From: "Strong, Lee" <StrongL@MTMC.ARMY.MIL>
To: "WSFAList (E-mail)" <WSFAList@keithlynch.net>
Subject: [WSFA] Constructing Realistic Solar Systems
Date: Tue, 17 Jun 2003 14:21:12 -0400
Reply-To: WSFA members <WSFAlist@keithlynch.net>

	Ron Kean provided a brief discussion of (1) Kepler's Third Law and
(2) the difficulty of having closely packed planetary orbits in response to
my request for help with designing a fantasy solar system.  Thank you, Ron;
I found your discussion very helpful.
	Ron alluded to the Sol System planets being spaced out according to
a rough formula.  You are probably thinking of Bode's Law, which states that
average planetary orbital distances from the Sun are (4+N)/10 astronomical
units where N is the series 0, 3, 6, 12, 24, 48, etc.  The "Law" fails for
Neptune but works for the other major planets, Ceres and Pluto.  The "Law"
should be understood as an approximation, not a hard description of orbits.
I used a variant of Bode's Law to design my first draft of the solar system
of the imaginary Sol-like star Fous, but changed the values to (6+N)/10,
where N is the series 1, 2, 3,...12.  This created 12 planetary orbits with
a uniform spacing of 9.3 million miles apart.  The innermost planetary orbit
replicates Venus and planetary orbit 10 replicates Mars.  This put 9 planets
in the habitable zone -- counting Mars as habitable -- and created a very
interesting night time sky for the inhabitants of the middle solar system.
(The 3 planets outside the habitable zone are essentially conversation
pieces thrown in for symmetry.)  There are no moons in the Fous system and
the inhabitants set calendars by the stars and other planets.  My knowldge
of astronomy failed when I tried to calculate the various planetary years
(in standard days)... which is desirable for the author to know when
discussing the timing of festivals and such.  Thanks again to Ron for the
pointer.
	WSFA:  the place to go for answers to life's questions.