Brad Klee kindly offered http://www.orbitsimulator.com/gravity/articles/pluto.html . So 247.92065 "JulianYears" is an oversimplification representing some average over some unspecified period. We need something much fancier than error brackets here, people. Definately. (Note in the following the hassle created by the Union thugs' demotion of Pluto.) On Fri, Apr 26, 2019 at 10:57 PM Bill Gosper <billgosper@gmail.com> wrote:
Wikipedia: Under some circumstances, a resonant system can be stable and self-correcting, so that the bodies remain in resonance. Examples are the 1:2:4 resonance of Jupiter <https://en.wikipedia.org/wiki/Jupiter>'s moons Ganymede <https://en.wikipedia.org/wiki/Ganymede_(moon)>, Europa <https://en.wikipedia.org/wiki/Europa_(moon)> and Io <https://en.wikipedia.org/wiki/Io_(moon)>, and the 2:3 resonance between Pluto <https://en.wikipedia.org/wiki/Pluto> and Neptune <https://en.wikipedia.org/wiki/Neptune>.
In[234]:= MinorPlanetData["Pluto"][EntityProperty["MinorPlanet", "OrbitPeriod"]]
Out[234]= Quantity[247.92065, "JulianYears"]
In[235]:= PlanetData["Neptune"][EntityProperty["Planet", "OrbitPeriod"]]
Out[235]= Quantity[164.79132, "JulianYears"]
In[236]:= ContinuedFraction[%%/%]
Out[236]= {1, 1, 1, 55, 1, 1, 1, 7}
That's a fairly lousy approximation to 2:3. What's going on? —rwg