Mostly cloudy = darker skies???

[Wurzil]

Hi all - ive noticed from time to time when the sky is mostly cloudy but has reasonable sized holes in, that the sky in those holes seems darker and the stars brighter and crisper.

Is this because the cloud is blocking most of the light pollution from lightening the sky (ie the only LP getting to the part of the sky seen through the hole is from one angle - not from all angles like on a clear night - hence giving a darker sky).

Am I right here? If so, I should be dragging the scope out even when its 80% cloud cover and battle to find the faint fuzzies.

PS - how weird is it not to see any planes and trails in the sky!!

Warren

[hunterknox]

I suspect it's because of the contrast between the bright clouds, which are reflecting light pollution back at you, and the relative darkness of the sky behing.

At a truly dark site it would be darker when the clouds roll over due to the absence of the light of the moon, stars, planets etc shining down.

I have heard it said that some cloud formations are associated with super good seeing conditions, but I would imagine these tend to be more stable formations than the shifting skies that I think you're talking about.

[Wurzil]

yeah its normally lowish cloud - last night for example and when we had snow a few months back.

maybe its is just the contrast playing tricks on me like you say - Ill check the magnitudes next time i see it just to make sure.

w

[brianb]

maybe its is just the contrast playing tricks on me

I think so - if your cloud is bright (illuminated from below ) the sky in the holes will appear darker.

Naked eye work, the extra light will probably actually worsen the limiting magnitude. With a scope / binoculars where the lit cloud is not in the field of view, no difference.