Hi all,
I'm from theopencd.org, where we have included Celestia on our CD. We'd like to include some add-ons too, but they must be open source. Are they?
Are plug-ins OSS?
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JackHiggins
- Posts: 1034
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- With us: 21 years 6 months
- Location: People's Republic Of Cork, Ireland
We've been through this before:
all addons are copyrighted by their authors unless they explicitly state otherwise.
That's the law. Wishful thinking won't change it.
Many people have put a lot of work into their products and are not about to let anyone else make money off their efforts.
If you want to publish someone else's work, you must have their explicit permission: either that permission must be included with the item, or you must ask for it.
all addons are copyrighted by their authors unless they explicitly state otherwise.
That's the law. Wishful thinking won't change it.
Many people have put a lot of work into their products and are not about to let anyone else make money off their efforts.
If you want to publish someone else's work, you must have their explicit permission: either that permission must be included with the item, or you must ask for it.
Selden
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HankR
I wonder if we could come up with a "Celestia Community License" (CCL) under which Celestia add-on creators would be encouraged to release their work. Just what the terms of the license would be is something we'd have to work out. But I presume that most add-on creators would be willing to make their work available on terms similar to those under which Celestia itself has been made available to them.
- Hank
- Hank
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JackHiggins
- Posts: 1034
- Joined: 16.12.2002
- With us: 21 years 6 months
- Location: People's Republic Of Cork, Ireland
Whoops... 
Ok so henrik - just email everyone whose addons you want, and get their permission to use whatever addons you'd like on the open CD. Credits included too, of course...
The CCL couldn't be that complicated... (There's probably something like it around already)
1. All Add-ons are provided free of charge, provided they are used for non-profit, personal, and/or educational purposes.
2. Add-on creators take no responsibility for any adverse effects their work has on your computer.
3. Add-ons may be redistributed on physical media, and/or mirrored on other sites, provided the original creator gives consent, and a credit is included
4. Add-ons may be modified and redistributed online, or as above, where the author gives consent, and a credit is given.
5. If the author cannot be contacted after a certain time period [like 3 months...?], the work can be redistributed as in 3, but must not be altered.
They're just ideas...
True. That's my feelings really.
Ok so henrik - just email everyone whose addons you want, and get their permission to use whatever addons you'd like on the open CD. Credits included too, of course...
The CCL couldn't be that complicated... (There's probably something like it around already)
1. All Add-ons are provided free of charge, provided they are used for non-profit, personal, and/or educational purposes.
2. Add-on creators take no responsibility for any adverse effects their work has on your computer.
3. Add-ons may be redistributed on physical media, and/or mirrored on other sites, provided the original creator gives consent, and a credit is included
4. Add-ons may be modified and redistributed online, or as above, where the author gives consent, and a credit is given.
5. If the author cannot be contacted after a certain time period [like 3 months...?], the work can be redistributed as in 3, but must not be altered.
They're just ideas...
HankR wrote:But I presume that most add-on creators would be willing to make their work available on terms similar to those under which Celestia itself has been made available to them.
True. That's my feelings really.
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Don. Edwards
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- Location: Albany, Oregon
This sounds very good to me. I recently was going around at various Orbiter add-on sites and saw some of my work there. Some of the links had my name or credited Earth Central but a few did not. So from here out I plan on including a type of CCL with my textures. It will allow for free distribution but any and all modifying or porting to other formats for other programs has to be brought to my attention for approval. I have no problem having my work ported over to Orbiter or any other space simulator or any game for that matter. I just simply want to know when it is done an for what program. That way I can at least point to the work and say it is mine and no one else’s.
Now if I do not start to here from these people porting my work over than I might have to start imbedding my own copy write/watermark somewhere into the texture that I only know about.
That is one way of keeping track but I would rather not have to go to this extreme.
