Viewing Jupiter's moons

[bluesilver]

Hi,  I currently have the 10 inch Skywatcher Dobsonian.

It is a fine scope,  when i am viewing Jupiter and looking at Jupiter's moons,  i can see them as tiny stars.

I was interested to know,  if i went up to say a 14 inch or 16 inch Dobsonian,  would i be able to make out the moons as tiny coloured dots rather than as stars?

I realise viewing conditions play a part in it,  but i was interested to know with the larger aperture of the 14 or 16 inch,  will this allow me to see more detail,  or is it just not really possible to make out the moons as coloured dots.

Any information would be appreciated.

Thanks.

 

[Geoff Barnes]

Hi Peter,

I have the 12 inch f5 model and with a 5mm EP giving 300x I can clearly see the moons as tiny discs, not points of light.

If your scope is f5 as well I reckon a 5mm EP giving 250x will enable you to see them as tiny discs as well in good seeing conditions.

We both have Jupiter at about 75 degrees altitude down here at the moment and at opposition too so this is your best chance to see them.

[bluesilver]

Thanks for the reply,  appreciated.

Yes very good seeing conditions for the planet here

Sounds like i might have to tweak the collimation a tad,  I thought it was fairly good.

I do pick up 4 moons, they stand out very clearly,  but only as bright stars,  definitely no distinct shape or colour to say they are not moons.

I thought the larger aperture would help bring them out more clearly.

 

[John]

I don't see anything much in the colour of the Jovian moons even with my 12 inch scope. They do appear as distinct but tiny circular disks though with my scopes from 100mm in aperture and upwards at 100x - 150x. You can just about tell which is which from their apparent diameters in the eyepiece with some careful observation. Their apparent sizes are very, very small though ranging from 1.6 arc seconds down to 1 arc second so visually observing any surface detail even on the largest (Ganymede) is immensely challenging.

 

[kirkster501]

Giant telescopes with high F ratios and great seeing conditions are needed to see the details on them visually.

Think about it......  The renowned planetary imaging expert Damian Peach, with a 14" SCT with perfect collimation at F22 and a high resolution camera in fantastic seeing conditions can process them to see the outline of details on Ganymede.  But I highly doubt he could see those same details visually if he took the camera off and popped an EP in.

[Geoff Lister]

With my 10" Dob., I have seen, simultaneously, one of the Galilean Moons and its transit shadow on the surface of Jupiter. To me, the moon seemed close to a point source, and yet its shadow had obvious width. I tend to use the moons to sharpen my focus for viewing Jupiter.

A quick check on "Stellarium" currently gives Jupiter's diameter as 44.86 arc-seconds, and Ganymede's as 1.65 arc-seconds. Neptune is 2.32 arc-seconds, and I have seen it as a light blue disc, with adjacent stars as white points. Currently, from the south of England, Jupiter is, at best, just over 15 degrees above the horizon, and I have started to lose contrast on Jupiter's surface features with magnification over x130. The atmospheric disturbance gives a wobble to the view, so everything has additional width. Perhaps I will have a better chance in a few years, when the UK's view of Jupiter improves.

Geoff

[Geoff Barnes]

6 minutes ago, Geoff Lister said:

To me, the moon seemed close to a point source, and yet its shadow had obvious width.

Yes I find that too, the black shadows on the Jovian surface always look much bigger than the moons themselves, perhaps an optical illusion?

I can't really say I've seen any colour in the moons either, though I did think Europa had the slightest yellow tint to it with the 4mm SLV the other night. 

[Stu]

Interesting how we all see things differently. I find the moons easiest to see as disks when they are just on the surface ie in the area of limb darkening so that the bright ones show up as a white disk. Agreed about the lovely jet black shadows though, circular when in the centre and becoming oval as the shadow is extended towards the limb.

I got caught out once by Callisto I think it was which appears dark when over the surface and can easily be mistaken for a shadow. Somehow it just doesn't look as jet black or quite as sharp around the edges when you look carefully. It doesn't transit as often but worth looking out for.

[Pete Presland]

55 minutes ago, Geoff Barnes said:

Yes I find that too, the black shadows on the Jovian surface always look much bigger than the moons themselves, perhaps an optical illusion?

I can't really say I've seen any colour in the moons either, though I did think Europa had the slightest yellow tint to it with the 4mm SLV the other night. 

Isn't that because of this effect

[Paz]

9 hours ago, Geoff Lister said:

 I tend to use the moons to sharpen my focus for viewing Jupiter.

This is a good idea, it's easy to miss out on focusing accuracy without realising it if using Jupiter itself to get focused.

