Computing the date of Thanksgiving (Was: food)

[Carol]

 Magpie:
> > > It's the third Thursday in November. Which sounds really random!
> > > 
> > 
> > Mike:
> > Ummm, it's the fourth Thursday, dear. :D
> 
> Magpie:
> It is? Oh well. I always thought it was the third. I just go with
when they tell me it is.

Carol responds:

At least it's easier to figure out than the first Sunday after the
first full moon after the twenty-first of March, which is how Easter
is computed.

Carol, who for some reason memorized that formula when she was about
ten and has never forgotten it