47 Tucanae (NGC 104)
Coordinates, Gaia distance (4.52 kpc), magnitude 4.09, millisecond pulsar core, and observing guide for 47 Tucanae (NGC 104).
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) | 4.09 mag | ± 0.05 mag | Integrated photoelectric aperture photometry | definitive | Catalog of Parameters for Milky Way Globular Clusters |
| Heliocentric distance | 4520 pc | ± 30 pc | Gaia EDR3 parallax + detached eclipsing binary + white-dwarf cooling sequence (J2016.0) | definitive | Catalog of Parameters for Milky Way Globular Clusters |
| Metallicity [Fe/H] | -0.72 dex | ± 0.04 dex | High-resolution spectroscopy of red giants | definitive | Catalog of Parameters for Milky Way Globular Clusters |
| Apparent diameter | 44 arcmin | ± 2 arcmin | Deep surface-brightness profile | high-confidence | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots 47 Tucanae (NGC 104 Globular Cluster) at RA 00h 24m 05.30s, Dec -72° 04′ 52.6″ within Tucana (Southern Sky), 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
47 Tucanae (NGC 104) is the second brightest and second most massive globular cluster in the sky after Omega Centauri, located just 4.52 ± 0.03 kiloparsecs (14,740 light-years) from Earth in the far-southern constellation Tucana. Originally given a Flamsteed-style star number before Nicolas-Louis de Lacaille recognized its nebulous nature in 1751, 47 Tuc sits visually adjacent to the Small Magellanic Cloud—though the dwarf galaxy is more than thirteen times farther away.
Unlike the loose, flat-cored profile of Omega Centauri, 47 Tucanae is a steeply concentrated Shapley-Sawyer Class III system caused by dynamical mass segregation over 11.8 billion years. Heavy stellar remnants and compact binaries have sunk into its dense core, producing at least 29 radio millisecond pulsars and dozens of X-ray binaries spun up by close stellar encounters.
Because 47 Tucanae is relatively metal-rich for a globular cluster ([Fe/H] = −0.72 dex, roughly 19% solar), its giant-branch stars are cooler and more orange-tinted than those in metal-poor halo clusters like M92.
Practical Visual Observing Guide
- At declination −72°05′, 47 Tucanae is circumpolar from much of the Southern Hemisphere and invisible north of +18°N latitude.
- To the naked eye it shines at magnitude 4.09 just west of the Small Magellanic Cloud, looking like a soft detached knot of starlight.
- Through any telescope from 80 mm upward, 47 Tuc displays a breathtaking golden-white core contrasting against a sprawling halo of thousands of pinpoint stars.
Catalog Cross-Identifications & Aliases
Common Aliases: 47 Tuc · NGC 104 · Caldwell 106
| Catalog Authority | Identifier |
|---|---|
| NGC | NGC 104 |
| SIMBAD | NGC 104 |
| WIKIDATA | Q14268 |
Related Objects, Comparisons & Guides
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.
Messier 13 (Hercules Globular Cluster)
Coordinates, Gaia DR3 distance (7.42 kpc), visual magnitude 5.78, and Keystone finder guide for Messier 13 (NGC 6205) in Hercules.
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.
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.
Binocular Deep-Sky Objects Observing Guide
How to observe open clusters, globular clusters, diffuse nebulae, and Local Group galaxies with 7x50, 10x50, and 15x70 astronomy binoculars.
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.
NGC & Caldwell Deep-Sky Cross-Walk Catalog
Cross-reference guide to Dreyer's New General Catalogue (NGC) showpieces, including southern gems Omega Centauri, 47 Tucanae, Carina Nebula, and the Veil.
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