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How cloudy do you find to cloudy?


SionR25
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Hi everyone,

Just wondering at what stage of cloud cover do you guys think is too much to go out observing :p?

I would go out if its about 25-30% (maybe pushing 40-50% if I really want to see something). Anything more than that I find frustrating waiting for clouds to pass or clouds observing your view.

Sion

EDIT: sorry, meant to be 'too' in title (a year after I finish English and my grammar is gone :p)

Edited by SionR25
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Hi

As long as there are gaps in the cloud it's still worth risking an ad-hoc observing session with the grab and go setup. Also, cloud actually helps observing as it reflects light pollution back down to the ground so the visible patches of sky are really dark.

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. Also, cloud actually helps observing as it reflects light pollution back down to the ground so the visible patches of sky are really dark.

Didn't know that, may go out observing more :).

Sion

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It depends really, if we are going out then we wont go unless its pretty much completely clear. For setting up in the garden we have been out in 70% cover before and then left the telescope out to see if it clears or gone out and grabbed some bits in the gaps.

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Hi

Also, cloud actually helps observing as it reflects light pollution back down to the ground so the visible patches of sky are really dark.

??? That's not what I've heard. I heard that clouds make light pollution worse because the light gets reflected between them.

Any way, I'd say that 60% cloud cover or less is what I could bear before I decide that it's not worth observing. Despite this, I went out with 85% cloud cover to see the transit of Venus, and I wasn't disappointed!

Yesterday though, I went out for some solar viewing (hours after I had seen the transit) and I was trying to do some astrophotography. I'de set up the camera adaptor and the sun would become covered by clouds. I'de aim my scope at a chimney and re-align the adaptor for a better picture but whilst the adaptor was off, the sun would return. By the time I set everything back up for the sun... It would disappear again.

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Also, cloud actually helps observing as it reflects light pollution back down to the ground so the visible patches of sky are really dark.

Now that's what I call looking on the bright side! As far as deep-sky observing is concerned, cloud and light pollution are invariably bad things, and when you've got both together then it's even worse. The sky looks dark between bright orange clouds because of contrast, nothing more. It's not really dark and won't help you see things any better. You can get the same effect by sitting in a brightly lit room for an hour or two then going out into the garden, which will look very dark indeed.

For grab and go, if there's a hole in the sky then just give it a try. If it's a case of driving a long way to set up in hope of a long session (which is what I do) then it's a case of checking Sat24 etc and hoping for the best. The worst kind of sky is one that looks hazy and murky, with large patches of slow-moving cirrus, even though stars may be visible through the gaps. For deep-sky this is useless, though for planets etc it might prove productive. On nights like that I don't leave the house. Less useless, though hugely frustrating, is drifting cloud with small clear gaps between. You spend a few minutes hopping to a target in a clear gap, only to find cloud rolling over it once you get there. I may make the drive on a night like that, but if it goes on too long then I might not get much observing done. Chasing the gap works only for binos, small scope etc, in search of easy targets. There are, though, times when the cloud appears almost static, with large gaps. If the gaps are haze-free then this can provide good opportunities.

The best night is obviously one that starts clear and stays clear. Almost as good, though, is one that has clear periods between overcast stretches. If you're patient then you can find a total cloud-out turning into an hour or two of perfect conditions. Similarly, a downpour can be followed by a fine clear sky. On many occasions I've arrived at my site in overcast conditions and ended up observing for hours. Equally, I've often arrived under a clear sky, only for it to cloud over.

On one occasion I had an observing session of a couple of hours under a completely overcast sky. This was during the Leonids of 1999, when I could see the flashes of the brightest meteors through the intervening cloud. If only it had been clear!

Some you win, some you lose. It's all just a case of how patient and determined you are.

Edited by acey
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One of the advantages of goto if there is sufficient gaps to align it. Just dial in what you want, object located and you just wait for the right gap and off you go observing. Given the amount of cloud we have been experiencing, I would rather go out in 30-40% cloud than do no observing at all, although I wouldn't bother if the cloud is accompanied by a lot of wind as it would make the whole thing very frustrating.

James

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