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Old 08-04-2008, 08:48 AM
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Good conditions in Melbourne?

I never thought I'd say this, but weren't the conditions in Melbourne quite good last night? In my admittedly minimal experience, the transparency was good and the seeing seemed to be excellent. I had the best views of Saturn that I've seen, with the Cassini division easily visible (first time for me!) with solid, clear views at over 300x (not sure if it was 4mm native or 9mm Barlowed.. really have to get my recording act together). There were not the dreadful wobbles of a few weeks ago. I even thought I had a glimpse of an inner ring (edit: division), or was I dreaming? And that's with my generic GSO Plossls! (The view with my Orion/Vixen Lanthanum Barlowed for 200x was also excellent, very bright and sharp.

I guess this means I might even have my collimation done pretty well? I did a star collimation test (as described in Astronomy Hacks) and it seemed to even pass that. I say 'seemed', as it was bloody hard to keep the star in the EP at the high powers required (up to 625x for me) and the optical quality of my 4mm, barlowed at that, is questionable.

I still don't have my planning act together, so wasted a lot of time seeing not much, but with the help of Carte du Ciel I'm hoping to get that together.

Last edited by programmer; 08-04-2008 at 09:17 AM. Reason: dumb error
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Old 08-04-2008, 08:55 AM
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I would say we have had some decent nights (especially the one when the power was off... much less light pollution ) However I am very new (or at least re-enthused) about star gazing so I'm by no means an expert on what makes great skies.

I do know that I'm fairly sure I have been able to spy Saturn out of my binoculars (I still need to get a telescope)... these are fairly basic binoculars but I was sure I could make out just a slight bulge on the edge (what I presume were the rings). So I would say that indicates it was reasonable viewing.
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Old 08-04-2008, 08:57 AM
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I thought it was stable albeit not transparent last night. There was a lot of haze, but the views of Saturn were great. Not a good night for looking at DSOs though.

I suspect at 625x you are using 'empty magnification', ie you won't see any more detail than at 300x or so. And as you say, it's hard to track manually at that mag too.
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Old 08-04-2008, 09:22 AM
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Quote:
Originally Posted by PhilW View Post
I thought it was stable albeit not transparent last night. There was a lot of haze, but the views of Saturn were great. Not a good night for looking at DSOs though.

I suspect at 625x you are using 'empty magnification', ie you won't see any more detail than at 300x or so. And as you say, it's hard to track manually at that mag too.
Interesting.. not sure if it was so hazy near me, but the sky was fairly bright to the north, perhaps scattered light from haze. hmm we're only 20km apart.

The 625x was purely for the star collimation. The limit for my scope is about 500x in perfect seeing anyway, so I wouldn't push that far normally.
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Old 08-04-2008, 09:23 AM
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A good rule of thumb for maximum useful magnification is to use an eyepiece with a FL in mm equal to your focal ratio. I've determined empirically , for my eyes at least, that in the fine seeing the first diffraction ring becomes detectable at this magnification and any more is essentially `empty' in that you are losing image brightness for no gain in resolution , and floaters in your eyes become much more problematic. A scope without tracking may need to use a little higher to exploit the seeing as the eye cannot grasp and mentally co-add image detail as well.

It happens that this rule also equates to a magnification equal to your aperture in mm or a 1mm exit pupil. If you are not seeing a clearly defined and occassionally recognisable airy pattern then you are allready in the realm of empty magnification.

Bright objects like the Moon, and Saturn with its sharp edges and little in surface detail seem to flout this rule at least on an aesthetic level, as there is so much light to play with.
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Old 08-04-2008, 09:25 AM
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Quote:
Originally Posted by cpoc View Post
I would say we have had some decent nights (especially the one when the power was off... much less light pollution ) However I am very new (or at least re-enthused) about star gazing so I'm by no means an expert on what makes great skies.

I do know that I'm fairly sure I have been able to spy Saturn out of my binoculars (I still need to get a telescope)... these are fairly basic binoculars but I was sure I could make out just a slight bulge on the edge (what I presume were the rings). So I would say that indicates it was reasonable viewing.
Hey Phil. I think it was overcast here for Earth Hour so I didn't get to try.

Yes I put the binos (10x) on the tripod for the first time and could see the slightly distended orb. Bloody hard using binos on a tripod! Nearly gave myself 2 black eyes at one point.
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Old 08-04-2008, 10:22 AM
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Quote:
Originally Posted by programmer View Post
I never thought I'd say this, but weren't the conditions in Melbourne quite good last night? In my admittedly minimal experience, the transparency was good and the seeing seemed to be excellent.
The seeing may have been okay, but in the south east, the transparency looked ordinary. There seemed to be a lot of brown muck in the sky as I was walking home around sunset. I had to go out at 7:30pm and had a glance up - barely make out Eta Crucis.

I've messed up this new moon period - been out every night since Friday. Hopefully that will change tonight!
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Old 08-04-2008, 12:49 PM
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Transparency was trashed in Melbourne for the last few nights, as a matter of fact yesterday I could smell smoke when I walked the dog at sunset. Days are also very hazy, looks like Bangkok or something. Woke up at 2:30am this morning and there was very little twinkle in Arcturus and stars overhead were rock steady. Seeing must've been great but was so tired and felt sick from unsettled sleeping plus I have uni today so I potentially missed out on some corker views of Jupiter I just couldn't be stuffed dragging the 10" outside. In the state I was in I probably would've tripped down the stairs and killed myself, or worse yet killed the scope.

Last edited by 你B; 08-04-2008 at 01:00 PM.
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Old 08-04-2008, 12:55 PM
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Well I'm glad I said transparency was only 'good' and not great or excellent Sounds like it was actually average or poor. And you know what I do remember smelling smoke after work yesterday! Think it will be as bad tonight? Good time to check out the planets I guess. Might have to wait up for Jupiter.
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Old 08-04-2008, 02:23 PM
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Dunno, transparency doesn't look great at the moment - bit of cloud and the sky isn't that crisp blue colour it usually is. As you say, that's usually the time to go after planets (and double stars!). Leave the fuzzies for a clear night!
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