The constellation Scorpio (Scorpius - Sco)


The Scorpio: a really beautiful constellation to observe in the summer evenings, without effort, without having to fear the torticollis, since we have it in front of us, low on the horizon, majestic and at the same time fearful. Even if we don't know where to look for it, all we need to do is look at the sky and sooner or later we will meet it, with its unmistakable tail. This fact always makes me remember when on TV they decide to talk about eclipses, apparitions of comets, planets, etc., in short, anything about the sky: invariably every time is repeated the usual phrase "everyone with the nose up", even when in reality we have to look straight ahead. Who knows what it is like, for some people the sky is only up there, not in front of us or simply around us.

Starting from this image taken from Stellarium, or observing directly the constellation in the sky, following the stars, from bottom to top, from the sting to the claws, we will arrive at a very bright star, Antares, red, shining, with a name that has always associated it with the planet Mars, with which it shares the color and against which it seems to fight when the red planet happens in those parts of the sky: and if this happens in opposition, then you can follow the brightest Mars near the giant star for a long time. The next two examples will be at the end of September 2014, with a close conjunction, while in the period April-May-June 2016 on the occasion of the opposition of Mars, the red planet will approach Antares, but will retrace its steps (retrograde motion) and then return to the star, which it will then overtake to go further. Write it down somewhere!

Those who know well the Astronomy or those who are lucky enough to travel the world, know that below the equator the sky undergoes a kind of metamorphosis, with the appearance of constellations never seen before or with those we know well that are, how to say, crooked. If with imagination, or with a nice flight by plane, or even with Stellarium, we go to Cape Town, in South Africa, do you know how we can see the Scorpio, when it's about to set? Here it is almost unrecognizable in the picture above: and on August 15th, just think, you would even have it at the zenith!

Like all constellations, also the Scorpio appears flat, drawn in the celestial vault, with its stars, from the brightest to the weakest, which seem to be attached to a black background, all at the same distance. No! Now we can see with our own eyes that the truth is quite different. On our PC.

Thanks to our program we can in fact get an idea of how much once again the stars that make up a constellation are there, in the sky, only by virtue of a perspective game, forming only in some cases a real physical group. I'll never get tired of pointing this out: the stars of any constellation are very far away from us but also from each other! The fact of seeing two stars close together is an optical pious illusion: take for example ι1 and κ Sco, at the bottom left, in the hairpin bend leading to Shaula, the fearsome sting. You see? The first one is at an amazing distance from us (1929 light-years away) and the other just 483... unimaginable and absolutely deceptive for the human eye: they have almost the same magnitude and seem very close, but they are not! Also Antares doesn't joke with its 554 light-years: among the stars I used in this representation the nearest (or better the least distant) is ξ Sco, up there on the top right, 59 light-years away from us. Precisely because of its proximity, we will see from the sky this little star where the Sun and other known stars are: I said "little star" since it is just a little bigger than our yellow dwarf, companion of our days. Antares no! Instead, we will discover that it really is a cosmic monster, even bigger than Betelgeuse.

The name, the story, the myth

The brightest star of this ancient constellation, Antares (alpha Scorpii), indicated the position of the Sun at the autumn equinox at the dawn of the Mesopotamian civilization, about 5000 years ago. In tablets dating back at least 3500 years ago it appears with the name of GIR.TAB

In Egypt the stars of Scorpio were for a time seen as a snake. The constellation was once much larger: in the classical Greek and Roman period of the first centuries BC. (Ovid reports it in his writings), its claws included the stars that now form Libra, the Greeks called Chelai this area of sky. Since the late Middle Ages, the claws of the scorpion have been reduced and the whole animal is enclosed in the constellation of Scorpio. The remains of this confusion are still present in the names of the stars of Libra: for example sigma Lib is sometimes still called gamma Scorpii.

Scorpio has always been tied to his bad reputation. In Greek myth, Gaea orders the great beast that has escaped from the earth to sting Orion and kill him. The hunter will be resurrected by Aesculapius. In the movement of the celestial vault, when the Scorpio rises in the East, Orion sets in the West; Orion rises again, reborn, but as soon as he appears in the East, the Scorpio sets, crushed by Ophiuchus.

In Maori tradition, the Scorpio represents the fish hook of the ancestral hero Maui. While fishing in the ocean, one day Maui found himself pulling up a piece of land on the hook. The edges of this land gradually frayed until it split in two and New Zealand was born. But the hook came away from the island with such force that it flew into the sky, where it remains to this day.

In ancient times the Scorpio was depicted as follows

Modernly speaking, the Scorpio has another aspect, but however absolutely similar, as it is obvious: as always Hevelius has represented the body in a specular way with respect to how it appears in the celestial sphere: to see it correctly you have to turn the photo.

This is instead the 20 lire commemorative stamp issued by the Republic of San Marino in 1970. Nice the image, even if very essential and also very nice the initiative of San Marino: stamps in astronomical theme have appeared several and of several states. When the occasion arises, we will add the relative image as a curiosity.

