Milky Way spiral arms and bar resonances revealed by Gaia DR2. Panel a: Gaia DR2 based spiral arms shown by symbols with error bars, while two grey-shaded areas show the location of stars likely associated with corotation and OLR of the Milky Way bar, all structures were identified using guiding coordinate space densities and radial velocity distributions. Large symbols without error bars depict the position of high-mass star-forming regions with trigonometric parallaxes measured by the VLBA (Reid et al. 2014). These sources trace the gaseous and young star spiral arms in the Milky Way (Scutum-Centaurus, Sagittarius, Local, and Perseus). The grey oval represents the orientation of the Milky Way bar, and the solar position is indicated by a yellow star. Panels b and c: two new artistic renderings of a Milky Way spiral galaxy including the four-armed tightly wound spiral arms revealed by Gaia DR2. Modified images of original Milky Way galaxy rendering by Robert Hurt and Nick Risinger.