The constellation Dragon (Draco - Dra)

The constellation Dragon

As in the case of the Eridan and the Serpent, the inventor of the constellation of the Dragon did not have to use his fantasy to imagine a Dragon among stars close to the Polar star: it was enough to "join with a stroke of a pen" more bright dots and there the Dragon is as beautiful as ready. Just think that not even H.A.Rey, an expert in the field, had been able to do more: a sinuous dragon wrapped between the stars of the sky.

The name, history and myth of the Dragon

The constellation of the Dragon, or Dragon, is a northern constellation, which starts near the North Pole and creeps between the two Bears.

The constellation was from time to time seen as a snake, a hippopotamus and, in ancient India, a crocodile or an alligator. The shape of the Dragon is instead native to Mesopotamia, where it appears as a winged dragon bigger than the present one, therefore, wrapped spirally towards the head of the Big Bear; in the VI century B.C. the philosopher, astronomer, Greek mathematician Thales took off the wings of the dragon to form the Big Bear and since then, it was no longer flying.

According to a first myth, the Dragon represents the dragon that devoured the men of the founder of Thebes, Cadmus, sent to the well of Ares (Mars) to seek water. Cadmus would then slay the dragon and sowed his teeth, from which were born armed men, the Sparti or "sown", progenitors of the Theban.

Another myth tells of how, at Jupiter's marriage to Juno, the Earth gave fruit trees that every spring gave birth to golden apples. The garden was guarded by four nymphs, the Hesperides, who guarded the precious trees with a dragon, Ladon, with a hundred heads, capable of speaking and imitating any kind of human or animal voice.

When some malicious person approached the garden, the dragon began to scream in a hundred different shades, making him run away. Eurystheus, assigning the twelve fatigues to Hercules, understood just the theft of one of the apples, and Hercules managed to pass this test thanks to the help of Atlas, shooting an arrow that hit Ladon to death.

The dragon was thus killed, but to remember him, she was deeply troubled and placed him in heaven as a constellation.

Again, it is told how the dragon fought together with the Titans in the war against the gods of Olympus. Then ten years of war had passed, when the dragon engaged in a battle against the goddess Athena (Minerva), who grabbed him by the long tail and threw him twirling in the sky. As it fell from above, the dragon's body knotted and became entangled around the celestial North Pole. The air up there was so cold that the beast froze in that twisted position around the North Pole.

According to a Chinese interpretation, during the eclipses of the Sun or Moon, the light is swallowed up by the celestial dragon.

In ancient times the polar star was Thuban, the alpha draconis star, and it will become again around the year 26000 as a consequence of the precession of the equinoxes.

The figure of the Dragon contained the North Pole, but also the ecliptic pole. Already in Mesopotamia the Dragon was represented as a pivotal symbol: the terms 'head of the Dragon' and 'tail of the Dragon' indicate the ascending and descending knots of the apparent motion of the Sun.

The Moon also crosses the apparent motion of the Sun in two points, and the interval between them is called 'Draconic Month'.

An eclipse of the Sun or Moon can only occur when the Moon and Sun are near the Dragon's Head or Tail.

Representation over time

Let's see immediately how the ancients represented the Dragon: Hevelius depicts it as a kind of big snake several times rolled in coils and with a long tail.

the Dragon according to Hevelius

Practically identical is the representation of the Uranometry

the Dragon according to the Uranometry

Instead Stellarium gives a different meaning to the appearance and especially to the animal, which is now more similar (albeit stylized) to medieval flame-spitting dragons, with two pairs of legs.

the Dragon according to Stellarium

Nearby stars

In particular we have a dozen stars below the threshold of 60 light years, a distance from which the Sun would appear (but in reality "appears") of sixth and therefore invisible to the naked eye. As already done other times I have grouped these stars in a table in which I have reported for each one the distance in light years, the name (clicking on which opens an image that represents the star field around our Sun, if seen near the star considered) and the spectral class of the star itself.

[table "12" not found /]

The nearest stars, because it is a double star, are Gliese 725A and B, both of class M3 and 11.5 light-years away from us: from the vicinity of these two stars, the Sun shines 2.5 in a star field of our southern sky, with stars of the caliber of Canopus, Sirius, Alpha Centauri and others of the constellation of the Ship of Argos (Vele and Poppa of the ship). The presence of all these stars of our southern hemisphere should appear very clear: the constellation of the Dragon is located in the parts of the North Celestial Pole and observing the sky from that area, the Sun is projected in the opposite part, near the South Celestial Pole: all this because, let's always remember it, stars have three-dimensional coordinates in a three-dimensional space and those closer to us allow the occurrence of perspective games completely new and to which we are not accustomed.

Speaking of news, if you look at the photo of Gliese 687 (located a little less than 15 light years from us) you will discover that from that star, our Sun (of 3) is inside the so-called LMC (Large Magellanic Cloud), a star cluster very close to the Milky Way, visible even to the naked eye as a nice cotton ball, but not from our latitudes: the Sun is right in the middle of it, thus giving the impression to our friends of being part of it.
From σ Dra and from χ Dra instead the Sun, almost fourth, now is no longer apparently part of the LMC, from which it is well detached: from GJ 1221 instead the Sun appears right at the edge of the star cluster, while (jumping to the star HIP 85235) now exceeded the fifth appears so dim as to be confused this time with the stars of the LMC!

