Comet 15P/Finlay

Comets are icy bodies from the outer solar system that develop glowing heads (comae) and tails when they approach the Sun. As a comet nears perihelion — its closest point to the Sun — solar heating vaporises its ices, releasing dust and gas that form the characteristic tail. Comets have fascinated humanity for millennia and remain among the most unpredictable and rewarding objects to observe.

A comet's tail always points away from the Sun, pushed by solar radiation and the solar wind. There are typically two tails: a curved, yellowish dust tail and a straight, bluish ion (gas) tail. The comet's apparent brightness depends on its distance from both the Sun and Earth, its intrinsic activity, and how much dust and gas it produces. Some comets undergo sudden outbursts or fragment, making brightness predictions uncertain.

Periodic comets return on predictable schedules — short-period comets like Halley (76 years) and Encke (3.3 years) have well-known orbits. Long-period comets may take thousands of years to return, and some are on hyperbolic orbits that visit only once. New comets are discovered regularly by automated surveys such as Pan-STARRS, ATLAS, and the Zwicky Transient Facility.