We fly among the stars of Scorpio

We set sail aboard the spaceship Celestia to go and see closely the stars of this beautiful constellation: the first stop is obviously Antares. When our space navigator takes us to 100 astronomical units from the star, it already looks as dazzling as the Sun (the same brightness, -26), but it's time to stay wide open. From 100 UA, ten times the distance of Saturn from the Sun, Antares appears to us as a disk almost 4° in diameter! We are evidently in the presence of a monster, an enormous star, and in fact we already know that since we are 100 UA from the surface of the star, the radius of Antares is 3.38 UA, 730 times the radius of the Sun. Hugely larger than Betelgeuse...

We can imagine that from Antares our little Sun is an insignificant star and in fact it is no less than 11 in a zone of sky where the only known star is Betelgeuse: really a disappointment, to which we are slowly getting used. And from a monstrous star like Antares, the brightest one is π Sco, which shines more than Sirius in our sky: in this photo we see it while we are in close orbit around Antares, which appears absolutely threatening on the left. Fortunately our spaceship has a good air conditioning system!
But how much bigger? Instead of doing too much math, I made a drawing where I scaled the orbits of the planets in the Solar System back to Saturn and the two sky monsters Betelgeuse and Antares. And if Betelgeuse had already looked like a giant reaching half the orbit of Jupiter, now Antares is even closer to the gas giant: but there are even bigger stars, which we will know both when we travel between the constellations and on virtual journeys. In all this display of grandeur, the Sun in the diagram is much less than a dot.

Despite all the tricks, it's definitely too hot in these parts, even after turning on all the onboard fans: it's better to move towards the tail of Scorpio, going to the parts of Shaula Sco), a star humanly bigger than the Sun (just 13 times) that welcomes us with its intense blue light. From a distance of 1 astronomical unit it appears to us with a disk of almost 6 and a half degrees of diameter. The Sun, seen from Shaula, is as weak as before and I spare you the bleak photo of an area of the sky where once again the only known star is Betelgeuse.

In good company

We had seen before that some stars taken into consideration to represent the constellation of Scorpio, the nearest is ξ Sco: being clearly closer to the Sun, the latter will appear to the eyes of the Csiscorpians as a fourth star this time in a zone of sky in good company of well known stars such as Aldebaran, the Hyades, the Pleiades (that we know to be part of Taurus) and Bellatrix (Orion) and that we will know later Sirius (in the Major Dog) and Capella (in the Charioteer). All in all a stellar condominium with worthy and nice neighbors.

Delusions of grandeur

Remember the star size comparison diagram? As long as they fit, I add each time the stars I'm talking about in the articles: this time it's impossible not to notice Antares, which I drew concentric with respect to Betelgeuse. Below I added the star ι Sco only for the remarkable fact that it has a radius equal to 20 times that of the Sun and therefore it is the second of the constellation in order of magnitude: once again, simply looking at the stars on a map or directly in the sky you can't even imagine how big the stars can be or how far away they can be. Finally I have added a pair of stars (β1 and β2 Sco) for an astronomical reason linked to memories of youth, which I will now explain.

My first astronomical observations

It was the year 1971 and in mid-May there would have been a particularly rare event in the astronomical field: the gaseous planet Jupiter would have hidden a star of 2.6 (Acrab, β1 Sco), therefore very bright and easily visible to the naked eye. The additional peculiarity of the event, which made it even more rare and important, was that the star in question is a double optic: the companion (β2 Sco) also very bright ( 4.8) is not distinguishable with the naked eye, but a pair of binoculars is enough to see it. At that time I had at my disposal a beautiful Russian binoculars and so I was able to observe the final part (the emersion of the star) of this wonderful event, which only we Astronomy enthusiasts knew and that the media had ignored completely. Since then and for a good period of time until 2050, there have been and there will not be any occultations of stars so bright by Jupiter.

The names of the stars

In this episode we met and saw in the drawing several stars that have a proper name: let's see their meaning.

  • AntaresSco): means similar to Ares or against Ares (Mars)
  • AcrabSco): Arabic word meaning scorpion.
  • DschubbaSco): from Arabic the scorpion's forehead
  • GirtabSco): from Sumerian the scorpion
  • ShaulaSco): from the Arabic sting of the scorpion
  • Al NiyatSco): from Arabic the arteries
  • LesathSco): from Arabic the foggy spot (referring to the nearby M7 nebula)
  • JabbahSco): from Arabic the forehead (of the scorpion)
  • WeiSco): from the Chinese the tail (of the scorpion)

When can we watch it?

The constellation of Scorpio is typically visible in the summer: at 9 p.m., a convenient time for those who do not want to get up or want to show it to friends usually interested in something else, is visible in the months from May (when it will be seen low on the horizon in SE) until September (when it will be about to set in SW). The climax, with the Scorpio still low on the southern horizon, is in August every year.

With this we greet the beautiful constellation Scorpio and I give you the appointment to the next episode. Stay tuned!

Audio Video The constellation Scorpio (Scorpius - Sco)
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