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The Milky Way is the barred spiral galaxy containing the Solar system. Its galactic disk, central stellar bar and surrounding stellar halo are viewed from inside the disk, so distance and obscuration complicate attempts to reconstruct the whole system. Radio astronomy supplies a geometric route through the obscuring interstellar dust: masers near young massive stars act as compact markers whose parallaxes and proper motions can be measured by very-long-baseline interferometry. A 2019 analysis of about 200 such markers mapped spiral structure and constrained the rotation curve using their three-dimensional motions. These measurements connect the familiar bright band along the galactic plane with a spatial and dynamical model.^[ref]

Face-on, the Milky Way is a barred spiral galaxy: a central bulge and bar of scale a few kiloparsecs lie inside a disk of stellar radius roughly $15\mathrm{kpc}$, with spiral arms containing gas, dust, H II regions and young stars. Recent star formation is concentrated in molecular clouds and arm complexes. The Sun lies in the disk about $8\mathrm{kpc}$ from the centre in the source's convention. Old stars are also present throughout the disk, while the bulge, thick disk and extended stellar halo contain important old populations. Globular clusters occupy a roughly spheroidal halo extending well beyond the bright disk.