The constellation Cepheus
The constellation of Cepheus with a very famous star highlighted
The constellation of Cepheus in its northern part borders with the Lesser Bear and just enough to make it a circumpolar constellation, that is, visible at any time of the night and at any time of the year: its location next to Cassiopeia makes it easy to find it even in the bright city skies, also because of its rhombus shape with a small star in the centre. And right next to the southern star of the rhombus, a little to the left, there is a very famous star (δ Cep), progenitor of a class of variable stars, called cepheids: since we have already talked about it in this site other times, I will not go back to the subject and vice versa I report with pleasure this article in which we pay homage to the one who formulated the relation period-luminosity of these variable stars, which allowed to calculate the distances of the galaxies.
Three stars nearby
In this constellation there are three stars below the distance of 60 light years: the nearest one has a disturbing name (Kruger 60) and is a binary system located 13.1 light years from our Sun. With such a low value it could seem very far ahead in the list of proximity, but in reality it is placed just at the 26th place in the list: this fact, together with the dislike and lack of friendliness of my Krugerian friends, has not however prevented me to take a picture of our Sun, which from that heath of the universe appears of third magnitude and placed inside the Milky Way. I forgot to say that these friends of mine have some noteworthy peculiarities: the males are all called Freddy (who knows why, maybe because of a habit) and are equipped with very particular hands and such as to advise against friendly handshakes. Moreover, they have a rather thrown face, perhaps due to exposure to their star, without an atmosphere capable of filtering radiation: in short, they are not very pleasant looking little people, particularly sharp in their language.
I add a curiosity that I found in an American astronomical site: it mentions the fact that the star with the disturbing name, Kruger 60, within 88,600 years will approach the Sun at the minimum distance of just over 6 al. What should I add?
The second and third stars of this little group are HIP 117712 and γ Cep, respectively located 35 and 46 light years away from us: the vision that my friends Hippoliti and Gammacephali have of our Sun is quite disappointing, with a small star of fifth magnitude placed in an area of sky poor in stars but with the Milky Way nearby. Since I took the picture going to visit the first friends, I say that the second ones live on a rocky plateau with a wide sea, rich in very tasty fish (the mullets, of course) of which there is a wide range of subspecies: from this fact they get their name and they are very proud of it.
The representation of Cepheus
Said that Cepheus was king of Ethiopia, husband of Cassiopeia and father of Andromeda (a pot-pourri of constellations placed in the same area of the sky), we see that Hevelius represented him, from behind, with the crown and a funny plume in his head and the scepter in his hand
while the Uranometria depicted him in more warrior's clothing, but with a helmet that was not possible...
Finally Stellarium represents him as an old sage
Lots of very big stars, but how big?
I confess that in collecting data of the 10 very large, large and medium stars present within the constellation I had some perplexities and doubts, caused by the fact that there are disagreements and uncertain sources about the values found on the internet and in my usual programs (Celestia above all). You know that I usually use the latter as a source of reference, since it is known the care of the programmers in being always updated and precise in their task of representing in three dimensions the space around us. But while the position of a star is known with good accuracy thanks to the work of the Hipparcos probe that has provided all the parallax values, vice versa on the dimensions of stars there are not yet so precise methods and then it happens that different sources provide values in some cases absolutely incomparable and contrasting. As you know I trust Celestia, whose sources are expressly declared (the most important star catalogues, among which SIMBAD and CHARM2), while I can't say the same about Wikipedia, which on the contrary provides information in some cases without reporting the origin.
Since on wikipedia the list of the biggest stars provides quite discordant data for the very first positions, salomonically I created a table where this time there is one more column than usual: in the first column there is the name of the star, followed by two columns with the values of Celestia and Wikipedia: in order to create the photos related to the missing values, I created a special file to modify the basic values of Celestia and adapt them to the new needs. Thus were born the photos for V0345A Cep that doesn't exist in Celestia, with a ray equal to 1520 times the solar one and so on: in this way you can have a comparison between the sizes of these star monsters, always taken from a distance of 10 UA.
What a drag! All this because Wikipedia may be the most up-to-date (changes may occur in real time), but unfortunately it doesn't mention sources, just when you need them. Celestia on the other hand is linked to the official databases and is updated only when new versions of the program itself are released, or if some programmer provides a new version of some of the data files, but to do this you have to frequent the forum assiduously and be careful of reports of updates ...
In the inevitable colorful diagram I reported the stars of Cepheus with amplitudes corresponding to the values of Celestia: I couldn't even insert μ Cep because of the enormous uncertainty about its diameter and because I should have drawn an almost vertical line even more to the right of that monster that is VY CMa, just 2100 times the Sun! That other T Cep monster can also be glimpsed just to the left, while His Majesty VV Cep can be seen halfway up. Maybe if this dozen or so stellar monstrosities weren't all concentrated in a single constellation, I would have dedicated more space to each of them: we are definitely in front of a constellation that breaks all records!
As I say in every episode, the usual considerations always apply. Apart from the stars of monstrous size, the ones a bit more human (but how human can a star be?) are really spectacular: the smallest one I considered (13 Cep), an anonymous star of magnitude 5.7 and therefore visible only with a really dark sky, since it's at the limit of visibility to the naked eye, it's to all intents and purposes very comparable with His Majesty Rigel, not to mention ζ Cep which is almost 4 times Aldebaran.
At this point I can't help but say hello to my Microcepal friends, who live on a planet orbiting the largest of the stars seen: even they don't know whether their star is 3900 or 1420 times larger than our Sun. They are quiet several hundred UA away from their stellar monster: I forgot to say that contrary to what their name suggests, their head is 1420 times bigger than ours and that they are governed by a President (the only one with a head 3900 times bigger than ours) that they, not by chance, call Big Chief. Since they also have hair like ours, I let you imagine that the most profitable, but very tiring, business in their area is that of a barber...
Deep sky objects
After all these numbers, diagrams, tables, photos and faces, we leave the floor to the powerful Hubble Space Telescope to see real images of three deep sky objects present in the constellation of Cepheus. I remember that clicking on the photo will open the high resolution version.
Let's start with an open cluster, composed of many stars quite far apart and identified with the acronym NGC 188
the open cluster NGC 188
The galaxy we see now is the NGC 6946, also known as the Fireworks Galaxy, a very appropriate name. Fantastic!
the galaxy NGC 6946 (Fireworks Galaxy)
Finally we see a nebula known as NGC 7538, also very spectacular.
the NGC 7538 Nebula
Names of the stars of Cepheus
We've arrived at the list of Cepheus' stars that have received a name:
- Alderamin (α Cep): the right arm.
- Alfirk (β Cep): the flock
- Errai (γ Cep): the shepherd
- Kabalfird (η Cep): flock stars
- Al Kidr (θ Cep): the pot
- Al Aghnam I and II (κ and π Cep): sheep
- Erakis (μ Cep): also known as Grenade Star
- Castula (ν Cep): also known as Cor Regis, the Heart of the King
- Kurhah (ξ Cep): splendour on the horse's snout
- Kalbalrai (ρ Cep): shepherd dog
The visibility of Cepheus
We already know that Cepheus is a circumpolar constellation and therefore visible every night of the year. Let's observe it!