Fun with doubles and Questions on Light Pollution
Posted 03 December 2012 - 10:30 PM
Two quick, probably answered, but not that I could find questions. First, I'd guess light pollution doesn't hurt double splitting a bunch as long as the components aren't particularly faint, is that accurate?
Second, when in focus, I never see any rings around stars, just the central visual disk of the airy pattern, but most of the pictures of doubles appear to have it. I had a couple of ideas, namely that either my light pollution is washing that ring out (I'm solidly in the white area of the D/FW metroplex on the maps) or that the rings show up more clearly in pictures with their increased light gathering. I'm hoping it's one of those things and not something I'm doing wrong.
PS This is fantastically helpful for understanding what everyone's talking about, http://www.cloudynig.../resolution.pdf thanks Ed.
Posted 03 December 2012 - 10:41 PM
Posted 04 December 2012 - 12:01 AM
Seems everyone agrees light pollution has no affect on resolution. And by that, I think they mean contrast between two resolved features. But, resolution requires contrast, as you might agree. I am not entirely convinced light pollution does not dampen contrast, thus dampen resolution.
Light pollution is a type of noise imposed over a signal, say from Jupiter. This noise can be strong enough to dampen some of Jupiter's most delicate contrast features. Now, I suspect this to be the case both in theory and, I tend to believe, in practice. The effect may be minimal, but I do seem to observe slightly degraded views of Jupiter (and Saturn) when the full moon is nearby.
One might imagine enough sky glow would do the same. And maybe more so on extended objects with bright, low contrast detail than the higher contrast between sufficiently separated point sources. But enough sky brightness, say like the daytime sky, could even dampen contrast between point sources. That's why we cannot see them, normally.
Anyway, that's just an opinion with no hard evidence to back it, and it's certainly debatable.
Posted 04 December 2012 - 07:29 AM
I totally agree about planets, though. At the Okie-Tex SP I observed Jupiter under the worst light pollution possible - daylight - and found the disc to be wan, washed out and very bland. Bad nighttime LP must have the same but lesser affect. And, while I'm on about it, just check out the difference in the moon's features naked eye between night and daylight views. The contrast is noticeably affected......
Posted 04 December 2012 - 08:29 AM
Posted 04 December 2012 - 10:18 AM
Posted 05 December 2012 - 02:02 AM
For an observing program, you might try the Astronomy League double star list. Another good one for the urban environment is the Hass book, by constellations, Yes, there are some faint ones, but also plenty of bright pairs to enjoy.
Relative to you questions, I think Dave answered them. And yes, Jupiter was washed out, I saw it myself through Dave's scope. On the other hand, it was my first look at Jupiter if Daylight. Thanks Dave!
Posted 05 December 2012 - 03:09 AM
There's a certain patience required (something I often lack) and it's very rewarding to have a pair that when first viewed you see one star or perhaps a hint of two, but then once you've seen it for a while, even after looking away you can't see just one star anymore.
Posted 05 December 2012 - 08:32 PM
Posted 09 December 2012 - 09:35 AM
I observe from suburban Pittsburgh, also with a Nexstar 8SE. I quickly began to focus (so to speak!) on double stars after attending a star party under really dark skies and realizing my backyard is not a very good site for deep sky observing.
Unfortunately, the built-in list of double stars in the Nexstar database is rather meager -- only about 50 or 60. So I make extensive use of the Eagle Creek Observatory double star database, nicely arranged by constellation, and available in the "LINKS to double star resources" thread at the top of this forum. Here it is
Eagle Creek Observatory Double Stars
One nice feature of this database is the inclusion of the SAO number for nearly every double star. These make finding the stars with our Nexstar hand controllers very easy.