Jupiter and its moons

[Piero]

After many nights of clouds and dense fog, last night the sky was visible despite the bright moon and a fair amount of humidity. Jupiter was in a good position and I focused on this target.

Overall, it was a nice and interesting session.

I wonder whether viewing a tiny disc for Ganymede is really possible at 343x and not a simple artifact due to the Airy disc. What is your experience about this?

Best wishes and Merry Christmas

Piero

Date 24/12/2015
Time 02:00-02:50
Location Venice Area, Italy
Altitude 8m
Temperature 3C ( 4 km/h)
Seeing 2 - Slight undulations
Transparency 3 - Somewhat clear
Telescopes Sky-Watcher Skyliner 200 F6
Eyepieces Panoptic 24, Nagler 13, Nagler 7, Nagler 3.5, PM2.5x
Filters

Jupiter - Planet 92x, 125x, 171x, 231x, 343x
The sky was not transparent enough for seeing subtle details on Jupiter's clouds. At all magnifications, the two equatorial belts were visible, but did not show inner details most of the time. After the eye became adapted to the view, I was able to perceive some shade on the central part of the belts, but nothing more. These shades appeared as small irregularities of tones which were inclined with respect to the belt direction. At 343x, Ganymede seemed to show a tiny disc. The other 3 main moons also appeared more rounded but still smaller than Ganymede. Although details were not visible for this target, it was amazing to be able to see a tiny increase in size for a moon orbiting on another planet. On Jupiter, the amount of detail was similar to the amount visible at lower magnifications, but the features were much softer.
 

[laudropb]

Don't think my skies are ever good enough to get up to 343x Piero.

[John]

I think it's quite possible to discern the "big 4" Jovian moons as disks, albeit very small ones. Occasionally I've tried a little game of putting the 4 moons in order of apparent size then checking to see if my order matches the positions of the appropriate moons. More often than not, I've got the match correct.

Now whether we are seeing an actual disk or a type of airey disk which varies in size I'm not 100% sure but I have seen the effect both with my 120mm refractor and my 12" dob.

I believe some very acute observers have recorded vague surface features on Ganymede ?

[faulksy]

i love the planets and jupiter in particular seeing the features and the red spot (usually pink or orange), i have viewed this planet at over 350x but never looked for features in its moons doubt i will see any. there was a lovely pic the other day with a gent who took a pic with his sky and vision dob, what lovely detail he captured

[jetstream]

Great report Piero!

I find that when observing planets it takes a few times at the scope to tune the eye into the detail available and I like certain EP for their presentation of Jupiter such as the 10mm BCO/barlow, very rich colors from this set up. The views here supports 250x-300x quite a bit which is nice.

Do you find yourself certain EP's are tailored for Jupiter?

[Piero]

Great report Piero!

I find that when observing planets it takes a few times at the scope to tune the eye into the detail available and I like certain EP for their presentation of Jupiter such as the 10mm BCO/barlow, very rich colors from this set up. The views here supports 250x-300x quite a bit which is nice.

Do you find yourself certain EP's are tailored for Jupiter?

Thanks Gerry!

I agree with you. It is here on SGL where I read from members how to observe planets and how much dedication this task requires. It is very interesting and a good way to learn how to discern out details.

In this region in Italy, I believe one can push to 250x quite often because air turbulences are quite rare. I tried 343x because I have a 3.5mm with me. I did not expect to get better views of Jupiter, but was curious to see whether its moon changed in size. The fact that the moon looking 'bigger' was Ganymede was checked later using an online application. There was no detail on the surface and the target was not crisp, but very soft. That is the reason why I wonder whether this was due to the increase in Airy disc size due to high magnification. On the other hand, its size was larger than the other 3 visible moons, and this was noticeable. Possibly, measuring the diameter of the visible disc and comparing this with the airy disc size of a star at that magnification would give an answer.

I only have little experience with eyepieces and never seen through a BCO. After comparing my Naglers with Vixen SLV 5mm on planets+moon+sun, apart from the different magnifications, I always appreciated the views of the Vixen SLV better. To my eye, the parameter showing more difference was the light scatter control. Possibly scientifically unsound, but I believe that the higher contrast I perceive with the Vixen is due to a better control of light scatter. A few times I saw features on planetary targets that I was never been able, or I struggle, to see using a Nagler 13+PM2.5x (=>5.2mm). With my TV60, examples are the Cassini division at the rings sides, more obvious solar granulation, more obvious north and south polar belts on Jupiter.

This is a very picky comparison. I consider Naglers excellent DSO eyepieces which are very good on solar system targets.

