Sanna, Alberto, Reid, Mark J., Dame, Thomas M., Menten, Karl M., and Brunthaler, Andreas. 2017. "Mapping spiral structure on the far side of the Milky Way." Science 358:227-230. https://doi.org/10.1126/science.aan5452
Little is known about the portion of the Milky Way lying beyond the Galactic center at distances of more than 9 kiloparsec from the Sun. These regions are opaque at optical wavelengths because of absorption by interstellar dust, and distances are very large and hard to measure. We report a direct trigonometric parallax distance of 20.4-2.2 2.8 kiloparsec obtained with the Very Long Baseline Array to a water maser source in a region of active star formation. These measurements allow us to shed light on Galactic spiral structure by locating the Scutum-Centaurus spiral arm as it passes through the far side of the Milky Way and to validate a kinematic method for determining distances in this region on the basis of transverse motions.