The constellation of the Bird of Paradise (Apus - Aps)


The constellation of the Bird of Paradise

The constellation we are about to analyze is even further south of the Southern Triangle, now very close to the South Celestial Pole: its Latin name is Apus (to the genitive apodis) and literally means without feet. In this photo we see a specimen of rare beauty of a bird of paradise and on wikipedia it is reported that there are many species of these sparrows, characterized by a bright coloration to say the least. But we are interested in the celestial version, the constellation of the same name.


The name, history and myth of the Paraíso bird


First called Avis Indica, the Indian bird, the constellation was reported on celestial maps by Dutch navigators Pieter Keyser and Frederick de Houtman in the 1890s during their travels in the southern hemisphere. Plancius also referred to it as Paradys-vogel, the Bird of Paradise. The constellation inserted by Bayer in 1603, is recent to have its own mythological connotation.

Meanwhile we see the representation of Hevelius: immediately to the left of the more recognizable Southern Triangle we meet a kind of swan with a long straight neck, which frankly I can not interpret

the Bird of Paradise according to Hevelius...

A better image is the one provided by Stellarium

the Bird of Paradise according to Stellarium

A gigantic star

comparison between Apus stars and other notes

It's been a long time since we met a very big star: it is the main component of a double star, δ1 Aps, a red supergiant of class M5, with a radius equal to 220 times that of our small Sun. Even its secondary component, δ2 Aps is no joke: it is an orange giant of class K3 which is once again larger than Aldebaran.


I was saying that it's a double star: actually, thanks to the distance measurements by the Hipparcos satellite, the supergiant component is far away from us the beauty of 762 al, while the secondary component is much closer, at only 613 al. So the two stars are separated in space by the beauty of 149 al, so they would represent a double optic whose components are practically very close visually.

Let's talk about the bike itself

On wikipedia it is reported that it could be instead a proper motion pair (a pair of stars with similar motion), but this is not true either as the values of the proper motion pair are quite different (-10.23 mas/y in RA and -37.43 mas/y in decl for the first and -1.75 mas/y in RA and -31.58 mas/y in decl for the second). These are the official values taken from the SIMBAD star catalogue.

I translate these hieroglyphics for the uninitiated: I remind you that the proper motion of a star represents the value of how much the star moves in the sky because of its true motion among the stars of our galaxy: it is a very low value (except for some cases where it is so large that it can follow the star year after year, or rather decade after decade), expressed not in degrees every year, but in milliseconds of arc every year. In one degree there are 3600 seconds and therefore 3,600,000 thousandths of a second of arc (mas): the main component of this double arc travels 10.23 milliseconds of arc every year in straight ascension (RA) in the opposite direction (sign "-") to the increasing coordinates, then it moves in the sky from East to West, while the celestial longitude increases going from West to East. In declination it moves 37.43 milliseconds of arc towards the South (here it's easier!) towards the South Celestial Pole.


Now that we know everything about the bike itself, let's compare the two pairs of values: -10.23 and -1.75 for the bike in RA and -37.43 and -31.58 for the bike in declination. Surely I'm missing something, but I think I can say that these values are not really comparable: especially the values in RA are not such as to be able to say that in space the two stars travel to preserve, even if separated 149 al , as would instead think of the term proper motion pair.

Let's make a comparison with a very well known star group (α1 Cen, α2 Cen and Proxima Cen) that we know is a physical ternary system of stars at the same distance from us: the values in mas/y for the three components, in RA and in decl, are (-3608 and 686) , (-3614 and 802) and finally (-3775 and 765). Apart from the values that in this case are very large (obviously, due to the distance of 4 al of the group compared to 600 and more al), but at least if we take the values in RA (-3608, -3614 and -3775) these are definitely comparable and so are the values in declination: this fact tells us that the three stars, even if they are at a certain distance between them, all three of them travel around the galaxy: a proper motion triplet.


Maybe with the new GAIA (Global Astrometric Interferometer for Astrophysics) satellite that will make even more precise measurements, we will review all these arguments. By the way I didn't remember that the name of the Hipparcos satellite is actually an acronym: HIPPARCOS stands for High Precision Parallax Collecting Satellite...

I conclude. Dive into the information provided by wikipedia is never wise: you have to at least compare it with other sources, or you have to think about it together, as we have done now. Since anyone can write on wikipedia and anyone can make mistakes, then wikipedia is certainly not immune to errors.

Are you still there? I asked my friends Deltaunòpici and Deltaduèpici for information, but they grained their eyes (4 and 5 respectively) when they heard me talking about mas and other weirdness. The first ones, however, sent me the photo of their giant star (as always creepy and threatening) taken from a distance of 10 UA and never as in this case it can be said that a diameter of 220 volts is electrifying.

The other two big stars are θ Aps and α Aps, respectively a red giant of class M6 with a radius equal to 80 times that of the Sun and an orange giant of class K5 with a radius equal to 58 times, almost double the blameless Aldebaran.

Deep sky objects

Among the deep sky objects inside the Bird of Paradise we find a rich globular cluster called NGC 6101

the globular cluster NGC 6101

followed by another globular cluster, IC 4499...

the globular cluster IC 4499

and finally we have the spiral galaxy IC 4633.

the spiral galaxy IC 4633

That said, we have finished: the constellation has no stars that have received a denomination and the visibility from our latitudes is null.



Audio Video The constellation of the Bird of Paradise (Apus - Aps)
ForConstellationsLovers is a website created by constellation lovers, our aim is to share all the information about the world of stars and mythology. Here you can find both the meanings of the constellations, as well as their mythology or location, apart from that, you can play the best online constellation games. Discover the history of the constellations and their beauty!
The Constellation of the Shield (Scutum - Sct) ❯
Add a comment of The constellation of the Bird of Paradise (Apus - Aps)
Comment sent successfully! We will review it in the next few hours.