Peculiar seeing conditions

[MartinB]

On Tuesday night I had a couple of visitors who had successfully bid for a stargazing evening at a charity auction. I set up an ED120 refractor, a 190mm Mak Newt and a 12" Dob. The transparency was poor with hazy conditions but I thought this could be ideal for looking at Saturn. The stars were steady, with very little twinklying. The view through the ED120 was excellent using a 5mm orthoscopic giving x180. Views through the other 2 scopes appeared steady but I couldn't get any more resolution than with the ED120, in fact the views were very disappointing. Cassini was seen more with the eye of faith than anything. The ED120 gave the best views and my visitors agreed.

I tried some imaging through a 10" SCT with disappointing results.

I'm used to poor seeing but haven't come across this type of seeing problem before, everything seemed steady but obviously wasn't.

Last night the transparency was worse still but the observing results were dramatically different. I had the most pristine views of Saturn I have had for several years. I could take the 12" dob up to x300 (didn't try beyond this) and the view was exquisite - detail in the bands and a clear, black Cassini, no hint of any focus variation or shimmer. The ED120 still put in a good performance but nothing close to the 12" reflector.

Have others come across these poor seeing conditions?

[cathalferris]

I've seen this when the seeing is so spectacularly bad that the seeing disk may be ~4-6 arcseconds in size, so large that the naked eye sees no difference moment to moment, but scopes are nothing more than blurs.

Sometimes I can focus on a planet or a star then I can pull focus a little closer (away from the tube) and I can momentarily see the actual boundaries of the seeing cells moving at huge speeds across the slightly defocused star or planet.

Nights like this make be cry sometimes! Not clear enough for deep sky, and nowhere near steady enough for any detailed work. Long exposures with camera lenses make for pretty pictures under these conditions sometimes though.

[John]

Yes the conditions are very odd at the moment. I had a really good night with Saturn 2 nights ago but tonight it's very hit and miss, mostly miss to be honest.

As I watch Saturn moving across my eyepiece field of view I can see it jump forward or appear to hesitate slightly. If I used a driven mount I'd suspect my drive was playing up but my alt-azimuth mounts are undriven so I reckon that this is the effect caused as Saturn passes through atmospheric cells.

I'm getting nice detail momentarily then it's gone, as if a veil has been drawn over the planet.

Still it's nice to be out under the stars

[George]

Our resident weather guru will probably explain the conditions but its something todo with the time of year and moisture at higher altitudes. Spring 2008/2009 was very similar, clear skys but very poor transparency and I believe there's lots of airborn sand from North Africa around at the moment.......we just carnt win in the UK

[Jon65]

After setting up at dusk last night I was hoping conditions would improve as the hours ticked by,usually by midnight the skies have improved greatly but by 1am no change,as you say, very strange seeing conditions. For the past three to four nights of clear skies when I've had an opportunity for some deep sky object viewing the hazy conditions have blown it.Objects can be seen but little or no detail can be made out.

Last night Saturn was good when there was momentary lapses in the stillness of the air so all was not lost.

I think we need a daytime downpour :eek:and a blast of wind to improve seeing conditions.

Jon