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Updated: Feb 21, 2026

Bringing the Visible Universe into Focus with Robo-AO
Published on: February 12, 2013
Mapping spiral structure on the far side of the Milky Way
Alberto Sanna1, Mark J Reid2, Thomas M Dame2
1Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany.
Abstract:
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 [Formula: see text] 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.
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