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Anyone else notice this? Early after it gets dark I see lots of naked eye stars but after a couple hours there seems to be less. I am guessing that the summer humidity around here is the culprit. OTOH my scope isn't covered with moisture so I don't know.

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humidity? no man....its all about the moon and dark adaptation...nothing else. Humidity or transparency doesn't have much to do with how bright the sky is.

For the past 3-7 nights from 9pm-11pm it has been 5/5 Darkness. When 11pm comes, the moon is like 1/2 way risen in the sky but still getting blocked by trees.

Your dark eye adaptation at this point is completely adapted unless you have annoying lights in your back yard or observing site.

Since at 11pm your dark adaptation is so high....the light from the moon appears much brighter when it hits the air and causes "sky glow". This is just a natural form of light pollution.

The moon always washes out details in the sky, its better when its not there.

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Meade 8.25"(209.55mm) LX-90 EMC (SCT)

Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”

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Anyone else notice this? Early after it gets dark I see lots of naked eye stars but after a couple hours there seems to be less.

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I was reading through Stephen Saber's astronomy blog and he mentions a similar observation.

Quoting him " After being under beautiful dark skies for 4 or 5 hours, one might take a break from the eyepiece and notice that the sky and especially the surroundings look brighter. The black just isn't so black anymore Even those 7+ mag skies that begin as *pitch-black* lose their aesthetic contrast after hours of dark adaptation. But our eyes are only doing what they're supposed to. The rods are in overdrive and the cones are doing their best to catch up.
The ability to read and walk safely by the Milky Way's skyglow alone is a common sign of hyper-adaptation."

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Hyper-adaptation is a common occurence at the Nebraska Star Party with ZVLM 7.54 skies a common occurrence as verified by David Knisely and myself - not bad for a couple of 50-somethings! It almost seems like a let-down sometimes when you lose dark adaptation due to Jupiter. Our Prairie Astronomy Club President rides his bicycle between his camp site and the observing site using NO lights without a problem. The sky's so bright ya gotta wear (Red) shades!

John

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John "Have eyepiece - will travel!"

8" f/5 Dob w/2.14" sec in a 12" alum tube 'The Mortar' - w/PCorr 2° TFoV @ 36.5X ~70% illum *NICE*
Typical eyepieces: 32 Burg, 24 Pan, 20T5, 5-8 SW, Others ALL 2": Pcorr, 2X PwrMt, Ast H-b, Lum UHC + OIII
60mm $50 Walmart Special in training - aka "Backpack Observatory"
Minolta Activa 12x50 , Steiner 15X80

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Hyper-adaptation is a common occurence at the Nebraska Star Party with ZVLM 7.54 skies a common occurrence as verified by David Knisely and myself - not bad for a couple of 50-somethings! It almost seems like a let-down sometimes when you lose dark adaptation due to Jupiter. Our Prairie Astronomy Club President rides his bicycle between his camp site and the observing site using NO lights without a problem. The sky's so bright ya gotta wear (Red) shades!

John

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"In the cold air (like after the sun goes down)water vapor quickly condenses, thus showing up as a fog or mist of water droplets blocking seeing..."

and

"I live in a fairly dark town and wondered if the ballfields were lit up, even though the season was over at that point."

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Unfortunately, that happens far more often where I live!

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