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Saturns Moons....

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#1 azure1961p

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Posted 10 March 2013 - 05:30 PM

While Sky and Tels Jupiter app : Jupiters Moons, is very useful and particularly handy via phone app, the Saturns Moons app looks like it s a winner too. Haven't used the latter but on good nights especially it'd seem to be the handy app in ferreting out some of the more difficult moons.

Pete

#2 nirvanix

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Posted 11 March 2013 - 09:03 AM

Thanks Pete, I forgot about that app. I've been using calsky.org for moon hunting. About 10 days ago I got the 5 moons of Saturn - the dimmest one was just blinking in and out of view. I thought it was Iapetus, but perhaps it was Enceladus. For some reason it's reported that Enceladus is easier to spot although it's dimmer than Iapetus?

#3 azure1961p

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Posted 11 March 2013 - 10:16 AM

You know I don't know if I've ever seen Iapetus lol. It would seem odd that they say its more difficult than Enceladus (which i have seen) particularly when you consider its proximity to all that glare - especially now with the open rings. Congrats on that detection. The way I read it is that Iapetus with its varying magnitude due to surface reflectivity can actually be 2/10s of a magnitude fainter than Enceladus. Again though, that Enceladus is so very close to those glaring rings, ill day you made the more difficult catch. I need to finally look up Iapetus - I'm guessing I've seen it already figuring it was a field star.

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#4 nirvanix

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Posted 11 March 2013 - 01:01 PM

Thanks for the info - I didn't know Iapetus varied in brightness. Enjoy the hunt.

#5 azure1961p

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Posted 11 March 2013 - 03:27 PM

Yes apparently one hemisphere is akin to snow the other akin to coal. At least that's what I've read . Therefore as it moves in its orbit - and its now tidally locked - its dim at one end and brighter at another in revolutions around Saturn. Ganymede too for example is tidally locked presenting the same face to Jove. The serendipity of these matters then is that you can calculate which hemisphere you will see in regard to where it is in its orbit. Ganymede for example I know where it will show particular features when its just off jupiters limb.

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#6 azure1961p

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Posted 11 March 2013 - 03:28 PM

Yes apparently one hemisphere is akin to snow the other akin to coal regarding reflectivity. At least that's what I've read . Therefore as it moves in its orbit - and its now tidally locked - its dim at one end and brighter at another in revolutions around Saturn. Ganymede too for example is tidally locked presenting the same face to Jove. The serendipity of these matters then is that you can calculate which hemisphere you will see in regard to where it is in its orbit. Ganymede for example I know where it will show particular features when its just off jupiters limb.

Your big aperture could potentially get you Mimas - quite the difficult prize. But you have high res so....

Pete

#7 nirvanix

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Posted 11 March 2013 - 05:32 PM

Good for you if your looking for features on Ganymede - never tried that one! I remember that Iapetus has that 'seam' running around the middle, like it was two halves that someone smacked together - by the looks of that giant crater, maybe the seam was caused by a large asteroid strike.

#8 azure1961p

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Posted 11 March 2013 - 08:07 PM

I think Mimas is the one with the huge strike that inspired Lucas with the Death Star .

Pete

#9 james7ca

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Posted 12 March 2013 - 12:44 AM

As an aside, I was able to capture all eight of Saturn's brightest moons in a single photo using my 5" refractor. Hyperion was the most difficult, at a magnitude of only 15.1. The next most difficult was Mimas, because it appeared so close to the rings.

In fact, given the eight moons plus Saturn I wonder whether this is the maximum number of extraterrestrial, solar-system objects that can be recorded by an amateur astrophotographer in a single photo. Can anyone suggest a subject that would total more than these nine?

#10 azure1961p

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Posted 12 March 2013 - 06:27 AM

Jupiter has a slew and within CCD capability if only one suppresses or occults the amazing glare of Jove itself. Amalthea again is easy as far as magnitude but the sheer challenge of the glare off Jupiter would necessitate the need for the most transparent sky's and again an occulting mask. A timed exposure showing satellite movement would be invaluable . Many of the moons though are 20v or fainter. This IS an unrealized undertaking it would seem but a time lapse of these extremely faint objects spiriting around is extremely compelling.


Pete

#11 Achernar

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Posted 12 March 2013 - 10:16 AM

I have used Sky and Telescope's app for Saturn's moons, and I have located all of the larger moons except Mimas with my 10 and 15-inch Dobs.

