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Observing The Cassini Division of Saturn.


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Overt the years I have seen The Cassini Division of Saturn on several occasions. With an 80 mm f15 achromat refractor and and American made Meade LX 90 eight inch.

Over the last fifteen years I have found it really differcult to see. In fact I can't remember when I last observed it. This through a host of telescopes; an 80 mm Equinox ED refractor, a 120 mm ED refractor , a Celestron C8.

I now have a Celestron C6 and my 80 mm Equinox and I am taking every opportunity to observe Saturn at this opposition.

Is it a combination of poor seeing along with a telescope that is not capable of resolving The Cassini Division?

Possibly my aging eyesight!

Do you need a large apature and long focal length telescope?

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I have seen it in my Tal 100RS, fleetingly in good seeing. Not easy but definitely there. I saw it in my Tal 1 the other night and was surprised by how easy it was. Only 10mm more aperture made quite a bit of difference. Didn't get to compare them at the same time as Saturn disappeared below the neighbour's roof.

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In good seeing conditions  it is easy in my ED80 at x190.. With my 180 Mak, it needs good seeing and high mag - I assume that this is because with more aperture, the apparent width of the rings is much less ( we observe a convolution of the true width of the rings modified by the instrument function -  resolution in effect). I normally use x250 to x350 for the Mak.

Chris

 

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I've sometimes had to work quite hard to see the Cassini Division clearly with scopes smaller than 100mm. I've never seen it with my (very old) 60mm refractor. At 100mm and above I've found it's a regularly observable feature, often strongly defined when the seeing is decent and the eye adjusted.

If I can't see the division reasonably well I usually knock planetary observing on the head for that session !

Of course it was much harder when the rings were edge on to us around the mid 1990's !

 

 

Edited by John
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And the altitude, the gas giants aren't favourably placed at the moment. Tried last night and it was just mush from bortle 6 skies. May be better in a month or so when they are on the meridian at an earlier hour. Seen Cassini Division many times with 4" refractor but only in good seeing and at more favourable apparitions. Saturn seems to take magnification better than Jupiter, upto 200x when seeing allows. I also have found that a yellow filter such as the wratten #15 helps bring out the Cassini Division as well. Never seen banding on Saturn like I do on Jupiter in the 4".🙁

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I should have added that seeing the division at the ring ansae is one thing but seeing it clearly defined all the way around the ring system can be a greater challenge / test.

Edited by John
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I've managed the Cassini Division in all my scopes, from the first 130p newtonian to the current Skymax 102 and 102mm ED refractor. Although 102mm is the lowest aperture I've owned. I'd guess in your case it's a combination of poor seeing, just barely enough aperture and old eyes! 😉

I imagine local light pollution would also be a factor. If a street lamp is in the direction you're looking through the scopes that won't help. Likewise viewing over buildings. However I'm sure you already know that.

Also remember since 2017 Saturn's full tilt of 27° seen from Earth is decreasing until 2025 when they gradually return to full tilt in 2032. We all just need to stay alive until then!

 

 

Edited by ScouseSpaceCadet
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1 hour ago, ScouseSpaceCadet said:

I've managed the Cassini Division in all my scopes, from the first 130p newtonian to the current Skymax 102 and 102mm ED refractor. Although 102mm is the lowest aperture I've owned. I'd guess in your case it's a combination of poor seeing, just barely enough aperture and old eyes! 😉

I imagine local light pollution would also be a factor. If a street lamp is in the direction you're looking through the scopes that won't help. Likewise viewing over buildings. However I'm sure you already know that.

Also remember since 2017 Saturn's full tilt of 27° seen from Earth is decreasing until 2025 when they gradually return to full tilt in 2032. We all just need to stay alive until then!

 

 

From what I've read, light pollution is relatively unimportant for planetary viewing provided a nearby lamp isn't close enough to your FoV to cause glare.

Viewing over buildings or things like dark asphalt surfaces can mean looking through very turbulent heat plumes that can severely degrade local seeing even if the sky itself is relatively steady and transparent.

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1 hour ago, MarsG76 said:

Seeing is a big factor, but did you check collimation of your C6? The C6 should show the CD quite easily.

I've only had it a fortnight. It is collimated. So waiting for a long period of good seeing. I am hopeful though. Thanks.

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Saturn is low even from Texas.  I was able to easily make out the Cassini division and a band on the night of July 30th when it was crossing the meridian in the middle of the night.  This was with an 8" Dob with an Arcturus binoviewer and 3x Barlow to reach focus with 15x microscope eyepieces.  Using two eyes helped immensely to pick out fine details.  I used the same setup at the Mars opposition to pick out fine details on it as well.  It wasn't as effective on Jupiter, though.  I was only able to pick out bands and a few dark barges on it.  The contrast was just too low for festoons or white ovals.  I tried some filters, but nothing helped much.

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14 hours ago, Grumpy Martian said:

I've only had it a fortnight. It is collimated. So waiting for a long period of good seeing. I am hopeful though. Thanks.

