Mirfak

Mirfak, sometimes spelled Mirphak or Marfak, brightest star in the constellation Perseus, the Warrior. The star is also known as Algenib and is designated Alpha Persei. The name Mirfak is derived from the Arabic phrase Mirfaq al Thurayya, the “Elbow Nearest the Many Little Ones.” This refers to Mirfak’s position in Perseus near the Pleiades star cluster. Mirfak lies near the north celestial pole, a point in the sky about which the stars in the northern hemisphere appear to rotate. This appearance is actually due to the rotation of Earth. Observers who are north of latitude 40° north can see Mirfak all night long throughout the year, circling the north celestial pole. For this reason, Mirfak is called a north circumpolar star. Observers in the southern hemisphere can see Mirfak low in the northern sky from September through November.

Stars that are visible to the unaided eye, such as Mirfak, belong to Earth’s home galaxy, the Milky Way, and tend to be very bright or relatively close. Mirfak is a very bright star that shines in the night sky as one of the 50 brightest stars as seen from Earth.

Mirfak owes its brightness to a moderately high surface temperature and very large size. Mirfak’s estimated surface temperature is 6200°C (11,000°F), which is about 10 percent greater than the surface temperature of the Sun and gives the star a yellow-white color. Its diameter is estimated at 124 million km (77 million mi), which is about 90 times greater than the diameter of the Sun. From its composition, temperature, and size, astronomers classify Mirfak as a supergiant star—an older star that has used up the hydrogen fuel in its core and is now burning hydrogen in its outer shell and helium in its core. These changes have caused it to grow much larger than its original size, which has increased its luminosity tremendously.

Mirfak is the brightest star of a large cluster of about 70 loosely bound stars collectively known as the Alpha Persei Association. This cluster, which covers an area of sky equal to six full moons, is easily visible through binoculars. Many of its stars are in pairs, trios, and quartets. Studies indicate that the average age of the stars in the Alpha Persei Association is only about 51 million years, younger than many diamonds found on Earth.