Space Forum / Space Science / January 2008

-> -> | According to my calculations, Saturn passes Jupiter in its orbit once  
-> -> | every twenty Earth years.  
->    
-> How did you figure that out? Jupiter revolves around the sun every 11  
-> years, roughly, and Saturn does so every 29 years. In order to  
-> calculate how often they pass each other, so Jupiter passes between  
-> Saturn and the sun, you must first figure out theur angular velocities,  
-> as seen from the sun. Subtract Saturn's angular velocity from  
-> Jupiter's, then take the reciprocal of the result, and you'll get the  
-> time you're trying to calculate. So the formula is:  
->    
-> T = 1 / ((1 / 11) - (1 / 29))  
->    
-> According to the calculator I have beside me here, the answer is about  
-> 17.7 years.  
->    
->                            dow  
 
I put in more accurate values for the orbital periods of Jupiter and
Saturn, and the time does indeed come out to nearly 20 years.
 
Sorry about that.
 
                              dow

Leafing through alt.sci.planetary, I read David Williams's message of
Fri, 11 Jan 2008:

[Samuel, cross-posting:]

Presumably he used more accurate source figures.  (I'm also guessing he
is not reading alt.sci.planetary to reply for himself, but I could be
wrong about that.)

I repeated your calculation with an extra decimal place (11.9 and 29.5,
respectively), and found Samuel is accurate to the nearest year.