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 program 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.
However, beware of assumptions. A few years ago, engineers of CERN
(European Center for Nuclear Research) were baffled by some errors in
experiments conducted with the LEP particle accelerator. As the
formidable amount of data generated by such devices is heavily
processed by computers before being seen by humans, many people
suggested the software was somehow sensitive to the phase of the
moon. A few desperate engineers discovered the truth; the error
turned out to be the result of a tiny change in the geometry of the
27km circumference ring, physically caused by the deformation of the
Earth by the passage of the Moon! This story has entered physics
folklore as a Newtonian vengeance on particle physics and as an
example of the relevance of the simplest and oldest physical laws to
the most modern science.
[glossary]
[Reference(s) to this entry by made by: {cosmic rays}{POM}{sunspots}]