Transparency versus Seeing

[rmcpb (Rob)]

Well after the storms of the past couple of days the wind died down and the sky was clear last night. You beaut, so out with the scope and have a go. BUT......

The transparency was beautiful ie. the sky looked so clear but try looking at Saturn with any power higher than 133x and it was hopeless, 96x gave the best views. Oh well, it started out so promising

If low power works how about deep space objects so using an eyepiece that gave me 49x I could easily view clusters and nebulae with perfect clarity. Hmmmm Tried to split some doubles and any that needed high power were hopeless.


This thread is to point out that just because the sky is clear (transparent) you may not be able to view just anything. The seeing has to be good to use high power and in this case it was ruined by upper level winds we were not aware of at ground level. So when you plan a viewing session don't get too hooked on a fixed plan but remain flexible and you can enjoy any session, even if you don't get to see what you would prefer . Just keep looking up

[gaa_ian (Ian)]

Good advice Rob ... would be nice to be able to get an upper atmospheric forcast.
Or even a good high level cloud forcast !

[Starkler (Geoff)]

Sometimes the reverse is true, the air is still, seeing is great but the transparancy is rotten.

[Dave47tuc (David)]

I have had only a couple of nights in the past year,
with the seeing and transparancy good to very good at the same time.

The last time was late August 2004, it was after a big cold front came in and it was a very steady night. But very cold.

Best.

[ving (David)]

Originally posted by Starkler
Sometimes the reverse is true, the air is still, seeing is great but the transparancy is rotten.

and sometimes the seeing and transparence are lousy but the clouds are great

think i need to work on that one some more

last night the transparency was great bu seeing was bad.... as in the original post.
Just couldnt zoom in on planets at all

[rmcpb (Rob)]

A continuation of the story

Last night, after a really hot day, the ground level wind was zero but the seeing was not good. Could barely make out the Cassini Division at 133x as the image went in and out of focus on a regular basis. Understandable after the day we just had. So what to do? Take my own advice and look at low power objects like star clusters and nebulae - great.

Looked up Jupiter in Aussie Sky and Telescope and found the GRS transition time was 0541 this morning and from Astronomy 2005 Mars would be up so an early morning was called for and surely the atmosphere would have settled own by then. Left the scope on the back deck so it would be at ambient temperature, all systems go!! Up and ready, stuck my head out and.... light cloud A weak southerly had moved in and dropped the temperature so it was more pleasant but cloudy!! Anyway there were enough holes to have a go, Mars was a write off as the cloud to the east was quite dense but, to the north Jupiter was up in all its glory. Very average seeing, could make out the cloud bands and GRS with a 80A filter but that was all.

Why?? The cold front puts a wedge of cool air under a layer of warmer air and increases turbulence reducing the seeing. Generally the seeing is better in the morning as I had hoped but weather changes consire against us.

Take a philisophical approach, if the seeing was perfect all the time what thrill would there be when you finally grabbed that window, it would be there all the time.

Oh well, will have to try again.

Cheers