I think you are looking for an answer like this. A user has asked for help on how to open
fits file type that is not supported by default ubuntu programs.
IraGainesUK has posted the answer at http://ubuntuforums.org/showpost.php?p=12242314&postcount=5
I also can't believe it me took this long to figure out how to do such
a simple thing in 12.04(!!), but the simple way is this:
1) Install Ubuntu Tweak:
sudo add-apt-repository ppa:tualatrix/ppa
sudo apt-get update
sudo apt-get install ubuntu-tweak
2) Open it up on the command line:
3) Navigate to
File Type Manager and click
All. This may
take a moment whilst it scans all your mimetypes.
Only show filetypes with associated applications at the
bottom (again, may take some time).
5) Click anywhere in the right-hand panel and start typing
begin searching for the
FITS document mimetype. Hopefully you should
6) Double click it, and click
Add and then your custom command (for
me, topcat, for you, ds9).
I should note that I have tested the solution and it worked well for me.