The constellation Sagittarius

Here is a constellation really rich in stars, both those visible to the naked eye and those that make up the spectacular Milky Way that in that area is full of stellar objects and the "deep sky": in the direction of the constellation Sagittarius in fact there is the center of our galaxy. From the photo taken with Stellarium we can see the unmistakable milky spot that whitens a good part of the constellation.


We know that Sagittarius is a zodiacal constellation and that therefore it is crossed by the Sun: this happens more exactly in the period of the year that goes from 18th December to 20th January. This is always thanks to Stellarium, a photomosaic that indicates the path of the Sun (the ecliptic) within the constellation, between the two dates that from year to year may however differ by a couple of days more or less: this deviation is due to the irregularities of the Earth's orbital motion around the Sun, which affect the apparent motion of the Sun on the celestial sphere, along that line called the ecliptic. If you look closely at the "diagram with two Suns", you will also see a mysterious red arrow that indicates a particular point in the Sun's annual path, the one where the star in our day sky crosses the imaginary line that traces the Milky Way in the sky, the so-called galactic equator. I highlighted the word "annual" to underline the fact that at that point the Sun passes through it every year (apart from the discrepancy I mentioned earlier): do you know what day the Sun is at that point? December 21st. And doesn't that date remind you anything, perhaps associated with the year 2012? Among the many inventions that led to the 2012 hoax, there is the one that states that the much-trumpeted end of the world should also occur because of the passage of the Sun through the plane of the galaxy at the point indicated with the arrow. The ridiculousness linked to this statement is evident precisely because the Sun passes through that point every year, thus making 2012 an ordinary year.



The name, the history, the myth

The Greeks associated Sagittarius with Crotus, son of Pan, a satyr of partly human and partly caprine forms, with a long ponytail, often depicted standing on two legs.

Roman mythographers sometimes identified it with the peaceful and wise centaur Chiron, which caused confusion with the southern constellation Centaur. The nature of the two celestial centaurs is different: Sagittarius is in fact a hunter, linked to the ancient Mesopotamian deity Nergal, son of Enki for the Sumerians, in turn associated with the rabid god of war and fire Irra (Ares for the Greeks, Mars for the Latins).

The nearest stars in this case are 77 and 78 light years from the Sun (Kaus Borealis and ω Sgr), but at the beauty of 28 light years between them. North Kaussian astronomers see the Sun as a sixth magnitude star, so barely visible even to their three eyes placed vertically like traffic lights. In that area of the sky we find some old acquaintances, such as Alnath and Aldebaran del Toro, Betelgeuse and Bellatrix of Orion, as well as a star that we will meet later on, Capella, the little goat of the constellation Auriga.

Just going to visit our Kaussian friends, you can see the star in question, yellowish, occupy more than 5° of the sky if we place ourselves at the distance of the Earth from the Sun, at 1 UA. Looking at the photo, we read that the star has a radius equal to 11 times that of the Sun: large but not too much... As for the other nearest star (ω Sgr), we have to say that the Sun is more or less in the same area of the sky and always not very bright: in this case our Omegasgrian friends, with their strong colorblindness, don't worry about it so much. Their star is a yellow dwarf, just a little bit bigger, with a diameter 2.8 times that of the Sun.


Stars in comparison


The constellation Sagittarius has a number of stars of remarkable size compared to the Sun: not those real giants we have encountered so far, but stars of all respect. In the diagram, next to the usual stars that I always use as comparison, some stars of Sagittarius of good size have appeared and apart from the 62 Sgr and the 24 Sgr (both with a ray equal to 120x), all the others in the upper row are below the threshold of 100 times the solar ray and I have chosen them this time with a criterion related to the spectral class and we will visit them just to appreciate their color, as well as their size.

Going back for a moment to the diagram of comparison of the sizes, we see that Kaus Media is practically as big as Rigel, while among the stars I put of Sagittarius, the only Albaldah is smaller than Aldebaran: remember when I was talking about this beautiful star (nothing but the α of Taurus) and its size? Well since then, too many stars have passed under the bridge of command, that of the spaceship Celestia...

The representations of Sagittarius

We have arrived at the moment of the representation of Sagittarius: here is the image taken from the Uranometria 



the one according to astronomer Hevelius

and finally according to the Stellarium program


As for the other constellations of the zodiac, at this point we see the stamp issued in 1970 by the Republic of San Marino and representing a Sagittarius ready to shoot his own arrow: it is a 70 lire stamp, which was not little for the time. You will have noticed in the pictorial representations that our four-legged archer was either very sure of his skills or a little careless: the one he is hurling is his only arrow, as there is no trace of quiver. What if our mythological William Tell had missed the target?

Some fantastic nebulae

At the beginning of the article I pointed out that in this constellation there are a lot of deep sky objects (in English it sounds better: deep sky objects), so much so that you will be spoilt for choice. Let's start from M17, the seventeenth nebular object of the Messier Catalogue, the so called Swan Nebula, here framed by the mythical Hubble Space Telescope, which revealed wonderful details.

 Another truly spectacular and famous object is the so-called Trifid Nebula, the twentieth nebula in Messier's catalogue (M20), which takes its name from the fact that it seems to be divided into three parts.

Let's close the review of absolutely fantastic photos with the phantasmagorical Lagoon Nebula (Lagoon Nebula) also known as M8 and therefore one of the first nebula objects in the Messier catalogue. Because of the beauty of the photos, it made my heart ache to reduce them, so by clicking on the next three pictures you can see each of the life-size photos with unlikely details, thanks to the eye of the Hubble Space Telescope. I suggest you to put on full screen this page so that clicking on the image you can open the corresponding photo in high resolution.

This other photo is basically the detail of the area at the top left of the previous photo: if the previous one seemed rich in details, the latter is so detailed that it seems to be there a short distance away.

Finally we close with an overview of the M8 nebula, also in this case very rich in stars and details that make it a work of art that no artist on the face of the Earth could conceive!



Audio Video The constellation Sagittarius
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