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Why Are Jupiter's Moons Positioned Incorrectly? (Answer: Look At Settings > Precession > Other > Light Time Options

On Saturday evening, July 13th, the moons of Jupiter formed an interesting rectangle pattern on the west side of the planet. An hour or two later the movement of the moons changed to a parallelogram. While showing this to folks at a public outreach event, I tried showing the detail on Sky Safari 6 Pro on my iPad. The app showed the moons as behind the planet. I was wondering why the app didn't show this correctly. One of our club member showed me that Stellarium showed it correctly. I use Sky Safari for my Evolution and we also use it to control a scope at our observatory. We were all a little surprised that it did not show this correctly. 

 

Is there a reason for this, or maybe a setting we missed?

 

Thanks

9 comments

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    Dean

    I'm just another SkySafari user, but I tried duplicating your example and have included two screen captures of my results. My location is on the west coast of California so the image occurring at 7:30 PM would have been before sunset, but not knowing your location that is probably not relevant. The first image shows the rectangle pattern that you described, and the second, two hours later, shows the parallelogram.

    If you posted a similar screen capture showing the time and location data, it might help to figure it out what's happening.

     

     

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    Tonymanchi

    Thanks Dean, this is really a puzzle. It shows correct on my iPhone but not on my iPad. I have checked that the settings are the same on both devices. I have restarted the iPad and ran a memory cleanup program. My next step will be to uninstall the app, restart the device, then reinstall. I have also posted this on Starry Nights to see if anyone there has an idea.

    Here is what I see at the same time, I’m in CST. I’ve also included my settings.

     

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    Tonymanchi

    I had to put the settings in a new post.

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    Tonymanchi

    Oh jeez, I found the issue! I looked through the settings and found one called Planet magnification.  It was set to 12x and I set it to 2x. Looks like it was magnified so large that it covered the moons. It looks normal now.  I feel a tad stupid finding this was the issue.

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    Dean

    Mystery solved!

    :-)

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    Keiron Smith

    Hi Tony, 

    Notice also the Light Time option.

    Light Time: adjusts the positions of objects in the solar system for the finite velocity of light. We see Saturn in the sky not where it is right now, but instead where it was about 90 minutes ago, because light from Saturn requires about 90 minutes to travel to Earth.

    For most objects, the effect of light time amounts to only a few arc seconds. Where light time makes a noticeable difference is in the positions of the outer planets' moons, and especially in planetary rotation.

     

    Thanks!

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    Tonymanchi

    Thanks Keiron,

     

    Right now I have it on. Per your response, is that where you suggest setting it? If I understand this correctly, I'm thinking I'd want it off so that what I see in a scope and in the app are the same.

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    Dean

    I believe I can answer that.

    If you want what you see in the sky to match what you see in SkySafari you will want 'Light Time' to be ON.

    Because it takes a certain amount of time for the light from astronomical objects to reach earth, enabling 'Light Time' will add that delay to the computed 'real time' positions of the objects.

    In the case of Jupiter, that's about 37 minutes.

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    Tonymanchi

    Thanks

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