Hi everyone MareroQ and me joined forces to create Cosmo plugin with preview window. It create beautiful Stars and the planet of your choice. It have plenty of user adjustments for your delight.
Here a taste:

Looks good! I will surely try it when you publish.

Boldly go for it!

We provide version 0.1 for testing.

In menu: Filters ➤ Astronomy ➤ Render Planet & Stars...

There will be future versions with possible bug fixes and new options.
Python Preview has its limitations - we are trying to get around them, but not everything works the way we want.
In the preview, you will only get an approximate final look (because several values are generated randomly).
We welcome Your comments and suggestions.

Example:
Saturn photographed through a telescope:


Saturn created in P&M Cosmos:

Please leave comments and concerns about the plugin. Enjoy everyone!

The ring aren't too realistic. The top one looks made of terry cloth and is all warped. The bottom one is all glittery (no shadow of the planet on it???). In addition both rings are way too close to the planet. In the lower one, put to scale on earth, the inner part of the ring is around 300km from the surface. This is a Low Earth orbit, were atmospheric drag exists (which is why the ISS has to be boosted regularly). The ring would last a couple of years. Rings are also made of rather fine particles, the grain you put it them assumes they are made of battleship-sized elements (the picture of Saturn you use is photographic grain, look at closer pictures from the Nasa site). But these will either collide and break up, making them fine or sometimes coalesce into a small moon (creating a gap in the ring, as it happens on Saturn).

If you want to make a realistic ring:
* Make a large circle selection (3 times the planet radius) concentric to the planet
* Subtract a smaller circle (2 times the planet, also concentric)
* Fill with a radial blend, made from a gradient with bands (I happen to have gradient sample from the actual Saturn rings...)
* Scale the ring vertically, keep it centered on the planet.



Used this gradient:


If you want to make it look like you are close to the ring, make a bigger ring and use the perspective tool instead of the scale tool:



The shadow is not missing, the shadowed part of the ring is behind the planet

Ah... ofnuts we have the same thought. I'm working on it. I created a plugin that creates a Planet Ring from the same Saturn color image you post it for the next version.
Here is the hard code:

Not bad. Shadow should be opposite light source but otherwise good...

Thank you for your comments so far.
Add a Ring is one of the many options and was supposed to be in Ver.0.2.
However, in order to go in the right direction (no plugs forming a planet and ring at the same time) we need to agree * on many issues:
1. How to create a Ring (the easiest to implement selected: selection-to-gradient-border.py by Tin Tran)
2. How to wrap a Ring around the Planet:
- cut the Ring? (it's in this version),
- cut the Planet?
Cutting the layer at an angle and re-joining them loses at the 1px contact - so only the overlay remains.
Probably the best solution would be a mask of a layer from the planet over the ring.
We don't want to merge layers without absolute necessity - they have to be adjusted by the user - but this complicates the subsequent options a bit.
We did not consider the Ring scaling option (an elliptical selection is created taking into account: Distance,Thickness,Angle).


* we are separated by a 6-hour time difference, so theoretically our day lasts 30 hours (far from the Skinnyhouse record of 32 hours/day ), but it causes a big slowdown.

1) As said in my post, the easiest way to have a correct geometry is to do concentric circles and scale them to ellipses, otherwise the width of the bands isn't going to be correct.

2) Neither. You make two copies of the ring, one in front of the planet, and one behind the planet. Then you make a selection on the planet (and atmospheric haze...) grow it (no need to be accurate, intersect it with a rectangle(*) (top half or bottom half depending on ring direction) and use to delete the top ring.



(*) If the ring is canted, this can be a polygon selection computed with kindergarten trigonometry. Otherwise it can be useful in 1) to do the ring as two halves (chain-linked or in the same group to be moved/rotated/scaled together), so that in 2) you make 2 rings (4 parts) but only delete the planet selection on the "back" half of the front ring.

Can I add my two cents. This has made me cringe since it was first mentioned.
Whose to say that things in space are the same as they are here on earth? Or should be for that matter. Could there not be other sources of light in a planets ring and do they have to be exactly as we think they should be? Surely their would be other forces in play which would mean different physics etcetera.

A whole bunch of astronomers and astrophysicists... As far as we can tell, the laws of physics as we know them also work in the rest of our universe. Granted, there can be "effects" here and there where the application of know "universal" laws in specific conditions can have strange results, but they are still the application of laws that are valid on Earth. Rings have to be circular and flat because if they are not, the orbits of particles will intersect, leading to high-speed collisions that make the ring evaporate or morph into a flat circle.

