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minimum aperture to resolve discs of jovian moons

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#1 space junky

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Posted 04 January 2009 - 06:03 PM

I think there might be a thread on this, but I am new here. Please could someone guide me to where this thread might start.
Thanks a lot.

#2 spaceghost

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Posted 04 January 2009 - 11:30 PM

Hi space junky, and welcome to the best astronomy website in the known universe!

I don't know where the thread you're looking for is. I'm sure there's one here somewhere. Last summer I was viewing Jupiter with my 12.5" f/6 Dobsonian and a 7 mm UO ortho, which gave 272x magnification. Best view I've ever had, the seeing was good and I could see whorls all over on Jupiter. To me it looked like the moons were were tiny disks and had different sizes.

#3 spaceghost

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Posted 04 January 2009 - 11:33 PM

I forgot something: one good way to search for threads is to use google. Type your search terms and at the end type in "site:cloudynights.com" That tells google to only look on this website. Works pretty good.

#4 HellsKitchen

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Posted 05 January 2009 - 12:11 AM

A good 6 inch scope at 200x mag is sufficent to show differences in the sizes of the moons. However, I've found that seeing plays a big part in your success, as the tiny disks are blurred during slight turbulance. I've yet to see clearly defined disks with my 12".

#5 David Knisely

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Posted 05 January 2009 - 02:42 AM

Under good seeing, I can easily tell the differences in size between the moons in my 9.25 inch SCT at from 200x to 400x. A good six inch probably would still show the disks of Ganymede and Callisto with ease, while the disks of Io and Europa might require observation at a time when Jupiter is well placed in the sky and closest to the Earth. Clear skies to you.

#6 timokarhula

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Posted 05 January 2009 - 05:43 AM

Five years ago, I was able to discern the disc of Ganymedes with a Celestron-5 inch SCT when the moon's apparent diameter was 1.64 arc-seconds. The similarly bright star Chi Leonis was in the same field of view (only 6' from Jupiter) and Ganymedes was clearly larger than Chi. The observation was done with a telescope owned by a Danish guy visiting Värmland Star Party in Sweden in February 2004.

/Timo Karhula

#7 Greg Morrison

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Posted 05 January 2009 - 01:29 PM

A 5" apochromatic refractor will get you there on nights of excellent seeing. I've seen the moons as discs under these conditions in a 5" Takahashi refractor when Jupiter was at or near opposition.

#8 David Knisely

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Posted 05 January 2009 - 06:20 PM

The apparent diameters of the various Galilean moons at mean opposition are as follows:

Io: 1.20 arc seconds
Europa: 1.02 arc seconds
Ganymede: 1.73 arc seconds
Callisto: 1.58 arc seconds

Thus, a 5 inch or larger aperture should be able to resolve the disks of all four moons around opposition. Clear skies to you.

#9 EdZ

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Posted 06 January 2009 - 07:06 AM

Some additional info here

Seeing Jupiter's moons as disks

If I were to write this again today, I might write it a bit differently, but, you'll get the gist of it.

search the Planetary forum on the word disks for much more.

edz

#10 tboss70

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Posted 07 January 2009 - 10:00 PM

Excellent! Thanks for the info Edz


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