The name, the story, the myth
The constellation of Serpent is mythologically linked to that of Ophiuchus which crosses it.
Wrapped to Ophiuchus, meant as the one who holds the serpent and for this reason also known as Serpentarius, is the god of the medical arts, Aesculapius, and the serpent is his mythological symbol.
It is said that Aesculapius was forced to helplessly witness the death of a friend, and soon after he saw a snake near the corpse. He immediately killed it, but another snake arrived and placed it on the wounds of the dead reptile of medical herbs. The snake came back to life, and it was then that Aesculapius began to take an interest in the medical arts.
The constellation Serpent divided in two
This is the only case of a constellation divided into two distinct parts, separated by that of Ophiuchus: since ancient times the giant Ophiuchus (the Serpentarius) was depicted, holding a big serpent in his arms, whose head is on the right while the tail is on the left of Ophiuchus himself. When the starry vault was subdivided into constellations, the astronomical community had decided to divide the Serpent in two, keeping the constellation and above all the official nomenclature unique, just as if it was a non fragmented constellation.
You can also sometimes find a name of Serpens Caput and Serpens Cauda for the head and tail respectively, but they are not officially recognized.
Pretty big stars
In this constellation we find a monster star and four others a bit smaller, but always many times larger than our Sun. In our usual diagram we can see in comparison with other more famous stars (but usually much smaller!) and other real star monsters encountered during the various episodes: if you remember what we said about the star VY CMa, you will better understand why in the diagram this star appears represented only as an arc, since it has nothing to do with the sheet!
Let's start from the first star, the biggest one, τ4 Ser, a red giant 236 times bigger than our yellow dwarf: my Tauserioni friends advised me, but it is already my custom, to take back their star from a distance of 10 UA. In this photo we see an orange-red star that covers more than 11° of the sky. A little more reddish is instead the star 47 Ser that from 10 UA shows an apparent diameter of little more than 5°, being its radius 99 times that of the Sun, which is not at all little. Then we find τ1 Ser, with a diameter of 80 times, which I didn't photograph because the Tauserini (unlike the already mentioned Tauserioni) that I know had gone on vacation.
Coming back serious, we find k Ser with a diameter of 67 times and close with ρ Ser, of "just" 41 times our Sun.
Deep sky objects
The constellation of the Serpent presents three remarkable objects that I now show you, as they were taken by the very powerful HST.
The globular cluster M5
The first object is a globular cluster, known since the times of Messier, who catalogued it at the fifth place, therefore calling it M5: clicking on the picture you can see a high-definition image of the star cluster, very rich in multicolored stars.
The open cluster M16 (Eagle Nebula)
The second object is an open cluster catalogued as M16 by Messier and otherwise known as Eagle Nebula, practically a furnace of stars in formation.
A marvel called Hoag's Object
The last object I chose in the Snake is the so-called Hoag's Object, from the name of the discoverer: from the photo you can see that it's a particular galaxy, ring shaped, composed of very young stars, which surround a nucleus of much older stars. Really fascinating.
The representation in time...
... of the Snake has never caused big headaches to the artists who have tried to represent a reptile firmly held by the good Ophiuchus:
Hevelius shows it not very happy to be almost crushed by the mighty hands of the Serpentarium, while in the Uranometria
the Snake in the Uranometry
the serpent is depicted alone, with a rightly sinuous body. Finally in Stellarium
There is a representation in which a young man appears this time rightly perplexed (at least) in keeping a disturbing snake at bay.
The names of the stars
In this constellation, all things considered not very bright stars, few of them have received a name...
- Unukalhai (α Ser): Arabic name, the neck of the snake
- Nasak Shamiya I and II (β and γ Ser): name meaning northern border
- Nasak Yamani I and II (δ and ε Ser): name meaning southern border
- Alya (θ Ser): the tail of the snake
We close the episode by learning together when and where to observe this double constellation.
At nine o'clock in the evening, the Serpent's head begins to appear on the eastern horizon in the second decade of April. The culmination in the south for the two parts of the constellation takes place one month apart: the head appears high in the south in the second half of July, while the tail is found in the same position just after mid-August.
At the end of October, the Serpent's tail now appears low on the western horizon at the turn of October and the beginning of November.
Now that you know where it is and when you can find it in the sky, I wish you good observations.