Lunar Eclipse

erostosthenes · Post #1by **erostosthenes** » 11.05.2003, 22:09

I remember there being a patch for an old version of celestia which turned lunar eclipses red. Is this a difficult thing to implement for future versions of celestia?

Guest · Post #2by **Guest** » 11.05.2003, 23:27

Why?...and why red.

Post #3by **granthutchison** » 12.05.2003, 00:38

The Moon turns a dim red during total lunar eclipses - it's caused by light refracting through the Earth's atmosphere. In effect, the Moon is being faintly illuminated by every sunset and sunrise going on in the world at that moment.

Grant

MB · Post #4by MB » 12.05.2003, 07:10

I was me that plays with the colored moon eclipse. The corresponding modified source file as well as a .exe for windows was posted in the "Bruckner storage" . It was a rather old version. I tried to update for the new versions but the "pre126" were too many to follow the changes. Following the last CVS version, I understand that celestia131 is well on the way. I will try to re-introduce this gadget. Actually it is not more than that, I just try to reproduce the color I saw in real ones or on papers like Sky and Telescope. Although it is obvious that celestia does not render at all the "colored visual effect" of a moon eclipse, it would be extremely difficult to implement the light scattering equations that account for this coloredeffect and it would even more difficult to render the same effect for eclipes of all moon of the solar system ( only planets with atmosphere creates such effect and the color depends on many thigs in particular the nature , density and depht of the varoius components of the atmosphere, an effect that probably nobody saw!
I will tell you when ready.
MB

erostosthenes · Post #5by **erostosthenes** » 12.05.2003, 07:16

I wonder if it'd be too much trouble to simply add a

Penumbra color = [#,#,#]

line to the code so anyone could code in whatever color they wanted for their fictional planets. then there could be a line that determines how close a moon would have to be to be within the penumbra.

MB · Post #6by MB » 12.05.2003, 07:34

Penombra AND umbra change color! But incidently it is roughly what I did!
To leave the choice to the user is actually an other problem, since others files should be involved that would require more time, If tme permi, I will look at it
MB

MB · Post #7by MB » 13.05.2003, 14:14

erostosthenes
I just put again my colored moon eclipse in the last version of celestia (actually the cvs celestia131) Unfortunately the "Bruckner storage" seems to be gone and I have no way to post this "colored " version (656 MB compressed for the .exe).
I can send you if you give a e-mail. I also can send to any "good willing guy" who can afford to post it!
MB

Borg Collective · Post #8by **Borg Collective** » 13.05.2003, 14:51

Seems you DEcompressed it somehow... [Borg Smiley goes here] 656 MB sounds too large... even by Borg Means...

MB · Post #9by MB » 13.05.2003, 15:42

Borg Collective :
"Post" is not the right wording! that you meant? But you understand
MB

erostosthenes · Post #10by **erostosthenes** » 14.05.2003, 05:41

yeh 656MB is about 655MB more than my email account will allow :P . do you mean 656K?

MB · Post #11by MB » 14.05.2003, 07:09

Sorry, Of course it is 656 kB!! I was a bit tired yesterday. Now I understand the reaction.
MB

erostosthenes · Post #12by **erostosthenes** » 14.05.2003, 08:41

cool dude! i'd appreciate it if you emailed it to craskin@cachethomes.net i wonder why this hasn't become a standard feature by now?

MB · Post #13by MB » 14.05.2003, 12:03

Erostosthenes,
The zipped exe (for "windows") has been sent. Good question concerning the non inclusion in celestia. However I guess I fully understand the point of view of the promotors of celestia. A primary philosophy implied in building celestia is to accurately describe the astromical phenomena using the very laws of physics leaving the imaginary aspects and non scientific developments to be included as addons. This philosophy as clearly claimed in various threads of this forum, in particular in long discussions last year triggered by Fridger. As a scientist myself, I fully agree and I appreciate very much. Combinig this rigourous treatments together with the 3D OpenGL, Hypparcos data and beautiful textures now available makes the real success of the marvelous celestia. Therefore I was a bit deceived when I saw the moon eclipses in celestia since its render has nothing to do with a true moon eclipse show. I know a bit of the physics involved in the various colors of eclipse but I am fully unable to derive a code that allows including this physics in celestia. This effect depends on the chemical composition of atmospheres, various "light scattering cross sections" density, thickness etc...I think is by far beyong (at least for me) the possibilities of such a programme. Furthermore I don't know if such effect occur with other occulting planets having an atmosphere (may be it has been "seen" in pictures taken from spacecrafts?) It is the reason why just for fun, I tried to reproduce the colored eclipse by ajusting the colors ( from my memory and also using pictures published in "Sky and Telescope"). But of course (i) this just apply to OUR moon eclipse (ii) this has no physical basis at all and is therefore outside the scope of the celestia developpers. When the "Bruckner storage" was there, I just put it at your disposal. But (i) apparently this facility does not there anymore. (ii) contrarily to any other addon, the celestia code has to be modified at EACH update. I could not follow the flow of the pre5 and pre6 versions and I feared by possible drastic changes of the celestia code. Actually the relevant part of the code is not affected, so it was trivial to do in the last version. That the whole story. Sorry to be so long.
MB

Guest · Post #14by **Guest** » 14.05.2003, 16:40

mb,

if you want send it to me ill will put it on "my" site. Also tell me what the link name should be.

Gordon

erostosthenes · Post #15by **erostosthenes** » 15.05.2003, 01:57

i think my cachethomes.net address might not be working. could you try sending it again to codyraskin@hotmail.com? and as for including it in celestia releases, i was thinking of something along the lines of what you're doing, basically just changing the colour arbitrarily in the solarsys file. i'm certain other planets in our solar system produce similar effects, but since there are no other planets with atmospheres and moons as distant as ours, it might only occur for moons that are just barely entering the shadow of their planet, like jupiter's moons perhaps. another thing i'd like to see is limb darknening for the stars. this is probably easiest done with some sort of haze setting.

MB · Post #16by MB » 15.05.2003, 07:12

erostosthenes ,
I send you the exe at the other e-mail adress. I will look at the code to see if your suggestion is workable, but in any case, the developpers should answer your question
Gordon,
Of course, you can put it on "your" site, if you like. The name could be : "celestia with colored moon eclipse", or something like that. I send you the .exe right now. Don't forget, it is a pre version of celestia131, althought, I did not see any apparent bug. I zip it together with a copy of "render.cpp" the only file that is modified (for linux peoples)
MB

Gordon · Post #17by **Gordon** » 15.05.2003, 08:40

hello,

The file can be found at : http://mapage.noos.fr/celestia

MB,

Just tell me when you want to remove it or change it.

For information there are 20 megs free at this place so it can be used for other files if needed.

G.

MB · Post #18by MB » 16.05.2003, 07:27

Gordon,
OK, Thanks
MB

Guest · Post #19by **Guest** » 16.05.2003, 10:06

http://sunearth.gsfc.nasa.gov/eclipse/e ... May15.html

Guest · Post #20by **Guest** » 16.05.2003, 10:09

http://sunearth.gsfc.nasa.gov/eclipse/e ... 3keen.html