Prendiamoci cura della Terra

Fatal Attraction!!!

The Andromeda galaxy is the farthest object visible to the naked eye, and it is coming upon us.

Andromeda Galaxy. This composite image shows a region of the halo in the nearby Andromeda galaxy that astronomers used to accurately measure the galaxy’s lateral motion in the sky. This allowed them to predict a direct collision between Andromeda and the Milky Way in approximately 4 billion years.
The astronomers compared this region with images of the same area taken seven years later. They measured the small amount of lateral drift in the halo stars relative to the field of the stationary background galaxy.

We know that since the beginning of time, since the Big Bang, the Universe has been expanding, and therefore all galaxies, since they were born, have moved away from each other. But there are exceptions.

There are actually galaxies that are coming closer to each other because their proximity means that gravity wins over the expansion motion of the Universe. This is exactly what is happening to our Milky Way in relation to the Andromeda galaxy, i.e. our closest sister galaxy which contains nearly 1000 billion stars.

Are we moving towards Andromeda or is Andromeda travelling towards the Milky Way? Well a bit of both, the attraction is mutual.
The distance between us and Andromeda is about 2 and a half million light-years, which corresponds to the incredible figure of 23 billion billion km; according to the latest estimates made by astronomers, it seems that the great clash will take place between 3.5 and 4 billion years.

In the upper part of the photo, we see another small “wad”: the satellite galaxy M110 which was the last to be included in the Messier catalog because it had not been seen. In this regard, I like to quote the words of the astronomer Charles Messier who was looking for nebular objects in the sky.
“On 10 August 1773, while observing the great Nebula with care and in a perfectly beautiful and clear sky, I discovered a smaller one that I had never noticed since it was very difficult to see. It appeared above the big one and they all were visible in the field of the instrument. It is surprising that I didn’t see it while I was working on my nebulae catalog. It is less bright and it can be assumed that if it had not been seen it was because the great light of the great Andromeda Nebula had prevented me. “

Contrary to what one might think, however, there will be no fireworks because the space around us and the distances between the stars are enormous. To give an example, if the Sun were a 1 euro coin, the nearest star would be 1000 km away, and if I reduced it to a grain of sand, in a city like Rome I would find between 6 and 10 of these. grains. What will happen, therefore, will not be a real confrontation, but a merging without many shocks.

And if in a few billion years any of us will still be here, they will see a magnificent sight because Andromeda will appear very large in the sky and after a while, the two galaxies will become one, twice as large.

How to locate Andromeda in the sky by following the two path methods starting from the constellation of Cassiopeia

As mentioned at the beginning of the article, the Andromeda galaxy is in fact the farthest object visible to the naked eye, provided we are under a very dark sky (which is now very difficult to find in Italy). Some might not believe that with your eyes alone, on a clear night and away from the lights of the cities, we would be able to see an astronomical object that is 2 and a half million light-years away, but if you happen in the late autumn or early nights winter to look up in the sky between the constellations of Cassiopeia, Pegasus and Andromeda, maybe with the help of binoculars, you should be able to see a faint elongated whitish speck immersed in the point-like stars: it is she.

Spectacular image of 2 galaxies’ merging. The image was taken by the Hubble space telescope (NASA)

Andromeda in mythology

Daughter of Cassiopeia who was the queen of Ethiopia and wife of Cepheus. The vainmother of the poor Andromeda, one day claimed that she was more beautiful than the Nereids, sea nymphs and seductive daughters of Nereus. At that point, the nymphs decided that the time had come to punish Cassiopeia for her vanity and asked for Poseidon’s help.
Cepheus, however, turned to Ammon’s oracle who revealed to him that to appease Poseidon’s anger he had to sacrifice his virgin daughter Andromeda, who was chained to a cliff overlooking the sea.

Andromeda constellation

While the young woman was there, unable to escape, Perseus passed by, astride Pegasus. The young hero’s heart was conquered by the girl’s beauty and he approached her and tried to start a conversation with her.
Andromeda decided to tell her sad story. So Perseus, after asking Andromeda’s parents for her hand, killed the monster sent by Poseidon and freed the young woman. From their marriage six children were born, one of whom, Perse, is considered the progenitor of the Persians.


Author: Giancarlo Neccia is an amateur astronomer and astrophotographer of the “La via delle Stelle” association of which he is vice president. He is the technical manager of the “La via delle stelle” observatory in Montelanico (Rome) and the Maurizio Cassandra observatory in Carpineto Romano (Rome) equipped with a 400 mm Marcon telescope.

Translation by Maria Antonietta Sessa