The constellation Andromeda


Nome latino
Emisfero nord
All year round
722 deg²
Brightest star
Sirrah (HIP number 677)
Galaxies, star cluster, planetary nebula
The constellation Andromeda

The constellation Andromeda is named after a princess from Greek mythology. It is one of the 48 classical constellations of antiquity, described by the Greek-Roman astronomer Claudius Ptolemy. It is located in the northern night sky and includes three very bright stars and a unique galaxy, the Andromeda Galaxy.

Hemisphere, visibility, and area

Andromeda lies in the northern night sky. Due to its position, it is visible throughout the entire northern hemisphere and can be observed south of the equator up to the 35th parallel. This corresponds to approximately Sydney in Australia or Santiago de Chile in Chile.

The constellation is partly circumpolar, meaning it is visible year-round but disappears below the horizon at certain times. In some nights, it can only be seen for about an hour. The best months to observe this constellation are still September to February when it is high in the night sky.

It covers an area of approximately 722 square degrees. Compared to all other 88 constellations, Andromeda is at position 19 with this size.

Andromeda is surrounded by the constellations Pisces, Triangulum, Lacerta, Pegasus, Cassiopeia, and Perseus. The last three constellations are also named after figures from Greek mythology.

Andromeda's three most noticeable stars are Sirrah, Mirach, and Alamak, which form the main stars and are roughly aligned on a line. Sirrah (Latin: α Andromedae, Alpha Andromedae), also known as Alpheratz, is the brightest star in Andromeda, with an apparent magnitude of approximately 2.06. It is a double-star system located about 100 light-years away.

Specialties in the constellation

In the area of Andromeda are several interesting deep-sky objects, including several galaxies, two open star clusters, and a planetary nebula.

The most well-known object is the spiral galaxy called M31 (Messier 31). It is the farthest object visible to the naked eye from the earth under good conditions. It is about 2.5 million light-years away and can be seen as a faint nebulous patch, similar to the Milky Way. This is why it is commonly called the "Andromeda Nebula." The galaxy contains up to 300 billion stars and is estimated to collide with the Milky Way in approximately 10 billion years as it constantly moves towards it.

The Andromeda Nebula is located near the star μ Andromedae (My Andromedae).

Spiral galaxy M31, Andromeda Galaxy, Andromeda Nebula
Spiral galaxy M31, Andromeda Galaxy, Andromeda Nebula

Mythology and history

In Greek mythology, Princess Andromeda was the only daughter of King Cepheus and his wife, Cassiopeia. At the same time, there were the Nereids, 50 daughters of the Titan Nereus, and his wife, Doris. Each of these 50 women was considered the definition of beauty in ancient times. Poseidon, the god of the sea, took one of them as his wife.

When Cassiopeia, driven by her vanity, declared herself and her daughter as the most beautiful women in the world, the Nereids became angry. So, they compelled Poseidon to punish Cassiopeia. Therefore, he sent the sea monster Cetus to devastate the coast of Cepheus' kingdom.

To protect his empire, Cepheus sought the Oracle of Ammon. It stated that he must sacrifice Andromeda to appease the wrath of the sea god and his wife Doris. Therefore, he chained his daughter to a rock, where she waited in fear of her fate.

As the sea monster Cetus approached her, the hero Perseus appeared. He recognized the beauty and innocence of the young woman. So he ultimately saved her from death by destroying the monster.

There are different versions of how Perseus defeated the monster. According to one version, he utilized the head of Medusa to transform the beast into stone. However, another interpretation, recounted by the Roman poet Ovid in his work "Metamorphoses," tells that Perseus killed the monster with his sword made of diamond.

Later, Perseus married Andromeda and they became a family with nine children. They got seven sons and two daughters.

To commemorate this story, all those involved were placed as a constellation in the sky. Due to this story, Andromeda is often called "The Chained Woman" in English.

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