In general (see Fig. 3-24), comets have a dust tail, consisting of dust particles pushed awayfrom the Sun by the pressure of sunlight. Why is this tail often curved?

Comets consists of three main parts; tail, coma and the nucleus. Sunlight striking dust grains imparts a tiny force to them, a process known as radiation pressure. The tail of a comet pushed out by radiation pressure is made of dust particles. Magnetic fields carried along by the solar wind enhance its effect on the comet’s tail, helping to drag matter out of the coma and channel its flow, just as magnetic fields in the Earth’s atmosphere channel particles to form the aurora.
Thus, two forces, radiation pressure and the solar wind, act on the comet to drive a tail. Because those forces are directed away from the Sun, and the tail even points out ahead of the comet as it moves away from the Sun. That is why the tail of a comet is often curved.