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Advice on Finding a Darker Imaging Site

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#1 Reece

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Posted 26 February 2021 - 03:49 AM

Are light pollution map websites such as: www.lightpollutionmap.info generally accurate?

How far away from a large 700.000 population (Bortle 8-9) city should the dark site be?

 

I can only take ~ 6 second exposures at present (ISO= 800, Aperture= F/2.8).

What Bortle Scale would I be looking at for 30 second exposures at ISO 800, Aperture F/2.8?

 

Thank you so much for your help!



#2 ngc7319_20

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Posted 26 February 2021 - 04:08 AM

Are light pollution map websites such as: www.lightpollutionmap.info generally accurate?

How far away from a large 700.000 population (Bortle 8-9) city should the dark site be?

 

Yes the maps are pretty good for relative sky brightness.  The absolute mag/sq arcsec numbers often are not very accurate.

 

I would say 60 miles from 700k city.  But there may be bright suburbs, etc., to reckon with.  Depends how spread out the city it is.


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#3 sg6

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Posted 26 February 2021 - 04:22 AM

Add in where you are it helps, cannot say if the LP at Melbourne Aus is as bad as 8-9, and you may not even be there. When a question has a relevance to where you are a location helps. I cannot even look up what the LP maps indicates for you and at least then have the same data to work from.

 

In general LP maps seem to be based on population. Presumption being more people = more light. Reasonable bu fails to take into account smaller places and also terrain.

 

One place I visit has a reasonable town about 3 mile away, but there is a small rideg of hills between the 2  and so darker then indicated. 2 or 3 villages around me are on the LP maps but none actually have street lights. They are therefore actually dark, very dark.

 

How far you want to drive is a big aspect, time and distance. I travel only some 12-15 miles, and there are as dark or darker locations on the drive out but where I go is very convenient so I do the extra distance. In effect I will drive 12-15 but could as easily do 8-10. The closer location(s) are used by one local astro club a lot.

 

Finding one or two or three means a few visits to different areas, and checking places out. I use a nature reserve a lot, well the access road to it. So maybe look on a map for something similar. Easier is find a club and ask where they go and what they do.

 

Use an LP map as an indication. When I used to go to Cambridge the LP map was poor for the West side. The LP for the West of the M11 was bad, but everything stopped before the M11 and the West side was reasonable. Also they were installing the low intensity LED lights in the whole area, so agian the LP was lowered. The maps didn't take any of that into consideration. They just had a distribution based on X thousand people.


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#4 Reece

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Posted 26 February 2021 - 04:32 AM

I live in Winnipeg, Manitoba (Canada).

My parents recently retired and are in the market for a cottage. My dad likes astrophotography as well so we are looking for a family cottage somewhere we could take nice astrophotography pictures. It could be up to ~ 80 miles away.


Edited by Reece, 26 February 2021 - 04:34 AM.


#5 bokemon

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Posted 26 February 2021 - 04:43 AM

Use the VIIRS 2020 data for more resolution.

Having a set of hills block the light from a city helps a lot.

There are some neighborhoods (typically in the hills) where there are no streetlights and everybody turns off their lights at night.

Best way to know is actually visit at night.


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#6 BQ Octantis

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Posted 26 February 2021 - 07:07 AM

Are light pollution map websites such as: www.lightpollutionmap.info generally accurate?

How far away from a large 700.000 population (Bortle 8-9) city should the dark site be?

 

I can only take ~ 6 second exposures at present (ISO= 800, Aperture= F/2.8).

What Bortle Scale would I be looking at for 30 second exposures at ISO 800, Aperture F/2.8?

 

Thank you so much for your help!

Hey, that's my setting! ~Bortle 3-4.

 

BQ


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#7 rhart426

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Posted 26 February 2021 - 07:32 AM

The VIIRS data will show you light pollution sources; the 2015 ATLAS data will show you zenith brightness (albeit from 5 years ago).  Cause and effect.  Toggle between the two to see how they interact.  VIIRS data alone can be misleading.  You also have to consider the local geography.  Potter county, Pennsylvania (home of Cherry Springs State Park) is sparsely populated, but what really keeps it dark is the geography.  It seems mountainous, but it's really a plateau with glacial fissures carved into it, and most of the population lives in those fissures.  The power company also distributes fixtures to shield outdoor lights from shining upwards.  Those details make a big difference on whether a light pollution dome is visible at a distance or not.


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#8 havasman

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Posted 26 February 2021 - 07:41 AM

All the dark sky maps have +/- factors. Some are better than others. None are as good as checking out the properties you may consider to see their night sky conditions. Explain to the seller and go see for yourself how dark it gets. An SQM-L light meter from Unihedron should give you good objective readings with which you can compare different sites.

I drive 106 miles outside of the Dallas light dome to get to my dark site. Dallas' satellite towns extend quite a way from the city.


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#9 fishonkevin

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Posted 26 February 2021 - 08:27 AM

Reece, are there any Astro Clubs in the area?  They are always good for info.  I would think though that anywhere north of Winnipeg would be a good place to start.  Here is a link to a list of various private/public observatories from ClearDarkSky that are in Manitoba.

 

https://www.cleardar...oba_charts.html


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#10 T~Stew

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Posted 26 February 2021 - 11:04 AM

I was curious about this as well. I am looking for a cabin site / future home and reasonably dark skies is a requirement. I feel kind of odd having that as a requirement, even before getting into AP I really wanted a property with a nice unobstructed view to the west at least for sunset. People think I am crazy, but hey I really enjoy watching the sunsets without houses and man made stuff in the view.

Anyhow, New York would probably not come to mind as a good place for dark skies, but it is where I grew up and looking to move back. One of the properties I was most interested in I checked on www.lightpollutionmap and its Bortle 2, nice! Not easy to come by that in the north east U.S.


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