Costellazione Andromeda, stelle principali e mitologia

30 Mag 2017

OSR blog post

Ognuno di noi, volendo gli occhi al cielo, in una notte stellata si sarà accorto delle innumerevoli stelle, più o meno luminose, che lo animano, e probabilmente qualcuno si sarà anche accorto che alcuni insiemi di stelle vicine tra di loro formano come delle figure di linee rette, semicurve, quadrati o triangoli. Ad uno sguardo più attento e costante, queste figure s'incontrano tra loro e si legano, andando a disegnare in modo stilizzato la sagoma di una figura vera e propria come un cigno, un delfino, un'orsa: ebbene sono le costellazioni.

What really is a constellation? Let’s see Andromeda..

We can therefore define the constellations as groups of stars that are linked to create an animal representation or that refers to the mythological tradition.

The idea of ​​dividing the sky into constellations to orient oneself and establish a sort of “astral boundaries” dates back thousands of years ago, since then the constellations identified have been numerous, so much so that today the sky has 88 (identified by the Union International Astronomy). In astronomy they are considered real “portions” that make up the sky, each of which contains galaxies, clusters and various other celestial objects. Among the best known we mention the twelve constellations of the zodiac, that of the Big Dipper, the Dragon, Andromeda, Cassiopeia and so on up to 88. Obviously most of them are not visible to the naked eye, but the most curious can arm themselves of telescope and explore, in different seasons, the celestial vault, in search of these hidden figures in the sky.

The constellation of Andromeda is one of the best known constellations, with a V shape, a sort of wedge that is outlined starting from a double curved line. In the sky Andromeda tells a story that sees her associated with her mother, Cassiopeia, with the Whale by which she is about to be devoured and with Perseus, by whom she will be saved: all these characters identify various constellations that border Andromeda.

The constellation of Andromeda, (Latin name) is easily identified having as a reference the Square of Pegasus or Cassiopeia: in the first case, starting from what for many years was considered a star of Pegasus, or α And, Alpheratz (or Sirrah), continuing from this, to the left we can identify three other stars δ, β and γ1, the brightest in the constellation, which form the outline of a figure which, in mythological tradition, refers to the story of a “chained princess” ,

Andromeda indeed. The identification of this constellation is also facilitated by the figure of Cassiopeia, which is located further north; essentially, it can be stated that Andromeda is located in that portion of the sky that borders the stars of Pegasus and those of Cassiopeia, which lies on the Milky Way. Andromeda, in its celestial boundaries, extends for 722 square degrees, from +51° North to +21° South, and goes from 2h 35m East to 22h 55m West. Despite its large size it is not always visible to the naked eye, usually the best period to admire it, in the northern hemisphere, is from September to January, while in our latitudes it is possible to admire it in the month of November.

The constellation of Andromeda owes much of its fame to the galaxy of the same name found within it: the Andromeda galaxy, M31, similar to ours due to its spiral shape, which however is not the only one in the constellation, we also remember and M32 and M110, both satellite galaxies.

The main stars of the constellation Andromeda

The main stars of Andromeda, as well as the brightest ones, are α Andromedae better known as Alpheratz or Sirrah and α, β and λ Pegasi: together, they form the Square of Pegasus. In particular, Alpheratz is ideally identified with the vertex that represents the young daughter of Cepheus, has a white-blue color and has a greater magnitude than the others (2.1). On the other hand, it often happens that the star β Andromedae surpasses it in brightness. Alpheratz, previously known as Sirrah (from the Arabic “Al Surrat al Faras”), or “the horse’s navel”, was once considered a star belonging to the constellation of Pegasus with the acronym δ Pegasi, subsequently combined with both the constellations and finally attributed to Andromeda. Another fundamental star is Mirach or β Andromedae, its name comes from Arabic and means belt or bodice, in relation to the representation of Princess Andromeda. It is a red giant of magnitude 2.1, 88 light years away which, in some periods, by virtue of its oscillations, shines brighter than any other. Following is the star γ Andromedae also known as Almach, it is actually a system made up of three stars (yellow-blue in colour), the two main ones of which are clearly visible with a simple telescope, it is located at the extreme south of the constellation.

In addition to the main stars, the borders of Andromeda obviously see numerous other stars, such as 56 And or a pair of giant stars, but also galaxies such as M31, the Andromeda galaxy and nebulae such as NGC 7662, one of the brightest in the sky.

The mythology of Andromeda

The mythological figure that gives its name to this constellation is that of the young Andromeda, daughter of Queen Cassiopeia and King Cepheus. The story goes that to appease the anger unleashed in Podeidon by his wife Cassiopeia who had dared to boast of being more beautiful than the sea nymphs, the king decided to offer his daughter, Andromeda, as a sacrifice to the sea monster Ceto (a whale) sent from the god of the sea. Suddenly, however, while the young girl was lying tied to the rock where she would have been sacrificed, Perseus, son of Zeus, arrived and, captivated by her beauty, decided to face the sea monster who won with cunning, so much so, in the end, he rescued Andromeda and her. groom.