Hoag's Object (PGC 54559)
J2000 coordinates, distance (613 Mly), magnitude 16.00, golden E0 core inside detached blue star-forming ring, and observing guide for Hoag's Object.
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) | 16 mag | ± 0.15 mag | HST WFPC2 & deep CCD integrated photometry | definitive | SIMBAD Astronomical Database (CDS) |
| Distance in light-years | 613000000 ly | ± 20000000 ly | Optical & H I 21-cm cosmological redshift (z = 0.0425, 188 ± 6 Mpc) | high-confidence | SIMBAD Astronomical Database (CDS) |
| Apparent diameter (outer blue ring) | 0.75 arcmin | ± 0.05 arcmin | HST WFPC2 outer ring diameter (45″ × 45″ = 0.75′) | definitive | SIMBAD Astronomical Database (CDS) |
| Heliocentric recession velocity | 12740 km/s | ± 15 km/s | Optical core absorption & WSRT H I 21-cm ring spectroscopy | definitive | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Hoag's Object (PGC 54559 Polar Ring Galaxy) at RA 15h 17m 14.20s, Dec +21° 35′ 08.0″ within Serpens, 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
When astronomer Arthur Hoag discovered this object in 1950 on photographic plates of Serpens Caput, its geometry was so uncanny that he initially proposed it was either a planetary nebula or the first gravitational Einstein ring produced by a foreground galaxy lensing a background quasar. Positioned 613 million light-years (188 megaparsecs) away, Hoag's Object (PGC 54559) consists of an almost perfectly spherical 24,000-light-year-wide core of ancient, golden-yellow stars encircled—across a 35,000-light-year empty gap—by a detached, symmetric ring of luminous blue OB star clusters spanning 120,000 light-years in outer diameter.
In 1974 and 1987 spectroscopists proved that the golden inner sphere and the blue outer ring share the exact same recession velocity (+12,740 km/s) and therefore belong to a single extraordinary galaxy. Unlike the Cartwheel Galaxy, Hoag's Object has no nearby 'bullet' intruder galaxy, its central core is a slow-rotating triaxial E0 spheroid rather than a disk, and no luminous spokes connect the core to the ring.
Modern cosmological hydrodynamical simulations and Westerbork 21-centimeter H I observations suggest that the ancient central elliptical core formed over 10 billion years ago, and subsequently accreted a massive 2-billion-year-old ring of cold atomic hydrogen gas directly along a cosmic web filament (or dissolved an early triaxial stellar bar that swept all outer gas into an outer resonance ring). Remarkably, in Hubble Space Telescope images of Hoag's Object, a second, even more distant ring galaxy (SDSS J151713.93+213516.8) can be seen shining right through the empty dark gap at the one-o'clock position between Hoag's core and ring!
Practical Visual Observing Guide
- Located in northern Serpens Caput, 1.8° northeast of Beta Serpentis (β Ser).
- At magnitude 16.0 and 613 million light-years distance, visually spotting the 6-arcsecond central core of Hoag's Object requires a 450–600 mm (18–24 inch) telescope at 300×–450× under pristine dark skies.
- For backyard astrophotographers with 200–350 mm telescopes, capturing the distinct golden core and 45-arcsecond blue ring of Hoag's Object is one of the ultimate deep-field trophies.
Catalog Cross-Identifications & Aliases
Common Aliases: Hoag's Object · PGC 54559 · PRC D-51
| Catalog Authority | Identifier |
|---|---|
| SIMBAD | NAME Hoag's Object |
| WIKIDATA | Q14084 |
Related Objects, Comparisons & Guides
Cartwheel Galaxy (ESO 350-40 Ring Galaxy)
J2000 coordinates, distance (489 Mly), magnitude 15.20, bullseye collisional ring, JWST dust spokes, ultraluminous X-ray sources, and observing guide.
Cat's Eye Galaxy (Messier 94 / NGC 4736)
J2000 coordinates, TRGB distance (15.0 Mly), magnitude 8.24, blazing inner starburst ring, outer pseudoring, and observing guide for Messier 94.
Sombrero Galaxy (Messier 104 / NGC 4594)
Coordinates, TRGB distance (9.55 Mpc / 31.1 Mly), edge-on dust lane, 1-billion-M☉ central black hole, and observing guide for M104.
Angular Size, Separation & Field of View
How angular diameter (degrees, arcminutes, arcseconds), spherical angular separation, and small-angle physical diameter relate to telescope field of view.
Proper Motion, Radial Velocity & Redshift
How astronomers combine tangential proper motion (mas/yr), Doppler radial velocity (km/s), and cosmological redshift (z) to reconstruct 3D space motion.
Scientific Sources & Dataset Provenance
- 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
- SH0ES Local Distance Ladder Hubble Constant (2022 Baseline Cepheid + SN Ia): Riess, A. G., et al. 2022, ApJL, 934, L7 (A Comprehensive Measurement of the Local Value of the Hubble Constant) — SH0ES Collaboration (HST / JWST)