The name, the history, the myth
The Eagle is an ancient constellation and as such has a very strong mythological history.
This constellation has Mesopotamian origins and appears in the most ancient maps, represented as an eagle on a stone relief dated around 1200 BC. For the Greeks, the eagle, like all the creatures of the air, fell under the dominion of Zeus; it was the king of the birds, privileged servant and fighter charged in particular to trace the lightning launched by the great god of the sky.
A particularly known myth concerns the abduction and the seduction of the beautiful Ganymede by Zeus, transformed in eagle; in some pictorial representations the Eagle appears in the act of carrying the young man upward between his claws, and Ganymede himself is represented among the stars south of the constellation with the head in alpha Aql. The bird became dear to the god when, as reported by Eratosthenes and Igino, about to make a sacrifice in order to attract good omens for the imminent battle against the Titans, an eagle appeared: he considered the manifestation a auspicious omen.
Another myth reveals the ferocious nature of the eagle. According to some tales, Prometheus (whose name means "prescient") belonged to the last generation of the Titans, descendants of the first deities Uranus and Gaea. Originally a fire deity, it is said that he was the creator and the divine protector of the human race. He would have taught mankind the arts and sciences, gifts considered by Zeus too great for the weak human race, and he would have given fire to men, stealing it secretly from the Sun and hiding it in a fennel stalk. Angry at this predilection for men, the father of the gods would devise an atrocious punishment: chained Prometheus to a column in the Caucasus mountains, he would send his eagle to devour his liver, from dawn to dusk. Since Prometheus was immortal, his liver grew back every night and every day, when the eagle arrived, the torment was renewed.
Many years later, according to one version of the myth, Zeus would finally show clemency by accepting a plea from Heracles. The wise centaur Chiron would give up his immortality in exchange for Prometheus' freedom and Heracles would strike the eagle in the heart.
A story of Igino sees the constellations of the Eagle and the Swan united: Zeus - besides turning into a swan to conquer the goddess Nemesis, had Aphrodite pretend to hunt him, turning her into an eagle. Since the operation was successful, Zeus also placed the eagle in the sky.
Another legend still tells of Antinous, a royal character who became the lover of the Emperor Hadrian. He sacrificed himself by throwing himself into the Nile to save the life of his beloved. A constellation was dedicated to him under the eagle's claws.
Julius Schiller, a Jesuit astronomer, turned the eagle into Saint Catherine of Alexandria, messenger of divine wisdom.
I've just talked about the famous Altair, present in many science fiction stories and movies thanks to the fact that it is very close to our Sun (just 17 light years away): generally all the stars of our galactic condominium have given inspiration to the authors, given their proximity and the relative ease to reach them with comfortable and short trips thanks to sophisticated spaceships.
An Eagle flying over our heads
In the introduction I said that for at least 40 years the Milky Way has not been seen from the city's skies: since I began to become passionate about Astronomy I have never seen it from Rome, but only in the mountains, where it appears as a milky band that goes from one side of the sky to the other. Many times I happened to explain to unsuspecting citizens on holiday in the mountains that what they saw was not a malignant band of clouds, but our galaxy seen from the inside!
Summing up, this constellation has half a dozen stars up to a little over 60 light years away (and among them there is another one very close, a little further than Altair), as well as a similar number of big stars: now accustomed to monstrous stars, 300 times the size of our Sun, here we have one above 100 and others up to 50 times, which is absolutely not little!
This, as for what we will see in the simulation (very truthful) of Celestia and Stellarium, trustworthy travel companions, while as for the real photos, of the excellent Hubble Space Telescope, we will see really wonderful subjects, within the reach of very large eyes such as those of very powerful telescopes.
The representation of the constellation in time
Starting as always from Hevelius, we see that among the raptor's claws there was a young man, Antinous, the beloved of the emperor Hadrian, here with a bow in his hand: it's an old constellation that has been later incorporated in that of the Eagle.
while in the Uranometry the young man appears unarmed
Instead, according to Stellarium, the eagle is depicted in a classic way
The nearby stars
As said, we find two stars very close together and four others not too far away: here they are listed in a table with the distance, the name (with the link to the image showing the Sun seen from the parts of the star) and its spectral class.
