The tail of a comet is directed away from the sun primarily due to the radiation emitted by the sun exerting a radial pressure on the comet. This phenomenon is known as the solar wind effect.

The sun continuously emits a stream of charged particles called the solar wind. These charged particles, mainly electrons and protons, flow outward from the sun in all directions. When a comet approaches the sun in its elliptical orbit, the solar wind interacts with the comet`s nucleus and coma (a cloud of gas and dust surrounding the nucleus).

The solar wind particles collide with the coma and nucleus of the comet, exerting a pressure on them. This pressure pushes the lighter particles, such as gas and dust, away from the sun, creating a glowing tail that points away from the sun. The tail always extends in the opposite direction of the sun, regardless of the orientation of the comet.

It`s important to note that the tail of a comet does not always exist in the same orientation. As a comet moves along its orbit, the orientation of its tail can change due to various factors such as the direction and intensity of the solar wind, the shape of the coma, and the interaction with the magnetic field of the sun.

Therefore, the correct explanation is that the radiation emitted by the sun exerts a radial pressure on the comet, throwing its tail away from the sun.