Answer + Explanation:
Well, first of all, a star is a large ball of gas that undergoes nuclear fusion. So by this definition, a comet is not a star, since it is made of ice and dirt that is running around in space. Stars shine on their own or omit light within their own wavelengths, but comets only shine because they reflect light, hence they are not a star. Comets are created by gravitational pulls and formations broken off of actual planets when they are destroyed, which is why it takes a long time. So as for the tail of the comet, it is more unique. Radiation from the sun pushes dust particles faraway from the coma, forming a dust tail, while charged particles from the sun convert a number of the comet's gases into ions, forming an ion tail. Since comet tails are shaped by sunlight and also solar radiation, they always point far from the sun.
Hope this helped!! :)