We can see that from Altair the Sun appears as a star of third magnitude to form an isosceles triangle with Sirius and Raccoon, while from Gliese 752 the Sun is halfway along the segment that connects the two stars. From the star β Aql a curious fact happens, always linked to the three-dimensionality of the stars in space: the Sun is always close to the two mentioned stars, but this time it appears close to Altair itself. From 31 Aql instead the Sun is very close to Sirius, near Altair, but this time Raccoon is much weaker and finally from δ Aql Sirius has moved away from our star.
A few big stars but not too much
From the diagram I made to compare the biggest stars of the Eagle compared to other stars we met in the previous episodes, we can see that the two biggest ones (70 and γ Aql) are both class K, while the third one (η Aql) is practically identical to Rigel. The other four in order of size (e, 66, ν and 56 Aql) are of different spectral classes and in all four cases are much larger than Aldebaran.
I couldn't miss the appointment with my friends Settantaquìli, who, unlike their name, have a very fragile appearance with body and limbs that look like burnt twigs: from the distance of 10 UA their star appears yellow-orange, big, bright and warm, which contributes a lot to their appearance, since in their planet it rains very little. But let's move on to deep sky objects, which is better...
Very beautiful Deep Sky objects
In the constellation of the Eagle there are many objects, given the presence of the Milky Way and among these I have chosen six of them: the first one is a nebula, called Cosmic Bubble, to the century the NGC 6781
the Cosmic Bubble nebula, NGC 6781
The second nebula is the colorful and suggestive NGC 6751 called Glowing Eye: seen from afar it looks like the first floor of an eye!
the Glowing Eye Nebula, NGC 6751.
Then we have three star clusters, the first is NGC 6709.
the Open Cluster NGC 6709
followed by NGC 6755, decidedly poor in stars...
the Open Cluster NGC 6755
while the third is NGC 6760, a beautiful globular cluster full of light spots
the Globular Cluster NGC 6760
Finally, in strict numerical order, I left the planetary nebula NGC 6741, called Phantom Streak Nebula (the ghost track), which appears definitely three-dimensional
the Phantom Streak Nebula, NGC 6741
The names of the stars of the Eagle
This constellation is well visible and flashy in the night sky and its stars have received a name from the ancient Arabs.
- Altair (α Aql): the flying eagle
- Alshain (β Aql): the peregrine falcon
- Tarazed (γ Aql): flashy star
- Almizan I, II and III (δ, η and θ Aql): the balance plate
- Dhanb al okab (ε Aql): eagle tail
- Debeb okab (ζ Aql): eagle tail
- At Thalimain I and II (λ and ι Aql): ostriches
Let me add a couple of space curiosities: remember the Pioneer 11 probe, launched back in 1973 and now slowly moving away from the Solar System? Well they have calculated that its flight trajectory will bring it to arrive near the star λ Aql, always assuming that this last one still exists! In fact it's expected to arrive in just 4 million years and the strange thing is that it's safer that the probe arrives at the appointment rather than the star: in this enormous lapse of time in fact the star will follow its own stellar evolution, while the Earth's artifact (unless absolutely unlikely clashes or close encounters with objects that even from a distance can burn it for example) should remain intact. Let's leave the difficult sentence to posterity.
ρ Aql has crossed the Eagle's borders
Another strange news concerns the star ρ Aql, called (I don't know by whom) Tso Ke, name that in ancient Mandarin means the flag on the left, which has a not very common peculiarity: since 1992 it is no longer part of this constellation, having moved inside the constellation of the Dolphin, because of its own high motion. Already in ancient times it was close to what would later become the border of the constellation and would later cross it. In this photo taken with Stellarium we see an enlargement of the sky area with the red trace representing the border between the constellations.
It is a constellation placed astride the celestial equator, so it is well visible at our latitudes. L'Aquila rises in the East, at the usual time, 9 p.m., in mid-June, and then culminates in the South, high in the sky towards mid-September. We will find it low on the horizon exactly to the west towards the end of November.