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Jupiter moon distance

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#1 yesplease

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Posted 10 October 2013 - 05:55 PM

I didn't know if someone could answer this question for me. I've read that Jupiter is 46 arc sec in diameter. I've also heard that the moons can be about 2 arc minutes away. Does this mean that the moon would be about 3 jupiters away at any magnification. Does anything happen at higher mags.?

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Dave

#2 brianb11213

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Posted 10 October 2013 - 06:05 PM

Well, the relative proportions remain the same irrespective of magnification.

Jupiter's four moons orbit at different distances. Because the planes of the orbits are almost in the line of sight they can all appear very close to the planet, or even in transit in front of it or hidden behind it (occulted). The only reliable way of identifying them is to use an ephemeris or similar: the freeware WinJupOS program works well.

#3 yesplease

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Posted 10 October 2013 - 06:26 PM

Thanks much appreciated.

#4 azure1961p

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Posted 10 October 2013 - 09:08 PM

Sky Safari does a phenomenal job.

Pete

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#5 Asbytec

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Posted 10 October 2013 - 09:53 PM

The only reliable way of identifying them is to use an ephemeris or similar: the freeware WinJupOS program works well.

Sure, ephermeris software is very handy. Here's another.
http://www.skyandtel...ascript/jupiter

But you can identify them visually through size, brightness, and color with some experience.

Ganymede is big and bright with a golden hue.
Callisto is big and dim with a more gray-ish hue. It's also often farthest from the planet.
Both Io and Europa are small and bright, Io is more reddish and Europe is almost white.

#6 yesplease

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Posted 10 October 2013 - 09:56 PM

Wow that's incredible. It makes my iPhone app look like child's play.

Thanks
Dave

#7 brianb11213

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Posted 11 October 2013 - 02:46 AM

But you can identify them visually through size, brightness, and color with some experience.

Yes, but it does require good seeing conditions, a scope of at least moderate aperture and a high magnification. Even then there are background stars which occasionally work themselves into the mix and can easily be confused with (in particular) Europa ... when I look at Jupiter without checking satellite positions beforehand I find I've got the IDs right about 80% of the time when I check against WinJupOS afterwards but doing the checking first is the best way of IDing the satellites & also checking for interesting phenomena like transits, occukltations and eclipses.

#8 Asbytec

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Posted 11 October 2013 - 06:48 AM

Its interesting that Europa can be confused as a star. I totally agree, but most people prefer to label them as discs. That requires a modest aperture, sure. When there are not other stars in the field, you can get them right most of the time. It's always nice to check, especially on transits.

As for the OP, I think you covered that well enough.

#9 azure1961p

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Posted 11 October 2013 - 08:44 AM

The discs seen at around 200x or more can clinch ID for me with the 8" , Io has a slightly golden hue, Gaymede a slight cream, Callisto has an earthy kind of brown cast and Europa just seems whitish. Even in my 70mm all Callisto has that odd dirty hue though everything else is one come shade of grey/white. I've heard of some folks seeing Ganymede as larger than the others with an 80mm but I can't recall seeing that with the 70mm, though again the brightnesses help here.

Pete






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