I along with many other artists here in the forum want to be able to possibly create a portfolio of our work as time goes by and that is difficult if your work is bastardized by every Tom, Dick, and Harry on the net. I know a certain amount of this is bound to happen. But when I consider the amount of time I am putting into my 32k Earth texture you can see my point. Sure it is a work of love for the shear joy of sharing it with everyone hear. But it is also a very big task that consumes a great deal of time and is not paid for. I would never nor do I think I could ask for money for my work but it is the whole principal that counts.
So to some this up I feel that we need to institute this CCL as soon as possible and make it official. If we don't make it official it is leaving everyone’s work wide open to get ripped and used and then you can hold no copyright what so ever.
Ok I will now step down from my soapbox.
Don. Edwards
Now if I do not start to here from these people porting my work over than I might have to start imbedding my own copy write/watermark somewhere into the texture that I only know about.
That is one way of keeping track but I would rather not have to go to this extreme.
I along with many other artists here in the forum want to be able to possibly create a portfolio of our work as time goes by and that is difficult if your work is bastardized by every Tom, Dick, and Harry on the net. I know a certain amount of this is bound to happen. But when I consider the amount of time I am putting into my 32k Earth texture you can see my point. Sure it is a work of love for the shear joy of sharing it with everyone hear. But it is also a very big task that consumes a great deal of time and is not paid for. I would never nor do I think I could ask for money for my work but it is the whole principal that counts.
So to some this up I feel that we need to institute this CCL as soon as possible and make it official. If we don't make it official it is leaving everyone’s work wide open to get ripped and used and then you can hold no copyright what so ever.
Ok I will now step down from my soapbox.
Don. Edwards
I am officially a retired member.
I might answer a PM or a post if its relevant to something.
Ah, never say never!!
Past texture releases, Hmm let me think about it
Thanks for your understanding.
I might answer a PM or a post if its relevant to something.
Ah, never say never!!
Past texture releases, Hmm let me think about it
Thanks for your understanding.
Dear Celestia community,
First, let me thank you for making such a great space simulator, and for making it available as open source. It has been included in both editions of our disc, TheOpenCD. People who get the disc always give good feedback on Celestia, and often mention it specifically. Also note that we are known for being highly selective, and have currently only included 18 apps in total, out of many hundreds of available apps.
Now, it seems I have started something of a debate here about the licensing of plug-ins. For those artists and developers who have as a result started considering these issues, perhaps for the first time, I would suggest starting by reading some background information here 1, 2, 3, 4, before trying to compose your own licenses, as that can be tricky.
Does an OSS license protect you from being ripped of commercially? Yes and no.
I am not aware on an open source license that prevents sale of the software. Celestia is on our CD and I sell copies to schools etc. in bulk by the 100s for a nominal fee, others sell single copies for $3, which is fine. You could sell it for $100 if you found a buyer (and you might), but in that case the buyer gets badly ripped off and would have a bone to pick with the seller. I wouldn't really say that the developer gets ripped of in that case. However, if you wrote some code and placed it in the public domain, then someone came along, expanded it a bit, and baked it into a closed program, then they could charge $1000 for anyone to use it, including you yourself. Then I would say you would be ripped off. That's where an open source license can help, because an OSS piece of code just CANNOT be integrated into a closed program. Your current practice seems a bit risky because you are letting people use it without specifying a license, so someone might make the claim that it is now public domain. (And if they have lawyers and you don't, you loose by default.)
My suggestion to you would be to have the most active artists and developers set up a few add-on package collections, such as 'Planets', 'Space craft', whatever and then agree on some maintainers for each of these and a license. That would be a good start, and then smaller contributions and tweaks could be added with time. In that way maintainers will always be in a position of some control, and would ensure that everyone gets proper credit. Look at Linus Torvalds; he made Linux GPL but remained the maintainer. Later, when the big guys such as IBM and Sun started making their own version they could easily have forked it off, but they don't. People tend to stay with the main tree because there is more momentum there and there is always a certain respect for the original maintainers.
