comet tails

[Boux]

Hehe! You wrote "FT1.2"...
Does that mean ... hummm? Soooon?

[t00fri]

Boux,

Hehe! You wrote "FT1.2"...
Does that mean ... hummm? Soooon?

Well everything is fixed and ready for FT1.2.

Just some time (< 2 weeks) before everything will be wrapped up. This is plenty of work, since we always release Windows, Linux-KDE, Linux-gtk, Linux-gnome. The source archive should be building under all these ...

Another comet heading towards a FT1.2 galaxy


Actually I modified also two more subsequent methods as to color and increased the number of tail points by a factor of 2. Finally the comet head is now nicely round...Clearly it's a bit more strain for the graphics card...


Bye Fridger

[buggs_moran]

Would we be able to see the coma of the comet too? Or is that only visible in long exposure photos?

The coma is really what we "see" as the comet, the nucleus might show as a bright dot. I have only seen that once through a scope, and frankly I think my eyes were playing tricks on me. About 5 AU's from the sun the dust in the coma starts to reflect light and begins to flouresce due to the UV radiation. To be true to the "visual" aspects of comets we would need a few things.

1. Increase in coma brightness around 5 AU's
2. An ion tail forming a little further in, that points directly away from the sun.
3. A dust tail in the direction of the orbit, but slightly off kilter due to radiation pressure (hence the curl you see in most photographs).

For the time being, appearance and lengths of associated parts could all vary directly with the orbit/solar distance (and the percent compostition of the comet in the future) I think the coding for this might be a ways off since we have so many other things we're hoping for, so I'll be happy with the recent changes as they certainly look better.

[Boux]

Same trip to M31, looks good here too:



Yep, I have seen that a lot of parameters can be tweaked.
It seems there is some redundant code in there, am I wrong?

[Malenfant]

Same trip to M31, looks good here too:



Yep, I have seen that a lot of parameters can be tweaked.
It seems there is some redundant code in there, am I wrong?

That looks really nice

[Cham]

That looks like a huge step in the right direction !

What about the mesh resolution near the head ? It's so crude in the official version ! Can you show the head at a closer range ? How smooth is it, now ?

[Boux]

I am thinking of adding some random perturbations in the coloring and transparency to add some "life" to the tail.
Color covering a range of tints from white to purple-blue and local changes of transparency simulating some variations in density.
The effect should be very subtle though, no overkill.
Just an idea I will try to dig further.

Sorry Cham, we cross-posted. Any number of points can be put in the tail definition and the head can be made very 'round'. But of course, as t00fri wrote, this adds another overhead to the rendering. I do not think it is much worth to be too greedy here.

[t00fri]

That looks like a huge step in the right direction !

What about the mesh resolution near the head ? It's so crude in the official version ! Can you show the head at a closer range ? How smooth is it, now ?

Here is a comparison with 20 points and 80 points respectively. Look at the comet head....



Bye Fridger

[Cham]

LOTS better, Fridger !

This parameter should be accessible to the user, in Celestia's preferences panel., or at least in the cfg file.

[symaski62]

Here is a comparison with 20 points and 80 points respectively. Look at the comet head....



Bye Fridger

celestia.cfg ??

[buggs_moran]

Here is a comparison with 20 points and 80 points respectively. Look at the comet head....
Bye Fridger

celestia.cfg ??

No, we would like it there. It is within the code I believe, and unaccessable by the user..

[ogg]

Yeah the amount of 'degree of detail control' that's stuck in the pre-build source has aways frustrated the anal side of my nature. There was a 'KCelestia' build a year or so ago which increased the rendering points of xyz orbit lines and ring segments, and looked fantastic. Some of these changes were incorporated but it would be nice to have parameters like these sitting tweakable in a cfg for tuning up individual installations.
Sigh...

[buggs_moran]

I had the opportunity to play with the OSX build and I liked the increased configurability on the menu. I always use Windows, but I might have a Linux box soon to play with. Didn't someone have a build at one point that allowed you to load new textures/models even after the program was running? OK, I am wandering off topic...

[PlutonianEmpire]

*Clears throat*

Question: are comet tails really THAT wide? I think they should be made a bit thinner, IMO.

[ogg]

*Clears throat*

Question: are comet tails really THAT wide? I think they should be made a bit thinner, IMO.

Well there will be a bunch of factors which would influence the geometry of the tails at different points in a comet's orbit; I have no idea how many of them are taken into consideration in Celestia. Eg the speed and density of the solar wind, outflow rate from the nucleus (which in turn will depend on how much heating it's getting from the sun and the volitility of the material that ends up being ejected) etc etc.

So no, I have no idea if they're too wide or not. Do you have some comparison pictures between real comets as photographed vs as simluated? That's the only way to tell without doing some serious research. And anyway, no general way of setting the geometry will be accurate in all cases, comets are just too different from each other.

Edit: the following link looks interesting
http://www.geocities.com/zlipanov/comet ... tary_tails

[WOWspaceISbig]

Wow, I come back nearly a week later to find a 3pg thread!

Anyway, those tails look much better. Can anybody show me how to apply them?

And by the way, I found a few comet pics:
http://hubblesite.org/newscenter/newsdesk/archive/releases/2004/52/
http://wsx.lanl.gov/WebPub/images/comet-hale-bopp_wurden-3-6-97.jpg
http://www.wcnet.org/~kmkerr/Solar_system/Comets.htm
http://antwrp.gsfc.nasa.gov/apod/image/0012/halebopp_gleason_big.jpg
http://www.mlo.noaa.gov/HISTORY/Time%20line/HALEBOPP/Comet.jpg
http://www.fregger.com/space_content/8halley-comet.jpg

I hope they help

[fsgregs]

Hi:

It's great news that you all are working on comets. They have been a weak point in the program. Considering that the comet code is being modified, could you add some code to turn off comet tails when the comet passes the point of tail solar vaporation? I read somewhere that it is around the orbit of Jupiter and beyond, but I'm not certain.

Frank

[buggs_moran]

Hi:

It's great news that you all are working on comets. They have been a weak point in the program. Considering that the comet code is being modified, could you add some code to turn off comet tails when the comet passes the point of tail solar vaporation? I read somewhere that it is around the orbit of Jupiter and beyond, but I'm not certain.

Frank

I've read that it is approximately 5 AU's out

[fsgregs]

Buggs:

Yep, that sounds about right ... near the orbit of Jupiter.



Frank

[t00fri]

Buggs:

Yep, that sounds about right ... near the orbit of Jupiter.



Frank

Checking the comet's distance from Sol and turning the tail smoothly off beyond some appropriate limit is quite easy to incorporate.

Could someone help digging for /reliable/ info about what that distance is? Please, NO "popular" science WEB sites

Bye Fridger