[Paul M]

10 hours ago, Pete Presland said:

Isn't that because of this effect

I don't think we can see the penumbral shadow. It's outer edges are extremely diffuse but the inner portions will give the umbra a less defined edge and maybe increase it's perceived size. 

I think the apparent size difference is illusory as demonstrated in this image from: https://www.skyandtelescope.com/observing/jupiter-jumps-back-into-the-evening-sky021720161702/

 

[cletrac1922]

From where I am, can see moons very clearly

Around 7pm, last night, had clear skies, and Jupiter was almost over head

From other forums on here, have read that in UK, Jupiter is much closer to the horizon, hence looking through a thicker atmosphere, due to angle of viewing

With respect to seeing Jupiter's moons in colour, human eye will not pick up colour of DSO.

Bigger is not always better

I use a 17mm wide angle eye piece, when out doing presentations in schools/scout groups with my club

The 17mm gives great views of Jupiter's moons, with 7-9yo's

I also have a 10" flex Dob

John 

[John]

1 hour ago, cletrac1922 said:

From where I am, can see moons very clearly

Around 7pm, last night, had clear skies, and Jupiter was almost over head

From other forums on here, have read that in UK, Jupiter is much closer to the horizon, hence looking through a thicker atmosphere, due to angle of viewing....

 

This is my Tak 100mm refractor aimed directly at Jupiter this evening at 23:00 hrs here in the SW UK. And thats about as high as it gets in our sky currently.

The seeing though is superb tonight - I can make out 7-8 cloud bands, polar darkening with the SEB apparently divided into two bands and a line of festoons down the centre of the equatorial zone between the NEB and SEB. The apparent size differences of the moons on show (Ganymede, Io and Callisto) were clear as well. 180x was delivering these excellent contrasty and sharp views ......... until Jupiter slipped behind the branches of a large Chestnut tree across the road from me

So while low in the sky, the views can be good if you persist

 

[bluesilver]

Thanks for all the replies,  appreciated.

Pretty much answered my questions and appreciate it.

What i am seeing sounds pretty spot on to what it is suppose to be.

Sounds like a good setup could be the 16 inch dobsonian and use aperture masks possibly,  just to dull out the light if it is too bright.

Cheers.

 

Edited July 10, 2019 by bluesilver

[cletrac1922]

The attached took last night, around 7pm, of a small Bushmaster, 6yo grandson was given, pointing towards Jupiter

Gives idea angle Jupiter is from where I am

Also aimed at quarter moon, which was almost over head

Scope is a department store variety, and came with a 4mm, 10mm 40mm eyepieces, as well 1.5 and 3 times barlow

Instruction book indicated use 4mm objects closer than the moon, 10mm objects further away from the moon, 40mm over land and sea

Eyepieces very cheap plastic, and 0.9" instead of standard 1.25"

Have managed to focus on Jupiter, using the 3x barlow

John

PS

Early next year, NASA is sending another Rover to Mars

The attached link, will enable you to register, to have your name included on the Rover, and download a Boarding Pass

Bit of a fun thing

https://www.nasa.gov/press-release/nasa-invites-public-to-submit-names-to-fly-aboard-next-mars-rover

 

 

[bluesilver]

Thaks again for the replies,  appreciated.

So if i am correct,  most likely not,

Would it best to say that i should instead be looking for something with a longer focal lenght rather that a larger aperture?

Something like the SkyWatcher Black Diamond 180/2700 Mak-Cassegrain,  where it has a focal lenght of 2700 mm ?

 

[John]

Actually I think your 10 inch scope is quite capable of showing the 4 Galilean moons as tiny disks, especially from your Australian vantage point. I can see them as disks with my 100mm refractor at 100x and upwards from here in the UK and Jupiter is, as has been said, much much lower in the sky here.

You may or may not see any subtle colour tints on them but that is due to the human eye rather than the scope.

I don't think there is any need to change your scope, unless you want to for other reasons.

The 180 mak-cassegrains are great double star and planetary scopes but not as versatile on other targets as your 10 inch dob is.

 

[cletrac1922]

14 hours ago, bluesilver said:

Thaks again for the replies,  appreciated.

So if i am correct,  most likely not,

Would it best to say that i should instead be looking for something with a longer focal lenght rather that a larger aperture?

Something like the SkyWatcher Black Diamond 180/2700 Mak-Cassegrain,  where it has a focal lenght of 2700 mm ?

 

 

Where about in Oz are you, and what is your light pollution

I live Goldcoast Hinterland, and shielded from light pollution from Glitter Strip of the Goldcoast

Looking north, I loose lot of objects, due to light pollution been reflected from Brisbane

With my 10" Flex Dob, using 17mm wide angle which got from Sirius Optics, moons really clear

Couple of years ago, was out doing grade 2 primary school presentation, with my club, and using my Dob

Picked up a slight blip appear, top of Jupiter, and called out to one of the other club guys, check this out

We watched a moon rise over Jupiter

Kids were using mobile devices to eyepiece to image it

Attached pic taken recent public viewing night, parkland adjacent to Broadwater, adjacent to Seaworld

John

   

[bluesilver]

Thanks for the replies,  appreciated.