There also seems to be an issue of people porting add-ons to Orbiter, which is not open source. If those people have not asked the originator for permission, and the originator has not placed it in the public domain, then this is a breach of copyright. You could ask them to stop, but you are then in a weak position if they don't because you are letting people use it in some cases, but not others, without being clear about it. That's when you start needing a proper license. If a large amount of plugins for Celestia were to accumulate under an open license, then these could not be ported to the non-open Orbiter without a double license. (And authors could insist on their already ported plug-ins being removed; Perhaps LGPL plug-ins could work with Orbiter, I don't know.) In a perfect world, this might eventually persuade the Orbiter people to go open source as well, so that they would have direct access to the Celestia plug-in packs and code. Just a thought.
I know that it can be hard to let go of your code, but it is often the case that you get even more recognition from an open source project, because it will tend to grow more quickly from pooling your efforts, and it will get a wide distribution on CDs like ours.
Cheers,
Henrik
First, let me thank you for making such a great space simulator, and for making it available as open source. It has been included in both editions of our disc, TheOpenCD. People who get the disc always give good feedback on Celestia, and often mention it specifically. Also note that we are known for being highly selective, and have currently only included 18 apps in total, out of many hundreds of available apps.
Now, it seems I have started something of a debate here about the licensing of plug-ins. For those artists and developers who have as a result started considering these issues, perhaps for the first time, I would suggest starting by reading some background information here 1, 2, 3, 4, before trying to compose your own licenses, as that can be tricky.
Does an OSS license protect you from being ripped of commercially? Yes and no.
I am not aware on an open source license that prevents sale of the software. Celestia is on our CD and I sell copies to schools etc. in bulk by the 100s for a nominal fee, others sell single copies for $3, which is fine. You could sell it for $100 if you found a buyer (and you might), but in that case the buyer gets badly ripped off and would have a bone to pick with the seller. I wouldn't really say that the developer gets ripped of in that case. However, if you wrote some code and placed it in the public domain, then someone came along, expanded it a bit, and baked it into a closed program, then they could charge $1000 for anyone to use it, including you yourself. Then I would say you would be ripped off. That's where an open source license can help, because an OSS piece of code just CANNOT be integrated into a closed program. Your current practice seems a bit risky because you are letting people use it without specifying a license, so someone might make the claim that it is now public domain. (And if they have lawyers and you don't, you loose by default.)
My suggestion to you would be to have the most active artists and developers set up a few add-on package collections, such as 'Planets', 'Space craft', whatever and then agree on some maintainers for each of these and a license. That would be a good start, and then smaller contributions and tweaks could be added with time. In that way maintainers will always be in a position of some control, and would ensure that everyone gets proper credit. Look at Linus Torvalds; he made Linux GPL but remained the maintainer. Later, when the big guys such as IBM and Sun started making their own version they could easily have forked it off, but they don't. People tend to stay with the main tree because there is more momentum there and there is always a certain respect for the original maintainers.
There also seems to be an issue of people porting add-ons to Orbiter, which is not open source. If those people have not asked the originator for permission, and the originator has not placed it in the public domain, then this is a breach of copyright. You could ask them to stop, but you are then in a weak position if they don't because you are letting people use it in some cases, but not others, without being clear about it. That's when you start needing a proper license. If a large amount of plugins for Celestia were to accumulate under an open license, then these could not be ported to the non-open Orbiter without a double license. (And authors could insist on their already ported plug-ins being removed; Perhaps LGPL plug-ins could work with Orbiter, I don't know.) In a perfect world, this might eventually persuade the Orbiter people to go open source as well, so that they would have direct access to the Celestia plug-in packs and code. Just a thought.
I know that it can be hard to let go of your code, but it is often the case that you get even more recognition from an open source project, because it will tend to grow more quickly from pooling your efforts, and it will get a wide distribution on CDs like ours.
