Messier 15 (NGC 7078)
Coordinates, Gaia DR3 distance (10.71 kpc), magnitude 6.20, core-collapse physics, Pease 1 planetary nebula, and observing guide for M15 in Pegasus.
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) | 6.2 mag | ± 0.05 mag | Integrated photoelectric & CCD photometry | definitive | Catalog of Parameters for Milky Way Globular Clusters |
| Heliocentric distance | 34900 ly | ± 350 ly | Gaia EDR3 parallax + kinematic modeling (10.71 ± 0.10 kpc) (J2016.0) | definitive | ESA Gaia Archive — Data Release 3 |
| Apparent tidal diameter | 18 arcmin | ± 1.5 arcmin | Outer surface-density profile fitting | high-confidence | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Isochrone turnoff age | 13.2 Gyr | ± 0.5 Gyr | HST ACS metal-poor main-sequence turnoff calibration | model-dependent | Catalog of Parameters for Milky Way Globular Clusters |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Messier 15 (NGC 7078 Core-Collapsed Cluster) at RA 21h 29m 58.33s, Dec +12° 10′ 01.2″ within Pegasus, 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 15 (NGC 7078) is one of the oldest, densest, and most metal-poor globular clusters in the Milky Way, orbiting 34,900 light-years (10.71 ± 0.10 kiloparsecs) away in western Pegasus. Discovered by Jean-Dominique Maraldi on September 7, 1746, and cataloged by Charles Messier in 1764, M15 has an iron abundance of [Fe/H] = −2.37 dex—less than 0.45% of the Sun's heavy-element ratio—and an isochrone age of 13.2 ± 0.5 billion years, dating back to the earliest assembly epoch of the Galactic halo.
Unlike normal globular clusters with flat isothermal cores, M15 is the textbook archetype of a 'core-collapsed' cluster: gravothermal instability driven by two-body stellar encounters has caused its central region to contract into a razor-sharp power-law density cusp. Half of M15's entire ~560,000-solar-mass stellar population is packed within a radius of just 10 light-years, where intense dynamical interactions have spawned at least nine radio millisecond pulsars (including the relativistic double-neutron-star binary PSR B2127+11C) and two ultraluminous low-mass X-ray binaries (M15 X-1 and X-2).
In 1928, Francis Gladheim Pease used the 100-inch Mount Wilson reflector to discover K 648 (Pease 1) inside M15—the very first planetary nebula ever identified within a globular cluster, formed just ~4,000 years ago probably from a merged blue-straggler progenitor.
Practical Visual Observing Guide
- Easy to locate by extending the line from Theta Pegasi (Biham) through brilliant orange Enif (ε Pegasi) 4.2° further northwest; a 6th-magnitude field star sits 7′ east of the cluster.
- Visible in 7×50 binoculars at magnitude 6.20, M15 immediately displays a blazing, star-like central nucleus surrounded by a softer outer halo in any 80–120 mm telescope.
- With a 200–300 mm aperture at 200×–300× and an O-III filter blinked in and out of the light path, experienced observers can detect the 13.8-magnitude planetary nebula Pease 1 just 27 arcseconds northwest of the core.
Catalog Cross-Identifications & Aliases
Common Aliases: M15 · NGC 7078 · Great Pegasus Cluster
| Catalog Authority | Identifier |
|---|---|
| MESSIER | M 15 |
| NGC | NGC 7078 |
| SIMBAD | M 15 |
| WIKIDATA | Q11330 |
Related Objects, Comparisons & Guides
Messier 2 (NGC 7089 Globular Cluster)
Coordinates, Gaia DR3 distance (11.69 kpc), magnitude 6.47, Gaia-Enceladus origin, and observing guide for Messier 2 (NGC 7089) in Aquarius.
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.
Messier 30 (NGC 7099 Core-Collapsed Cluster)
Coordinates, Gaia DR3 distance (8.46 kpc), magnitude 7.19, core-collapse double blue-straggler sequence, and observing guide for M30 in Capricornus.
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.
Measurement Uncertainty & Optics in Astronomy
How random vs systematic errors, asymmetric error bars, model dependencies, and optical aperture/exit-pupil limits shape astronomical measurements.
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