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Pages: 1 WRAK sage Reged: 02/18/12 Light Pollution Seeing Paradoxon       #5423516 - 09/16/12 10:36 AM Edit   Reply   Quote Quick Reply   I do visual astronomy since a few years using basically two backyard sites as I do not like travelling with my gear. One site is at the fringe of a large city with heavy light pollution and the other at the fringe of a quite small town or village in the hinterland with only a bit of light pollution but basically a quite dark sky. And now comes the paradoxon: I have regardless of equipment never been satisfied with the quality of the visual image at the "dark" site except when looking at deep sky objects especially global clusters and quite satisfied with my equipment when looking at double stars and open clusters from my "bright" site. Only lately I found a possible explanation for this phenomenon: The drop of temperature in the evening is quite intense at the hinterland site and not so in the city where the dome of haze and temperature is rather stable also in the evening. So in everage I have calmer and drier air and therefore longer lasting stable seeing at the light polluted site and more turbulent and humid air and therefore poor seeing at my dark site. Anyone with same experiences? Wilfried Post Extras:       Bonco Post Laureate Reged: 04/17/06 Loc: Florida Re: Light Pollution Seeing Paradoxon [Re: WRAK]       #5424076 - 09/16/12 04:51 PM Edit   Reply   Quote Quick Reply   Don't know where you live and what weather patterns exist there. But I think you are on the right track. It has to do with the atmospheric dynamics at each site. Bill Post Extras:       drollere Pooh-Bah Reged: 02/02/10 Loc: sebastopol, california Re: Light Pollution Seeing Paradoxon [Re: Bonco]       #5424163 - 09/16/12 06:01 PM Edit   Reply   Quote Quick Reply   the best way to zero in on the seeing is with a seeing scale, for example HERE. if you use magnification sufficient to visualize the airy disk, then the diffraction artifact is highly informative about the quality of the seeing and the composition of the turbulence. cities are actually huge heat reservoirs, soaking up heat in the masonry and pavement, which can cause thermals far into the night. these tend to be low frequency turbulence of the wiggle and dance variety. (high altitude turbulence is more of the seething speckle type.) i'd think the landscape, especially as it might channel low altitude air flows or be proximate to mountains or bodies of water, would be a major factor at both locations. humidity can be very significant; dispersion can cause serious light scatter even when the sky appears to be fairly transparent. final thought -- light pollution around the city may make brighter double stars easier to see, for the same reason that Sirius B and details on jupiter are often easier to catch when viewed in twilight. Post Extras:       Ed Wiley professor emeritus Reged: 05/18/05 Re: Light Pollution Seeing Paradoxon [Re: drollere]       #5426507 - 09/17/12 11:55 PM Edit   Reply   Quote Quick Reply   Some of the best seeing I experienced was through a Newtonian parked outside Cafe du Monde in New Orleans. Good seeing, like gold, is where you find it and sometimes the finding is pleasantly unexpected. Ed Post Extras:       azure1961p Postmaster Reged: 01/17/09 Loc: USA Re: Light Pollution Seeing Paradoxon [Re: Ed Wiley]       #5428067 - 09/18/12 07:04 PM Edit   Reply   Quote Quick Reply   I've heard more than a couple times that city seeing can be very good in terms of stable images. Pere Post Extras:       Pages: 1

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