Volcanic ash and astronomical seeing conditions

[Gem (Grant)]

Hi all

Lots of cloud lately, but in the few minutes here and there between clouds the viewing seems terrible. Is it the ash? Is it just bad seeing? Is it the collimation on my scope (which needs doing)?

I haven't seen clearly in over a week (ever since the new scope was set up...). Will these conditions continue for weeks??

[renormalised (Carl)]

If it's the ash, and it's a fine ash, it could stay in the air for weeks but it will progressively thin out as it spreads and also falls to the ground.

[asimov (John)]

The ash won't effect the seeing as such, but it will effect the transparency to a point. So I'd say it's just bad seeing.

[pgc hunter]

Seeing has been absolute garbage here everytime I've been out this year, I'm not sure how or if ash affects seeing but what it will do is impair transparency much like thin cirrus cloud.

[Gem (Grant)]

Ok, maybe I need to be more precise between "seeing" and "transparency" but what I mean is there hasn't been a really blue sky (during the day) or a really black sky at night (even allowing for the moon).

[pgc hunter]

Originally Posted by Gem

Ok, maybe I need to be more precise between "seeing" and "transparency" but what I mean is there hasn't been a really blue sky (during the day) or a really black sky at night (even allowing for the moon).

Sounds like you are seeing the effects of the ash. Yesterday morning I think it was, the sky here was quite milky. The stars last night appeared more subdued than usual, even accounting for the moon.

[Paul Haese]

You gave a small clue as to what is really going on there. You said,"Lots of cloud lately, but in the few minutes here and there between clouds the viewing seems terrible".

Typically cloud creates lots of wakes and eddies as it moves through the atmosphere. Whenever you have lots of cloud around the seeing will be much more disturbed. Sometimes when I am out and the seeing is very good and cloud starts to come in I can see the seeing deteriorate rapidly. So my recommendation is wait for nights where fogs are predicted in your area. Also just keep an eye out for high pressure systems. Canberra can produce startling seeing, so just keep at it for now. Those conditions listed above often produce good seeing.