Algol vs Mira Variable Star Comparison
Contrast extrinsic eclipsing binary Algol (Beta Persei) against intrinsic pulsating AGB giant Mira (Omicron Ceti) in mechanism, period, and amplitude.
Compared Celestial Objects
Algol (Beta Persei Eclipsing Binary)
Coordinates, Hipparcos distance (90 ly), 2.8673-day eclipse cycle, Algol Paradox mass transfer, and visual timing guide for Algol.
Constellation: Perseus · Coords: 03h 08m 10.13s, +40° 57′ 20.3″
Mira (Omicron Ceti Pulsating Giant)
Coordinates, Hipparcos distance (100 pc), 332-day pulsation cycle (mag 2.0 to 10.1), white dwarf companion, and observing guide for Mira.
Constellation: Cetus · Coords: 02h 19m 20.79s, -02° 58′ 39.5″
Normalized Shared Parameter Table
| Parameter | Unit / Scale | Algol (Beta Persei Eclipsing Binary) | Mira (Omicron Ceti Pulsating Giant) |
|---|---|---|---|
| Visual Magnitude Range (V) | mag | +2.12 to +3.39 (Δm = 1.27 mag) | +2.0 to +10.1 (Δm ≈ 8.0 mag) |
| Gaia/Hipparcos Distance | pc | 27.57 ± 0.56 pc (89.9 ly) | 91.7 ± 8.5 pc (299 ly) |
| Variability Period | days | 2.867328 days (68h 49m) | 331.96 days (~11 months) |
| Spectral Classification | type | B8 V + K0 IV semidetached binary | M5e–M9e III + white dwarf (Mira B) |
| Primary Mechanism | type | Extrinsic geometric orbital eclipse | Intrinsic AGB pulsation + TiO opacity |
Astrophysical & Observational Synthesis
Every 2 days, 20 hours, and 49 minutes, Algol drops by a factor of 3.2 in visual brightness (+2.12 to +3.39) over five hours and recovers over the next five hours—not because either star pulsates, but because its orbital plane is inclined 81.4° to our line of sight, causing the larger, cooler K0 IV subgiant (Algol Ab, 4,500 K) to pass directly in front of the brilliant B8 V primary (Algol Aa, 13,000 K).
Mira (Omicron Ceti, discovered by David Fabricius in 1596), by contrast, undergoes a colossal 8-magnitude (~1,500-fold) change in visual brightness over a 332-day cycle due to intrinsic radial pulsations of its asymptotic-giant-branch envelope (~330–400 R☉). Although Mira's total bolometric output varies by only ~2.5× across its cycle, cooling from 3,200 K at maximum to 2,900 K at minimum triggers massive formation of titanium oxide (TiO) molecules that act like a Venetian blind across the visual V band while shifting its radiation into the infrared.
In addition, Algol resolves the famous 'Algol Paradox' (why the less massive 0.79 M☉ K0 subgiant is more evolved than the 3.17 M☉ B8 primary) via ongoing Roche-lobe mass transfer, whereas Mira sheds 10⁻⁷ M☉/yr into a 13-light-year ultraviolet tail and feeds an accreting companion (Mira B).
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.
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.
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