資料來源 : WordNet®

phase of the moon
     n : a time when the moon presents a particular recurring
         appearance

資料來源 : Free On-Line Dictionary of Computing

phase of the moon
     
        Used humorously as a random parameter on which something is
        said to depend.  Sometimes implies unreliability of whatever
        is dependent, or that reliability seems to be dependent on
        conditions nobody has been able to determine.  "This feature
        depends on having the channel open in mumble mode, having the
        foo switch set, and on the phase of the moon."
     
        See also {heisenbug}.
     
        True story: Once upon a time there was a {bug} that really did
        depend on the phase of the moon.  There was a little
        subroutine that had traditionally been used in various
        programs at {MIT} to calculate an approximation to the moon's
        true phase.  {GLS} incorporated this routine into a {Lisp}
        program that, when it wrote out a file, would print a
        timestamp line almost 80 characters long.  Very occasionally
        the first line of the message would be too long and would
        overflow onto the next line, and when the file was later read
        back in the program would {barf}.  The length of the first
        line depended on both the precise date and time and the length
        of the phase specification when the timestamp was printed, and
        so the bug literally depended on the phase of the moon!
     
        The first paper edition of the {Jargon File} (Steele-1983)
        included an example of one of the timestamp lines that
        exhibited this bug, but the typesetter "corrected" it.  This
        has since been described as the phase-of-the-moon-bug bug.
     
        [{Jargon File}]
     
        (1995-02-22)