Question

why does the tail of a comet always point away from the sun

Answer 1

The streams of dust and gas thus released form a huge, extremely tenuous atmosphere around the cometcalled the coma, and the force exerted on the coma by the Sun's radiation pressure and solar wind cause an enormous tail to form, which points away from the Sun.

Answer 2

In order to answer that question, you need to understand how the body of comet interacts and build itself according to gravitational field of the sun .. as the gravitational field of the head of the comet is more than the gravitational field on the tail, so head experience greater force as compared to tail.. so the head gets clump up more where as the tail due to the comet's motion and less force gets spread out and less denser.. like a ray of flashlight.. so the body of the comet changes its shape everytime slightly what we perceive as its tail always point away from it..