Image Credit: NASA, CXC, GSFC, Stephen Walker, et al.
The constellation of Perseus; is a constellation located in the northern sky. The constellation resembles the Greek hero Perseus who raises his diamond sword above his head with one hand and holds the decapitated head of Medusa in the other. In the 19th century, the constellation was known as Perseus et Caput Medusae. Today, Perseus is called the hero. The three-letter abbreviation for it is Per.
Ptolemy described Perseus and 47 other constellations in the 2nd century. Today, Perseus is one of the 88 constellations recognized by the International Astronomical Union. It is the 24th largest constellation in the sky.
Perseus the hero is not as bright or as easy to recognize as some of the other constellations. Fortunately, he is close to Cassiopeia the Queen, one of the most visible formations in the sky.
To locate Perseus, look north where Cassiopeia forms a glowing “W” or “M” (depending on her orientation). If Cassiopeia looks like a “W”, Perseus will be the group of stars below the left side of the zig-zag. If Cassiopeia looks like an “M”, Perseus will be the group of stars below the right side of the zigzag.
Once you’ve spotted Perseus, look for his two brightest stars. The brightest is Mirfak, a yellow star at the midpoint of the constellation. The other notable star is Algol, a blue-white star that forms a line with Mirfak to identify the center of the constellation.
The constellations Ares and Auriga (with the bright yellow star Capella) lie to the east of Perseus. Camelopardalis and Cassiopeia are to the north of Perseus, and Andromeda and Triangulum are to the west. Perseus is prominent in the northern sky of the Northern Hemisphere in the spring, and is also visible in the northern part of the Southern Hemisphere.
Without a traditional name, the star is simply known as Gamma Persei, it is actually a binary system located around 240 light-years from Earth, the primary star outshines the other every 15 years causing it to appear darker in the night sky by a couple of weeks.
Also known as Alpha Persei, Mirfak is located about 500 light years from Earth and is the brightest star in the constellation, it is a white super giant with a diameter about 30 times that of the Sun.
Also known as Beta Persei, Algol is actually a three star system located about 90 light years from Earth, the primary star is eclipsed by one of its dimmer companions every 3 days causing its brightness to dim considerably for several hours. In the late 18th century, the star was the first eclipsing binary to be discovered. Historically Algol has been referred to as the “Demon Star”, this may be because the ancients perceived its dimming in brightness as an omen of bad luck.
Also known as Rho Persei, Gorgonea Tertia is a red giant about 300 light-years from Earth, 150 times larger in diameter than the sun.
Epsilon Persei is a binary or possibly triple system 640 light years from Earth, the primary star has surface temperatures 5 times higher than the sun with a mass about 14 times greater.
Zeta Persei is a blue supergiant about 750 light-years from Earth, is more than 25 times larger in diameter than the Sun, and nearly 50,000 times more luminous.
Key stars in the Perseus constellation
There are 19 stars in the main asterism of the constellation, but in areas with light pollution only two of them (Mirfak and Algol) are bright. Notable stars in the constellation include:
Mirfak: The brightest star in Perseus is a white-yellow supergiant. Other names for this star are Mirphak and Alpha Persei. Mirfak is a member of the Alpha Persei group. Its magnitude is 1.79.
Algol – Also known as Beta Persei, Algol is the best known star in the constellation. Its variable brightness is easily seen with the naked eye. Algol is not, however, a true variable star. It is an eclipsing binary that varies in magnitude from 2.3 to 3.5 over a period of 2.9 days. Algol is sometimes known as the Demon Star. The color of its primary star is blue-white.
Zeta Persei: The third brightest star in Perseus is a blue-white supergiant with a magnitude of 2.86.
X Persei: This is a binary star system. One of its two members is a neutron star. The other is a bright, hot star.
GK Persei – GK Persei is a nova that reached its maximum brightness in 1901 at magnitude 0.2. Seven of the stars in the constellation are known to have planets.