The constellation Big Beard (Ursa Major -Uma)


Introduction

The Big Beard is one of the many boreal constellations that accompany us in all the nights of the year, without ever setting: it is in fact a circumpolar constellation that even during a single night of astronomical observations you can see moving slowly in the sky, thanks to the rotation of the Earth around its axis. It is for this reason, together with the fact that it is formed by a group of 7-8 very bright stars, that this constellation is so well known by practically anyone who only by chance looks among the stars at night.


It's the famous Big Dipper, a kind of rudder or a pan and you immediately learn that by ideally extending the line that connects the first two stars of the wagon, you get to the polar star. If of this you hear wrongly that "it is the brightest star in the sky" (how many times it has happened to me!), then immediately correct the person saying that it is the most immobile star in the sky because it is located very close to the North Pole and therefore remains in the same position all night long, on any day of the year. Also add that it is not very bright (magnitude 2.2) and that it allows you to immediately find the direction of the geographic North (to know more)

But let's go back to the Big Dipper and its 7 (plus one) main stars, the brightest: in ancient times they were also called the "Seven Oxen", in Latin "Septem Triones". That's why to find the North you looked for these Septem Triones, from which the term North was born. On the term "Big Dipper" I frankly do not know how to give any explanation, precisely because with all my good will and imagination I have never been able to understand how to depict a wagon, moreover big compared to the Little Bear, called instead the "Little Dipper".


Rather, let's talk about Bear... Evidently, these main stars do not form the Big Dipper by themselves, since you need almost all the other less bright stars in the constellation to see it. When you launch the program, you can see the tail to the left, the snout to the right and the two pairs of front and back legs on the home screen, but even so it takes a lot of imagination to see a bear. This is why we are met by H.A.Rey, pseudonym of Hans Augusto Reyersbach, a skilful illustrator of the twentieth century, author of children's books with a fervid imagination. In 1952 he wrote a book in which he gives an admirable interpretation of some constellations all his own, giving a remarkable display of fantasy: he definitely succeeded, in front of the set of stars of the Big Dipper, to join the dots with skilful pencil strokes, pulling out of his magic hat a real Bear, that we can imagine, white, on the polar ice. Would you like to see her too? Press the "f" button in the program! Press this button several times to switch from one performance to another. After all, it was enough to join the dots that had been there since time immemorial... Who knows why nobody had thought of it before and who knows why it hasn't yet been adopted as the official image! Go back to the program of the Taurus constellation and use the new command: you will find another funny version of this animal, I dare say much more beautiful than the original one, where frankly the bull is not so identifiable!


The name, history and myth of the Big Beard

This group of stars has been known since the earliest times, and the stories that are linked to it are the most varied, and cover not only time but also space.

Among the first quotations, the one in the Book of Job, where the constellation is mentioned as Mez'-a-rim, the "North". For the Arabs the four stars of the Chariot were "the coffin", while the three of the helm were the funeral procession.

In its seven stars have been seen the chariots of various legendary heroes, gods, objects... Starting from the Babylonians, what represented the seven stars was a simple "long chariot", but for the Welsh, and the Saxons in the Middle Ages, it was, for example, the chariot of King Arthur, for the Vikings, the chariot of Odin, while in the Germanic populations it was the chariot of the god Thor; the Celts and the Gauls represented this asterism on their coins like a boar. For the Japanese it was sensha kotei the "chariot of the Emperor", for the Chinese the seven stars represented the Government, the seven astronomical rulers, those who presided over astronomical influences, guardians of the seven gates and the seven entrances to the sky, but among the peasants were known as Bei Dou or Pé Teou (the "agricultural chariot").

Since we touched the East, the Ainu ethnic group of the Hokkaido peninsula (Japan), performed ancient sacrificial rituals in honor of the god Kim-Un-Kamui, the god of the mountains. The victim, a bear, was killed to free its soul from its body, which would then return to heaven and reunite with the great spirit/god who inhabited it, the pact between the Ainu and the latter was thus renewed, and the soul of the bear became a messenger of the prayers and wishes expressed during the ceremonial.


If for the English it is a plough, as in many Euro-Asiatic populations, for the Americans today the group of stars is a big ladle, which partly recovers the charm in the mythology proper of the Indian tribes, which generally see in the four stars of the Chariot the head of a beheaded sacred bear, chased by the rest of the body (rudder) which wants to reunite, the chase proceeds from the origins of the man, and when they will reunite, it will be able to take revenge on the men and the end of time will come. There are well-known variations, such as the one that sees the stars of the Chariot as two bears, four wolves and a hunting dog (Alcor). Wolves and dog are intent on hunting the two escaped bears.

Curiosity

And now a couple of curiosities. The first concerns one of the United States of America: did you know that the national flag of the state of Alaska represents the Big Dipper with the North Star? Other states have a constellation in their flag: in due course I will not fail to point it out. The other curiosity I found almost by chance on the internet and I say from the beginning that I will only report it, without pronouncing. I must admit that I had never heard it before!

