From: Trans <transfire@...>
Date: 2008-08-06T08:57:28+09:00
Subject: Re: State of the Onion



On Aug 5, 10:08 am, Phlip <phlip2...@gmail.com> wrote:
> However, there's a difference between adding new features to a system and
> patching up flaws in its original design. In astronomy, the latter technique is
> called "adding epicycles".
>
> If you plot the relative course of planets around the Earth - the way they
> appear to move over time against the backdrop of stars - you will occasionally
> notice Mars moving retrograde.
>
> This is because you should be plotting Mars's absolute motion around the Sun. To
> plot it around the Earth, you must "add an epicycle" to Mars's presumed path -
> an extra loop it occasionally takes. Then, because of elliptical orbits, the
> more accurately you plot Mars's motion, the more small epicycles you must add.
> That's why "adding epicycles" means adding patches and compromises to maintain a
> bad design.

Ptolemy would be proud ;)

T.