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Seeing in city vs rural area

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#1 astrosatch

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Posted 18 February 2019 - 07:51 AM

Hi.

Is there difference in seeing in town where there are houses and roads and especially in winter with chimneys and heated houses vs countryside where is grass and forest? I have telescope on balcony looking above block of flats. Would my autoguiding improve if I change the scene to more remote site?

 

Andrej



#2 Starman47

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Posted 18 February 2019 - 08:02 AM

Looking over houses with heat rising from the house degrades seeing quite a bit, (I have probably observed over a hundred nights over my neighbors roofs. And I have been in the woods and in the desert. Outside of town is much better).

 

But I cannot speak about autoguiding as that is not how I observe.


Edited by Starman47, 18 February 2019 - 08:03 AM.


#3 calypsob

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Posted 18 February 2019 - 11:00 AM

Hi.

Is there difference in seeing in town where there are houses and roads and especially in winter with chimneys and heated houses vs countryside where is grass and forest? I have telescope on balcony looking above block of flats. Would my autoguiding improve if I change the scene to more remote site?

 

Andrej

Ideally you want to be imaging around zenith no matter where you are, this helps reduce gradients and allows you to image the darkest part of the sky. Heat plumes should not matter as much at zenith unless you are very close to a building. 


Edited by calypsob, 18 February 2019 - 01:05 PM.


#4 astrosatch

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Posted 18 February 2019 - 01:13 PM

Thanks for answers. Yes zenit is best,but not every object goes near it. Like orion nebula is only 45 degrees above horizon. Perfect view above rooftops😉

#5 RedLionNJ

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Posted 18 February 2019 - 01:19 PM

I don't believe autoguiding is particularly affected by seeing. You're imaging through essentially the same atmosphere as the guider, so there are two ways to look at this:

 

1. Long enough autoguider exposures will average-out high frequency shifts in a star's apparent position

 

2. Think of it as a form of adaptive optics - you're accounting on-the-fly for small changes in the target's apparent position :)

 

 

I'm at the point where I don't even try imaging if the seeing is too bad (more than 3 arcsec) here.



#6 Jerry Lodriguss

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Posted 18 February 2019 - 05:32 PM

Hi.

Is there difference in seeing in town where there are houses and roads and especially in winter with chimneys and heated houses vs countryside where is grass and forest? I have telescope on balcony looking above block of flats. Would my autoguiding improve if I change the scene to more remote site?

Hi Andrej,

 

This is a bit more complicated than you probably realize.

 

Telescope on a balcony.  What happens if the building sways a bit in the wind?  That has nothing to do with seeing.

 

You're going to have 3 or 4 different kinds of seeing, no matter where you go.

 

1. Inside the scope.  If the scope hasn't acclimated to the outside temp, you will have bad seeing inside the scope itself with tube currents.

 

2. Local seeing around the scope... like dome seeing, or your body heat drifting across the light path of the scope.

 

3. Local seeing in the area, such as heat plumes from chimneys, or heat rising off rooftops or pavement.

 

4. Atmospheric... like wind becoming turbulent when it goes over the mountains, or from the jet stream being overhead.

 

So you really have to consider each of these.

 

And just to complicate things, I've seen great seeing in the middle of a big city, and terrible seeing in the Pine Barrens where I observe in New Jersey because Pine trees are notorious for outgassing and messing up the seeing.

 

In general, the seeing is going to be better in the summer, and then the heat island of the city won't matter much except you don't want to be looking over any hot roofs that will re-radiate heat all night long.  In the winter, the seeing is usually going to be worse, and going to the forest might not help.  And if the jet stream is overhead, no matter where you are, you can forget about it.

 

In any event, disregarding seeing, if you can get to the woods to shoot, it's going to be darker, and you will get better pictures in a shorter amount of time then from your balcony, so if you can go to the woods, why wouldn't you?

 

Jerry


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#7 Kendahl

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Posted 18 February 2019 - 06:31 PM

Telescope on a balcony.  What happens if the building sways a bit in the wind?