Cheers,
Henrik
Ok, reading that, I think I have to be a little bit more specific:
My addons are freely redistributable, without further permission, as long as the are part of a celestia compilation, or a compilation of which celestia is a part of, or a compilation which is intented to be an extention to an existing celestia compilation.
In all other cases I want to be noticed before usage.
maxim.
My addons are freely redistributable, without further permission, as long as the are part of a celestia compilation, or a compilation of which celestia is a part of, or a compilation which is intented to be an extention to an existing celestia compilation.
In all other cases I want to be noticed before usage.
maxim.
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revent
- Posts: 80
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- With us: 20 years 7 months
- Location: Springfield, MO, USA
selden wrote:We've been through this before:
all addons are copyrighted by their authors unless they explicitly state otherwise.
That's the law. Wishful thinking won't change it.
Many people have put a lot of work into their products and are not about to let anyone else make money off their efforts.
If you want to publish someone else's work, you must have their explicit permission: either that permission must be included with the item, or you must ask for it.
That's partly true, Selden, but for what he's asking it's somewhat irrelevant.
Celestia is distributed under the GPL, and it is EXPLICITLY REQUIRED by the GPL that any 'derivative work' also be distributed under the GPL. The meaning of 'derivative work' includes any work that is designed to work only with Celestia (such as an ssc, stc, the stars database, etc), because it is using the Celestia 'API' (not really, but you get the point). Unless the copyright holder of Celestia (chris?) has explicity and publically stated that he will not consider such items to be derivative works (look at Linus' comments about Linux user-space programs for an example) they MUST be distributed under the GPL, no matter whether they are copyrighted or not. The copyright holder of the 'derivative work' has no choice about the license, and so can't complain about distribution under the GPL. If they did, Chris could sue them under intellectual property law. AFAIK, he's never limited what he considers to be a derivative work. (Such a statement doesn't violate the restrictions on altering te GPL, BTW, it just restricts Chris' ability to sue via the principle of estoppel.) Even if he did make such a statement now, it would only /strictly/ apply to add-ons made after when he said it, unless he explicitly said it was retroactive.
The copyright holder could complain about 'commercial' distribution, though, but if that was the case then Celestia couldn't be included either.
What you said is correct for models and textures, though, since they aren't Celestia-specific (they don't incorporate Celestia's 'intellectual property' like sscs and stcs do.) To distribute them, he will need permission.
The point is that if you use someone else's intellectual property, they can restrict how you exercise your copyright, and if their intellectual property is under the GPL then they ARE restricting it.
revent wrote:Celestia is distributed under the GPL, and it is EXPLICITLY REQUIRED by the GPL that any 'derivative work' also be distributed under the GPL. ... ... If they did, Chris could sue them under intellectual property law. AFAIK, he's never limited what he considers to be a derivative work.
Wow! I didn't know the nature of the add-ons well enough to see this point! But if it integrates as you say, then you are right: all the add-ons must be GPL. Since I guess each add on only has one contributor, they can be withdrawn from circulation. Looks like some people need to do some hard thinking ...
It seems we may get the chance to welcome lots of new developers to the world of free software
But seriously, we would love to make a comprehenive Celestia installer with lots of plug-ins installed. That would be truly great! Remeber, our CD will go out to hundreds of schools and colleges, and generally to non-technical users who may not find it easy to download and install these things. I hope that you plug-in developers will help make this possible.Revent,
Thanks for your attempt at clarification, which seems to make sense. Unfortunately, it means that many existing Addons probably are illegal.
(This is separate from the issue that people often fail to give credit for the images that they use in the Addons that they've created.)
Many Addons include astronomical pictures which are derived from images which are not in the public domain. Paragraph 2b of the GNU General Public License essentially requires that all components of a work derived from a GPL'd product be covered by the GPL. Unfortunately, for example, the use of images provided on the Web by NOAO must comply with the terms of NOAO's license, which is not the GPL.