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#12 james7ca

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Posted 12 March 2013 - 03:45 PM

Amalthea has a magnitude of around 14, so it seems to be a little brighter than Saturn's Hyperion. However, it's so close to Jupiter that it would be quite difficult to capture (as you've suggested, you'd probably need a mask to occult Jupiter).

Wikipedia says the following about Amalthea:

"Amalthea was discovered on September 9, 1892, by Edward Emerson Barnard using the 36 inch (91 cm) refractor telescope at Lick Observatory. It was the last planetary satellite to be discovered by direct visual observation (as opposed to photographically) and was the first new satellite of Jupiter since Galileo Galilei's discovery of the Galilean satellites in 1610."

So, it sounds like a pretty difficult target even visually.

As far as I can recall, I've never seen an amateur-made photo that has shown more than the four Galilean moons of Jupiter. The maximum I've seen on Saturn is eight moons in a single photo (which I was able to do once with some difficulty, and I've seen a few who have done the same).

One additional issue to consider is that it is also possible for a moon to be effectively too far away from Saturn/Jupiter to be photographed in the same field as the planet itself (since you'll need a fair amount of magnification to see the inner moons). For example, Saturn's moon Phoebe has a magnitude of 17 but it is currently almost one half degree from Saturn and its orbital period is about 1.5 earth years so you'll have to wait maybe another three or four months before it will be close enough to capture with the other moons.

I've attached my annotated copy of the eight moons around Saturn, this was done with a 5 inch refractor and a series of five second exposures at ISO 6400 (it's been reduced in size to meet the Cloudy Night guidelines)

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#13 buddyjesus

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Posted 20 March 2013 - 03:12 AM

Windy night but got my first peek. I have always had a soft spot for moons. 4/10 seeing interfered with seeing deeper, but got my best view of Titan, Rhea, Dione, and Tethys at 78x. I didn't sketch far enough out to record Iapetus, but given the distance from Saturn tonight, it would have been in the FOV of my 40x 25mm plossl.

Being able to see the moons can be done even in very unsteady seeing if one is patient. Part of the reason I like them.

#14 nirvanix

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Posted 20 March 2013 - 03:43 AM

Nice buddy. When seeing is poor the moons tend to dance around quite a bit. Have you seen iapetus in your 4" scope? It would be tough to spot because it's only about mag 11.5 -
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#15 buddyjesus

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Posted 20 March 2013 - 12:09 PM

Iapetus has variable brightness. It is dark on one side, bright on the other and tidally bound to Saturn resulting in a regular brightening when it has the bright side pointed at us. My notes say when at western elongation the magnitude can brighten to 8.6

Yeah the moons can dance, but since they are point sources, they can be seen steadier at low magnifications.

At its current magnitude of over 11, it would be questionable but I don't think impossible. I never did a test to see what my deepest magnitude is at this site.

#16 David Gray

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Posted 20 March 2013 - 12:12 PM

I believe that WinJupos now correctly shows which hemisphere of the various planetary satellites is on view. So I checked out Iapetus for the date of the attached drawing and inset. Two other BAA observers also caught this very rare event that night The details for this are in this BAA Saturn Section report pages 216-17 (bit of a scroll!): http://www.britastro...7/Saturn App...

From the looks of it we may well have had more difficulty if mostly the light side was facing us. Perhaps it then may have been more like similarly sized Rhea which I have several times caught as a light spot against the darker limb shading in very good conditions and, with more difficulty, Tethys & Dione but soon lost further into the disk.

Someone later sent me a link to an image by a French observer, Christophe Guillou, on this report page 15/16 (scroll!): http://www.astrosurf...ix-Oppositio...

Due to its orbital geometry these events for Iapetus occur some two years before the edge-on rings and are very hard to catch. Phoebe’s orbit is currently closing and will be edge-on in 2016 but being considerably smaller than any of the above-mentioned – forget it; even if we caught it in going front/behind Saturn at the right time! Going to the JPL Solar System Simulator site and experimenting with the various settings you can find that, for instance, it is behind Saturn 2016 May 22. As I say beyond us; but the site will prove useful for those with ambition to catch and image it amid the other satellites. http://space.jpl.nasa.gov/

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#17 nirvanix

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Posted 20 March 2013 - 02:12 PM

Nice report David, and great picture of the transit.

#18 Asbytec

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Posted 02 April 2013 - 01:29 AM

Great thread, guys. I found Iapetus to be much easier than Enceladus. The latter was the most difficult moon in my 6" MCT and never seen any of Saturn's moons more difficult that Enceladus. Catching Enceladus or Mimas in a 5" is an amazing feat, IME.






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