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Magnitude 5.2 stars seen in a "white" zone!

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#1 Starman81

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Posted 08 December 2012 - 05:36 PM

This past Tuesday the transparency was forecasted to be 4/5 'above average' per Clear Sky Clock and it was probably even better than that. In fact, it was the most transparent that I have seen the sky since I started observing this year. Long story short, in my suburban 'white' zone backyard, I had previously seen stars down to mag 4.6-4.7 when the moon is not out (Zeta Delphini, Gamma Cancri) and even down to 4.95-5.0 (Epsilon Canis Minoris) with a lot of trying. Well, getting back to this night, I came outside and right away I could see the string of stars towards the middle of Auriga, close by M38. As I got dark adapted, the fainter ones started to show clearly including 14 & 19 Aurigae (mag 5.0 each) and Phi Aurigae (mag 5.1). I looked towards Triangulum and Delta Trianguli (mag 4.9) was easy and I was surprised to see a third star next Gamma and Delta Trianguli. I carefully noted its position and checked and saw that it was 7 Trianguli, a magnitude 5.2 star! All in my white zone backyard! :cool:

Have others had similar experiences of discovering that while your skies are light polluted that it could be much worse?

#2 David Knisely

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Posted 09 December 2012 - 01:02 AM

I find that the "color zones" in many light pollution maps are sometimes inaccurate, especially at the smaller scales where their resolution can be quite poor. I generally find that just making decent estimates from calibrated star charts and citing my naked-eye zenith limiting magnitude (with averted vision) from that in my observation log entries is more than enough. In the end, the magnitude limit you see is your own and is not subject to somebody else's light pollution map. Clear skies to you.

#3 Tony Flanders

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Posted 09 December 2012 - 10:15 AM

Magnitude 5.2 is my typical naked-eye limit on a clear night at the outer edge of the zone shown in white for the Boston area on the original Light Pollution Atlas.

Note that the white zone in the snow-corrected version is considerably smaller than the one in the original atlas.

#4 mark8888

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Posted 09 December 2012 - 11:06 AM

Have others had similar experiences of discovering that while your skies are light polluted that it could be much worse?


YES, absolutely. For more than a year of observing I concentrated almolst solely on the planets, moon, and sun, because where I live the light pollution is awful. You can look at half the sky sometimes on a clear night and see 5-10 stars, total. However, I happened to receive an ipad, so I got skysafari and linked it to encoders in my alt/az mount that I had never made use of before. Suddenly, I found that in entire regions of the sky where no naked eye stars were visible at all, I could see amazing open clusters everywhere, such as the Wild Duck Cluster, M23, NGC 6613... planetary nebula like M27 and NGC6572... double stars all over the place. I had really not been able to use star maps on paper very effectively at all for star hopping because of the lack of visible stars, but with a little electronic help, wow, what pleasant surprise!!

#5 blb

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Posted 09 December 2012 - 11:17 AM

By your own admission this was an exceptional night. I too have experanced one maybe two exceptional nights each year from my house in a white zone. It is just that sometimes the moon is shining brightly on some of those nights so there are only about one night every other year that I can observe on a great night from home in town (in my white zone) and see really faint objects. It is wonderful when they happen and I do not have to travel to observe. :bow:

#6 rdandrea

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Posted 09 December 2012 - 12:22 PM

Transparency has an effect on NELM in light-polluted areas (and on moonlit nights). On nights of good transparency, there are fewer moisture droplets and/or particulates to scatter light.

#7 Tony Flanders

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Posted 09 December 2012 - 01:43 PM

I too have experanced one maybe two exceptional nights each year from my house in a white zone.


It's intriguing; this is quite different from my experience. I wonder if it's a regional thing or a difference in perception.

I classify nights as having poor transparency (ranging down to total overcast), mediocre transparency, and good transparency. There are also, of course, many nights of variable transparency.

In New England, I would say that nights with good transparency are fairly rare -- averaging perhaps one or two a week over the year. But I find the transparency on those nights to be pretty much of a piece. Some nights are marginally better than average-good, and obviously there's a continuum between average-good and mediocre. But I have never had a night when the limiting magnitude was more than 0.1 or 0.2 better than on the kind of night I expect once a week.

Measurements with my Sky Quality Meter confirm my jubjective judgment; there don't seem to be any extraordinarily dark nights in my part of the world. The only exceptions are when fog is covering the nearby city.

This may be because I'm in New England, and when the wind is blowing right it's coming straight in from the Canadian wilderness, which is not very far away at all. In the Southeast, when the wind is blowing in that same direction, it will have picked up air pollution from all the coal-burning plants and automobiles in the U.S. Midwest.






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