The stars plugin provides a sky of stars in the globe mode for Marble. However, it only works for Earth. There are currently three other bodies available, the moon, Mars, and Venus. None of them have stars. However, the other downloadable Earth maps do have stars. Does anybody know a way to enable stars for those other bodies as well? I assume it involves manually editing a file somewhere, which is fine.

TheBlackCat wrote:The stars plugin provides a sky of stars in the globe mode for Marble. However, it only works for Earth. There are currently three other bodies available, the moon, Mars, and Venus. None of them have stars. However, the other downloadable Earth maps do have stars. Does anybody know a way to enable stars for those other bodies as well? I assume it involves manually editing a file somewhere, which is fine.

Hi,

We've intentionally disabled the stars for the other planets as the current algorithm to display the stars only gives a proper depiction of the sky on earth.
Changing this would require only a few but "math intensive" changes to the stars plugin. The changes require some familiarity with euler angles, coordinate transformation and a bit of testing and tinkering.

Unfortunately it's not so high on our TODO list, but feel free to send source code patches or add a wishlist item to bugs.kde.org, so your wish doesn't get lost.

Best Regards,

Torsten Rahn

Marble Project

What, exactly, is the problem? Is it parallax, the polar tilt and rotational period, or something else? Because I checked the parallax for the nearest star (besides the sun) between Mars and Earth at the furthest extremes of their orbits. Assuming my math is correct, we are dealing with about 1/1,800 of a degree difference here, so even if the entire computer monitor only showed 1 degree of the star field most displays wouldn't even show a 1 pixel difference. Of course the screen shows a much larger angle than that, it would be much less for most of their orbit, and would also be less for every other star since they are further away.

Well of course it's not about the parallax (which is way below the screen resolution).
It's about the polar tilt indeed which would require two or three rotations be applied to the earth-based coordinates: the amount of the tilt (which is rather trivial) and making sure that the tilt goes into the right direction. And then you need to make sure that angle rotation along rectaszension (which resembles longitude) is properly chosen.
Once that is done one would need to testing: Of course one needs to test whether the planet axis points into the correct direction on the starry sky: that is probably some work again as you'd need to figure out a workable Polaris "replacement" for Mars, Venus and the Moon that one could verify this with.
And of course one would need to check that e.g. Orion appears in the right direction on the horizon on a certain place on mars at some day time and a certain time of the year.

Personally I'd estimate that implementation and full testing and verification would cost me about a full day.

So most of the time wouldn't be spent on coding (as we are basically talking about performing 3 rotations into the right directions and in the correct order). But instead of verification that everything is alright afterwards (most likely according to Murphy it's not and you need to adjust further).