The tail of a comet always points

Concept

A comet develops two distinct tails when it nears the Sun: solar heating vaporises ices in its nucleus, releasing gas (which ionises) and dust. The solar wind -- a stream of charged particles from the Sun -- sweeps the ionised gas almost exactly along the Sun-to-comet line, forming a straight tail; radiation pressure from sunlight pushes the heavier dust particles outward too, though the dust tail curves slightly because the dust also carries the comet's own orbital motion. Both tails, straight or curved, extend on the side of the comet away from the Sun.

Application

Because both driving forces -- solar wind and radiation pressure -- originate at the Sun and act outward from it, the ion tail's orientation depends only on where the Sun is relative to the comet at that moment, never on the comet's direction of travel or on a fixed compass bearing; the dust tail also extends broadly away from the Sun, though it curves somewhat toward the comet's orbital path since dust particles retain some of the comet's own motion. Either way, the tail always points away from the sun.

Cross-check

This explains an observation that a simple 'trailing behind the motion' idea cannot: after a comet passes closest to the Sun and starts moving away, its straight ion tail still points away from the Sun, which means that tail now leads the comet rather than trailing it -- confirming that the Sun's position, not the direction of motion, governs the ion tail's orientation; the dust tail, while also swept outward, curves partway toward the comet's own orbital path.