How do I convert a date such as 12/31/1979 to Julian date in FME?

Should be able to do this with the DateTimeConverter. 

Set the Input format to:

%m/%d/%Y

And the output format to:

%y%j

More Date/Time Functions and explanations here if needed.

Hope that helps. 

%m/%d/%Y

%y%j

Thanks chrisatsafe. A follow up question, how can I extract a four digit year instead of two?

Ignore the follow up question. I figured it out, I use uppercase "Y" instead of lowercase "y". Thanks a lot for your help.