->  -> That's when we are at perihelion. 
 
->  DW> That is one of the two factors that are involved. The other
is the tilt 
->  DW> of the Earth's axis. The two factors almost cancel each other out 
 
-> Kepler's Law plays a role. 
  
The one that is equivalent to the Law of Conservation of Angular 
Momentum is certainly relevant. It means that Earth's orbital motion 
around the sun is more rapid when Earth is close to perihelion, in 
January, than at aphelion. Since the rate of the sun's apparent motion 
across the sky is (roughly) the difference between Earth's rotational 
and orbital speeds, the sun apparently moves more *slowly* in January 
than in July, so sundials lose time in northern winter. 
  
But there's another effect that makes sundials run slow close to the 
solstices (both of them), and fast near the equinoxes. Added to the 
perihelion effect, this makes sundials lose time *a lot* during northern 
winter, and only a little in northern summer. 
  
I posted a program that shows the math. It's really not hard. 
  
                           dow 
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