Messier 30 (NGC 7099)
Coordinates, Gaia DR3 distance (8.46 kpc), magnitude 7.19, core-collapse double blue-straggler sequence, and observing guide for M30 in Capricornus.
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) | 7.19 mag | ± 0.05 mag | Integrated photoelectric & CCD photometry | definitive | Catalog of Parameters for Milky Way Globular Clusters |
| Heliocentric distance | 27600 ly | ± 300 ly | Gaia EDR3 parallax + dynamical fitting (8.46 ± 0.09 kpc) (J2016.0) | definitive | ESA Gaia Archive — Data Release 3 |
| Apparent tidal diameter | 12 arcmin | ± 1 arcmin | Outer surface-density profile fitting | high-confidence | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Isochrone turnoff age | 13 Gyr | ± 0.5 Gyr | HST ACS metal-poor turnoff calibration | model-dependent | Catalog of Parameters for Milky Way Globular Clusters |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Messier 30 (NGC 7099 Core-Collapsed Cluster) at RA 21h 40m 22.12s, Dec -23° 10′ 47.5″ within Capricornus, 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 30 (NGC 7099) is an ancient, extremely metal-poor ([Fe/H] = −2.27 dex) globular cluster situated 27,600 light-years (8.46 ± 0.09 kiloparsecs) away in southeastern Capricornus. Discovered by Charles Messier on August 3, 1764, as the final object logged during his intense 1764 observing campaign, M30 spans roughly 95 light-years physically and travels along a retrograde Galactic orbit inclined steeply against the Milky Way disk.
Like M15 in Pegasus, M30 has undergone gravothermal core collapse: half of its ~160,000-solar-mass stellar population is compressed inside a sphere only 17 light-years across, and its central stellar density exceeds one million solar masses per cubic parsec. In 2009, Hubble Space Telescope WFPC2 photometry of M30 made a landmark discovery by resolving two distinct, parallel sequences of blue straggler stars in its color-magnitude diagram.
The bluer sequence of M30's blue stragglers matches hydrodynamic models of direct head-on stellar collisions driven by the rapid density spike during core collapse 1–2 billion years ago, whereas the redder sequence traces ongoing binary mass transfer—providing a fossil clock for when the cluster's core collapsed.
Practical Visual Observing Guide
- Located 0.6° west-southwest of the 5.4-magnitude star 41 Capricorni, about 3.3° southeast of Zeta Capricorni.
- In 10×50 binoculars M30 sits immediately alongside 41 Capricorni as a 7.2-magnitude fuzzy spot.
- Through a 120–200 mm telescope at 120×–180×, M30 earns its 'Jellyfish' nickname from three prominent linear chains ('tentacles') of 12th-magnitude stars streaming northward from its hyper-dense, pinpoint core.
Catalog Cross-Identifications & Aliases
Common Aliases: M30 · NGC 7099 · Jellyfish Globular
| Catalog Authority | Identifier |
|---|---|
| MESSIER | M 30 |
| NGC | NGC 7099 |
| SIMBAD | M 30 |
| WIKIDATA | Q11378 |
Related Objects, Comparisons & Guides
Messier 15 (NGC 7078 Core-Collapsed Cluster)
Coordinates, Gaia DR3 distance (10.71 kpc), magnitude 6.20, core-collapse physics, Pease 1 planetary nebula, and observing guide for M15 in Pegasus.
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 55 (NGC 6809 Summer Rose Star)
Coordinates, Gaia DR3 distance (5.35 kpc), magnitude 6.32, loose Class XI structure, and observing guide for Messier 55 in Sagittarius.
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.
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.
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