Again, agreed that the question was lacking. I was not aware the original post was back-modified; that explains your reply.
I was led to this post in the first place after reading the pod for Time::Julian, which had a bothersome Errata that refered me to Astro::Time which uses the term Modified Julian day with only (JD-
2400000.5) as a definition. I got a hit for perlmonks and was reassured, but then disappointed reading the responses. I think I'll write my own code rather than use a module. Probably wont post it though.