The Constellation of Fox (Vulpecula - Vul)


In the introduction I said that it is a constellation that is easily visible once you know where to look for it and provided you have a fairly dark sky: the ideal is in the mountains in summer, when in the evening it is almost at the zenith. From the map of Stellarium you can see that it is quite extensive and is attached to the constellation Swan, next to nice constellations such as the Arrow and the Dolphin, just before the Eagle.


While the Arrow and the Dauphin are really recognizable in a dark sky, the Fox is conversely formed by a few weak stars, but as we will see soon inside it there are quite big stars, no stars close to the Sun and some well-known deep sky objects.

The name, history and myth of the Fox

In 1687 the Polish astronomer Johannes Hevelius established through his Prodromus Astronomy/Firmamentum Sobiescianum (1690) the "Vulpecula cum Ansere", or "Vulpecula et Ansa", the "fox with the goose" or "the Fox and the Goose", but the goose - which was represented among the fox's teeth - was made to disappear. In fact they seem too many two animals for an asterism composed of only two stars...

Officially the International Astronomical Union in the 20th century accepted only the first part of the original name.


Let's now see the representation of the constellation in the star maps that we know well: according to Hevelius, we have a fox with its long tail and that holds a goose in its jaws


the Fox in the representation of Hevelius

while according to Stellarium we have this visualization.

The Fox according to Stellarium

A few stars big enough

comparison between the stars of the Fox and other very large and very well known stars

In the comparison diagram with other larger and better known stars encountered during the various episodes of the column, we see that there are as many as six of them of important size. From the color with which I have represented them (through Illustrator) we know at a glance the spectral class: also this time the blameless Aldebaran will be brought into play.

The biggest star is an orange giant of spectral class K3, 19 Vul, whose size is equal to 84 times that of our Sun and more than twice the size of Aldebaran.

Less big is the yellow giant 22 Vul, of spectral class G2, with a diameter equal to 64 times the Sun, its spectral relative: also in this case Aldebaran is overtaken for more than two times.

The third star in order of magnitude is still class K4, star 32 Vul, with a diameter of 46 times our Sun and once again larger than Aldebaran. Then we meet the main star of the constellation, α Vul, a red giant of spectral class M0, with a diameter of 41 times that of our yellow dwarf.


The last bigger stars of the Fox are of a size comparable to α Tau and are the orange giants 23 Vul and 33 Vul, both of spectral class K4, with a diameter equal to 30 times that of the Sun.

I made a collage of the photos that my stellar friends just sent me (respectively Vulcanic, Vulcanologist, Vulitive and Vulteggianti): in all cases the star was photographed (thanks to Celestia, let's not forget it) from the distance of 10 UA , which is on average that of the planet Saturn from the Sun. About my interstellar friends, I can say that the first ones have strange pointed ears like elves, the second ones are avid smokers, the others are very lazy by nature and finally the last ones are great fans of group dances: from their name you could maybe guess ...

Two important celestial objects

Let's leave now the facetiousness to talk about two objects present within the constellation: two very important pulsars.

The pulsar PSR B1919+21 was the first object of this type to be discovered in 1967 by Jocelyn Burnell and Antony Hewish (for which they won the Nobel Prize in 1974): it has a period of 1.3373 seconds, with a pulse duration of 0.04 seconds.

I report from Wikipedia that, having been the first pulsar to be discovered, astronomers had compared it to a beacon and for some time, with a good dose of humor, they called it with the acronym LGM-1 (Little Green Man 1, since for English speakers aliens have always been called little green men). Immediately after the discovery, the well-known astronomer Fred Hoyle hypothesized for the pulsars the presence of a neutron star in very fast rotation.


I gladly report the translation of what the two discoverers said on the occasion, considering seriously enough the possibility of extraterrestrial life, before the true nature of pulsars was determined:

We do not really believe that we have picked up the signal from another civilization, but obviously the idea has touched our minds since we still had no proof that it was a pure natural radio emission. The problem is very interesting: if you think you have discovered life in another part of the universe, how do you announce the news responsibly?

The second pulsar present in the constellation is the PSR B1937+21 and it is also important because it is the first millisecond-pulsar, whose period is only 1.5577 milliseconds ! How to say that in this case the neutron star rotates on itself 642 times per second...

Never as in this case the regularity of the period of emission of this celestial object makes it a serious candidate for time measurement in place of atomic clocks. Moreover, it must be said that occasionally it is one of the few pulsars to emit strong radio pulses, which in the case of the object under examination is the largest radio emission ever discovered.

Deep sky objects

In this constellation there are some remarkable deep sky objects that we will see in photos made by HST.

The Dumbbells: The well known gymnastic tools are

Let's start with the famous Dumbbell Nebula, which takes its name because it has the shape of a dumbbell: this name deceives those who do not know English well and it may happen that it is literally translated as a mute bell (bell) (dumb), even if you don't understand exactly what a mute bell may be, maybe a broken bell. Instead the term is a classic false friend and refers more prosaically to those gymnastic gym equipment called dumbbells, in turn not to be confused with the most famous bicycle dumbbells ...

We see therefore the Dumbbell Nebula, also known since the time of the Messier Catalogue with the initials M27.

the Dumbbell Nebula, M27.

We then move on to the beautiful elliptical galaxy NGC 7052

The elliptical galaxy NGC 7052...

Now it's the turn of the NGC 6820 emission nebula.

the object NGC 6820, a beautiful emission nebula

Really unusual and curious is the object CR 399, which on closer inspection resembles a small hanger crutch, so much so that it's nicknamed The Coathanger: at first it seemed that it was a very large open cluster (with an apparent diameter of 60′) formed by about ten stars, but then the analysis of the parallaxes and their own motions derived from the Hipparcos satellite established that they're not stars with gravitational interactions typical of a globular cluster. It is therefore a very curious alignment of stars.

the Coathanger

Names of stars and visibility

Among the stars of the Fox, only one has received a name, quite consistent with the representation of Hevelius seen previously

  • Anser (α Vul): the Latin term for goose, the prey of the young fox.

As for the visibility of the constellation at the convenient time of 9 p.m., I have already anticipated that in summer it appears practically at the zenith: in particular it appears low on the horizon in the Northeast between mid-May and mid-June, then it appears high in the sky between September and mid-October, while finally it appears low on the horizon between December and mid-January of the following year.



Audio Video The Constellation of Fox (Vulpecula - Vul)
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