It still might need a little tweak... I was trying to observe Saturn and Jupiter the other night, it wasn't the best seeing, and I didn't see any details on either planets.. just a soft yellowish fuzzy shape...

I decided to check collimation before giving up due to poor seeing, and collimation was only slightly out.... I centered the concentric circle with only the slightest turns of the bobs knobs and the view was night and day.... suddenly I saw cloud bands on Jupiter, moon shadows on the globe, shadowing on the rings behind Saturn, the shadow of the rings along the equator and the Cassini division on the rings edges.... It still wasn't the sharpest view I ever seen due to seeing conditions but the difference a small secondary mirror adjustment made was amazing... definitely worth a try.

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I find that because its been stuck low down in the southern constellations for what seems like 10+ years,

that makes it all the more difficult to see it, and to manage it you need better than average seeing.

Derby city centre is only about a mile to the south of me and directly below Saturn as it reaches it highest point,

and i have not only all that atmosphere to look through, but the heat plumes and city pollution mixed in as well.

Not a good situation. i'm geographically challenged !!

All about getting good seeing, or should i acceptable seeing. I don't think we hardly ever get very good seeing in the UK. Maybe once or twice a year if we're lucky ?

Thats my experience anyway.

I would say i've only had one really good Saturn session with my 140 refractor in the 2 years i've had it.

That night Cassini was easy, and almost visible all the way around the rings, with the shadow of the rings on the planet easily visible as well.

We need more nights like that !!

Jupiter is now starting to climb a bit higher for us now, and thats making a difference. 

Saturn seems to move so slowly but i reckon in another 3 years it will be much better for observation and will then keep getting better and better.

 

Edited by Space Hopper
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One feature of Saturn that I'm finding tougher to spot with the planet lying low in the sky is the "C" or Crepe Ring. When the planet has been higher in the sky I've been able spot it regularly with my scopes from 100mm to 300mm in aperture when the seeing is decent but it seems much more elusive over the past couple of years. I've seen glimpses and hints of it, usually where it crosses the planetary disk and shows against the disk, but not those lovely clear and contrasty Crepe views in the gap between the ansae of the rings and the planetary limb that I've had in the past.

Enke minima? - Observing - Planetary - Stargazers Lounge

 

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58 minutes ago, John said:

One feature of Saturn that I'm finding tougher to spot with the planet lying low in the sky is the "C" or Crepe Ring. When the planet has been higher in the sky I've been able spot it regularly with my scopes from 100mm to 300mm in aperture when the seeing is decent but it seems much more elusive over the past couple of years. I've seen glimpses and hints of it, usually where it crosses the planetary disk and shows against the disk, but not those lovely clear and contrasty Crepe views in the gap between the ansae of the rings and the planetary limb that I've had in the past.

 

 

I've spotted the Crepe Ring when Saturn has been high in the sky, but I've never spotted the Encke Division.

John 

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Even down here in Oz with Saturn almost overhead it takes really good seeing to be able to see the C Ring,  which I have managed a few times with my 12 Inch Dobsonian.

I am sure I have seen glimpses of the Encke Division at very high power, like 375x with a 4mm eyepiece, but as can be seen from @John image above it is like the very finest of gossamer threads and takes the very best of seeing that only occur maybe once a year, and even then it is fleeting and not possible most of the time. 

I am lucky that the Cassini Division is not even a challenge here even with poor seeing. 

Saturn will be rising above the tree tops in the evenings in the next month here and I can't wait, Jupiter too which is my favourite.  😀

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1 hour ago, Geoff Barnes said:

Even down here in Oz with Saturn almost overhead it takes really good seeing to be able to see the C Ring,  which I have managed a few times with my 12 Inch Dobsonian.

I am sure I have seen glimpses of the Encke Division at very high power, like 375x with a 4mm eyepiece, but as can be seen from @John image above it is like the very finest of gossamer threads and takes the very best of seeing that only occur maybe once a year, and even then it is fleeting and not possible most of the time. 

I am lucky that the Cassini Division is not even a challenge here even with poor seeing. 

Saturn will be rising above the tree tops in the evenings in the next month here and I can't wait, Jupiter too which is my favourite.  😀

I second that... all but the Encke divisiion, I easily saw heaps of fine details.... and this is in a 8" SCT... Seeing stability and beind almost overhead definitely make the difference in seeing the finer features.

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I've only ever seen the C ring twice with a large observatory cassegrain, but not with amateur scopes in recent years. Enke seems very difficult with my 180 Mak - I've had hints once or twice, when Saturn has been higher in the sky. It does show up in a stacked image though.

Chris

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Well I setup the C6. Could do more work on collimation. I may well buy an artificial star for that. But there were moments when I did see the Cassini Division ( Monday evening ). I am very happy with the C6 for planetary and Luna observing. It has a very manageable weight.while the C6 does not have the light gathering power of the C8. It does have a very noticeable increase in brightness compared to my previously owned C5.

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