Saturn's ring particles are always behind S/2009 S1, never in front of it.
Only when looking towards the planet; looking away from Saturn, the rings will sort properly with that moon. It's a limitation of how the ring rendering works for now.
There already are brown dwarfs.
Add mergers of black holes or neutron stars
This is not possible.
Saved locations don't work in flight simulator mode
That is intentional, since changing time would mess up the locations and orbits of all spacecraft.
Nebula RN 8496-8003: Central stars appear dark red, even when the nebula is behind the stars
Stars always render behind nebulae, it is a limitation of how the engine works right now.
From about 2000000km distance, the moon appears brighter than the earth
Only in HDR mode, because there needs to be a seamless transition between rendering it as an object and as a point of light.
Implement a realistic user-defined start location on earth, for example with several equirectangular drone images at height 0m, 10m, 20m, ... 100m? I would really like to start my spaceship from my own location.
If you're saying what I think you're saying, then it doesn't make any sense.
Display" menu: What's called "Cylindrical" is in fact "Equirectangular". At least when we use the nomenclature from FFmpeg.
Equirectangular projection is also called "simple cylindrical projection".
Add the Cirrus nebula = NGC 6960 and NGC 6995
Add the Blue snowball = NGC 7662
It is impossible for us to create models for every nebula in existence. If you would like to help by making models for them and submitting them for inclusion in the program, that would be great.
After centering the Neutron star at the center of M 1, rotating around this star doesn't work correctly (with right mouse button).
I cannot reproduce the issue, it works perfectly for me.
Adding details for specific regions of planets is not easy. It would also be totally flat, with no height variation, unless you can also find a detailed DEM (height map) for it.
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Otherwise, good suggestions.