The Sextant Constellation (Sextans-Sex)

The name, the story, the myth


The development of astronomy during the 17th century led to the study of areas of the sky not previously considered. The weak Sextant (originally Sextant Uraniae, the "Sextant of Urania", muse of astronomy) was fixed in an area between the Hydra and the Lion by Johannes Hevelius (1611 - 1687), who wanted to remember the instrument he lost during the fire of his observatory Stellaeburgum in 1679. A bronze instrument of 1.8 meters that had to be handled by at least two people (him and his wife Elisabeth?).


The Constellation of the Sextant

In this episode we analyze a constellation with few bright stars: the brightest is in fact of 4th magnitude, which makes it invisible in the bright skies of cities, while it could be easy to find it in the sky. In the star map made as always with Stellarium, we see that the Sextant is adjacent to the constellation Leo, very close and south of that night lighthouse that is Regulus: this fact alone should allow an easy localization of the constellation wedged between the king of the forest and the coils of Hydra.

We will see shortly that the constellation presents a number of deep sky objects, a nearby star and a large star within its boundaries.

What we're analyzing is a young constellation that only appears in Hevelius' work...

The Sextant according to Hevelius

and of course in the Stellarium


The Sextant according to Stellarium

Two important stars

comparison between the stars of the Sextant and those of other constellations

In this constellation we find a single star of large dimensions, which is yet another star slightly smaller than Her Majesty Aldebaran...

It is the anonymous 35 Sex, an orange giant of spectral class K3 and with a diameter equal to 28 times that of our Sun: in writing these articles I had set myself the limit of 30 times the solar ray to talk about a certain giant star, but this time I make an exception with just 28 times.

In fact this value is almost nothing compared to stars like Antares (730 times the Sun) or the enormous VY CMa with a diameter equal to 2100 times that of our yellow dwarf, but try to imagine a diurnal star 28 times bigger than our Sun!

Just to show this comparison, I asked my Sexual friends to send a picture of their sun taken from the distance of 1 UA, just to compare it to our daytime star: the comparison is really dramatic.

Besides this big star, in the constellation we find a nearby star, called LHS 292 (or GJ 3622 depending on the catalogue used), a red dwarf of spectral class M6, placed in space at a distance of only 14.8 light years from our Solar System and very weak (of 16a ).


My friends, who live on a planet in those parts of the cosmos, the Elleacchesi (but who proudly call themselves Sexists among them) have sent me a picture of our Sun seen from that small distance: our yellow dwarf is an anonymous third star in a star $campo$ star without any famous and bright stars.


Some Deep Sky objects

As said, within the constellation there is a small number of deep sky objects, as always very interesting. Let's start with the Spindle Galaxy (the "molten galaxy", catalogued as NGC 3115) : it is a beautiful lenticular galaxy with a cut view

the Spindle Galaxy, NGC 3115

Here instead we see a pair of galaxies that are interacting, the NGC 3169 and the NGC 3166: the fate of the two is to merge into a single galaxy and already the one we see on the left shows the first effects of gravitational interaction, in the form of a distortion in its aspect

the galaxies in interaction NGC 3169 and NGC 3166

Now we can admire a small spiral dwarf galaxy called Sextans A (UGCA 205).

the dwarf galaxy irergolare Sextans A

while here we see the irregular galaxy UGC 5373 also known as Sextans B

the irregular Sextans B galaxy

Names of stars and visibility

Within the constellation Sextant none of the component stars has ever received a name, since they are too weak to be seen and recognized even in the presence of dark skies.

As for the visibility of the constellation, at the usual time of 9 p.m., it is low on the horizon, in the East, in the first ten days of January, culminating in the South at the end of April, and then it is low on the horizon, in the West, in the second half of July.

Now that we know it and we know where to find it, let's also begin to observe the Sextant.



Audio Video The Sextant Constellation (Sextans-Sex)
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