Sometimes, I feel tempted to get BCO 10mm and 6mm for planetary observation though..

Do you see any difference at 250x-300x in any Jovian moon's size?

[jetstream]

When I'm at that mag level, I just concentrate on the planet features, I don't recall seeing them as disks at this mag. I do see them as disks when I crank up the mag with my zooms/barlow or use the 3-6 Nagler zoom. The problem with zooms is that I never really know the mag...and don't care lol! I know roughly of course, within 10x or so, but it doesn't matter.

I did calc all the mags for the zooms/VIP, but never bother to use it. Seeing the moons as disks for sure is over 300x by quite a bit, closer to 400x if I remember.

Now I have to check!

Jupiter and Saturn like different tone EP's IMHO..... the unique thing about the BCO is that they do well on both.....very well IMHO. I love these eyepieces Piero, better than the excellent KK ortho's I have. They also have a time and place though.....

It would be great if you could try a few select orthos first to see what you like!

[John]

The Vixen SLV is a superb planetary eyepiece. I compared it at some length with the Baader Genuine Ortho of the same focal length and found the SLV matched the Baader GO all the way. The comfortable eye relief and large eye lens makes the Vixen a more comfortable eyepiece to use than an ortho and I feel that helps concentrate on the object being viewed.

Jupiter rarely seems to respond to really high magnification as well as, say, Saturn or Mars do. I guess it's something about the nature of the surface features, which are basically contrast variations, that makes them stand out better with slightly lower magnifications ?

[Piero]

It seems it's going to be clear over here and again no wind at all. I guess I am the only person happy about the weather as everyone else would like rain in the cities and snow on the mountains. Apparently, it hasn't rained for the last two months..

Anyway, if clear, I will observe the Moon and Jupiter again.

@Gerry: I look forward to reading your future test on Jovian moons then!

[Stub Mandrel]

Ganymede is 5,200 km across, while the Red spot is 12,000 km top to bottom. As the spot is visible as a significant area, it should be easily possible to see it as a disk. I think that their shadows are more obviously disks.

They can come out as disks in photos, but I am always a bit suspicious of the accuracy of the size of small bright objects in my images. This is Jupiter with Io (2,600km) and Ganymede.

[John]

I believe Ganymede has an apparent diameter of around 1.5 arc seconds. Neptune is currently around 2.1 arc seconds, for comparison.

[Piero]

Thanks Neil and John for the information 

I only found this thread on CN about Ganymede and Io: http://www.cloudynights.com/topic/447820-ganymede-and-io/. They even discuss about features on these moons

Anyway, I will observe this again, but unless somebody else manages to see tiny discs at similar magnifications, I consider these as Airy discs.

Managed to see the Moon an hour ago, but now the sky is cloudy. Will check later tonight hopefully.

[Dave In Vermont]

If anyone out there would like to try imaging the moons of Jupiter, it helps to know which moon is which. So here's a cool little software-program for identifying the moons you see through your scope. As well as locating the Great Red Spot, or GRS, and more:

http://www.astrosurf.com/rondi/jupiter/

Free - of course!

Dave

[Special K]

Nice job Piero! Even an average view of Jupiter is worthy of mentioning.........especially in the current weather cycle.

If Dawes limit on your Skyliner is 0.579 arc seconds and Ganymede has an angular diameter of 1.7 then the rest is down to atmospheric conditions and your personal acuity whether a disc seen is indeed the disc. Seems possible to me, though I'm not sure I'd trust my eyes! Your test against the other moons sounds promising and certainly the star test at equal magnitude would be telling. Tough call but would certainly be an exciting prospect at the eyepiece

Clear Skies

[timwetherell]

I think one can definitely see the Jovian moons as discs in telescopes of moderate aperture operating at higher magnifications. looking at mag 6 stars close by for comparison the difference in apparent size is quite noticeable on a good steady night. As for seeing surface features, I've heard people say this, especially owners of big expensive refractors! I once thought that one side of Ganymede was a different colour to the other in an 8" scope, but it was most likely a case of averted imagination

[Coachella Valley Astronomy]

Took this shot of Jupiter, Io, Ganymede, and Europa on 1-1-16 after a bit of new years celebrations. Seeing was average, equipment used was a Nexstar 6SE + spc900nc webcam 2x barlow

[Piero]

Nice shot!

The proportion between the sizes of the moons and Jupiter in your image seems to me close to what I saw, except for some extra dimmer light surrounding the moons (which I believe was a consequence of large airy discs at high magnification in my 8").

It would be interesting if somebody else could try a high power ep and report his/her findings on those moons.