The Perseus Constellation

Find and Identify This Stellar Mythical Hero in the Northern Sky

Double Cluster NGC 869 NGC 884 in Perseus

malcolm park / Getty Images

Perseus, the 24th-largest constellation, is located in the northern sky. The stellar configuration is thought to resemble the Greek hero Perseus raising a diamond sword above his head with one hand while holding the decapitated head of the Gorgon Medusa in the other.

Ptolemy described Perseus and 47 other constellations in the second century. In the 19th century, the constellation was known as Perseus et Caput Medusae (Perseus and the Head of Medusa). Today, it's called Perseus the Hero or simply Perseus (Per.), and is one of 88 constellations recognized by the International Astronomical Union.

How to Find Perseus

Stars above the Wasatch Mountains in Utah
Locate Constellation Cassiopeia in order to find Perseus.

Scott Smith / Getty Images

Perseus the Hero is not as bright or as easy to recognize as some of the other constellations. Fortunately, it is located near Cassiopeia the Queen, one of the most visible formations in the sky.

To locate Perseus, look to the north, where Cassiopeia forms a bright "W" or "M" (depending on its orientation). If Cassiopeia resembles a "W," Perseus will be the group of stars below the left part of the zig-zag. If Cassiopeia resembles an "M," Perseus will be the group of stars below the right part of the zig-zag.

Once you have spotted Perseus, look for its two brightest stars. The brightest is Mirfak, a yellow star at the mid-point of the constellation. The other notable star is Algol, a blue-white star that forms a line with Mirfak to identify the middle of the constellation.

The constellations Aries and Auriga (with bright yellow star Capella) lie to the east of Perseus. Camelopardalis and Cassiopeia are to the north of Perseus, while 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.

The Myth of Perseus

Perseus holding head of Medusa, bronze statue created by Benvenuto Cellini

fotofojanini / Getty Imageds

In Greek mythology, Perseus was a hero born of a union between the god Zeus and a mortal woman, Danae. To rid himself of Perseus, Danae's husband, King Polydectes, sent Perseus to retrieve the head of the winged, snake-haired Gorgon Medusa. (The decapitation of Medusa is the scene depicted in the constellation.)

While rescuing Andromeda, the daughter of Cassiopeia and Cepheus, Perseus also slew the sea monster Cetus. Perseus and Andromeda went on to have seven sons and two daughters. Their son Perses was said to be the ancestor of the Persians.

Key Stars in the Constellation

Alpha Persei cluster of stars and Mirfak main star
Mirfak is the brightest star in Perseus and the easiest to spot.

xalanx / Getty Images

There are 19 stars in the constellation's main asterism, but in light-polluted areas only two of them (Mirfak and Algol) are bright. Notable stars in the constellation include:

  • Mirfak: The brightest star in Perseus is a yellow-white supergiant. Other names for this star are Mirphak and Alpha Persei. Mirfak is a member of the Alpha Persei Cluster. Its magnitude is 1.79.
  • Algol: Also known as Beta Persei, Algol is the best-known star in the constellation. Its variable brightness is readily seen with the naked eye. Algol is not, however, a true variable star. It is an eclipsing binary that ranges in magnitude from 2.3 to 3.5 over a period of 2.9 days. Sometimes Algol is 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 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 peak brightness in 1901 with a magnitude of 0.2.

Seven of the stars in the constellation are known to have planets.

Deep Sky Objects in Perseus

The California Nebula
The California Nebula, NGC 1499, has a shape similar to that of the state of California. blackphobos / Getty Images

While the galaxy is not very obvious in this region, Perseus does lie in the galactic plane of the Milky Way. The constellation contains interesting deep-sky objects, including several nebulae and the Perseus cluster of galaxies.

Highlights in the Constellation

  • NGC 869 and NGC 884: Together, these two objects form the Double Cluster. The double star cluster is easily observed with the use of a small telescope.
  • M34: M34 is an open cluster that may be seen (barely) with the naked eye and is easily resolved with a small telescope.
  • Abell 426: Abell 426 or the Perseus cluster is a massive group of thousands of galaxies.
  • NGC 1023: This is a barred spiral galaxy.
  • NGC 1260: This is either a tight spiral galaxy or a lenticular galaxy.
  • Little Dumbbell Nebula (M76): This nebula looks like a dumbbell.
  • California Nebula (NGC 1499): This is an emission nebula that's hard to observe visually, but takes on the shape of the eponymous state when viewed through a telescope.
  • NGC 1333: This is a reflection nebula.
  • Perseus molecular cloud: This giant molecular cloud blocks a lot of the light of the Milky Way, making it appear dim in this region of space.

The Perseid Meteor Shower

Perseid meteor shower over the United Kingdom
Christopher Furlong / Getty Images

The Perseid meteor shower appears to radiate from the constellation of Perseus. Meteors may be observed starting in mid-July and peaking in mid-August. The meteors are debris of the comet Swift-Tuttle. At its peak, the shower produces 60 or more meteors per hour. The Perseid shower sometimes produces brilliant fireballs.

Perseus Constellation Fast Facts

Constellations of Perseus, Andromeda nad Pegasus above the Columbia Icefields

Alan Dyer / Stocktrek Images / Getty Images

  • Perseus is a constellation in the northern sky.
  • The constellation is named for the Greek mythological hero and demigod Perseus, known for slaying the Gorgon Medusa.
  • The constellation is fairly faint and difficult to see in light-polluted areas. Its two brightest stars are Mirfak and Algol.
  • The Perseid meteor shower radiates from the constellation in July and August.

Sources

  • Allen, R. H. "Star Names: Their Lore and Meaning" (p. 330). Dover. 1963
  • Graßhoff, G. "The History of Ptolemy’s Star Catalogue" (p. 36). Springer. 2005
  • Russell, H. N. "The New International Symbols for the Constellations". Popular Astronomy: 30 (pp. 469–71). 1922