The tail of the comet Halley is directed away from the sun due to the…

as the comet moves around the sun, the higher mass of the comet is pushed away due to centrifugal force only

as the comet rotates, the lighter mass of the comet is attracted by some star situated in the direction of the tail

the radiation pressure on the comet throwing its tail away from the sun

the tail of the comet always exists in the same orientation