Messier 13 – The Hercules Globular Cluster

Messier 13 is one of the finest globular clusters in the northern sky, located in the constellation Hercules at a distance of about 25,000 light-years. It contains several hundred thousand stars packed into a sphere roughly 145 light-years across, making it a spectacular target even for modest apertures. On a good night it is faintly visible to the naked eye, and through a telescope it resolves into a stunning tapestry of individual stars with a bright, condensed core.

This image combines three exposure lengths — 58 × 30 s, 44 × 60 s, and 101 × 90 s — all shot in a single night from San Pedro de Alcántara, Málaga, Spain (Bortle 7) using a Sky-Watcher Evostar 100 EDX refractor and a ZWO ASI 533 MC Pro cooled to −10 °C. The multiple exposure times were captured specifically to manage the wide dynamic range of the cluster, preserving detail in both the bright core and the faint outer halo simultaneously.

Processing was done entirely in PixInsight. The three integrations were color-calibrated with SPCC and combined using HDRComposition to recover the full dynamic range of the core. BlurXTerminator was applied for sharpening, NoiseXTerminator to reduce noise, and the stretch with Seti Astro’s Star Stretch was followed by some curves and colour saturation for final colour and tone adjustments.