While the GPL explicitly does not cover items which just happen to be aggregated on the same medium with a GPL'd product, I don't think one can argue that a Zip archive which automatically installs files into appropriate directories for use with Celestia is merely an aggregation.
Thanks for your attempt at clarification, which seems to make sense. Unfortunately, it means that many existing Addons probably are illegal.
(This is separate from the issue that people often fail to give credit for the images that they use in the Addons that they've created.)
Many Addons include astronomical pictures which are derived from images which are not in the public domain. Paragraph 2b of the GNU General Public License essentially requires that all components of a work derived from a GPL'd product be covered by the GPL. Unfortunately, for example, the use of images provided on the Web by NOAO must comply with the terms of NOAO's license, which is not the GPL.
While the GPL explicitly does not cover items which just happen to be aggregated on the same medium with a GPL'd product, I don't think one can argue that a Zip archive which automatically installs files into appropriate directories for use with Celestia is merely an aggregation.
Selden
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HankR
IANAL, but...
I don't think most Celestia "add-ons" would be considered derivative works of Celestia, because they don't include any of Celestia's copyrighted code. I don't believe that simply using Celestia file formats would be sufficient to make an add-on a derivative work subject to the GPL.
- Hank
I don't think most Celestia "add-ons" would be considered derivative works of Celestia, because they don't include any of Celestia's copyrighted code. I don't believe that simply using Celestia file formats would be sufficient to make an add-on a derivative work subject to the GPL.
- Hank
The more I think about it, I think I have to agree with HankR.
Like CEL and CELX scripts, the catalog files and other components of Addons can be thought of as programs which are interpreted by Celestia.
There are quite a few program interpreters which are GPL'd. Programs written in Mumps, for example, do not inherit the GPL just because they're written in a language that can be interpreted only by GPL'd software.
Like CEL and CELX scripts, the catalog files and other components of Addons can be thought of as programs which are interpreted by Celestia.
There are quite a few program interpreters which are GPL'd. Programs written in Mumps, for example, do not inherit the GPL just because they're written in a language that can be interpreted only by GPL'd software.
Selden
Ok, so I just downloaded stardust.zip from Jack's site, containing an .xyz file and a xyz.ssc file, which both seem to be simply parameter files, so in such a case you are right. Are any of these plug-ins acctually compiled? (sorry, I'm new to this stuff {despite having a big mouth } ) I guess the 3ds files are compiled. How are those made?
} ) I guess the 3ds files are compiled. How are those made?Henrik,
3DS files are 3D models generated by the use of 3D design programs.
There's nothing about them that's specific to Celestia.
The 3DS file format originally was used by 3D Studio Max (hence the acronym). Today, most 3D design programs can import, export and display models using the 3DS format. Anim8or is a 3D design program that's popular among people on this forum, since it's free and relatively easy to use. Blender is a much more sophisticated free 3D design program.
Does this answer your question?
3DS files are 3D models generated by the use of 3D design programs.
There's nothing about them that's specific to Celestia.
The 3DS file format originally was used by 3D Studio Max (hence the acronym). Today, most 3D design programs can import, export and display models using the 3DS format. Anim8or is a 3D design program that's popular among people on this forum, since it's free and relatively easy to use. Blender is a much more sophisticated free 3D design program.
Does this answer your question?
Selden
selden wrote:Does this answer your question?
Yes, thanks. Now I'm starting to get it. Sorry about all the fuss.
So, are those the main kind of plug-ins? The script files and the 3ds files? Those sound ok. That just leaves the issue of the image copyrights; how does that work? Are you ok to include those NASA images etc. in your 3ds files and redisribute?That just leaves the issue of the image copyrights; how does that work? Are you ok to include those NASA images etc. in your 3ds files and redisribute?
That depends on the image and its source. Unfortunately, many people are being careless and don't include information about where they've gotten the images they're using -- which means, of course, that those Addons shouldn't be redistributed by anyone else.
