Star Facts: Mirfak

Image Credit: Fred Espenak

Mirfak (Alpha Persei) is a yellow supergiant located about 510 light years away in the constellation of Perseus that is about sixty times bigger than our sun. It is the most luminous star in the constellation Perseus, but with an apparent visual magnitude of +1.8 it just barely outshines Algol, the best-known star in the constellation, and one of the most celebrated eclipsing binary stars in the whole Universe.

Quick Facts

• Constellation: Perseus
• Coordinates: RA 03h 24m 19.37009s |Dec. +49° 51′ 40.2455″
• Distance: 510 light years
• Star Type: F5 Ib
• Mass: 8.5 sol
• Radius: 68 sol
• Apparent Magnitude: +1.806
• Luminosity: 5,000 sol
• Surface Temperature: 6,350K
•Rotational Velocity: 20 km/second
•Proper motion: RA +23.75 milliarcseconds/year |Dec. -26.23 milliarcseconds/year
•Age: 41 million years
•Other Designations: Mirphak, Marfak, Algeneb, Algenib, a Persei, a Per, Alpha Per, 33 Persei, BD+49 917, CCDM J03243+4951A


Note the location of Mirfak within the Perseus constellation, which is almost in the middle of Melotte 20, a famous open cluster consisting of mostly blue-white stars, the brightest of which are found just south of Mirfak. This has resulted in the Alpha Persei Cluster being sometimes referred to as the “Attendants of Mirfak”.

Its brightness and prominent location also makes Mirfak an easy target for binoculars and small telescopes, which is further helped by the fact that the star is north circumpolar when viewed from mid-northern latitudes, and so visible throughout the year.

Physical Properties

Mirfak is a F5 Ib-type supergiant star in the last stages of its life, with its spectrum having served as a standard against which similar stars have been measured since 1943. Another noteworthy aspect of Mirfak is that its spectrum is similar to that of the better-known, but slightly smaller and dimmer star Procyon, which has a F5 IV classification.

In general, though, supergiant stars like Mirfak inhabit the topmost part of the Hertzsprung–Russell diagram, and as a class, F-type stars are among the most luminous and massive of all stars. However, this class of stars account for just 3.03% (one in every 33) of all main-sequence stars in the Sun’s immediate vicinity.

Typically, F-class stars have absolute visual magnitudes from about -3 to about -8, while their temperatures fall into a wide range of between 3,00K to more than 20,000K. Mirfak falls neatly into the F-class of stars; it weighs about 8.5 times as much as the Sun, it has expanded to about 60 times the Sun’s diameter, and with an effective surface temperature of 6,350K, it shines about 5,000 times brighter than the Sun. Thus, if Mirfak’s position were to be plotted on the Hertzsprung–Russell diagram using these data points, it would fall almost in the middle of the region where other Cepheid variables are found, which makes it a useful tool with which to study the Cepheid variable stars as a class.


Some of the star’s traditional names for the star, such as “Mirphak”, “Marfak”, or “Mirzac”, derive from the Arabic word for ‘Elbow’, while other traditional names including Algenib, also spelt “Algeneb”, “Elgenab”, “Genib”, “Chenib”, or “Alchemb” means “side” or “the flank”.

In some native Hawaiian traditions, Mirfak is known as “Hinali’i”, in commemoration of a great tsunami that marks the commencement of the Maui. In other Hawaiian traditions, the star Hinali’i marks the point where the Earth and sky are separated, which separation had occurred when the Milky Way was created.

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