June 2020 - 09:02 PM

i'm at 8 almost 9, i'll take 5 right now.


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#9 BrooksObs

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Posted 19 June 2020 - 10:57 PM

Ok. I've been reading about Bortle scale in different areas. Where do I find the Bortle scale for my city? I know when we lived in town you could only see, maybe, a few hundred stars if that, in the night sky. But when we moved on my mom's new farm next to the county line, it was almost a religious experience. It went from a few hundred to a few thousand. And I could see the Milky Way. Yes, I could see the faint glow from Owensboro and a few security lights from the neighbors but that's about it. And I have a clear sky chart bookmarked on my computer, Yeah, I know that's totally different, but I can't seem to pull up any data from it. What is going on?

 

~Robin

 

Robin - The Bortle Dark Sky Scale  is intended as a means of evaluating the night sky at the date and time you are making your own observations from there. It was never intended as a predictor of typical conditions at any site and it is a mistake to use it for that purpose, as sky conditions can vary widely night to night.

 

BrooksObs


Edited by BrooksObs, 19 June 2020 - 11:02 PM.

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#10 stargazer32864

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Posted 20 June 2020 - 04:39 PM

Robin - The Bortle Dark Sky Scale  is intended as a means of evaluating the night sky at the date and time you are making your own observations from there. It was never intended as a predictor of typical conditions at any site and it is a mistake to use it for that purpose, as sky conditions can vary widely night to night.

 

BrooksObs

Thank you for clearing that up.



#11 rmatscott

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Posted 23 June 2020 - 02:13 PM

Someone may have already suggested, but I use the Light Pollution Map (LPM) and Dark Sky Map apps on my Android phone.  



#12 jcj380

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Posted 24 June 2020 - 08:21 AM

i'm at 8 almost 9, i'll take 5 right now.

I'm with you on that one although I might be just a tad lower than 8.  

 

I'm going to be near Jasper, IN in a few days, so maybe I'll get a little observing in under SG's skies.  wink.gifsmile.gif


Edited by jcj380, 24 June 2020 - 08:24 AM.

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#13 PEterW

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Posted 29 June 2020 - 07:01 AM

Satellite maps measure light going upwards, much urban light pollution escapes outwards laterally, so not well assessed by satellite tools, not to mention the switch to LEDS affects the accuracy of the satellite estimates. As mentioned it is seeing specific, I have got the same SQM reading but seen radically different amounts depending on transparency.
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#14 Eddgie

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Posted 04 July 2020 - 03:56 PM

Bortle Scale lacks precision and even at a given location, a map may show a given level of light pollution but conditions could be better or worse depending on many different factors.  For example, if I view to the south, I am viewing into what would be considered Bortle 9 because I live 4.5 miles from the center of the city, but when I view at zenith the sky is typically much darker (and this is true almost anywhere, but more so in semi urban and urban areas) and it is darker in the north, east and west than to the south.

 

When I want to actually report observations, I try to use my SQM-L meter to take quick read.  Because of the light pollution dome over the city center, I use the SQM-L so I can take my reading in the same part of the sky that I made the observation so someone else on the forum can have a very objective and accurate idea of the exact sky quality when the observation was done.

 

In spite of the shortcomings I think the Bortle scale is quite superb at giving a general idea of the light pollution conditions for a given area.  It is not perfect, but for something like this, where every night can have some variation, it serves us well enough that the shortcomings can be dismissed. 



#15 stargazer32864

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Posted 04 July 2020 - 04:08 PM

I don't think the Bortle is very accurate either. Where I live, my subdivison they have expanded the neighborhood to include new houses with security lights and street lights. There's a big difference in the sky at night now. What few stars I could see, are gone now.




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