What is one way of determining the direction of writing ?

The ending of sentences. Sometimes shorter sentences end before others, leaving a gap. They gap can show you where the writing is beginning through the ending of the words used.

radiative zone

explanation    

radiative zone is the layer of the sun which energy is transferred away from the core by radiation. although, the core is the only part of the sun that produces an appreciable amount of heat through fusion. in fact, 99% of the energy produced by the sun takes place within 24% of the sun's radius.