Free Astronomy Magazine September-October 2026

SEPTEMBER-OCTOBER 2026 XMM-Newton & Chandra revise distance to the outer spiral arms by ESA P erhaps surprisingly, we don’t know much about the structure of our galaxy’s outer regions. It’s difficult to observe our galaxy from the inside; the Solar System is well embedded in its disc, prevent- ing a bird’s eye view, and many re- gions are obscured by thick clouds of cosmic dust. But this is changing: we’ve learnt a huge amount since the launch of ESA’s star-surveying Gaia space telescope. Using data col- lected by Gaia, scientists are cur- rently mapping the Milky Way galaxy in more detail than ever be- fore by measuring precise distances to its stars. Before Gaia, we weren’t even sure if our galaxy had two or