It's even worse than that. My graduate school owned an 18" reflector mounted on a pillar that ran from the top of the building down to bedrock. During construction, the contractor ignored instructions that the pillar was supposed to remain unconnected to the surrounding building. It was necessary to turn off the air circulation system to stop vibrations that made the telescope unusable.



#8 astrosatch

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Posted 19 February 2019 - 02:37 AM

Wow!

I didn't know things are so complicated. I would be better off if I go away from town in any way I guess. For serious imaging I will definately do it. At the moment I'm testing new gear and learning as much about astrophotography as I can. And want to really improve my imaging.

 

Thanks all for your help.

 

Andrej



#9 Jon Rista

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Posted 19 February 2019 - 03:01 AM

Jerry pretty much covered it all. It's a pretty complex subject when you get into it.

 

The big thing here is sky darkness. Pretty much nothing beats getting out to dark skies. Doesn't matter what the seeing is like, doesn't even matter if it is very windy (use the car as a shield). Dark skies are the AP trump card. You can usually do in 2-3 hours what it could take 40-60 hours or more to do in the city. 



#10 ks__observer

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Posted 19 February 2019 - 05:51 AM

Re benefit of dark skies, there is a good chart here:

https://www.cloudyni...flux/?p=9092701



#11 Daniel Dance

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Posted 19 February 2019 - 11:00 AM

Hi Andrej,

 

This is a bit more complicated than you probably realize.

 

Telescope on a balcony.  What happens if the building sways a bit in the wind?  That has nothing to do with seeing.

 

You're going to have 3 or 4 different kinds of seeing, no matter where you go.

 

1. Inside the scope.  If the scope hasn't acclimated to the outside temp, you will have bad seeing inside the scope itself with tube currents.

 

2. Local seeing around the scope... like dome seeing, or your body heat drifting across the light path of the scope.

 

3. Local seeing in the area, such as heat plumes from chimneys, or heat rising off rooftops or pavement.

 

4. Atmospheric... like wind becoming turbulent when it goes over the mountains, or from the jet stream being overhead.

 

So you really have to consider each of these.

 

And just to complicate things, I've seen great seeing in the middle of a big city, and terrible seeing in the Pine Barrens where I observe in New Jersey because Pine trees are notorious for outgassing and messing up the seeing.

 

In general, the seeing is going to be better in the summer, and then the heat island of the city won't matter much except you don't want to be looking over any hot roofs that will re-radiate heat all night long.  In the winter, the seeing is usually going to be worse, and going to the forest might not help.  And if the jet stream is overhead, no matter where you are, you can forget about it.

 

In any event, disregarding seeing, if you can get to the woods to shoot, it's going to be darker, and you will get better pictures in a shorter amount of time then from your balcony, so if you can go to the woods, why wouldn't you?

 

Jerry

Jerry,

 

You beat me to it.  I was going to bring up our discussions about the Pine Trees outgassing.

 

And of course, in the winter time, don't forget about the guys (like myself) who like to sit in their car with engines running.  I'm sure that hot air from the exhaust can be another contribution to poor seeing.

Dan


Edited by Daniel Dance, 19 February 2019 - 11:02 AM.


#12 nimitz69

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Posted 19 February 2019 - 12:40 PM

Wow!

I didn't know things are so complicated.

 

Andrej

Everything to do with AP is ‘complicated’ ... that’s what makes it interesting ...dalek12.gif



#13 OldManSky

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Posted 19 February 2019 - 12:50 PM

Jerry Lodriguss wrote:

 

"Pine trees are notorious for outgassing..."

 

So are astronomers :)



#14 astrosatch

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Posted 20 February 2019 - 07:30 AM

Everything to do with AP is ‘complicated’ ... that’s what makes it interesting ...dalek12.gif

Yes. How many nights I was frustrated because nothing worked. Even  weather refuse to cooperate. And when I solved the problem it was working and I was happy like a baby. laugh.gif




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