Messier 13 (Great Globular Cluster in Hercules)
Coordinates, Gaia DR3 distance (7.42 kpc), visual magnitude 5.78, and Keystone finder guide for Messier 13 (NGC 6205) in Hercules.
Provenance-Backed Scientific Measurements
Every measurement below preserves its unit, uncertainty interval, observational method, reference epoch, quality status, and primary catalog source. See Uncertainty & Provenance for how competing measurements are handled.
| Parameter | Value | Uncertainty | Method & Epoch | Quality Status | Source Archive |
|---|---|---|---|---|---|
| Integrated visual magnitude (V) | 5.78 mag | ± 0.05 mag | Integrated photoelectric & CCD aperture photometry (J2000.0) | definitive | Catalog of Parameters for Milky Way Globular Clusters |
| Heliocentric distance | 7420 pc | ± 80 pc | Combined Gaia EDR3 parallax, RR Lyrae & dynamical modeling (J2016.0) | high-confidence | Catalog of Parameters for Milky Way Globular Clusters |
| Distance in light-years | 24200 ly | ± 260 ly | Converted from 7.42 ± 0.08 kpc (Vasiliev & Baumgardt 2021) (J2016.0) | high-confidence | Catalog of Parameters for Milky Way Globular Clusters |
| Apparent tidal diameter | 20 arcmin | ± 1.5 arcmin | Outer surface-density profile fitting | high-confidence | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Metallicity [Fe/H] | -1.53 dex | ± 0.04 dex | High-resolution red-giant branch spectroscopy | high-confidence | Catalog of Parameters for Milky Way Globular Clusters |
| Main-sequence turnoff age | 11.65 Gyr | ± 0.45 Gyr | HST ACS main-sequence turnoff isochrone fitting | model-dependent | Catalog of Parameters for Milky Way Globular Clusters |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Messier 13 (Hercules Globular Cluster) at RA 16h 41m 41.24s, Dec +36° 27′ 35.5″ within Hercules, alongside peak meridian transit altitudes for 40°N and 30°S observers. Use the RA/Dec Coordinate Converter to compute exact culmination altitude for your latitude.
Astrophysical Context & Structure
Messier 13 (NGC 6205) is the premier globular cluster of the northern sky, orbiting in the Milky Way halo at a heliocentric distance of 7.42 ± 0.08 kiloparsecs (about 24,200 light-years). First noted by Edmond Halley in 1714 and cataloged by Charles Messier on June 1, 1764, the cluster binds roughly 400,000 ancient Population II stars within a physical diameter of 145 light-years. In the central parsec, stellar densities exceed 100 stars per cubic parsec—more than a thousand times denser than the solar neighborhood.
Spectroscopic surveys show that M13 has a mean iron abundance of [Fe/H] = −1.53 dex, meaning its stars contain roughly 3% of the Sun's heavy-element ratio. Despite this low overall metallicity, Hubble Space Telescope ultraviolet photometry and high-resolution ground-based spectroscopy reveal multiple stellar subpopulations with strong sodium–oxygen and aluminum–magnesium anticorrelations, indicating rapid chemical self-enrichment by asymptotic giant branch winds or fast-rotating massive stars during the cluster's first 100 million years.
Because M13 lies 40.9° above the Galactic plane, foreground interstellar dust extinction along our line of sight is almost negligible (E(B−V) ≈ 0.02 mag). That clean sightline makes M13 an essential benchmark for calibrating extreme horizontal-branch stars ('blue hook' hot subdwarfs) and testing stellar evolution isochrones against Gaia DR3 astrometry.
Practical Visual Observing Guide
- Located one-third of the way south from Eta Herculis (η Her) toward Zeta Herculis (ζ Her) along the western edge of the Keystone asterism in Hercules.
- At magnitude 5.78, M13 is faintly visible to the naked eye under Bortle 1–3 dark skies and appears as a bright, round glow in 7×50 or 10×50 binoculars flanked by two 7th-magnitude field stars (HD 150679 and HD 150998).
