How to Spot the Perseus Constellation in the Night Sky

Wide-field image of Perseus constellation
A wide-field image of Perseus (captured from the ground).

 ESA / Hubble (A. Fujii)

Perseus is a constellation located in the northern sky. The constellation resembles the Greek hero Perseus raising his diamond sword above his head with one hand and holding the decapitated head of Medusa in the other. In the 19th century, the constellation was known as Perseus et Caput Medusae. Today, it is called Perseus the Hero or simply Perseus. Its three-letter abbreviation is Per.

Ptolemy described Perseus and 47 other constellations in the 2nd century. Today, Perseus is one of 88 constellations recognized by the International Astronomical Union. It is the 24th largest constellation in the sky.

How to Find Perseus

Night Sky with Constellations
Night Sky with Constellations. goodgraphic / 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 Ares and Auriga (with 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.

The Myth of Perseus

Constellation of Perseus, showing him carrying the head of Medusa, c1820.
Print Collector/Getty Images / Getty Images

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

Perseus slew the sea monster Cretus, thus rescuing Andromeda, the daughter of Cassiopeia and Cepheus. Perseus and Andromeda had seven sons and two daughters. Their son Perses was said to be the ancestor of the Persians.

Key Stars in the Constellation

The yellow star Capella (left) may be used to help locate Perseus (upper center).
The yellow star Capella (left) may be used to help locate Perseus (upper center). DAVID NUNUK/SCIENCE PHOTO LIBRARY / 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, NGC 1499, has a shape similar to that of the state of California.
The California Nebula, NGC 1499, has a shape similar to that of the state of California. blackphobos / Getty Images

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

Highlights in the constellation include:

  • NGC 869 and NGC 884: Together, these two objects form the Double Cluster. The double star cluster is easily observed using 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 is hard to observe visually, but takes on the shape of the 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, August 13, 2013.
Perseid meteor shower over the United Kingdom, August 13, 2013. 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

  • 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. (1963). Star Names: Their Lore and Meaning. New York: Dover. p. 330.
  • Graßhoff, G. (2005). The History of Ptolemy’s Star Catalogue. Springer. p. 36.
  • Russell, H. N. (1922). "The New International Symbols for the Constellations". Popular Astronomy. 30: 469–71.
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Helmenstine, Anne Marie, Ph.D. "How to Spot the Perseus Constellation in the Night Sky." ThoughtCo, May. 16, 2018, thoughtco.com/perseus-constellation-4165255. Helmenstine, Anne Marie, Ph.D. (2018, May 16). How to Spot the Perseus Constellation in the Night Sky. Retrieved from https://www.thoughtco.com/perseus-constellation-4165255 Helmenstine, Anne Marie, Ph.D. "How to Spot the Perseus Constellation in the Night Sky." ThoughtCo. https://www.thoughtco.com/perseus-constellation-4165255 (accessed May 24, 2018).