ANSWER:
IDL 8.2 is not officially supported on Mac OS X 10.10 (Yosemite). The officially support platforms for the current and various prior versions of IDL can be found though this page:
http://www.exelisvis.com/Support/Help...
That said, I understand that some IDL users have been able to get IDL 8.2 to run on this platform. Here is a link to an IDL forum thread that discusses this topic:
http://www.exelisvis.com/Support/Foru...
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Finally, note that the current version of IDL, v8.5.1, is officially supported on Mac OS X 10.10. Additional system dependencies are needed to run IDL 8.5 on Yosemite. See also:
http://www.exelisvis.com/Support/Help...
Regards,