- A 100–150 mm aperture telescope at 100×–150× resolves hundreds of 12th-to-14th magnitude red giants across the outer halo; apertures of 200 mm and larger resolve the dense core and reveal the dark three-armed 'Propeller' dust/star-poor lane near the southeastern rim.
Catalog Cross-Identifications & Aliases
Common Aliases: M13 · NGC 6205 · Hercules Globular Cluster
| Catalog Authority | Identifier |
|---|---|
| MESSIER | M 13 |
| NGC | NGC 6205 |
| SIMBAD | M 13 |
| WIKIDATA | Q11312 |
Related Objects, Comparisons & Guides
Messier 92 (NGC 6341 in Hercules)
Coordinates, Gaia distance (8.50 kpc), metal-poor [Fe/H] = −2.31 dex, and observing guide for ancient globular cluster Messier 92 in Hercules.
Omega Centauri (NGC 5139 Cluster)
Coordinates, Gaia DR3 distance (5.43 kpc), magnitude 3.68, and multi-population core data for Omega Centauri (NGC 5139) in Centaurus.
47 Tucanae (NGC 104 Globular Cluster)
Coordinates, Gaia distance (4.52 kpc), magnitude 4.09, millisecond pulsar core, and observing guide for 47 Tucanae (NGC 104).
Messier 13 vs Omega Centauri Comparison
Side-by-side comparison of Messier 13 (Great Hercules Cluster) and Omega Centauri (NGC 5139): mass, distance, apparent magnitude, and visual resolution.
Messier 13 vs Messier 92 Hercules Globulars
Compare the twin Hercules globular clusters Messier 13 (NGC 6205) and Messier 92 (NGC 6341) in age, metallicity, core concentration, and eyepiece resolution.
Globular Cluster Resolution & Southern Gems
How to resolve ancient halo globular clusters—Messier 13, Messier 92, Omega Centauri, and 47 Tucanae—from outer red giants to dense Shapley-Sawyer cores.
Small-Telescope Messier Objects Tour (80–150mm)
Curated seasonal tour of flagship Messier clusters, nebulae, and galaxies optimized for 80 mm to 150 mm (3-inch to 6-inch) refractors and reflectors.
Apparent vs Absolute Magnitude Explained
Understand the logarithmic Pogson astronomical magnitude scale, apparent visual magnitude (m), absolute magnitude (M at 10 parsecs), and bolometric corrections.
Surface Brightness & Extended Objects Guide
Why surface brightness (mag/arcsec²) governs nebula and galaxy visibility more than integrated magnitude, and how exit pupil controls eyepiece contrast.
Trigonometric Parallax, Parsecs & Gaia DR3
How trigonometric parallax (d_pc = 1 / p_arcsec), the distance modulus equation, Hipparcos, and Gaia DR3 microarcsecond astrometry measure cosmic distances.
Messier Catalog (M) Objects & Cross-Reference
Guide and cross-walk to Charles Messier's flagship deep-sky catalog (M1 to M104 in FastAstro), linking Messier numbers to NGC IDs, distances, and magnitudes.
Milky Way Globular Clusters Reference Catalog
Cross-reference catalog of Milky Way halo globular clusters (Harris / Gaia EDR3) comparing Messier 13, Omega Centauri, Messier 92, and 47 Tucanae.
Scientific Sources & Dataset Provenance
- Catalog of Parameters for Milky Way Globular Clusters (2010 / 2021 Gaia EDR3 revision): Harris, W. E. 1996 (2010 ed.), AJ, 112, 1487; Vasiliev, E. & Baumgardt, H. 2021, MNRAS, 505, 5978 — McMaster University / Gaia EDR3 Cluster Survey
- ESA Gaia Archive — Data Release 3 (DR3 (2022-06-13)): Gaia Collaboration, Vallenari, A., et al. 2023, A&A, 674, A1 (Gaia Data Release 3) — European Space Agency / Gaia DPAC
- SIMBAD Astronomical Database (CDS) (2026-10 release): Wenger, M., et al. 2000, A&AS, 143, 9 (The SIMBAD astronomical database) — Centre de Données astronomiques de Strasbourg