Monday, November 09, 2009

Andromeda

The constellation Andromeda is one of the six predominant evening constellations in the month of November for the Northern Hemisphere. The others are Cassiopeia, Phoenix, Pisces, Sculptor, and Tucana.

Greek Mythology

Named after the princess of Ethiopia in Greek mythology. Andromeda is sometimes called “the Lady in Chains,” “the Chained Lady,” or “the Chained Woman.”

In Greek mythology, Andromeda was the daughter of Cepheus and Cassiopeia, king and queen of Ethiopia. Cassiopeia had bragged that Andromeda was more beautiful than the Nereids, the nymph-daughters of the sea god Nereus. To punish Cassiopeia for her arrogance the main god of the sea, Poseidon, sent the sea monster Cetus to ravage the coast of Ethiopia. In desperation, Cepheus consulted the Oracle of Zeus, who told Cepheus that the sea monster would not stop until his daughter Andromeda was sacrificed to Cetus by chaining her to a rock on the coast of Jaffa (today called Japho or Joppa; in Hebrew Yafo; in Arabic, Yafa).

Fortunately for Andromeda, she was saved from this grim fate by the hero Perseus. Having just returned from slaying Medusa, the Gorgon, Perseus used the severed head of Medusa to destroy Cetus by turning the sea monster to stone. Perseus then set Andromeda free and the two were married.

Observing

Andromeda is visible in the northern hemisphere from August through January. It can be seen directly overhead on November 10 at 10PM local time.


In the above sky chart, Andromeda is bordered by Cassiopeia to the north, Lacerta to the west, Perseus to the east, and the constellations Triangulum, Pisces and Pegasus to the south. Image Credit: Your Sky, by John Walker (http://www.fourmilab.ch/yoursky/)

The four brightest stars in Andromeda are:


Alpha Andromedae - traditionally called Alpheratz (or Alpherat) and Sirrah (or Sirah). This is a binary star with an overall apparent visual magnitude of 2.06. Before the formalization of constellation structures, Alpheratz was also considered a member of the constellation Pegasus called Delta Pegasi. Alpheratz forms the asterism called the Great Square of Pegasus.

Beta Andromedae - traditionally called Mirach. Mirach is 200 light-years from earth and has a visual magnitude of 2.1.

Gama Andromedae - traditionally called Almach. Almach is actually multiple stars having contrasting colors.


Delta Andromedae - called Sadiradra, a 3rd magnitude star

Deep Sky

The most prominent deep sky object in Andromeda is M31 – Messier object 31. It is a spiral galaxy which is more commonly known as the Andromeda Galaxy, because it appears within the constellation Andromeda. This is one of the most distant objects visible to the naked eye, approximately 2,500,000 light-years away from Earth. In a dark sky, M31 can be seen as an elongated fuzzy patch near Mu Andromedae, roughly opposite of Beta Andromedae.

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