What constitutes a planetary system?

A planetary system is specifically defined as a system that includes a star and various celestial objects that orbit it, such as planets, asteroids, and comets. This definition emphasizes the relationship between the central star and the objects that are influenced by its gravitational pull. In our own Solar System, for example, the Sun is the star, and the planets, moons, asteroids, and comets all orbit around it. This characteristic defines a planetary system, making it distinct from other celestial structures.

The other options describe different astronomical concepts. A collection of moons orbiting a planet refers specifically to moon systems, which do not encompass the broader context of a star and its accompanying objects. A galaxy comprises numerous stars and their associated planetary systems, but it represents a much larger scale than a single planetary system. Lastly, a group of stars forming a constellation does not relate directly to any celestial objects that orbit those stars, as constellations are merely patterns seen from Earth rather than physical groupings in space.