Galaxies

A galaxy is a massive, gravitationally bound system consisting of stars, stellar remnants, an interstellar medium of gas and dust, and dark matter. Roughly one hundred billion galaxies are scattered throughout our observable Universe, each a glorious system that might contain billions of stars.

Let's make a portrait of the Milky Way!
The basics of galaxy classification, using Hubble Space Telescope images.
Build a model of the Milky Way to discover what our galaxy contains.