Polaris vs Delta Cephei Cepheid Comparison
Compare overtone Cepheid Polaris (Alpha Ursae Minoris) and fundamental-mode archetype Delta Cephei in pulsation amplitude, period, and distance.
Compared Celestial Objects
Polaris (Alpha Ursae Minoris North Star)
Coordinates, Gaia/HST distance (137 pc), 3.97-day Cepheid pulsation, Polaris B companion, and pole-alignment guide for Polaris.
Constellation: Ursa Minor · Coords: 02h 31m 49.09s, +89° 15′ 50.8″
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.
Constellation: Cepheus · Coords: 22h 29m 10.27s, +58° 24′ 54.7″
Normalized Shared Parameter Table
| Parameter | Unit / Scale | Polaris (Alpha Ursae Minoris North Star) | Delta Cephei (Cepheid Distance Ladder Anchor) |
|---|---|---|---|
| Mean Apparent Visual Magnitude (V) | mag | +1.98 (amplitude ~0.03–0.05 mag) | +3.95 (range +3.48 to +4.37 mag) |
| Gaia DR3 Heliocentric Distance | pc | 137.6 ± 1.6 pc (449 ly) | 295 ± 6 pc (962 ly) |
| Pulsation Period | days | 3.9696 days (1st overtone) | 5.36627 days (fundamental mode) |
| Mean Photospheric Radius | R☉ | 46.3 ± 1.5 R☉ (F7 Ib) | 43.3 ± 1.2 R☉ (F5 Ib–G1 Ib) |
| Mean Bolometric Luminosity | L☉ | 1,260 ± 60 L☉ | 2,000 ± 100 L☉ |
Astrophysical & Observational Synthesis
Every Cepheid variable owes its name to Delta Cephei—discovered by 19-year-old John Goodricke in October 1784—and its cosmological utility to Henrietta Swan Leavitt's 1912 Period–Luminosity Law. Pulsating in the radial fundamental mode via the He II ionization opacity valve, Delta Cephei expands and contracts by ~3 million kilometers every 5.366 days, producing a symmetric-free, asymmetric 0.89-magnitude sawtooth light curve easily tracked with the naked eye.
Polaris (Alpha Ursae Minoris), sitting more than twice as close to the Sun (137.6 pc vs 295 pc) and 0.74° from the North Celestial Pole, is actually the nearest and brightest classical Cepheid in the sky (V = +1.98). Unlike Delta Cephei, Polaris pulsates in the radial first overtone with a 3.97-day period and a nearly sinusoidal, millimagnitude-scale amplitude (~0.03–0.05 mag) that famously shrank during the 20th century before rebounding after 2000.
Remarkably, both Cepheids are multiple star systems that are easily split in small amateur telescopes: Polaris has an +8.7-magnitude F3 V companion (Polaris B) at 18.2 arcseconds, while Delta Cephei has a picturesque +6.3-magnitude blue-white B7-8 companion (HD 213307) at 41.0 arcseconds.
Related Reference Guides
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.
Primary Catalogs & Scientific Sources
- 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
- Revised New General Catalogue and Index Catalogue (RNGC/IC) (2024/2026 edition): Steinicke, W. 2010, Observing and Cataloguing Nebulae and Star Clusters (Cambridge Univ. Press); Verga, M. OpenNGC (CC-BY-SA 4.0 / data tables) — Wolfgang Steinicke / OpenNGC