Astronomy

How to Identify the Constellation of Cassiopeia in the Night Sky



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The constellation, Cassiopeia, the Queen, is found in the northern sky relatively close to the north celestial pole. This constellation is circumpolar for all sky watchers who live above 40 degrees north latitude, meaning it never rises or sets. Cassiopeia borders the constellations Cepheus (the King), Camelopardalis (the Giraffe), Perseus (the Hero), and Andromeda (the Princess).

In Greek mythology, Cassiopeia was the queen of Ethiopia. When she boasted that her daughter Andromeda was more beautiful than the sea nymphs, Poseidon sent a sea monster (identified with the constellation Cetus) to ravage the coast. Out of desperation to save her country, Cassiopeia allowed her daughter Andromeda to be chained to a rock as a sacrifice to the sea monster, but at the last moment, Andromeda was rescued by the hero Perseus. As a punishment for her arrogance, Cassiopeia was placed in the sky on a throne which faces downward for half of its celestial course.

When and Where to Look

Cassiopeia is visible on any clear night of the year from most locations in the northern hemisphere. For amateur stargazers, September through March are the optimal months for spotting Cassiopeia. In the southern hemisphere, the constellation is visible from May to August at locations north of the Tropic of Capricorn (23.5 degrees south latitude).

The easiest way to identify this constellation is to find the North Star (Polaris), which is at the end of the Little Dipper’s tail. The Little Dipper is the most noticeable feature of the constellation Ursa Minor. As a reminder, Polaris is always as many degrees above the northern horizon as you are north of the equator. Look approximately two hand widths or so away at the area of sky opposite the Little Dipper, and Cassiopeia should be visible as an M, W, E, or 3 shape depending on the season of the year and/or the time of night you are star gazing.  

Stars

Cassiopeia contains no first magnitude stars. It does contain several 2nd and 3rd magnitude stars, and its shape is rather distinctive. Schedar, meaning breast in Arabic, is the alpha star in the constellation. It is magnitude 2.2 and 120 light years from Earth. The beta
star in Cassiopeia is called Caph, meaning hand in Arabic and Hebrew. It is magnitude 2.3 and located 42 light years from Earth. The gamma star is called Cih, meaning whip in Chinese. It is 780 light years away, and its brightness varies sporadically from magnitude 1.6 to 3.0.   

Deep sky objects

Cassiopeia contains two Messier objects, M52 and M103. Both are 7th magnitude open star clusters, visible through a small telescope or binoculars on a clear night. The planetary nebula NGC 7635, sometimes called the Bubble Nebula, is fainter and best viewed through a medium size telescope. The elliptical galaxy NGC 185 is faint at 10th magnitude and also requires a medium size telescope to be seen. The Milky Way runs directly through Cassiopeia and is easily visible through binoculars or a small telescope.

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