Gaia, a mission from the European Space Agency (ESA), aims to chart a 3-D map of the Milky Way by surveying more than 1 billion stars, amounting to about 1 percent of the stars in the galaxy. Its goal is to make the largest, most precise map of where Earth dwells by observing the position of each of these stars 70 times over five years.
To pinpoint the position of a star in 3-D — a field known as astrometry — Gaia will measure the distance of the star from the Sun. The satellite will do so by watching how its position shifts over time. As the Earth orbits the Sun, the apparent positions of stars change with regard to each other due to how our viewpoint has moved, a phenomenon known as parallax.