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Hello Dennis,
Give me a day or so on this to look into how accurate SkyTools is plotting Iapetus.
I know that in the past SkyTools has always been rock solid on these things, and I would usually suggest an error, perhaps having to do with time zones. That said, Iapetus is one of the satellites that uses an older mathematical model, and it may be that it has lost accuracy in the last few years. I did test all of the satellites in ST4 against JPL horizons in ST4, but that was several years ago now. Maybe its time to check all of the ones that use the older methods.
Man, I really need to fix Saturn's rings too. I spent so much time on that, and had it working perfectly, and then one day they were suddenly broken. I suspect a change or bug in the (Windows) graphics library. I've been loathe to go back into that code because I might not come out for weeks!
Clear skies,
Greg
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Thanks Greg, I appreciate your quick reply and attention, although sadly, the long range weather forecast for Brisbane for the event does not look promising.
Cheers
Dennis
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Hi Greg,
Where does one go to find the latest position formulae for planetary satellites these days? I have the old 'Explanatory Supplement to the Astronomical Almanac' from ~1992, but that's sadly way out of date. I think they've stopped publishing The Astronomical Almanac in any case with all of the computer programs that are available now.
Phil S.
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Phil,
JPL HORIZONS. It takes some work to get a transit prediction of that though.
Clear skies,
Greg
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Thanks Greg. HORIZONS isn't very easy to use IMHO.
Phil S.
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Partial good news. I couldn't bear to look at Saturns rings while I was investigating the moon positions, so I fell deep into the rabbit hole... and finally fixed the rings!
I'll let you guys know tomorrow what I find out about the moons. Fixes coming soon.
Clear skies,
Greg
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Dennis,
My software has to be 100% reliable for these things. I will not accept anything else. I haven't taken the time to check the calculations for the main satellites of Saturn beyond eyeballing them in the telescope for maybe a decade, so its time to do a full review. Some of the moons use a polynomial algorithm to predict their position, and this was created twenty years ago. These things are created to fit past observations, but that doesn't mean they will be accurate into the future. Now, I don't know for sure yet that there is a problem with Iapetus, but it there is I'm going to fix it by adopting a different method.
Clear skies,
Greg
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