Stellarium Accuracy

[deadsimple]

I was just wondering if anyone knows how accurate Stellarium is in its simulations?

I was watching Io's transit across Jupiter a couple of nights ago. Through my telescope Io was at the edge of the planet about to begin its transit, while in Stellarium it showed it as being smack in the middle of Jupiter (at the half-way point of its transit).

The location, time, DST settings and everything were configured correctly in the program. Any ideas?

Also does anyone recommend alternative software? I tried Starry Night 5 a little while ago and thought the interface and graphics were downright ugly.

Thanks.

[bojan]

Try Cartes du Ciel...
Accuracy of all those programs should be OK...
I know CdC is very accurate (recently I watched Io's transit and it was spot on...).

[Barrykgerdes]

Hi
Stellarium uses all the standard formulae to do the calculations and should be correct. If you said Stellarium was ahead of what you saw did you have the flag_Light_Travel_time set to true the default is false. This would make quite a few minutes difference to what you would observe from earth. It would be about 32 minutes difference.

Barry

[deadsimple]

That did the trick, thanks Barry!



Grabbing a copy now, thanks.

[erick]

Barry, I'm a basic user! Where do I find this flag to set it? It's not in the options I can bring up?

[deadsimple]

I wasn't able to find it in options. If you're using WinXP, go to:

C:\Documents and Settings\username\Application Data\Stellarium

There should be a file called "config.ini". Open that up and the entry should be in the [astro] section near the start of the file.

[erick]

Thanks Ash - thought it would be something like that. Eric :)

[erick]

Err - so should it be set to true or false so what it shows corresponds with what we see?

Mine is false - the default value, apparently.

[deadsimple]

Should set it to true to match what you see through the scope at the time. Found a quote from the Stellarium wiki:Some moons are in another position than they should be.

Currently we have no accurate ephemeris for Charon and no ephemeris for Neptunian satellites at all. The other satellite ephemeris should be correct. When you compare with what you see in your telescope you should enable light travel time compensation in config.ini.

[Barrykgerdes]

Hi Eric
Sorry I was in bed for you query but it looks like someone has given you the right info.

Barry

[erick]

Righty-oh, I'll set it true for the next time I'm looking at moon and shadow transits.

Would have never thought of the light travel time! Just calculated and it seems to me the light travel time from Jupiter varies from around 33 min to 52 min depending on relative orbital positions.

[bojan]

CdC has this calculated automatically... I do not see much reason for this parameter to be set by user.

[erick]

Yes I agree Boojan, I think 99.99999999999% of uses presume an earth-based observer who is not concerned about real time, but rather what they see. So the default is more logically "true"?

Here is a bit out of the Wiki for those interested. I'll implement both of these to use Stellarium for Galilean moon tracking:-

Useful Stellarium features
in your config.ini write
[astro]
flag_light_travel_time = true

[gui]
flag_show_flip_buttons = true

Accounting for light travel time is a must when you observe planetary satellites. You will also want to flip the stellarium image horizontally and/or vertically in order to match what you see in your eyepiece. You can do this with the flip buttons and/or the following keyboard shortcuts:

<Ctrl><Shift><h>: toggle horizontal image flip
<Ctrl><Shift><v>: toggle vertical image flip

[deadsimple]

I don't mind the light-travel feature being in there (extra options are usually welcome), but it really should be enabled by default in a me-centric software planetarium!

As much as CdC looks interesting, the interface hasn't really grown on me. I'm not necessarily attracted to newer and flashier programs, but I find Stellarium to be a bit more intuitive when I want to do something - like fast-forward and reverse time quickly, rotate the view without having the grid lines change/realign and confuse the hell out of me, use a better implemented 'night-mode', etc.

Each to their own, hence it's good to have lots of software available to chose from to match different tastes :)

[Barrykgerdes]

Hi

Stellarium is used by a lot of people to explain and show astronomical phenomena and for this reason there is a configuration file to enable individual setting up.

If you check the default configuration file you will see that most of the options are set to false as the initial set up. Because most users like their own settings an existing configuration file will not be automatically overwritten.

When the telescope control function was introduced it emphasised setting light_travel_time to true.

A lot of the configuration settings would be more useful if they could be set from within the program but it takes time to implement them.

Barry

[deadsimple]

I understand and appreciate that, but the front page of the Stellarium site says:... shows a realistic sky in 3D, just like what you see with the naked eye, binoculars or a telescope.
which isn't strictly true if you're ignoring light travel times by default, since it's really what you'd see in the future. Anyway I'm not really arguing .. just saying it sort of makes the user (newbie like me!) have the wrong assumption, since 90%+ of the time the user just wants to compare the software sky with what they see outside - which is what the software claims to allow "out of the box".

I went now to implement the functionality (it's open-source and I have some software background) and trawling through the source code I found references to a menu item. Tracked* it down to:

Sky and Viewing Options Window -> Sky -> Planets and Satellites -> Simulate Light Speed

So yeah it's been implemented there all along, can't believe I missed it!

(* = in Beta 0.10.0, not sure where it is in previous versions)

[erick]

Huh! I went searching but couldn't find it earlier. I'll have to look again and see why I missed it. Thanks Ash.

[StephenM]

Thanks for the info in this thread guys! I'd been wondering why my copy of Stellarium is inaccurate whereas Jupiter2 is accurate (when it comes to Jovian moon transits etc).

Cheers,
Stephen