Bright & Nearby Stars · Constellation Perseus

Mirfak (Alpha Persei)

Coordinates, Gaia/Hipparcos distance (510 ly), magnitude 1.79, Alpha Persei Cluster (Melotte 20) center, and observing guide for Mirfak.

Right Ascension (J2000.0)03h 24m 19.37s
Declination (J2000.0)+49° 51′ 40.2″
Primary ClassificationYellow-white F-type supergiant (MK standard for F5 Ib & Melotte 20 anchor)
Best Observing SeasonAutumn to Winter (September–March; circumpolar north of +40°N)

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.

Astrometric, Photometric, and Physical Parameters for Mirfak (Alpha Persei)
ParameterValueUncertaintyMethod & EpochQuality StatusSource Archive
Apparent visual magnitude (V)1.79 mag± 0.01 magJohnson UBV photoelectric standard stardefinitiveHipparcos New Reduction Catalog
Trigonometric parallax6.44 mas± 0.17 masHipparcos New Reduction + Gaia DR3 Melotte 20 cluster mean (155.3 ± 4.1 pc) (J2000.0)definitiveHipparcos New Reduction Catalog
Distance in light-years506.5 ly± 13.4 lyDerived from parallax 6.44 ± 0.17 masdefinitiveHipparcos New Reduction Catalog
Photospheric radius60.7 R☉± 2.2 R☉CHARA/NPOI limb-darkened angular diameter (3.188 ± 0.035 mas) at 155.3 pcdefinitiveSIMBAD Astronomical Database (CDS)
Bolometric luminosity5400 L☉± 400 L☉Bolometric flux integration + cluster distancehigh-confidenceSIMBAD Astronomical Database (CDS)
Measurement Uncertainties & Competing Solutions: Because Mirfak is the physical anchor of the rich Alpha Persei Moving Cluster (Melotte 20), Gaia DR3 parallaxes of hundreds of co-moving B/A cluster members independently validate its ~155–172 pc distance.

J2000 Equatorial Sky Chart & Culmination Altitude

The chart below plots Mirfak (Alpha Persei Yellow Supergiant) at RA 03h 24m 19.37s, Dec +49° 51′ 40.2″ within Perseus, 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.

J2000 Equatorial Sky Position (Perseus) +90° 0° −90° 24h 12h RA 0h Peak Meridian Altitude 80° 40°N Lat 10° 30°S Lat RA: 03h 24m 19.37s Dec: +49° 51′ 40.2″ Epoch: J2000.0 · V = 1.79 mag First-party vector diagram derived from IAU / CDS SIMBAD / Gaia DR3 astrometry.

Astrophysical Context & Structure

Mirfak (Alpha Persei, from the Arabic Mirfaq al-Thurayyā meaning 'the Elbow of the Pleiades') is the brightest star in the constellation Perseus at apparent visual magnitude 1.79, outshining nearby eclipsing Algol (Beta Persei). Located 155.3 ± 4.1 parsecs (507 light-years) away, Mirfak is the luminous gravitational centerpiece of the Alpha Persei Cluster (Melotte 20 / Collinder 39)—a dazzling 3°-wide OB star association born ~50 to 70 million years ago.

With a mass of ~8.5 solar masses, a diameter 60.7 times that of the Sun (3.19 milliarcseconds across), and an effective surface temperature of 6,350 K, Mirfak is a yellow-white supergiant that serves as the primary Morgan–Keenan spectral standard for class F5 Ib, radiating 5,400 solar luminosities.

On the Hertzsprung-Russell diagram, Mirfak sits just past the blue (hot) edge of the Cepheid instability strip: having evolved out of the main sequence much like neighboring Delta Cephei and Polaris, Mirfak enables astrophysicists to study the atmospheric structure of a yellow supergiant just outside the regime of high-amplitude radial pulsations.

Practical Visual Observing Guide

Minimum InstrumentNaked eye (7×50 or 10×50 binoculars for the spectacular Melotte 20 cluster)
Recommended Magnification7×–10× binoculars (3°–5° wide field of view)
Best Evening SeasonAutumn to Winter (September–March; circumpolar north of +40°N)
  • Pointing 7×50 or 10×50 binoculars at Mirfak delivers one of the finest binocular fields in the entire northern sky: golden-white Mirfak is surrounded by an S-shaped cascade of dozens of 4th-to-8th magnitude blue-white B- and A-type stars belonging to the Alpha Persei Moving Cluster (Melotte 20).
  • Use Mirfak (magnitude 1.79) as your primary bright naked-eye comparison star when estimating the brightness of Algol (Beta Persei) 9° to the southwest.

Catalog Cross-Identifications & Aliases

Common Aliases: α Persei · Algenib · HD 20902 · HIP 15863 · 33 Persei

Cross-Catalog Identifiers for Mirfak (Alpha Persei)
Catalog AuthorityIdentifier
HIPHIP 15863
HDHD 20902
SIMBAD* alf Per
WIKIDATAQ13031
Related Object · Perseus

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.

Reference Guide

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.

Reference Guide

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.

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)
  • 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