Precisely because we are in the presence of stars to be considered not squashed on the celestial sphere, but always in three dimensions and placed in space each one at a certain distance, now it happens that from the star 26 Dra (placed at 46 to us) our Sun, which has become practically invisible to the naked eye, is in a star field where now has made its appearance no less than Altair, in addition to the already mentioned χ Dra. If you can "see" it, it is an amazing game of perspectives!

Polar Stars

No, the title's not wrong! It's just the plural! We all know the polar star, for better or worse, inside the Little Bear, which the ancients called Alruccabah: we call it "Polar" because in the last millennia it is precisely it that is close to the Heavenly North Pole. We know that as a result of the Precession of the equinoxes (at this link you can find my article) the PNC moves slowly in the sky describing a circle in about 26000 years, getting closer every now and then to bright stars.
The title of the paragraph speaks therefore of polar stars, since also the star α Dra (Thuban) can become for a certain time the "Polar" star: it was about 2700 BC (at the time of the construction of the Egyptian Pyramids) and it will be again in the year 21000 (about!!) .

I have underlined several times the word "about" because the indicated values are absolutely approximate, especially the period of the precession of the equinoxes (as I explain widely in the article): I want to specify it because not infrequently the usual "scientific" study of the usual long-haired scientist comes out, which links the above period to improbable events (usually catastrophic, how strange!). As always, adding to an initial value "of convenience" another value "of convenience" (close to 26000) for the precession you magically get the exact date of an event, which just to change then does not happen...

Deep sky objects

Among the many Deep Sky objects present inside the constellation of the Dragon, I have chosen four absolutely fantastic ones (I remember that clicking the photo opens an even more detailed one). Let's start from the planetary nebula NGC 6543: here we see it splendid in a photo to be applauded by the tireless HST.

A Wonder of Heaven: NGC 6543 with another marvel in the middle.

The mysterious object you can see in the center is the nebula called Cat's Eye Nebula : here we can see it in more detail (and we can click on the picture too!).

the beautiful Cat's Eye Nebula

The next photo instead concerns a lenticular galaxy, completely cut, known as NGC 5866, but also catalogued by Messier as M102.

the galaxy NGC 5866 cut view

In the midst of these gigantic wonders, here instead is the "Draco Dwarf Galaxy", a very interesting cluster of stars.

a small galaxy: NGC 6822

Returning to very large objects, here again is a barred spiral galaxy, called NGC 4319, accompanied by the smallest object at the top right, Markarian 205, a very compact, active galaxy, with strong ultraviolet emissions, in short a low light quasar

the galaxy NGC 4319

Big stars

comparison between the Dragon stars and other known stars

Let's now come to the Dragon stars of important dimensions: in the comparison diagram we see about ten stars that are not really monstrous, like the ones put in the background, but that have dimensions of everything. Let's start from 4 Dra, a red giant with a diameter "just" 104 times that of the Sun: nothing to do with the "underlying" Betelgeuse, Antares, ρ Cas, P Cyg and VY CMa real monsters of the sky, but always three times bigger than the blazoned Aldebaran.

4 Dra from the distance of 10 UA

In this photo, taken with Celestia, we see an intense reddish star of more than 5° of diameter at the beautiful distance of 10 UA (Saturn's star from the Sun): my Quattrodrai friends say that it is really annoying to look at closely. Nothing to object!

comparison between β Dra and the Sun of 10 UA

Going down in size, we find 7 Dra, of the same class as poor Aldebaran, which beats with an almost exactly double diameter. Subsequently we find the giant d Dra, of class F7 and going down even more we come across the β Dra (Rastaban) a star of the same spectral class of the Sun (G2), but 40 times big: my friends Rastabanani (with long hair, a bit smoked and greedy of chiquitas) invited me to photograph their yellow giant from the distance of 10 UA. It's very bright, the same color as the Sun but with a diameter of little more than 2°: in the photo I added on the left the Sun seen from the same distance, that of Saturn.

The names of the stars

In this constellation practically all the main stars have received a name, which we are going to analyze together.

  • Thuban (α Dra): tail of the dragon
  • Rastaban (β Dra): head of the dragon
  • Eltanin (γ Dra): Dragon head
  • Altais (δ Dra): the goat
  • Tyl (ε Dra): unknown meaning
  • Dhibah (ζ Dra): the hyena
  • Dhibain (η2 Dra): the hyena
  • Edasich (ι Dra): the male hyena
  • Giausar (λ Dra): the place of poison
  • Alrakis (μA Dra): camel on a trot
  • Alwaid (ν Dra): the mother of camels
  • Grumium (ξ Dra): lower jaw of the dragon
  • Tais I and II and ρ Dra): the goat
  • Alsafi (σ Dra): tripod of an open kitchen
  • Athafi I and II and τ Dra): tripods of an open kitchen
  • Aldhiba (φ Dra): other hyena
  • Alahakan (χ Dra): two black bulls
  • Dziban I and II (ψA and ψB Dra): two hyenas
  • Adfar Aldib I and II(f and ω Dra): the claws of the hyena

In short, it's okay to name all the stars, but there is little left of the poor Dragon (two heads, tail and jaw): for the rest there is a zoo of other animals including half a dozen hyenas, goats, camels, bulls ... And there is also space for a trip out of town ...

Visible at all times...

As said, it is a circumpolar constellation, visible every night at any hour: all that remains is to observe it!

Audio Video The constellation Dragon (Draco - Dra)
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