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4.0 KiB
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32 lines
4.0 KiB
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<?xml version="1.0" encoding="ISO-8859-1" standalone="no"?>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>phase of the moon</title><link rel="stylesheet" href="../../jargon.css" type="text/css"/><meta name="generator" content="DocBook XSL Stylesheets V1.61.0"/><link rel="home" href="../index.html" title="The Jargon File"/><link rel="up" href="../P.html" title="P"/><link rel="previous" href="phase.html" title="phase"/><link rel="next" href="phase-wrapping.html" title="phase-wrapping"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">phase of the moon</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="phase.html">Prev</a> </td><th width="60%" align="center">P</th><td width="20%" align="right"> <a accesskey="n" href="phase-wrapping.html">Next</a></td></tr></table><hr/></div><dt><a id="phase-of-the-moon"/><dt xmlns="" id="phase-of-the-moon"><b>phase of the moon</b>: <span xmlns="http://www.w3.org/1999/xhtml" class="grammar">n.</span></dt></dt><dd><p> Used humorously as a random parameter on which something is said to
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depend. Sometimes implies unreliability of whatever is dependent, or that
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reliability seems to be dependent on conditions nobody has been able to
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determine. “<span class="quote">This feature depends on having the channel open in
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mumble mode, having the foo switch set, and on the phase of the
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moon.</span>” See also <a href="../H/heisenbug.html"><i class="glossterm">heisenbug</i></a>.</p><p>True story: Once upon a time there was a program bug that really did
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depend on the phase of the moon. There was a little subroutine that had
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traditionally been used in various programs at MIT to calculate an
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approximation to the moon's true phase. GLS incorporated this routine into
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a LISP program that, when it wrote out a file, would print a timestamp line
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almost 80 characters long. Very occasionally the first line of the message
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would be too long and would overflow onto the next line, and when the file
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was later read back in the program would <a href="../B/barf.html"><i class="glossterm">barf</i></a>. The
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length of the first line depended on both the precise date and time and the
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length of the phase specification when the timestamp was printed, and so
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the bug literally depended on the phase of the moon!</p><p>The first paper edition of the Jargon File (Steele-1983) included an
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example of one of the timestamp lines that exhibited this bug, but the
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typesetter ‘corrected’ it. This has since been described as
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the phase-of-the-moon-bug bug.</p><p>However, beware of assumptions. A few years ago, engineers of CERN
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(European Center for Nuclear Research) were baffled by some errors in
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experiments conducted with the LEP particle accelerator. As the formidable
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amount of data generated by such devices is heavily processed by computers
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before being seen by humans, many people suggested the software was somehow
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sensitive to the phase of the moon. A few desperate engineers discovered
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the truth; the error turned out to be the result of a tiny change in the
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geometry of the 27km circumference ring, physically caused by the
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deformation of the Earth by the passage of the Moon! This story has
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entered physics folklore as a Newtonian vengeance on particle physics and
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as an example of the relevance of the simplest and oldest physical laws to
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the most modern science.</p></dd><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="phase.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="../P.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="phase-wrapping.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">phase </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> phase-wrapping</td></tr></table></div></body></html>
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