Elnath (Beta Tauri / Gamma Aurigae)
Coordinates, Hipparcos distance (134 ly), magnitude 1.65, B7 III mercury-manganese abundance anomaly, and observing guide for Elnath.
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 |
|---|---|---|---|---|---|
| Apparent visual magnitude (V) | 1.65 mag | ± 0.01 mag | Johnson UBV photoelectric photometry | definitive | Hipparcos New Reduction Catalog |
| Trigonometric parallax | 24.36 mas | ± 0.34 mas | Hipparcos New Reduction astrometric solution (41.05 ± 0.57 pc) (J2000.0) | definitive | Hipparcos New Reduction Catalog |
| Distance in light-years | 133.9 ly | ± 1.9 ly | Derived from Hipparcos parallax 24.36 ± 0.34 mas | definitive | Hipparcos New Reduction Catalog |
| Photospheric radius | 4.2 R☉ | ± 0.2 R☉ | Angular diameter (1.09 ± 0.05 mas) at 41.05 pc | high-confidence | SIMBAD Astronomical Database (CDS) |
| Effective temperature | 13600 K | ± 300 K | UV & optical B7 III quantitative spectroscopy | definitive | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Elnath (Beta Tauri Chemically Peculiar Giant) at RA 05h 26m 17.51s, Dec +28° 36′ 26.8″ within Taurus, 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
Elnath (Beta Tauri, from the Arabic al-Naṭḥ meaning 'the Butting') is the second-brightest star in Taurus at apparent visual magnitude 1.65, marking the northern horn tip of the Bull 16.5° northeast of Aldebaran. For centuries Ptolemy and Bayer assigned Elnath to two constellations simultaneously—as both Beta Tauri and Gamma Aurigae (forming the southern corner of the Auriga pentagon)—until the International Astronomical Union drew official constellation boundaries in 1930 and placed Elnath exclusively inside Taurus.
Located 41.05 ± 0.57 parsecs (133.9 light-years) from Earth, Elnath is a ~5.0-solar-mass, ~100-million-year-old B7 III giant star that has recently exhausted core hydrogen and expanded to 4.2 solar radii, shining with 700 solar luminosities at 13,600 K. High-resolution spectroscopy reveals that Elnath is a chemically peculiar Mercury-Manganese (HgMn) star: in its unusually calm radiative outer atmosphere, upward radiation pressure levitates manganese atoms to 25 times solar abundance while calcium and magnesium sink toward the interior.
From our vantage point in the Orion Arm, Elnath sits just 3.0° west of the Galactic Anticenter (the exact direction opposite Sagittarius A* at Galactic longitude l = 180°, b = 0°), making it the brightest naked-eye signpost looking straight outward toward the outer rim of the Milky Way disk.
Practical Visual Observing Guide
- Follow the northern arm of the V-shaped Hyades cluster 16.5° northeast past Aldebaran to locate Elnath, which completes the five-sided figure of Auriga the Charioteer.
- Use Elnath as a convenient star-hopping anchor for deep-sky objects along the Taurus–Auriga border, lying 8° northwest of the Crab Nebula (M1) and 5°–8° south of the open clusters M36, M37, and M38.
Catalog Cross-Identifications & Aliases
Common Aliases: β Tauri · γ Aurigae · HD 35497 · HIP 25428 · 112 Tauri
| Catalog Authority | Identifier |
|---|---|
| HIP | HIP 25428 |
| HD | HD 35497 |
| SIMBAD | * bet Tau |
| WIKIDATA | Q13049 |
Related Objects, Comparisons & Guides
Aldebaran (Alpha Tauri Orange Giant)
Coordinates, Hipparcos distance (66.6 ly), 45.1 R☉ radius, Hyades foreground alignment, and observing guide for Aldebaran in Taurus.
Capella (Alpha Aurigae Giant Binary)
Coordinates, Hipparcos distance (42.9 ly), twin G-giant 104-day interferometric binary orbit, and observing guide for Capella in Auriga.
Crab Pulsar (PSR B0531+21 Neutron Star)
Coordinates, 33.08 ms spin period, 16.5-mag optical flashes, spin-down luminosity, and high-aperture observing guide for the Crab Pulsar.
Celestial Coordinates (RA & Dec) Explained
Practical reference to J2000 equatorial coordinates: Right Ascension (RA in hours, minutes, seconds), Declination (Dec in degrees), and sexagesimal conversion.
Stellar Spectral Classification (OBAFGKM)
Reference guide to Morgan-Keenan (MK) stellar classification (O B A F G K M), luminosity classes (I–V, WD), color index (B-V), and the H-R diagram.
Scientific Sources & Dataset Provenance
- Hipparcos New Reduction Catalog (2007 New Reduction): van Leeuwen, F. 2007, A&A, 474, 653 (Validation of the new Hipparcos reduction) — ESA / van Leeuwen (2007)
- 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