How to chose a darker site.

[domstar]

Hi everyone,

What is better if you want to observe to the south- on the edge of a small town (30 000 people) but with the town behind you and a clear view south, or viewing over the same town 5 km away from a place with no lights? Galaxies in Leo and around Virgo would be my targets. 

Thanks.

 

 

[Timebandit]

 

 

Unfortunately light pollution just produces what I class as a glow over quite an area(depending how much light pollution is being produced). I travelled around 5miles from where I live. And even though is was darker, you still had that light glow from the light pollution town effecting the DSO observing considerably. 

Then I travelled further again to a true dark site . And those galaxy's then really do pop to the eyes and much better observed. Light pollution produces a glow that can stretch for many miles. Therefore to get the best for those fainter DSO then you need to get in the car and travel to a dark site well away from any source of light pollution. The effort is really worth it ,and you will be shocked and pleased at the results at true Dark site .

 

 

 

 

[cloudsweeper]

Dom - I'm sure someone with direct experience of this will comment, but I would have thought that having the town behind you would be better than viewing over  the town and through its "light dome" to faint targets.

Why not run your own tests?  I'd be interested to hear!

Doug.

 

 

[Stu]

It’s difficult to say, but I reckon as Doug says, better to be on the edge of town looking over dark fields.

It depends upon a few things. How large is the light dome from the town if you are trying to look over it from the North, and can you get dark adapted on the edge of town looking over dark skies to the south.

Maybe a couple of trial runs needed to prove the point.

[chiltonstar]

I live on the edge of a village with clear views to the S without LP, and having to look "through" the LP to the N - like your situation. IMO better to look S as even on nights with little haze and backscatter, the view across "civilisation" will not be good. For example, for me when M51 is N, I can see it but little detail, but now that it's E at 23:00 hours (2 nights ago), a good night shows glorious detail and the spiral arms.

Chris

[JAO]

If the weather relents enough, I would do as others have suggested and run some tests from the different sites. In general getting as clear and  unobstructed a view to the south is my preference. That said his isn't always possible and scouting sites under optimal conditions is time well spent in my humble opinion.

[domstar]

Thanks for the replies. I've done a little daytime scouting. Is observing through close power lines a problem? 

[Ed in UK]

Don't touch 'em...... 

From my photography experience, if I want to photograph animals at a zoo to try to remove the cage wires I get as close as I can to the cage then when I focus on my subject the cages wires are out of focus and are not readily visible/distinguishable in the image. Sure they cut down on the amount of light that I have available but I can, to a degree, see through them.

So I believe that you may not see a hard line going across your FOV but if an object gets dimmer for a while it may be down to the power wires. I would of thought that you should be able to track an object through the wires. Pylons will be too solid to focus/track through.

However personally, I would probably give it some thought, as whether I really want to be stood close to power lines with a lump of metal especially if the weather closes in.

[Stu]

It’s quite surprising what you can observe through without it having too dramatic an impact. Recently I was observing Jupiter and noticed a slight drop in brightness and detail. Only on defocusibg was it clear that it was partly obscured behind the leaves of a tree!

If it means only brief periods behind the wires then not too much of an issue.

[JOC]

FWIW, you could argue that I am on the edge of a town (well I'm about 3 miles away), I get on better looking away from the town, which for me is also South (and East), if I look West where I don't have a town for about 6 miles the light pollution is far worse than my views South and East, If I look North I'm out and over a factory which despite having bright lights and messing me up if I'm fairly close, is easier if I get about 200m away and look across above them - although bright their lights don't seem to have the 'persistence' into the sky that I get when even looking over a conurbation that is 6 miles away.  I would therefore say the answer is the edge of the town looking away from it.

[Tim]

On 08/04/2018 at 18:21, domstar said:

Thanks for the replies. I've done a little daytime scouting. Is observing through close power lines a problem? 

Not really, the target moves very quickly across them. You likely wont notice any difference on galactic targets, brighter stars and planets may show unwanted diffraction effects for a moment.

For best results on fainter galaxies, the transparency of the skies is important too, not just the darkness and the seeing. As usual, the higher in the sky the target, the better.

[Captain Scarlet]

On 08/04/2018 at 22:08, Stu said:

It’s quite surprising what you can observe through without it having too dramatic an impact. Recently I was observing Jupiter and noticed a slight drop in brightness and detail. Only on defocusibg was it clear that it was partly obscured behind the leaves of a tree!

If it means only brief periods behind the wires then not too much of an issue.

To emphasize this point: I have recently returned to observing after decades (ie since I was a teenager). On borrowing a friend's 5-inch scope recently I tried, whilst looking at the Moon, putting my entire hand in front of the scope. I barely noticed a difference ... the Moon is so bright, and there was a spare 2-3 square inches between my fingers for the light to get through! I also had a similar through-the-trees experience with Saturn the same night, which is actually what prompted my "whole hand" experiment.

Magnus

[James]

The site I use for most of my observing/imaging has pylons just to the north - I've not really noticed any problems and there's an added advantage of being able to tell if the humidity is rising as the pylons/wires constantly crackle and buzz if it's damp. In fairness they're only up to about 20 degrees and north is less important to me

 

[domstar]

 

 

18 hours ago, Tim said:

For best results on fainter galaxies, the transparency of the skies is important too, not just the darkness and the seeing. As usual, the higher in the sky the target, the better.

How true. How true. I was out last night and the conditions were abysmal (and not as dark as I'd hoped). Now I just need to find myself a transparent site.

[vlaiv]

On 4/10/2018 at 15:36, domstar said:

 

 

How true. How true. I was out last night and the conditions were abysmal (and not as dark as I'd hoped). Now I just need to find myself a transparent site.

These might help:

https://www.lightpollutionmap.info/#zoom=7&lat=6394939&lon=1792066&layers=B0FFFTFFFF

And for transparency (this is forecast, so not 100% certain):

https://atmosphere.copernicus.eu/maps/aerosol-forecasts#1._aerosol_optical_depth_at_550_nm_(provided_by_cams,_the_copernicus_atmosphere_monitoring_service)/6/50.054/16.155

Just select time of observation (1-2 days in advance, more than that, less chance it will be accurate, also note that khaki like color that is not in color scale is actually fully transparent).

These are for "global" values, there are always local influences, like local LP, and local transparency issues like fog or smoke from nearby sources.

Going up in altitude also helps a lot.

[domstar]

That's great @vlaiv. That transparency site is just what I wanted.

 

[knobby]

So sad, have you seen how much the pollution grows each year on that map