Two Geometric Constellations: Norma and Compasses


The Norma constellation or Carpenter's level

It is a modern constellation, created by the astronomer Lacaille in the middle of the eighteenth century and positioned in a zone of sky easily identifiable for the presence of other very famous stars, but then poor of stars: it is in fact next to the tail of Scorpio and has the peculiarity that in it two important stars are missing, the α Nor and the β Nor , while the brightest of the group, γ2 Nor (that we will meet soon) is of only 4th magnitude.


Some people translate the Latin name Norma as Carpenter's level (which I like best): since Rule would make her confused with the well-known Lion star, I will always use the other two terms. In our virtual sheet, which we open by clicking on the animation, we can see the few stars of Norma and by pressing "f" we see the wise representation created by H.A.Rey, which however has little to do with a Regulus or a Team. Turning the page with the right and left arrows, we can see that there is a very distant star, over 4000 al, that presses the representation of the constellation: remember that we can press on the "+" and "-" keys to zoom in and out. And there is also "esc" to return to the initial display, after you have zoomed too much!

Since the constellation is modern, it appears neither in Uranometria nor in Hevelius' work, so we see it as it is shown by Stellarium.



The name, the story, the myth

The Squadra (Norma) is one of the constellations introduced by Nicholas de La Caille as a tribute to one of the instruments used by surveyors and most used by astronomers, so it does not have its own mythology. Extracted from the stars at the edge of the Wolf (northwest), Altar (east) and Scorpio (north). Its introduction followed the expedition made to Cape of Good Hope by the abbot in the years 1751-1752. In fact, de La Caille called this group of stars in his 1756 memoirs "équerre et la règle de l'Architect" (team and ruler of the architect), but in 1763 he simply called it the Squad. Even in the maps of the sky drawn immediately after the introduction, the figure associated with this asterism included both instruments. Later, however, it was mutilated not only of an instrument but also of its two brightest stars, the alpha Nor and beta Nor, now part of the constellation Scorpio, which were the northernmost stars of Norma.

the Norma according to Stellarium

No stars nearby, but a medium-large one.

comparison between the stars of Norma and other notes

As the title says, the constellation does not present any star with a distance less than 60 al, the threshold I have chosen for this series of articles. As we see in the comparison diagram between its (few) stars and others we meet every time, there is only one star big enough, 42 times the ray of our Sun: it is γ2 Nor (5th , of class F9, distant more than 1400 al) apparently very close to the already mentioned γ1 Nor, that instead is a star of class G8 distant just 129 al: just for a casual perspective game they seem to create a binary star. The most careful of you had already noticed it by turning the virtual sheet: the others can verify it immediately!


As always, we can note that the star γ2 Nor is a bit more than half of Rigel, but definitely bigger than Aldebaran, omnipresent in these types of comparisons, which loses regularly.

Deep sky objects

Let us now go to know the beauties of the cosmos present in this constellation. Let's start with a rich open cluster, NGC 6067 (taken, like the other photos, from the HST: clicking the images you will see the higher resolution version)

the open cluster NGC 6067

Definitely poorer in stars is the other open cluster NGC 6087

the open cluster NGC 6087

Quite another aspect has NGC 6165, planetary nebula photographed by the 8 meters telescope of the Gemini Observatory in Chile.

the open cluster NGC 6165

Equally fascinating is the planetary nebula PK 329+02.1 , known as the Fine Ring Nebula.

the End Ring Nebula

Now let's move on to the more famous Ant Nebula, the Ant Nebula

the Ant Nebula

We now move on to a beautiful planetary nebula, Mz 1 or Menzel 1, named after its discoverer


the planetary nebula Menzel 1

Now let's see another nice globular cluster, NGC 6134.

the open cluster NGC 6134

followed by NGC 5927

the globular cluster NGC 5927

We arrived at another series of open clusters, this time photographed from the observatory on the Hawaii Islands: the first one is NGC 6031.

the globular cluster NGC 6031

followed by NGC 6167

the globular cluster NGC 6167

by NGC 5946

the globular cluster NGC 5946

It is also visible to us!

It is enough to go to the southernmost place of Italy, the very famous Pachino, in Sicily: at 9 p.m. of the evenings of the third decade of July, the Norma is at the meridian, just below the Scorpio, but low on the horizon, at a little less than 10° of .

I finish the analysis of the constellation saying that obviously no star of Norma has received a name: but for the presence of the deep sky objects just seen, this constellation is definitely interesting, even if elusive.

The Compasses constellation

I think it's very easy to visualize a compass between the stars: you just need to find a very long triangle and in fact it is so, as we can see from the Stellarium diagram. In Latin it is called Circinus and in English Compasses, which for English speakers means both Compass and Compasses: little imagination or little intelligence on the part of who decided its name?

The celestial compasses is located further south than Norma and therefore absolutely invisible even from Pachino: but it is adjacent to the Centaur and in particular to the pair of bright stars β Cen and α Centauri that we will find in a short time. I add that the brightest star of the constellation has an equal to 3.5 and moreover none of the component stars has ever received a name. However, we will be able to admire various galactic objects not bad.


Clicking on the animation we will be able to see the appearance of the Compasses in 3D, with in particular the star δ Cir which is more than 3600 al away from the virtual sheet. As anticipated let's not expect to see the appearance of the constellation changing by clicking "f": not even H.A.Rey could have done better! Let's be content to rotate the virtual sheet, ready to analyze the (few) characteristics of this constellation.

Also this is a constellation created by Lacaille, therefore its only representation is the one provided by Stellarium.

The Compasses according to Stellarium

Two stars

the comparison of the stars of the Compasses with other notes

In the comparison diagram between the (very few) stars of the Compasses and other stars we meet in each episode, we see that the biggest star as size is ε Cir , just 27 times our Sun (I said just, but think what 27 times our Sun means!!) this time slightly smaller than the much more famous and resized Aldebaran: once the biggest star of a small and unknown constellation is not bigger than a star vice versa known and a constellation that everyone should know and recognize in the sky.

the Sun seen by Alfa Circini

Speaking of nearby stars, or rather the nearest star, we have that the brightest star, α Cir is located at 57 al just below the 60 al chosen by me as the maximum distance limit to take into account the stars. In this case we are in a lucky and nice case: if tomorrow we could approach this star (of spectral class F1) and look back towards our Sun, we would find it very close to another star well known to us, Alpha Centauri: once again the three-dimensional perspective game of the sky makes that our star and its immediate neighbor are almost perfectly aligned in the direction of the brightest star of Compasses. It's therefore a delicious opportunity to visit my Circensi friends who have always thought that the two stars in the center of the picture were a double star (they had baptized Orpheus I and II): even from them the economy is not so prosperous and in fact they too make somersaults for a living.

Deep sky objects

I close the analysis of this constellation showing three galactic objects that are inside it and that nobody would think to find in an otherwise insignificant constellation: but we already know that the term insignificant never applies to a constellation!

The first celestial object is a planetary nebulose known by the acronym NGC 5315

The Planetary Nebula NGC 5315

Also belonging to the NGC catalogue, we find the open cluster NGC 5823

The open cluster NGC 5823

and finally we can admire the galaxy called Circinus Galaxy, belonging to the local group of galaxies, being very close to the Milky Way.

The Compasses Galaxy

With this I conclude the analysis of the constellation of the Compasses which, as we have seen, is rich in interesting characteristics, but invisible at our latitudes.



Audio Video Two Geometric Constellations: Norma and Compasses
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