Visitors from the outer Solar System, comets are among the most dynamic and unpredictable targets in astrophotography - each one unique, each one changing from night to night as it sweeps around the Sun.
Comets are ancient bodies, remnants from the formation of the Solar System, preserved in deep freeze in the outer reaches beyond Neptune. When their orbits bring them toward the inner Solar System, the Sun's heat begins to sublimate their ices, releasing gas and dust that forms the distinctive coma and tail that makes them visible from Earth.
The ion tail always points directly away from the Sun, pushed by the solar wind. The dust tail curves gently behind the comet's path, following its orbit. The two tails often have slightly different colours and structures, and both change on timescales of hours as the comet's activity fluctuates.
Comets present a unique trackingThe mount turning slowly to cancel out Earth's rotation, so a star stays in the same spot on the sensor instead of drifting into a line. challenge - they move against the background stars, meaning a long exposure will either trail the comet nucleus or trail the stars. Many astrophotographers capture separate exposures tracked on the comet and on the stars, then combine them in processing.
