sky conditions help

[mik]

Hello

In a recent observing report i was asked if i keep a record of sky conditions.

Well i dont but i would like to but i am not sure how to evaluate this information

is there a look up chart to help with this ?

How do i work out seeing conditions and how do i report this within a observing report.

Many thanks Mick. :?

[beamish]

Okay Mik, I might be wrong but I think GazOc posted this D Peach link on the site not too long back-I hope this helps !

http://uk.geocities.com/dpeach_78/pickering.htm

Karlo

[mik]

Thanks for that Karlo but i am still confused

Mick.

[The Warthog]

Me too. I have seen an airy disk when I crank the scope out of focus, but is there supposed to be a disk when the scope is in focus? Usually, stars resolve to more or less points. I don't often see twinkling in the scope. Of course, now that I've said that, I porbably will.

Could someone elucidate the information in the chart, and how to utilize it, please?

[lunator]

Mik

As a rule the seeing in the UK is rarely excellent. This scale is always a bit subjective and the scale 1-10 is more than is necessary to cover most nights.

Experience will be the best guide of conditions.

I use double stars as a good guide. In my 8" scope if I can split a 5" double using my 25mm eyepeice the seeing is better than average from my site in London. Once the scope has cooled down you can put a high mag eyepiece in and look at a moderately bright star. In my newt you can see a few rings when the star is de-focussed if they are steady then the the seeing is good , if they are wibbley-wobbley then the seeing is not good.

I hope this helps a bit.

Cheers

Ian

[mik]

Thanks Ian

I now understand the pickering scale

Mick.

[themos]

Doesn't that scale assume you have perfect collimation already?

[lunator]

Themos

The scale assumes excellent collimation & a scope in full equilibrium with the surroundings.

The seeing effect due to a 'hot' scope is different to the effects of poor seeing. What you see are the warm thermals rising from the scope. Poor seeing is as a rule much more random

Cheers

Ian

[The Warthog]

So I need to defocus my scope a little to see the Airy rings? I never see more than one ring, although it is circular when I have just collimated.

How much do I have to defocus? Just a little?

[beamish]

Hi there WH, my understanding is you can de-focus completely one way or the other as the rings ought to become more pronounced as you do.

Karlo

[lunator]

WH just de-focus a little.

Pick a mag 2 star as a target.

Cheers

Ian

[Astroman]

The Airy disk is visible under excellent seeing conditions with the image in focus. An in-focus star will show the disk and one diffraction ring in good conditions with a large aperture scope and under excellent conditions with a smaller scope. Defocussing obscures the Airy disk. I doubt seeing in UK would allow the Airy disk to be seen, except under extraordinary conditions.

[beamish]

There you go ! Thanks AM for putting me right .Sorry Mik !!

Honestly what a newbe I am.

Karlo