TIME AND MOTION 



65 



which is shown in Figure 13. The central core 

 represents the sun, which is assumed to be at 

 rest, and its space-time path is therefore repre- 

 sented as a straiglit Hne. The innermost helix 



Figure 13 

 Space-Time Map of Sun and Three Planets 



represents the orbital motion of the planet Mer- 

 cury ; the next represents Venus ; and the outer 

 one that interesting double planet, the earth 

 and moon. This outer helix goes through one 

 complete period of revolution, and therefore the 

 interval of time between the bottom of the pic- 



