The Southern Crown
The constellation of the Southern Crown
It is a small constellation that would be very easy to recognize if only its stars were brighter: the brightest (α CrA) is in fact of fourth magnitude. But it is in a position that is easily remembered: it is in fact attached to Sagittarius, just south of the Teapot (Teapot), the well known asterism I mentioned in this article.
According to the parameters chosen by me to classify the constellations and talk about them in this series of articles (in particular the number of nearby stars, the number of the biggest ones of a certain value and the apparently very low number of deep sky objects), the Southern Crown is at the bottom of the list. But we know that for us fans any constellation is always fascinating! The easy recognizability makes it jump forward of many positions ... and then we know that Nature has many surprises in store!
The name, history and myth of the Southern Crown
The constellation of the Southern Crown has very ancient origins since it already appears in many classical texts.
It is not a crown itself, but a crown made of leaves.
It is one of the 48 constellations described by Ptolemy, who knew it, precisely, as "southern garland". Its proximity to the Sagittarius explains why it has sometimes been said to represent the centaur's crown or the quiver of his arrows.
The best known myth related to the constellation is that of Semele, the daughter of the king of Thebes, Cadmus, and Harmony. Zeus would change into mortal being to secretly meet the maiden. But in order to put an end to adultery, Hera, Zeus' wife, would in turn take the form of an old friend of Semele's and instill in her the seed of doubt about the mysterious lover. Semele, now six months pregnant, would ask her lover to reveal her true identity, but when Zeus refused, she would kick him out of bed. The furious god would then show himself to her, and the unhappy young woman, according to Hera's predictions, would be incinerated by lightning struck by Zeus in a raptus. In another version Zeus complied with the girl's request, but the thing was fatal, since no mortal could stand the sight of the gods of Olympus: she was incinerated. It is said that the unborn child was sewn inside the father's thigh for the remaining months of gestation. That son of Semel and Zeus was Dionysus (Bacchus for the Romans), who later defied the dangers of the underworld to recover his mother's soul. The gods allowed Semeles to join them on Olympus and her garland became the Southern Crown. A different version tells of how Dionysus came to terms with Hades, to whom he asked for the soul, Hades in return wanted Dionysus to leave in the Underworld something he particularly cared about. Dionysus left his favourite plant, the myrtle, in fact the Southern Crown is often depicted on the cards as a garland of myrtle branches. So it was Hades who took it to heaven among the stars.
Let us now see the representation of the constellation in the star charts I took as a reference.
In Uranometry it appears as a garland
while according to Hevelius it's a crown
and finally according to Stellarium
is depicted as a serto.
An interesting star
Inside this constellation there is a variable star, R CrA, that presents in the vicinity an emission nebula (NGC 6729), that we will see later on in detail.
Particularity of this star is its very high motion and in particular, according to a first estimate, however, containing a margin of error still large, in a little more than 220,000 years could approach up to 1.77 to the Sun. In the meantime we hope that the technological progress will allow us to obtain a better estimate of the characteristics of his bike.
Deep sky objects
In the constellation of the Southern Crown there are a number of deep sky objects.
Let's start with the nebula called Corona Australis Nebula, photographed by the Australian Astronomical Observatory...
We now see two globular clusters full of stars, the first of which is NGC 6541,
the beautiful globular cluster NGC 6541
while the second is NGC 6723
the amazing globular cluster NGC 6723
This instead is a detail of the reflection/emission nebula, which is close to the variable R CrA, which I talked about previously
reflection/emission nebula NGC 6729
Finally we see an open star cluster, called Coronet Cluster
I conclude this paragraph with the link to a short but interesting film made by ESO, where starting from the image of the Milky Way we get closer and closer to the variable star R CrA and the nebula NGC 6729. Really suggestive! It has to be seen on the full screen!
Names of stars and visibility
This constellation is the austral counterpart of the Boreal Crown, whose main star, as we well know, is called Alphecca: it is therefore legitimate to expect that at least the brightest star of this small constellation has a name
- Alphecca meridiana (α CrA): Latin term indicating the Southern Alphecca star.
As far as the visibility of the constellation is concerned, at the usual and convenient time of 21 o'clock, it is low on the horizon, southeast of the last decade of July. It culminates in the South, just about ten degrees above the horizon, in the first days of September, and then lies low in the Southwest in the first decade of October.