Of course you can dream up different laws of physics, but they have to be consistent. If you change the laws of gravity stars and planets could not be possible under the new law. Another aspect is that if the laws are very different somewhere else, what happens in between? Is there a discontinuity? If so,what happens to a spacecraft that traverses it?

Finally, at one end you have gorgeous pictures of real space, thanks to NASA and ESA, and on the other end you have random pixels in a bitmap. Where to we draw the line of what a space picture is?

Sallyanne.
Thanks for Your comment.
"Alien" will be in the next version.

Ofnuts
- scaling looks better (we will apply),
- this math is already there (not from kindergarten but elementary school)
- I do not understand the geometry of the shadow on the ring (why is it smaller than the diameter of the planet?)

Because

* The shadow of Saturn is a cone whose axis is determine by the centers of the sun and Saturn (but given that the angle is about 0.05° you can also see it as a cylinder) .
* The rings are in Saturn's equatorial plane (*)
* The sun is above the equatorial plane by about 15° (the terminator is quite far from the pole)(can be up to 26° for Saturn)
* So the shadow cone/cylinder makes an angle with the plane of the rings
* The intersection of a cone or a cylinder and a plane is an ellipse: take a cylindrical glass, fill it with water to half height,and tilt it 15°, the surface of the water should assume something close to this.
* In other words, if you are in the big gap (Cassini's division), the sun is hidden behind Saturn's 60th parallel and the width of that part of Saturn is about half of its equatorial diameter. If you are at the tip of the ellipse (slightly off-image to the left) you would see the sun just above Saturn's pole.

In this image the sun is closer to the equator and the shadow on the rings has a more constant width (the ellipse is much more elongated)

PS: The shadow isn't too hard to compute:

1) you draw the rings as concentric circles
2) You create circle a selection which is the size of the planet
3) Assuming "sun" with an angle alpha above the equatorial plane you stretch the circle horizontally by 1/cos(alpha) (so yes if alpha=0 (sun in EP) your circle is inifintely stretched and becomes an horotoanl strip)
4) You keep one half of that and fill with black, so now you have an astromically correct sahdow on the circular ring
5) you apply the appropriate rotation on the ring plus scaling down to account for perspective


(*) Which is another consequence of the law of physics. Due to their rotation, planets aren't exactly spherical, and the bulge on their equator slightly distorts their gravity field and makes all orbiting objects slowly migrate to the equatorial plane. One exception: the rings around Uranus, but their story/origin seems quite different from others.

Done using the rules above (sort of, I hoped that MapObject would give lighting directions as angles so they would be easy to translate, but curses, foiled again...). So I eyeballed some angles.

Hi guys
So I did try your plug-in, I'll go straight to the point as I wrote white testing (so, please pardon me as it's quite raw )

first tab
ice thickness at 17 = no ice
ice thickness at 16 = it's a frozen planet?
ice thickness at 100 = no more ice on poles, but below the poles?
add a custom texture = flat earth?

|||Apply Lens...||| Um that's why your planet looks flat, I suggest to use map object or sphere designer as you will also have secular light and many more option for lighting

second tab
Add "Luminace"/ "Luminace" color / "Luminace" Thickness. Do you mean Luminance?

Oh... this just happened while playing with ice opacity (re-tab 1)


also throwing error when I restart the plug in -> need to restart GIMP...

Add clouds to planet... very cloudy planet, adding a slider to have less clouds would be nice.

Third tab
Add shadow... only by 45 degrees? why limiting?
Create long shadow .... Oh no again...



resume stuff I did before to restart gimp then again
create long shadow... Oh no again...
OK stop with long shadow

forth tab
adding stars and options looks good

fifth tab
add ring... so default setting, just clicking the button... I chuckled at the ring -> changing default setting would be a plus
ring thickness = 74 ... Um I was not aware about that universe...
ring angle = 18 I can see that the ring is cut


spread the ring = 23 ok it become "dust"

In the end, not counting the bugs, I got a "normal" ring even though on the preview it was very strange, is it possible to fix the preview?
final result... I think your rings got a serious problem


The idea is great, specially for new comers, but still I prefer doing it myself as your rings need a bit of work
Home made quick rings in just a minute


The last but not the least, Ctrl+Z... I want it to act like other plugins or filters, like when I Ctrl+Z it goes back before your plugin starts
In the hope that this lengthy post will help you.

Hi Patrice.

Thanks for testing. A few fixes will be for sure. When the new version is ready we will publish it again.

Pocholo/MareroQ, a big thanks for the plug-in , both for what it does and the coding which I'm interested in. I find your plug-in addictive, always wanting to try one more and have been experimenting most of the day

steve

Hi Steve thank you for testing the plugin. I'm glad you like it, but like MareroQ said the plugin still on the initial version.