How do scientists make a map of the Milky Way?

Mapping the Milky Way is challenging because we are embedded inside its disk and cannot step outside to photograph it. Astronomers combine parallax distances, proper motions, radial velocities, and infrared or radio observations of dust and gas to reconstruct the Galaxy’s structure. ESA’s Gaia mission has provided extraordinarily detailed measurements for more than a billion stars, revealing spiral arms, streams, and the Milky Way’s shape in unprecedented detail. Radio maps of gas and dust also help trace regions hidden from visible light.