Buy a watch (no digit watch, but with hour/minute hands);
Now is time A, Devide the time A by 2, you get time B
Point time B directly to the sun, and 12 o'clock points to north.
e.g. It is 2:40pm, then time A is 14:40, time B is 7:20
point the position of 7:20 to the sun, 12:00 points to north.
If you don't have a watch and don't want to buy one, a clock is OK, but
a little heavy to hold about.