There are over 200 moons in our Solar System alone, but what is it that makes a moon a moon? Venture out into the Universe and there are moons of all shapes and sizes to discover. Some are made of rock, others ice and many of these natural satellites are home to curious features like active volcanoes and underground oceans. Why do some planets have no moons and others dozens? How do moons form? Is it possible for a moon to have its own moon? And how much more is there yet to be discovered? Starting with our own moon, Anna Gammon-Ross leads us on a journey through space to uncover the science behind these astronomical objects.