How to Spot the Cassiopeia Constellation in the Night Sky

How to Spot the Cassiopeia Constellation in the Night Sky

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Cassiopeia the Queen is one of the brightest and most easily recognized constellations in the night sky. The constellation forms a "W" or "M" in the northern sky. It is the 25th-largest constellation out of 88, occupying 598 square degrees of sky.

Ptolemy cataloged Cassiopeia and other constellations in the Perseus family in the 2nd century. The constellation used to be called Cassiopeia's Chair, but the official name was changed to Cassiopeia the Queen by the International Astronomical Union in the 1930s. The official abbreviation for the constellation is "Cas."

How to Find Cassiopeia

The easiest way to find the constellation Cassiopeia is to look for a "W" on the other side of the North Star from the Big Dipper. Misha Kaminsky / Getty Images

The easiest way to spot Cassiopeia is to look for the "W" in the North. Keep in mind, the "W" may be on its side or inverted to form an "M." If you can recognize the Big Dipper (Ursa Major), the two stars at the edge of the Dipper point toward the North Star (Polaris). Follow the line formed by the two Dipper stars through the North Star. Cassiopeia is on the other side of the North Star, about as far away as the Big Dipper, but a bit to the right.

Cassiopeia never sets in northern regions (Canada, the British Isles, the northern United States). It is visible all year in the Northern Hemisphere and in the northern part of the Southern hemisphere in late spring.

The Myth: Queen Cassiopeia of Ethiopia

Cassiopeia is depicted as a queen sitting on a throne, sometimes holding a mirror or palm frond. Image Work/amanaimagesRF / Getty Images

In Greek mythology, Cassiopeia was the wife of King Cepheus of Ethiopia. The vain queen boasted that she or her daughter (accounts vary) were more beautiful than the Nereids, sea nymph daughters of the sea god Nereus. Nereus took the insult to the god of the sea, Poseidon, who rained his wrath down upon Ethiopia. To save their kingdom, Cepheus and Cassiopeia sought the counsel of the Oracle of Apollo. The oracle told them the only way to appease Poseidon was to sacrifice their daughter, Andromeda.

Andromeda was chained to a rock near the sea, to be devoured by the sea monster Cetus. However, the hero Perseus, fresh from beheading the Gorgon Medusa, saved Andromeda and took her as his wife. At the wedding, Perseus killed Andromeda's betrothed (her uncle Phineus).

After their deaths, the gods placed members of the royal family near each other in the heavens. Cepheus is to the north and west of Cassiopeia. Andromeda is to the south and west. Perseus is to the southeast.

As punishment for her vanity, Cassiopeia is forever chained to a throne. However, other depictions show Cassiopeia on a throne unchained, holding a mirror or palm frond.

Key Stars in the Constellation

Forming an expanded W across the image are Segin, Ruchbah, Cih (at center), Schedar, and Caph. © Roger Ressmeyer/Corbis/VCG / Getty Images

The "W" shape of Cassiopeia the Queen is formed by five bright stars, all visible to the naked eye. From left to right, when viewed as a "W," these stars are:

  • Segin (magnitude 3.37): Segin or Epsilon Cassiopeiae is a bright blue-white B-class giant star that is about 2500 times brighter than the Sun.
  • Ruchbah (magnitude 2.68): Ruchbah is actually an eclipsing binary star system.
  • Gamma (magnitude 2.47): The central star in the "W" is a blue variable star.
  • Schedar (magnitude 2.24): Schedar is an orange giant, suspected to be a variable star.
  • Caph (magnitude 2.28): Caph is a yellow-white variable star that is about 28 times brighter than the Sun.

Other major stars include Achird (a yellow-white star similar to the Sun), Zeta Cassiopeiae (a blue-white subgiant), Rho Cassiopeiae (a rare yellow hypergiant), and V509 Cassiopeiae (a yellow-white hypergiant).

Deep Sky Objects in Cassiopeia

A false color image of Cassiopeia A (Cas A) using observations from both the Hubble and Spitzer telescopes as well as the Chandra X-ray Observatory. NASA/JPL-Caltech

Cassiopeia contains interesting deep sky objects:

  • Messier 52 (NGC 7654): This is a kidney-shaped open cluster.
  • Messier 103 (NGC 581): This is an open cluster containing about 25 stars.
  • Cassiopeia A: Cassiopeia A is a supernova remnant and brightest radio source outside our solar system. The supernova became visible about 300 years ago.
  • The Pacman Nebula (NGC 281): NGC 281 is a large gas cloud that resembles the video game character.
  • The White Rose Cluster (NGC 7789): NGC 7789 is an open cluster in which loops of stars resemble rose petals.
  • NGC 185 (Caldwell 18): NGC 185 is an elliptical galaxy with a magnitude of 9.2.
  • NGC 147 (Caldwell 17): NGC 147 is an elliptical galaxy with a magnitude of 9.3.
  • NGC 457 (Caldwell 13): This open cluster is also known as the E.T. Cluster or the Owl Cluster.
  • NGC 663: This is a prominent open cluster.
  • Tycho's Supernova Remnant (3C 10): 3C 10 is the remains of the supernova of Tycho's Star, observed by Tycho Brahe in 1572.
  • IC-10: IC-10 is an irregular galaxy. It is the closest starburst galaxy and the only one identified to-date in the Local Group.

In early December, the December Phi Cassiopeiids form a meteor shower that originates from the constellation. These meteors are very slow-moving, with a velocity of about 17 kilometers per second. Astronomers believe the meteors are caused by a comet.

As Seen From Alpha Centauri

Our sun would be part of Cassiopeia if viewed from Alpha Centauri. Thingg

If you visit Alpha Centauri, the closest star system, the Sun and our solar system would appear to be part of the constellation Cassiopeia. Sol (the Sun) would be at the end of another line following the zig-zag shape.

Cassiopeia Fast Facts

  • Cassiopeia the Queen is the 25th largest constellation of the 88 modern constellations.
  • Cassiopeia is easily recognized by its five brightest stars that form a "W" shape in the northern sky.
  • The constellation takes its name from a queen in Greek mythology. Cassiopeia compared her daughter Andromeda's beauty to that of the sea god Nereus' daughters. The gods set her in the night sky near her family, but forever chained to her throne.


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  • Ptak, Robert (1998). Sky Stories Ancient and Modern. New York: Nova Science Publishers. p. 104.
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