Planetary moons are natural satellites that orbit planets in our solar system and beyond. They vary in size, composition, and number, with some planets having many moons while others have none. For example, Jupiter has over 79 known moons, including the largest moon, Ganymede, which is even bigger than the planet Mercury. Moons can be rocky, icy, or gaseous, and they often influence their parent planet's tides and rotation. Some moons, like Europa, are of great interest to scientists because they may harbor conditions suitable for life. Understanding these celestial bodies helps us learn more about the formation and evolution of planetary systems.