In fact, in order to find the really true north, you have to consider also the date and time of observation, your geographical location, your altitude, altitude of the horizon line, the temperature in your place and temperature gradient in atmosphere along the direction line to the Sun, the same for air pressure, and for air humidity. Everything else is just a basic math i.o.w. the answer depends on precision (or task) you are going to achieve from such an observation. Otherwise the answer is as simple as pointing to the right looking at sunset, and to the left at sunrise