Yes i am in Tasmania,  absolutely no light pollution at all where i am as i am out in the country on a large bit of land.

I can really only always make out 4 stars that are always around Jupiter when i am viewing it.

I could be completely mistaking them for the moons around Jupiter and they are actually stars that i think are moons,  but fairly sure that they the moons as they are always in different positions every time i observe Jupiter.

I have been told that the run of the mill Skywatcher Dobsonian don't always have to best mirrors,  so it could also come into play possibly.

 

 

 

[Ricochet]

What eyepieces do you own? I don't know why you're talking about other scopes as really the only two explanations are not using the correct magnification or, more likely, observer experience and eye "criticality". The scope you have is a good one and not going to make small disks into point sources. The only thing would be if all your point sources are fuzzy balls, in which case I would recommend masking the edge of the primary mirror to tighten things up.

[bluesilver]

Appreciate the reply,

The current eyepieces that i own are:

Tele Vue Delos 10mm,  Baader Hyperion 5mm Wide angle eyepiece Tele Vue 2.5X powermate,  and the original 10mm and 25mm eyepieces that came with the scope.

Collimation looks to be pretty good, can get a nice view of Jupiter and the bands,  tried it out again last night as it was a good cloudless night here.

Definitely can't make out any moons,  just 4 bright stars.  Bit of at a loss on what i can do to improve it to at least make out the moons as small disks.

Seriously looking to move possibly into the  SkyWatcher Black Diamond 180/2700 Mak-Cassegrain

 

 

 

 

[John]

Those 4 bright stars are the Gallilean moons of Jupiter. They change position night to night and even, slightly, hour to hour. Sometimes less are visible because one or more is passing behind or infront of the planet.

If you examine them closely under good conditions they do show really tiny disks but really, really tiny !

You are never going to see these moons with phases or looking anthing like our Moon of course. But very careful observation will show them as tiny disks rather than the points of light that stars show.

To change your scope just to see these moons as a touch more "disk like" might be a mistake I feel.

PS: what magnification are you using ?

Even though Jupiter is high in your sky (compared with the UK) you might find that the 10mm Delos eyepiece gives the sharpest views, followed by the 5mm Hyperion but that might be a bit too much. You won't need the 2.5x Powermate at all for this target I think.

 

 

 

[bluesilver]

I am using the 10 mm eyepiece,  i find that if i try to go higher with the 5 mm the planet gets a tad fuzzy,  some thing with the powermate.

I am not really changing the scope just to see the moons of Jupiter,  but really chasing down a dedicated planetary scope,  one specifically setup / designed for planetary viewing.

I realise the 10 inch Dobsonian i a great telescope,  but i am thinking they are more suited to deep space viewing instead.

I really am looking to have two dedicated scopes at this stage,  one for planetary viewing and one for deep space viewing.

I figured that the SkyWatcher Black Diamond 180/2700 Mak-Cassegrain would be the best bet for planetary viewing.

 

Sort of like if you went out and looked through the Dobsonian and the Cassegrain at Jupiter together,  i am guessing the Cassegrain would give the best viewing image and detail?

 

But if there is a better suited dedicated planetary scope,  i am very interested to hear any advice,  many say the Celestron C14 is way to big and heavy,  so appreciate that advice also.

 

 

Edited July 14, 2019 by bluesilver

[Geoff Barnes]

Are you absolutely sure your Dob is perfectly collimated? As others have said, it is absolutely capable of resolving Jupiter's moons as tiny discs. Using your 5mm eyepiece you should carry out a star test on a bright star (say Becrux in the Southern Cross) and follow these instructions from Gary Seronik (apologies if you've already done this)….

https://webcache.googleusercontent.com/search?q=cache:N-pi-KfT2OkJ:https://garyseronik.com/no-tools-telescope-collimation/+&cd=1&hl=en&ct=clnk&gl=au

I do this before every viewing session to ensure collimation and it literally only takes a minute or two.

[Ricochet]

7 hours ago, bluesilver said:

Bit of at a loss on what i can do to improve it to at least make out the moons as small disks.

Practice, I think. Changing scope won't make them any bigger unless you also increase the magnification, and you can do that more cheaply with eyepieces. As it stands you can already get 240X and 300X which might be too much for Jupiter itself and that really is the interesting object. I would be more inclined to get an eyepiece or binoviewer set up equivalent to 7mm.