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# Moving to darker skies

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### #1 PeteM

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Posted 14 January 2020 - 07:44 PM

This spring I will be moving to dark skies out in the county.  I currently image from my backyard observatory with typical SQM-L of around 18.5. My new location I have measured around 20.8 a couple of times. So going from Bortle 6/7 skies to 4. What can I expect with imaging LRGB with my 8300 based camera? I figured less gradients and "cleaner" data. What was your experience?

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### #2 DrGomer

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Posted 14 January 2020 - 07:51 PM

IIRC, each bortle stop is 2.51x, so from a 7 to a 4 is 2.51^3=15.8 difference in background sky glow. And if we treat it as noise, and integrate, it'll be sqrt of that better S/N, or about 4x better S/N...or another way to look at it is, what you can achieve in 15.8 hrs of bortle 7 of measurement can be done in 1hr in bortle 4.  This is for "LRGB/OSC. I think that's about right.

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### #3 PeteM

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Posted 14 January 2020 - 08:00 PM

Wow that really is going to have an impact on my images. I really have no issues going 8-10hrs per object now. Just never knew the math well enough to calculate the X hours roughly equal Y hours.

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Posted 14 January 2020 - 08:03 PM

I don't think you can treat the background glow as noise. It is a signal. The noise is the square root of that signal.

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### #5 17.5Dob

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Posted 14 January 2020 - 08:05 PM

IIRC, each bortle stop is 2.51x, so from a 7 to a 4 is 2.51^3=15.8 difference in background sky glow. And if we treat it as noise, and integrate, it'll be sqrt of that better S/N, or about 4x better S/N...or another way to look at it is, what you can achieve in 15.8 hrs of bortle 7 of measurement can be done in 1hr in bortle 4.  This is for "LRGB/OSC. I think that's about right.

Not correct. Bortle has no fixed ratio between the somewhat ambiguous units .

The SQM measure gives the OP what he needs to know. His new location will be 2 mag darker than his current site . 2.51 X 2.51 = 6.3 X faster than his current site.

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### #6 zxx

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Posted 14 January 2020 - 08:08 PM

I had the privilege to image at a bortle 4 sky, I now have no interest imaging from my home bortle 7/8 sky.

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### #7 PeteM

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Posted 14 January 2020 - 08:09 PM

Not correct. Bortle has no fixed ratio between the somewhat ambiguous units .

The SQM measure gives the OP what he needs to know. His new location will be 2 mag darker than his current site . 2.51 X 2.51 = 6.3 X faster than his current site.

So roughly 1hr at the new site will be like ~6.3hrs at the current site, which I will notice. Just also wondering if the DBE/ABE in PI is easier or less intensive and other such things.

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### #8 klaussius

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Posted 14 January 2020 - 08:28 PM

I don't know with PI, but when I did Bortle 3 after a lot of Bortle 9, ABE was a breeze.

### #9 Cali

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Posted 14 January 2020 - 09:19 PM

This spring I will be moving to dark skies out in the county.  I currently image from my backyard observatory with typical SQM-L of around 18.5. My new location I have measured around 20.8 a couple of times. So going from Bortle 6/7 skies to 4. What can I expect with imaging LRGB with my 8300 based camera? I figured less gradients and "cleaner" data. What was your experience?

Hey PeteM

Do you have a set of binoculars?

- Cal

### #10 PeteM

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Posted 14 January 2020 - 09:22 PM

Hey PeteM

Do you have a set of binoculars?

- Cal

Sure do, nothing massive...just my trusty 7x50

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### #11 calypsob

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Posted 14 January 2020 - 09:34 PM

So roughly 1hr at the new site will be like ~6.3hrs at the current site, which I will notice. Just also wondering if the DBE/ABE in PI is easier or less intensive and other such things.

Its entirely dependent on the environment.  If there are no local parking lots or stadiums, or streetlights, and its crystal clear then at and around zenith you will have minimal gradients.

If your neighbor has a huge flood light then its a different story.

My house is a mag 20.4, over christmas when my neighbors left town and left all their lights off I went outside at 1 am and it was a mag 20.8, thats the highest I have seen it.  Im guessing a bunch of places were closed down the road as well.  You can see the milkyway at zenith, Andromeda is pretty easy to see with direct and averted vision.  All of this is assuming htere are no nearby lights that will prevent your pupils from dilating.

The biggest cause of gradients will be thin clouds overhead and neighbors or buildings with bright lights, or the combo, neighbors with bright lights reflecting off of thin overhead clouds

### #12 TOMDEY

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Posted 14 January 2020 - 09:35 PM

Super! Going from 18.5 to 20.8 is such a huge improvement... no point in even trying to micro-quantify it. You will be delighted and might want to seriously add visual observing to your menu of ways to enjoy astronomy. I remember when I moved from a mildly light-polluted suburb to decent rural 21.4 mag/sec2 ... I addressed the eyepiece with the same 17.5-inch Dobsonian and instantly realized that "Galaxies are BIG!" All along, I had just been thinking the nucleus was the whole thing. Now I could (and still can) see the spiral structures, pan through Leo/Virgo and see piles of galaxies swimming thru the field. And the pleasure of discovering that lots of Deep Sky targets actually look better with the LP filter left on the table, not needed.

Here's my Cocoon onto film, single exposure, no filters, back around 1980. And it also looks nice just peering thru the eyepiece. Thankfully, that still is true here. Still rural and still decently dark.

Anyway, this brings up a point I'm generally reluctant to make. You decided to move rural for the enhanced astronomy and undoubtedly other reasons. My experience, going on forty years now... country living is so much better in so many ways. More space, fresh air, gardening, bird watching, bounteous fauna and flora all around, peaceful, kids can roam ~free range~, farms to visit, horses to ride, populated by freedom-focused folks...

I'm old and retired now. My today started with a three-mile hike in a nearby forever-wild State Park, then shopping with the wife, then another hour and a half of exercise in the home gym, then supper, and now relaxing with the three dogs and two cats. Some astronomy stuff and to bed. Tomorrow will be similar. I'm 72, going on 73, and still manage twenty hours of exercise a week and able to zoom up and down the warehouse ladder to the eyepiece of the 36-inch scope! So far... so good...  Tom

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### #13 PeteM

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Posted 14 January 2020 - 09:57 PM

Totally agree Tom/Wes. I am actually very familiar with where I am moving, it is my parents house for the last 30 years. So I have a solid understanding of the how the LP has grown over the years. Luckily it is just to the north and the small subdivision(10-15 homes of same age) has not changed much either. All to the south and west is solid farmland that is highly unlikely to be otherwise for decades to come. Even if so, I will still be in a better position for my astronomy (and family) being out there than my current location.

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