Hey.
Lots of suggestions so i'll keep it fast:
• Glows. At higher speeds all stars should glow, looking at the sun and other stars from up close or medium close even at higher speeds they look stale and dead. They should glow.
• Flares. To achieve the above this would be needed anyway. Flares & Glows should be separated, the glow itself and the flare arms themselves as well as the coronas, should move in different directions, at different speeds and zoom in and out at different rates. case in point: When a flare goes behind an object, as the core circle of the flare (glow) decreases, the flare arms augment and then die fast. They are all seperate parts of the optical effect - most 3d games do this these days. It probably just requires different (added) textures. I'd also vote for a new, bigger, more realistic flares & glows, i've seen NASA pictures of earth with the sun on the back and the flare is alot bigger than what appears in celestia - it's also not yellow, but bright white.
• Flare fades. Flares, Glows and Coronas don't just go behind the object; they fade behind it (and, as said above at different rates and behaviours), they also fade in. Again, most 3d games already have this - Even cooler, you know how if you stare directly into the sun the whole screen goes blank, that'd be cool; as an option though, for people who want to look at it unscientifically to see what's there, still be able to do it.
• Sprites. I really like the disc option in the star styles menu, however an evern better method would be a dual method where discs with size enough turn into a flare slash sparkle that twinkle (according to time speed).
• Fractals. Fractals would be great and a great tool for several effects. The Sun surface, moving, flowing like an ocean of lava; moving sunspots, etc. In Jupiter, the cloud winds would be able to move in opposite directions exactly as in real life, as well, the famous eye would move and rotate. Old demoscene demos would seldomly use that plasma effect. Celestia is a great program, and all i can point out are nitpicks - but this one, is probably the one that'd add unbelievable sense of life into the engine, right now the biggest flaw i'd point out would be the lack o animation, sense of life, sense of mutation with time. Could be also used in a system to emulate cloud movement.
• UI \ HUD questions. I'd really enjoy a interface clean up, for instance: The solar system browser takes way to much screen real state without need, making sometimes hard to see what's happening behind, it'd be very nice also to always see as much space as possible of space, pardon the pun. The information phrases on screen also would probably benefit - this a huge nitpick, or infinitesimal if you will - from being aligned with the screen edges; case in point: the "following earth" phrase is left aligned, even though its on the rightest border. Using a small font like, "small fonts" default with windows probably add great screen real state and make it look more professional, techy. The time info is also too much inside the screen, when it could be glued to it's right border, being less obtrusive.
• Acessability of functions. I'd really like to be focus on an object, right click another and make it track it - current it's not on the right click menu.
• Tracking objects. I'd really enjoy being able to track, let's say, the sun, with the Earth on 1st view. As is when i track the sun i see it from earth, without the earth on view, not as impressive as viewing both, a l? 3d games with 3rd person perspective. Also great to watch a comet heading into the sun - part of the pleasure is seing both objects.
• High resolution pack - A request that's probably better directed at the community, would be a fully DDS (they seem to load a lot faster even though they're more detailed) texture pack with high resolution, instead of having to pick around in several sites and assemble it yourself - something i guess most people will never do, and thus a pleasure they won't have.
• Saturn's Rings - Is it me or it went from a texture to fully rendered lines? Because it's incredibly slow on my P2.6Gigs with an ATI 9200 128 megs. At least the option to switch back and forth would be nice.
• Constelations. Would be nice to have the constelation label in bigger font, with the individual stars labbeled in a smaller one.
• Labels - A nitpick here - Would it be possible to add a drop shaddow, or send label in back under to outline them - if they go on top of a white surface you can't read them, an outline or drop shaddow would fix it.
• Frame limiting. It'd be nice to have it, say max 30, 40, 60 fps, that way it would go away from the 100% CPU usage more often. Vsync on or off, would be nice as well.
• Using the 2d\3d technique. To make the glows more realistic. It's used alot in games and doesn't eat up many CPU cycles, you put one 2d sprite in an angle and another one on a perpendicular angle. Can also be done with 4,8,16, etc. A cheap way so simulate depth in glows, liquids, fire etc. Used together with fractals animating the texture in can be incredibly real - One of the first games to use it was Unreal some years ago, it looked great.
• Cloud bump map. One of the most effects that impressed me on one of those out of earth shots was how 3d and with depth the clouds look - they even casted shadows.
• A Saving system. Most of the time i use Celestia to push space into friends, it's a royal pain in the ass to set it all up just for showing. Being able to set it up and save and load on the run with viewports and everything there would be great.
• Eclipses. Don't know if it's possible already, but it'd be great to stuck a camera in Earths surface, and look back at the sky and see an eclipse from there - With the above mentioned glare, glow, corona changes it'd be even more spectacular. I eman a full eclipse, with sky turning from blue, clouded to pitch dark, the glows, and the full gammut. It'd be also great for sunsets ;o) Could you, also, picture seeing moon eclipses, and sunsets in other planets? It'd be great stuff.
Ok, that's enough suggestions. Thanks for Celestia, its the most fun you can have with your pants on. I believe some of these changes would make Celestia even better that what it already is.