Equipment or conditions??

[vaztr (Andrew)]

Hi All,

I've been out most nights this week taking in many of the easier objects while I get used to my new 12" and 24-8 zoom EP.

Most nights have been great, Jupiter with cloud bands and the 4 moons, M42 and 43 with their huge 'wings' spread across the FOV and even the Sculptor galaxy (a first for me) tho I couldn't get NGC 247

Last night looked as clear as the other nights but the visual limiting magnitude look less (I could see less stars visually than previous nights), regardless I pointed my scope to the sky and noticed that it was V hard to get focus on anything at high power. 12mm seemed to be the limit after that stars in the trapezium were blurry. Jupiter became an 'animated' blob seeming to go in and out of 'egg' shape with only moments of clarity where any banding could be seen and again it's four moons were blurs at anything stronger than a 12mm EP.

I figured it was all due to bush fire haze and atmospheric turbulence, so didn't worry too much about it, but then I saw Baz's post!!!

I know Baz thought the sky was going to be brilliant for his first photography session in a while (he's V close to where I am) and that got me thinking that maybe it wasn't the atmosphere that was causing my problems, but maybe bad collimation (or worse!!!)

Any thoughts from anyone who had similar issues last night around Canberra

I guess I'll post a modified copy of this in the thread Baz posted about his photography to see if he had similar issues

Thanx

VAZ

PS. Should have mentioned that this was the first night I had 'fanned' my main mirror to get it to 'cool' all previous obs had been without the fan being used prior to viewing.

[Rodstar (Rod)]

Hi Andrew, I'll jump in before someone else does.

Seeing conditions will vary greatly from session to session. When the seeing is poor, you may be limited to only using your low power eyepiece(s). In very steady conditions you may get to use high power eyepieces.

When there is a large diurnal temperature range (summer), seeing issues will be worse, especially in the early evening. It is exaggerated in the early evening when you look over surfaces such as roofs where a lot of heat has been absorbed during the day. You will find seeing is much steadier in the wee hours of the morning.

Winter is generally steadier than summer as far as seeing is concerned.

Another issue is the thermal currents created in the tube of your scope when the mirror is more than about 2.5 degrees warmer than the ambient temperature. Generally in the early evening, the mirror will not keep up with the rapidly dropping external temperature, and so you will get poor seeing within your scope.

Sometimes the seeing is so crap, I give up. Other times I leave the scope set up, go inside for an hour, and come back to see if things have improved. You take the good with the bad.

Another trick is to get your scope outside as soon as the sun goes down, so that the mirror has the chance to start cooling as soon as possible.

Hope that helps!