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Mirfak, Alpha Persei, 33 Persei, HD20902, HIP15863, HR1017

Mirfak (Alpha Persei) is a blue to white very luminous supergiant star that can be located in the constellation of Perseus. Mirfak is the 36th brightest star in the night sky and is the brightest star in Perseus based on the Hipparcos 2007 apparent magnitude. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

Alpha Persei is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR1017. HIP15863 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD20902.

Mirfak has alternative name(s), Alf Per. In Arabic, it is known as Al-Mirfaq. Mirfak has at least 1 Extrasolar Planets believed to be in orbit around the star.

Location of Mirfak

The location of the star in the galaxy is determined by the Right Ascension (R.A.) and Declination (Dec.), these are equivalent to the Longitude and Latitude on the Earth. The Right Ascension is how far expressed in time (hh:mm:ss) the star is along the celestial equator. If the R.A. is positive then its eastwards. The Declination is how far north or south the star is compared to the celestial equator and is expressed in degrees. For Mirfak, the location is 03h 24m 19.35 and +49d51`40.5 .

Proper Motion of Mirfak

All stars like planets orbit round a central spot, in the case of planets, its the central star such as the Sun. In the case of a star, its the galactic centre. The constellations that we see today will be different than they were 50,000 years ago or 50,000 years from now. Proper Motion details the movements of these stars and are measured in milliarcseconds. The star is moving -26.23 ± 0.11 miliarcseconds/year towards the north and 23.75 ± 0.17 miliarcseconds/year east if we saw them in the horizon.

Mirfak Luminosity

Luminosity is the amount of energy that a star pumps out and its relative to the amount that our star, the Sun gives out. The figure of 16000.0000000 that I have given is based on the Spectral Types page that I have found on the Internet. You might find a different figure, one that may have been calculated rather than generalised that I have done. The figure is always the amount times the luminosity of the Sun. It is an imprecise figure because of a number of factors including but not limited to whether the star is a variable star and distance.

Physical Properties (Colour, Temperature, Radius) of Mirfak

Mirfak has a spectral type of F5Ib. This means the star is a blue to white supergiant star. The star is 7549.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24622.0708385600000000s. The star has a B-V Colour Index of 0.48 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 6,166 Kelvin.

Mirfak Radius has been calculated as being 65.00 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 45,229,831.35.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 55.84. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures. The star's Iron Abundance is 0.14 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

Mirfak Apparent and Absolute Magnitudes

Mirfak has an apparent magnitude of 1.79 which is how bright we see the star from Earth. Apparent Magnitude is also known as Visual Magnitude. If you used the 1997 Parallax value, you would get an absolute magnitude of -4.50 If you used the 2007 Parallax value, you would get an absolute magnitude of -4.17. Magnitude, whether it be apparent/visual or absolute magnitude is measured by a number, the smaller the number, the brighter the Star is. Our own Sun is the brightest star and therefore has the lowest of all magnitudes, -26.74. A faint star will have a high number.

Distance to Mirfak

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 5.51 which gave the calculated distance to Mirfak as 591.95 light years away from Earth or 181.49 parsecs. It would take a spaceship travelling at the speed of light, 591.95 years to get there. We don't have the technology or spaceship that can carry people over that distance yet.

In 2007, Hipparcos data was revised with a new parallax of 6.44 which put Mirfak at a distance of 506.46 light years or 155.28 parsecs. It should not be taken as though the star is moving closer or further away from us. It is purely that the distance was recalculated.

The star's Galacto-Centric Distance is 7,549.00 Parsecs or 24,622.07 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Source of Information

The source of the information if it has a Hip I.D. is from Simbad, the Hipparcos data library based at the University at Strasbourg, France. Hipparcos was a E.S.A. satellite operation launched in 1989 for four years. The items in red are values that I've calculated so they could well be wrong. Information regarding Metallicity and/or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

Mirfak Facts

Alternative Names

Traditional/Proper NameMirfak
Flamsteed Name33 Persei
Flamsteed Short Name33 Per
Short NameAlf Per
Arabic NameAl-Mirfaq
English Meaning'The elbow' of the Pleiades
Bayer DesignationAlpha Persei
Hipparcos Library I.D.15863
Yale Bright Star Catalogue (HR) Id1017
Bonner DurchmusterungBD+49 917
Henry Draper Designation20902

Visual Facts

Star Typesupergiant star
Absolute Magnitude-4.50 / -4.17
Visual / Apparent Magnitude1.79
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)03h 24m 19.35
Declination (Dec.)+49d51`40.5
Galactic Latitude-5.86 degrees
Galactic Longitude146.57 degrees
1997 Distance from Earth5.51 Parallax (milliarcseconds)
 591.95 Light Years
 181.49 Parsecs
2007 Revised Distance from Earth6.44 Parallax (milliarcseconds)
 506.46 Light Years
 155.28 Parsecs
Galacto-Centric Distance24,622.07 Light Years / 7,549.00 Parsecs
Proper Motion Dec.-26.23 ± 0.11 milliarcseconds/year
Proper Motion RA.23.75 ± 0.17 milliarcseconds/year
B-V Index0.48
Radial Velocity-2.04 ± 0.05 km/s
Iron Abundance0.14 ± 9.99 Fe/H
Spectral TypeF5Ib
Brightest in Night Sky36th
Colour(F) blue to white

Companions (Multi-Star and Exoplanets) Facts

Exoplanet Count1

Estimated Facts

Luminosity (x the Sun)16,000.0000000
Calculated Effective Temperature6,166 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

Multi-Star System

The star has been identified as being a multi-star system, one in which there is at least one star in close orbit to another star or two or more stars orbiting a central point. The stars may be of equal mass, unequal mass where one star is stronger than the other or be in groups orbiting a central point which doesn't necessarily have to be a star. More information can be found on my dedicated multiple star systems page. The source of the info is Simbad. The file is dated 2000 so any differences between this and any other source will be down to the actual source from where the information came from.


Proper Motion mas/yr
H.D. IdB.D. IdStar CodeMagnitudeR.A.Dec.SpectrumColourYear
20902+49 917.0A1.9000025.00000-22.00000F5Yellow/White
B11.900001909

Location of Mirfak in Perseus


Mirfak (Alpha Persei) Location in Perseus

The map was generated using Night Vision, an awesome free application by Brian Simpson.


List of Extrasolar Planets orbiting Mirfak


NameStatusMass (Jupiters)Orbital Period (Days)EccentricityDiscoveredSemi-Major AxisPeriastron
Alf Per BUnconfirmed6.6128.2000.120120.97208.000

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