Polaris (Alpha Ursae Minoris)
Coordinates, Gaia/HST distance (137 pc), 3.97-day Cepheid pulsation, Polaris B companion, and pole-alignment guide for Polaris.
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 |
|---|---|---|---|---|---|
| Mean apparent visual magnitude (V) | 1.98 mag | ± 0.02 mag | Space-based SMEI/TESS photometry (~0.03 mag peak-to-peak Cepheid amplitude) | definitive | General Catalogue of Variable Stars (GCVS) & AAVSO VSX |
| System distance (Gaia DR3 Polaris B) | 137.2 pc | ± 0.6 pc | Gaia DR3 parallax of physical companion Polaris B (7.289 ± 0.031 mas, 447.5 ly) (J2016.0) | definitive | ESA Gaia Archive — Data Release 3 |
| First-overtone Cepheid pulsation period | 3.9696 d | ± 0.0002 d | Radial-velocity & photometric pulsation tracking | definitive | General Catalogue of Variable Stars (GCVS) & AAVSO VSX |
| Cepheid primary mass (Polaris Aa) | 5.13 M☉ | ± 0.28 M☉ | CHARA interferometric + HST astrometric 29.3-year binary orbit (Evans et al. 2024) | high-confidence | SIMBAD Astronomical Database (CDS) |
| Photospheric radius | 46.3 R☉ | ± 0.9 R☉ | CHARA interferometric angular diameter (3.123 ± 0.008 mas) at 137.2 pc | definitive | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Polaris (Alpha Ursae Minoris North Star) at RA 02h 31m 49.09s, Dec +89° 15′ 50.8″ within Ursa Minor, 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
Polaris (Alpha Ursae Minoris), the current North Star, sits just 0.65° (39 arcminutes) from the north celestial pole at J2000 coordinates +89° 15′ 50.8″—and because of Earth's axial precession it is still drawing slightly closer, reaching a minimum separation of 27.15 arcminutes in February 2102.For northern observers, Polaris's altitude above the northern horizon equals the observer's geographic latitude to within two-thirds of a degree.
Far from being a steadfast, unchanging beacon, Polaris Aa is the closest and brightest Classical Cepheid variable star in the sky, located 137.2 ± 0.6 parsecs (447.5 light-years) away. It is an F7 Ib yellow supergiant with a radius 46.3 times that of the Sun and a luminosity of ~1,260 solar luminosities, pulsating in its first overtone mode every 3.9696 days. Intriguingly, Polaris's pulsation amplitude shrank from ~0.12 magnitudes in the 19th century to barely 0.02 magnitudes in the 1990s before recovering and stabilizing around 0.03–0.04 magnitudes.
Polaris is also a triple star system: at 0.17 arcseconds (~18.5 AU) orbits a 1.32-solar-mass F6 V companion (Polaris Ab) in a 29.3-year orbit resolved by Hubble and the CHARA interferometer, allowing astronomers to weigh a Cepheid variable dynamically (5.13 ± 0.28 solar masses). At 18.4 arcseconds (~2,400 AU) orbits magnitude 8.65 Polaris B, discovered by William Herschel in 1779.
Practical Visual Observing Guide
- Extend a line through the two outer 'Pointer' stars of the Big Dipper's bowl—Merak (β UMa) and Dubhe (α UMa)—northward by five times their separation (about 28°) to land directly on 2.0-magnitude Polaris.
- In any 50–80 mm telescope at 60×–100×, look 18.4 arcseconds southwest of yellow-white Polaris A to spot its 8.65-magnitude F3 V companion Polaris B—a favorite year-round double star for testing small refractors.
Catalog Cross-Identifications & Aliases
Common Aliases: α Ursae Minoris · North Star · Pole Star · HD 8890 · HIP 11767
| Catalog Authority | Identifier |
|---|---|
| HIP | HIP 11767 |
| HD | HD 8890 |
| SIMBAD | * alf UMi |
| WIKIDATA | Q12980 |
Related Objects, Comparisons & Guides
Delta Cephei (Cepheid Distance Ladder Anchor)
Coordinates, Gaia/HST distance (290 pc), 5.366-day pulsation period, Leavitt law calibration, and observing guide for Delta Cephei.
Mizar & Alcor (Zeta Ursae Majoris System)
Coordinates, Hipparcos/VLBI distance (82.8 ly), 11.8′ naked-eye pair, 14.4″ Mizar A–B split, and observing guide for Mizar & Alcor.
Vega (Alpha Lyrae Zero-Point Star)
Coordinates, distance (25.04 ly), magnitude 0.03 photometric zero point, rapid oblate rotation, and observing guide for Vega in Lyra.
Splitting Bright Double & Multiple Stars Guide
How to resolve showcase binary and multiple star systems—Albireo, Mizar & Alcor, Epsilon Lyrae, Castor, and Sirius B—and test telescope Dawes limit.
Tracking Bright Variable Stars Observing Guide
How to estimate visual magnitudes and light curves of naked-eye and binocular variable stars: Algol, Delta Cephei, Betelgeuse, Mira, and Eta Carinae.
Astronomical Epochs (J2000, J2016) & Precession
Why celestial coordinates specify a reference epoch (J2000.0 vs Gaia J2016.0), how axial precession shifts RA/Dec over time, and how ICRS anchors astrometry.
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.
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
- 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
- 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)
- General Catalogue of Variable Stars (GCVS) & AAVSO VSX (v5.1 (2026 update)): Samus, N. N., et al. 2017, Astronomy Reports, 61, 80 (General Catalogue of Variable Stars: Version GCVS 5.1) — Sternberg Astronomical Institute / AAVSO