The Triangle constellation (Triangulum - Tri)


Knowing where to look, it is easy to recognize three stars of third and fourth magnitude that form a Triangle (but look at that! unless they are aligned, three points always form a triangle. And it doesn't even take much imagination!). From the Stellarium diagram we can see that the Triangle is located right between Andromeda and Aries, both well recognizable thanks to their brighter stars. I was talking about the Perseids: every time in summer I organize evenings of observation of the Tears of St. Lawrence, waiting to see them fall, I always dwell on the constellations near Perseus and immediately show the Triangle, easy to spot and remember.


The name, history and myth of the Triangle

In ancient Mesopotamia the alpha and beta stars of the Triangle together with the gamma And formed the constellation of the plough, APIN.

For the Greeks, the constellation represented the letter Delta, and for similarity, the delta of a river, in particular that of the Nile, it is not surprising the strong connection with the representation associated to it just by the ancient Egyptians, for whom the small constellation recalled not only the delta of the Nile - precisely - but also the sacred eye of Horus, son of Osiris and Isis, taken from Seth.

There was also the triangular shape of Sicily - for Igino- (Trinacria), the island sacred to Demeter (Ceres) where the rape of Persephone (Proserpine for the Romans), kidnapped by Hades (Pluto) and taken to the Kingdom of the Underworld, took place.

The Triangle is a very ancient constellation and the names that have followed one another over time have always referred to the shape that the three brightest stars generate, an isosceles triangle.



The representation of the Triangle in ancient and modern times is quite obvious: here is the version of the Uranometria

the Triangle according to Uranometry

This is the Triangle according to Hevelius.

the Triangle according to Hevelius

and finally according to Stellarium

the Triangle according to Stellarium

The stars of the Triangle

comparison between the stars of the Triangle and other notes

This time I start with the biggest stars: there are two within the constellation. The biggest one is 15 Tri, a red giant of spectral class M3, with a diameter of 89 times that of our Sun: my friends Quindicìtri tell me that it is very bright and its light is very annoying to their three eyes. Astronomy enthusiasts, they have a rich supply of instruments like ours, with the exception of trinoculars, which they use very often, especially in the evenings of observation.

The other big star is 14 Tri, whose class, K5, immediately makes the comparison with the more famous Aldebaran: once again the star of Taurus is smaller than this other star, whose ray is 36 times that of the Sun. I don't know why, but my fourteen friends have always suffered from a (psychological, I guess) subjection to my other friends above: they have two eyes, definitely smaller and are skilled drivers. Unfortunately, however, they are very careless and not infrequently they get a fine because their car is not equipped with a mandatory device: guess what ... the triangle.


the binary system of δ Tri

Inside the constellation there is a fairly close star, the yellow dwarf δ Tri, a close relative of our Sun, given its spectral class G0, placed in the sky at a distance of 35 al. It is a spectroscopic double star whose secondary component (B) is an orange dwarf, which we can see in this photo taken with Celestia, from about 0.18 UA away from the barycentre of mass of the binary system.

If ever in the distant future we had the possibility to go near this star and then look towards the Sun, we would see it (of 5a ) in an area of sky populated by not very bright stars of Centaur, Libra and Wolf, with two illustrious intruders (Sirius and Raccoon) visible in that area because as we know they are two stars near the Sun. Waiting to be able to go there in person, we can in the meantime see the photo that my Δtri friends sent me, particularly angular characters.

Deep sky objects

Let's give up the facetiousness to devote ourselves to deep sky objects, which we can admire in all its splendor thanks to the photos of the HST and which are present in large numbers in this constellation. The most famous and fascinating object by far is M33, belonging therefore to the Messier catalogue, not very imaginatively called Triangulum Galaxy.


the spiral galaxy M33

Inside the galaxy M33 there are a lot of NGC and IC objects, as we can see in this image (NGC objects are indicated with "Nxxx", while IC objects are simply indicated with "xxx").

the galaxy M33 contains within it a series of NGC and IC objects

Of these objects we see the detailed image of two emission nebulae (two regions H II) , the NGC 595

the NGC 595 emission nebula

and the NGC 604, particularly impressive

the NGC 604 emission nebula

We now return to a series of galaxies, starting with the NGC 634, a magnificent spiral galaxy

the spiral galaxy NGC 634

and then contemplate the galaxy NGC 672 with the nearby IC 1727, just 88000 al and interacting.

spiral galaxies NGC 672 and IC 1727

Then we see the less conspicuous barred spiral galaxy NGC 784.

the galaxy NGC 784

followed finally by the glittering barred spiral galaxy NGC 925

the galaxy NGC 925

Names of stars and visibility

Among the few stars of the Triangle, two have received a name, decidedly little used in both cases

  • Ras Al Motallath (α Tri): the head of the triangle
  • Deltotum (β Tri): found in internet

As far as the visibility of the constellation is concerned, at the usual time of 9 p.m., it is found low on the horizon, to the North-East, at the end of August, to culminate almost at the zenith in the second decade of December, and then it is found low on the horizon, to the North-West, in the second decade of April of the following year.



Audio Video The Triangle constellation (Triangulum - Tri)
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