In general, images produced by NASA personnel are public domain. However, many images on the STSCI.EDU (Hubble) sites are not public domain: they're copyrighted by the people who performed the research, so the designer of an Addon has to read the credits carefully.
Images from NOAO (the U..S. National Optical Astronomy Observatory) or ESO (the European Southern Observatory) are free for use for educational purposes, but require explicit permission when used for commercial purposes. (Many of the pictures I use are from those two sites.) Images on the ESA (European Space Agency) Web sites can't be used for anything other than individual personal use without getting explicit permission. Other sites may permit their images to be used only for actual research, and some are even more restrictive.
I'm drasticly simplifying the situation, of course. Most of the "image servers" I've mentioned have usage licenses that are several pages long.
Does this help?
Selden
selden wrote:That depends on the image and its source.
Just a note: the bluemarble image should be free of copyright, at least there is no mention of any restriction on the visibleearth-page (and I quote: "Unless otherwise noted, all images and animations made available through Visible Earth are generally not copyrighted.")
So the 32k Earth-VT should be fine.
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revent
- Posts: 80
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I should probably disclaim that I'm not a copyright lawyer, and this is not legal advice, so don't sue me. I do have a clue, tho.
OTOH, if the holder of a copyright tries to object to someone else using his work (that should be GPL'd), proving that it's required to be GPL would be a valid defense.
You're misunderstanding what the GPL means.
The images are a separate issue. Yes, redistributing an NOAO image without attribution IS a violation of their copyright, any they could restrict redistribution (though they don't for personal or educational use). Including their image in a zip file with your addon is NOT producting a derivative work, though. You are only redistributing it. A derivative work from it would be something like an electronic christmas card program that has NOAO images hardcoded into it, or a poster. (As a side note, NOAO explicitly allows the authorship of derivative works for personal use, as long as you give attribution.) The only interaction between the SSC and the image occurs through Celestia, and both Celestia and the image using the gif, png, or whatever license. IOW, a zip file /is/ an aggregation, because the addon does not incorporate the image into it's substance. You do not own copyright on a zip file that you produce, and the addon is not, in a legal sense, the zip file, it is the actual work you created that is stored in the zip file.
SSCs, STCs, and the like are derivative works under intellectual property law. They are explicitly designed to work with a copyrighted program interface. The 'data format' of those files and the way the program interacts with those files is intellectual property that Chris owns, and has chosen to distribute under the GPL. Thus they must be under the GPL, and any other program that interacts with those files in the similar or a same way (not just a generic text program, but something like if they added SSCs to Orbiter) would have to be GPLed.
A perfect example of this is Linux. Linux is distributed under the GPL, and thus any derivative work (which includes both installable modules AND linux-specific user-space programs) is required to be distributed under the GPL, if you follow the terms of the GPL. The difference in that case is that Linus has specifically and publically stated that he will not consider them to be derivative works, and this means that someone who doesn't GPL his linux device driver will never have to worry about Linus suing him. (This whole issue has been widely discussed on the net, because RedHat is no longer GPLing their distribution. It contains proprietary user-space programs.)
In the case of a compiler, if I write a programming language and an interpreter for it, and distribute it under the GPL, any source code written in that language must be distributed under the GPL (it uses an interface that I own and have licensed under the GPL). This is not the case if I write an interpreter for a language I don't own, though, or if I write a compiler (because the compiled program no longer needs to interact with my software in order to function).
Anyone who writes an SSC holds the copyright on that SSC, but they can't distribute it under any license other than the GPL unless Chris either specifically gives them permission or gives everyone permission. He would do that by publically (in a way that could be documented, IOW) stating that he wouldn't consider certain items to be derivative works. Doing so doesn't change the GPL at all, but under the principle of estoppel he could no longer sue to enforce his license on those derivitave works. (Estoppel is the idea that if you take action on the basis of some statement that I assert to be true, I have no grounds to later sue you for doing so. I cannot lie to you in order to trick you into doing something that I can sue you for. When I say I won't sue, it is binding.)
