What is the name of the galaxy we live in?

The Milky Way, named for how it looks from the ground - a spilled band of light - and the word galaxy comes from the Greek for milk, so the name is a tautology in two languages. It is a barred spiral of a few hundred billion stars, and we are about two thirds of the way out on a minor arm.

That nobody knew it was one galaxy among many until 1925 is worth sitting with. The fuzzy spirals in telescopes were assumed to be clouds within our own system, and the question was serious enough to be staged as a formal debate in 1920. Edwin Hubble settled it by finding a particular kind of variable star in Andromeda whose true brightness is calculable, and therefore its distance - which put it far outside anything that could be called our galaxy. The universe got very much larger in a single measurement.

We cannot photograph it from outside and never will, so every image of the Milky Way is an artist's reconstruction from measurements taken inside it - which is a bit like mapping a forest from one tree. Its shape was worked out from star counts, radio surveys of hydrogen, and more recently the Gaia satellite, which has measured positions and motions for nearly two billion stars. It is also on a collision course with Andromeda in about four and a half billion years.