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Discrepancy between SkySafari & Stellarium

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#1 steveyo

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Posted 22 April 2014 - 08:33 AM

In searching for and viewing Vesta and Ceres, I've found that the two software programs (SkySafari on my Android device & Stellarium on my Windows desktop) are showing the objects at different coordinates (visibly different), and, from what I can see in the sky, SkySafari is right and Stellarium is wrong.

Example, at the current time,
Vesta's (alt/az) in SkySafari: 302*35'40.8",-25*12'06.7"
and in Stellarium it's shown : 301*55'15" ,-25*31'39"

Ceres in SkySafari : 304*38',-26*22'
Ceres in Stellarium: 303*13',-26*47'

Explanations anyone?

#2 star drop

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Posted 22 April 2014 - 08:42 AM

Do you have identical observing coordinates and time entered in both programs?

#3 steveyo

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Posted 22 April 2014 - 09:09 AM

Do you have identical observing coordinates and time entered in both programs?

Yes my location in Stellarium is correct, and the Android always knows its location. Even so, I checked and made sure time and locations were the same.

And, as I said, two nights ago Stellarium didn't agree with reality for the two asteroids, while the SkySafari did.

#4 Tony Flanders

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Posted 22 April 2014 - 10:38 AM

And, as I said, two nights ago Stellarium didn't agree with reality for the two asteroids, while the SkySafari did.


Most likely, you need to update the orbital elements for the asteroids in Stellarium. Not knowing Stellarium, I don't know how to do that.

Asteroids' orbital elements change surprisingly rapidly due to Jupiter's gravity. Using year-old elements gives significantly incorrect answers.

#5 WesC

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Posted 22 April 2014 - 12:23 PM

Easy way to check that would be to compare the locations of two other objects like stars at very long distances. If they are the same then your orbital elements need updating, if they are also way off, the something else is probably happening.

#6 Jon Isaacs

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Posted 22 April 2014 - 08:36 PM

Easy way to check that would be to compare the locations of two other objects like stars at very long distances. If they are the same then your orbital elements need updating, if they are also way off, the something else is probably happening.


:waytogo:

I looked at Ceres in both Sky Safari and Stellarium Mobile and saw discrepancy very much like Steve saw. I then looked at Jupiter's position in both programs and they essentially identical..

Ergo: It's the elements.

Jon

#7 steveyo

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Posted 23 April 2014 - 07:12 AM

Jon - thanks for confirming my findings.

Now to update those pesky orbital elements...

#8 Jon Isaacs

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Posted 24 April 2014 - 12:20 AM

Jon - thanks for confirming my findings.

Now to update those pesky orbital elements...


Steve:

If Sky Safari has the correct elements, why bother with Stellarium, why not just use Sky Safari?

Jon

#9 Man in a Tub

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Posted 24 April 2014 - 04:00 PM

Jon makes a good point. Stellarium has limitations. IIRC, there's a warning that loading too many orbital elements into ssystem.ini will slow the program. That is not a problem with, for example, Cartes du Ciel which is also free.

As much as I like Stellarium and always keep it up-to-date, I realize that Stellarium's eye-candy appeal has a price.

#10 Bagged Star

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Posted 25 April 2014 - 05:04 AM

You can update asteroid orbital elements in Stellarium with the Solar System Editor plug-in - it can pull data from the Minor Planet Center. If you need only a few objects, I suggest using the "search" feature instead of the mass-import lists. It uses a slightly different, more up-to-date source.

#11 Roger Corbett

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Posted 26 April 2014 - 07:57 AM

"eye-candy"? Has Stellarium improved dramatically in the past year? Every time, I had looked at it, it seemed amateurish, unpolished, cluttered, and poorly designed. (Sort of like the sloppy middle schooler's project that was near the bottom of the class! ). Maybe the program looks better in Windows World!

I agree with Jon on this one--little reason to use Stellarium unless there's some important feature it has that SS doesn't.

Still, it would bug me, too, if a major program was showing odd positions--and my first action is always to check observer location and update elements, especially for Earth satellites. Yet, doesn't it seem weird that *Ceres* would be that affected by out of date elements. I can see some of the oddballs, with more eccentric orbits, being affected by Jupiter, but Ceres? I'm sure Tony will enlighten us! :)

#12 skyeman1

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Posted 17 May 2014 - 10:57 AM

I realized the failure of Stellarium to show correct asteroid locations just last night. Vesta was clearly near three similar magnitude stars. Starry Night showed it ok. Astroplanner showed it ok. Even an Android phone app showed it the right way. Stellarium show it a couple FOV off. I did update the ephemerides. It changed nothing.

I wonder if the problem is how the coordinates are handled. It's weird enouh for me to think it could be the difference between J2000 and J(current) -- a precessional shift.

When I have the time to search for a direct link for bug reports, I'll send it off.

#13 skyeman1

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Posted 08 July 2014 - 07:27 AM

I actually think the problem is a precessional one, but so far, I can't see how to adjust how the Epoch is handled.

#14 astrogeoguy

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Posted 08 July 2014 - 10:33 PM

Stellarium's Solar System Editor by default is querying a 2011 datafile from the Minor Planet Centre, resulting in erroneous positions for comets and asteroids. At the MPC site, you can find the 2013 MPC file for bright minor planets and copy it into the spot that allows a URL to be specified. You can also make it a new bookmark. Same for comets.

Regards, Chris






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