BTW, Visible Earth images are copyright-free because NASA is an agency of the federal government, and the government is prohibited from owning a copyright. There's a bit of trivia for you.
I do have a clue, tho.
Not really illegal, since copyright is a civil issue. It's not a crime to violate a copyright, and only a probem if the copyright holder chooses to enforce it. If Chris doesn't care about addons that should technically be GPL'd but aren't, noone else can do anything about it or force him to do so.selden wrote:Revent,
Thanks for your attempt at clarification, which seems to make sense. Unfortunately, it means that many existing Addons probably are illegal.
OTOH, if the holder of a copyright tries to object to someone else using his work (that should be GPL'd), proving that it's required to be GPL would be a valid defense.
(This is separate from the issue that people often fail to give credit for the images that they use in the Addons that they've created.)
Many Addons include astronomical pictures which are derived from images which are not in the public domain. Paragraph 2b of the GNU General Public License essentially requires that all components of a work derived from a GPL'd product be covered by the GPL. Unfortunately, for example, the use of images provided on the Web by NOAO must comply with the terms of NOAO's license, which is not the GPL.
You're misunderstanding what the GPL means.
The images are a separate issue. Yes, redistributing an NOAO image without attribution IS a violation of their copyright, any they could restrict redistribution (though they don't for personal or educational use). Including their image in a zip file with your addon is NOT producting a derivative work, though. You are only redistributing it. A derivative work from it would be something like an electronic christmas card program that has NOAO images hardcoded into it, or a poster. (As a side note, NOAO explicitly allows the authorship of derivative works for personal use, as long as you give attribution.) The only interaction between the SSC and the image occurs through Celestia, and both Celestia and the image using the gif, png, or whatever license. IOW, a zip file /is/ an aggregation, because the addon does not incorporate the image into it's substance. You do not own copyright on a zip file that you produce, and the addon is not, in a legal sense, the zip file, it is the actual work you created that is stored in the zip file.
SSCs, STCs, and the like are derivative works under intellectual property law. They are explicitly designed to work with a copyrighted program interface. The 'data format' of those files and the way the program interacts with those files is intellectual property that Chris owns, and has chosen to distribute under the GPL. Thus they must be under the GPL, and any other program that interacts with those files in the similar or a same way (not just a generic text program, but something like if they added SSCs to Orbiter) would have to be GPLed.
A perfect example of this is Linux. Linux is distributed under the GPL, and thus any derivative work (which includes both installable modules AND linux-specific user-space programs) is required to be distributed under the GPL, if you follow the terms of the GPL. The difference in that case is that Linus has specifically and publically stated that he will not consider them to be derivative works, and this means that someone who doesn't GPL his linux device driver will never have to worry about Linus suing him. (This whole issue has been widely discussed on the net, because RedHat is no longer GPLing their distribution. It contains proprietary user-space programs.)
In the case of a compiler, if I write a programming language and an interpreter for it, and distribute it under the GPL, any source code written in that language must be distributed under the GPL (it uses an interface that I own and have licensed under the GPL). This is not the case if I write an interpreter for a language I don't own, though, or if I write a compiler (because the compiled program no longer needs to interact with my software in order to function).
Anyone who writes an SSC holds the copyright on that SSC, but they can't distribute it under any license other than the GPL unless Chris either specifically gives them permission or gives everyone permission. He would do that by publically (in a way that could be documented, IOW) stating that he wouldn't consider certain items to be derivative works. Doing so doesn't change the GPL at all, but under the principle of estoppel he could no longer sue to enforce his license on those derivitave works. (Estoppel is the idea that if you take action on the basis of some statement that I assert to be true, I have no grounds to later sue you for doing so. I cannot lie to you in order to trick you into doing something that I can sue you for. When I say I won't sue, it is binding.)
BTW, Visible Earth images are copyright-free because NASA is an agency of the federal government, and the government is prohibited from owning a copyright. There's a bit of trivia for you.