The Gaia spacecraft is an impressive feat of engineering. Its primary mission is to map the position and motion of more than a billion stars in our galaxy, creating the most comprehensive map of the Milky Way thus far. Gaia collects such a large amount of precision data that it can make discoveries well beyond its main mission. For example, by looking at the spectra of stars, astronomers can measure the mass of individual stars to within 25% accuracy. From the motion of stars, astronomers can measure the distribution of dark matter in the Milky Way. Gaia can also discover exoplanets when they pass in front of a star. But one of the more surprising uses is that Gaia could help us detect cosmic gravitational waves.