Weird Conditions Last Night

[dazza1639]

If this is in the wrong place can the mods please move.

I went out last night expecting the seeing to be pants. There was a lot of sky glow, the visability to the hills yesterday was poor both these are usually very good indicators of bad seeing & transparancy, But last night was amazing! There was very little turbulence the stars appeared tightly focused and didn't shimmer as the have been for the last few nights even at high magnification.

SATURN wow, cassini poped into focus straight away I could make out 5 moons easily and possibly 7 but I might have been imagining this. I decided to try and push the limits, so I started out with a 6mm eyepiece giving 338x mag, everything was rock steady focus was tight 1 could see 2 bands & the cassini. Next 9mm eyepiece & 2x celestron Ultima barlow giving 450x mag again everything was rock steady focus was tight 1 could see 2 bands & the cassini the image brightness appeared to be the same. Finally I pushed it to the limit 6mm eyepiece & 2x celestron Ultima barlow giving 677x mag, this time the image was about 70% as bright with some noticable but not too bad boiling, I could resolve the cassini & one band but this took a lot of delicate focusing using the peg on the focus knob trick. Saturn still look good even at this extreme magnification.

All this makes me wonder why when the sky looks this bad the seeing can be this good, and when we have a really clear dark night the conditions can be terrible

Darren

[proflight2000]

I think the moon generally being lower on some horizons helped last night as its light tended to be spread to the sides and below rather than high in the sky, I had no scope out last night but i could see all the plough stars very easily which isnt the case when the moon is high. I used to like the moon a lot, now I want to see more I am having a real moon issue.

[dogfish]

Darren

I'm having a stab at the original question of why the visibility is clearly poor but the seeing is good. But, and this is a big but, I'm an ignorant noobie, so anyone and everyone can feel free to call me an idiot. I'm also answering this in order to check that my understanding of this is right, so please correct me if I'm wrong.

You mention transparency in your original post and I think that's the issue. The hot weather (hasn't it been nice) has sent a lot of water vapour up into the atmosphere and this has made visibility poor but this hasn't affected the "seeing" necessarily. I'm guessing that seeing and transparency are not related to each other in that one can be good at the same time as the other being bad. As far as I understand it, the seeing is atmospheric turbulence (currents of air at different temperatures?) and that causes unsteadiness in the image through the eyepiece. As Saturn is a really bright object, it makes sense to me that it will shine through the muck and mist and still be visible regardless. If, at the same time, the atmosphere is steady, then I'm presuming you could still get a nice view of it.

This is why this hobby is so frustrating interesting. If it isn't the cl**ds and the rain, it's the seeing or the mist, or the moon being full, or worse of all the beeping neighbours floodlights! I'm moving to Arizona!

Cheers and (properly) clear skies to us all, Martin

[lunator]

Martin is right with his explanation.

I have found that seeing and transparency conditions swap. If the seeing is good the transparency is poor and if the seeing is poor the transparency is good.

Generally if you have high pressure then the seeing is better as the atmosphere is less active but high mist can make the transparency poor.

Both seeing and transparency can be poor after a hot day as the heat from the ground, houses etc causes the air to 'boil' away. This does improve as the night progresses.

For the best conditions you need a good strong blast of Artic Air.

Cheers

Ian

[dazza1639]

Thanks Guys, that was my understanding of it as well, water vapour in the air refracts the light from streetlights giving the sky its orange glow which also reduces the transparency of the air, layers of air in the atmosphere moving at different rates and heat rising from the ground cause the wobble or boiling which is the seeing. I think thats right, still weird tough when most of the stars are blocked out by the sky glow but through the eyepiece the image can be perfect.

Darren

[Whippy]

I think most of us are just happy to get a cloud free night!