you can not copyright an idea

I knew that, but I'm reading up on copyright law.
This made my day: According to copyright.gov one also can not copyright an Elvis sighting.

How do I protect my sighting of Elvis?
Copyright law does not protect sightings. However, copyright law will protect your photo (or other depiction) of your sighting of Elvis. File your claim to copyright online by means of the electronic Copyright Office (eCO). Pay the fee online and attach a copy of your photo. Or, go to the Copyright Office website, fill in Form CO, print it, and mail it together with your photo and fee. For more information on registration a copyright, see SL-35. No one can lawfully use your photo of your sighting, although someone else may file his own photo of his sighting. Copyright law protects the original photograph, not the subject of the photograph.

this ones great too

Can I get a star named after me and claim copyright to it?
No. There is a lot misunderstanding about this. Names are not protected by copyright. Publishers of publications such as a star registry may register a claim to copyright in the text of the volume [or book] containing the names the registry has assigned to stars, and perhaps the compilation of data; but such a registration would not extend protection to any of the individual star names appearing therein. Copyright registration of such a volume of star names does not confer any official or governmental status on any of the star names included in the volume. For further information on copyright protection and names, see Circular 34, Copyright Protection Not Available for Names, Titles, or Short Phrases