In this site I found the report that according to a scholar, some centers of Lazio were built in such a way as to represent the constellation of the Big Dipper in a map: in front of this statement the question of the three pyramids of the Giza plain and the three stars of the Orion Belt becomes a children's fairy tale! In fact, if you look well at the map after having joined the dots with a stroke of a pen, there it is the constellation of the Big Dipper. I leave all the considerations to you, just adding a couple of notes to think about. The first one is that I wonder if extending the stretch that connects Arpino with Ceprano towards North-East there is a center corresponding to the Polar. The second: needless to say that just go on Google Map to realize that there are many villages and towns in that area so finding coincidences with star positions is all too easy.

Let us turn the page!


Let's analyze what the program shows us, placing the sheet of our virtual map all on the left and cutting: with this visualization we have once again the certainty that the stars are scattered in the sky quite randomly, apart from a small assemblage of stars between 75 and 86 light years, formed by 6 of the 8 main stars of the Chariot and some other stars. I wanted to underline a fact that can deceive very easily and that is to be led to think that pairs of stars close to each other on the celestial sphere are also close to each other in reality.

Let's take two pairs of stars, which seem to have the same angular distance in the sky: Megrez and Alioth on one side, Dubhe and Merak on the other. The first and the second star of these two pairs are almost 5° and a half apart in the sky: naively we could think that their true distance in space is equal or very similar. But no, because it all depends on the distance at which the individual stars are located. I chose the first two because they have the same distance from the Sun (81 light years) and with a little bit of geometry (high school trigonometry, which for many people is a contagious disease to avoid...) we could roughly calculate their true distance: but we don't want to dwell on tangents and multiplications (that's all!) since we have the trusty Celestia that tells us in the blink of an eye: 7.98 light years that we can round beautifully to 8.

Let's see another example that brings to mind Orion, with the stars Betelgeuse and Meissa, also at 5° and passing an angular distance in the sky, but this time at very different distances, respectively 427 and 1055 light years. Absolutely further away! When questioned, Celestia tells us that their physical distance is now 604.5 light years! Calculate for yourself how many times more than the other two pairs of stars... So we can say that in addition to the deleterious effect of the flattening of the celestial vault on the distances of the individual stars, there is also this negative side effect that makes one whistle for flasks on the distances between pairs of stars.

Another misleading effect is what makes us think that a brighter star is closer than a less bright one, because in doing so we would completely ignore both the intrinsic brightness of each star and its physical and actual size. For those who are perhaps approaching Astronomy and are still fasting on difficult terms, but trivial for those who already know them, here is a slightly more earthly comparison. We all know light bulbs and their light power: if we put them at different distances, some close, some far away, some more powerful, some weaker, in the dark we will never be able to distinguish them, recognize them. Is a strong light given by a weak but close bulb or does it come from a powerful but farther away bulb?

Our spaceship Celestia is waiting for us


Let's go! As we will see later, of the 7-8 stars that make up the wagon, only one, Dubhe (α UMa) is big, 26 times our Sun, while the others are two to four times our star: by now we are used to monsters like Antares and Betelgeuse, so we are not so surprised.

But what is difficult to imagine is that, of all the represented stars, there are two decidedly bigger ones: Alula Borealis (ν UMa) has a ray 58 times that of the Sun, but even more Tania Australis (μ UMa) with a good 60 times, both almost double the well known Aldebaran: the why is obviously tied to their distance, to their physical greatness and to the intrinsic brightness and also to the fact that in this constellation there are stars more known than them. We start from Tania Australis, that from the name says that it is the most southern component of a pair of stars (on the map, given the enormous difference of their two distances): thanks to Celestia we see it imposing, with its reddish light even at a distance of 10 UA, with its 3° of diameter and a brightness equal to that of the Sun, as we see it however at a tenth of the distance.

Completely different is the other star, Alula Borealis, which from 10 UA appears to us equally luminous, but with a light decidedly more pleasant to our sight, being only a little more orange than our Sun. Surely we would not have expected that two stars barely visible in our cities full of smog and light would be two respectable little monsters.

You may have noticed that I have talked about the main stars of the Big Dipper several times saying that they are 7-8: but are they seven or eight? They are the brightest seven, to which we add one only slightly less bright and very close to another: they are the famous couple formed by Mizar and Alcor (respectively ζ and 80 UMa). Since ancient times they have been used to assess the visual acuity of a person: try to observe them on any night and first check if you can see Alcor and if so, challenge your friends without saying that Mizar is double or something similar. Usually I say: "look at the central star of the bear's tail: do you notice anything strange? Anyway (and it is the case to say, finally !) these two stars are close also in the three-dimensional reality of the cosmos, being one at 81 and the other at 86 light years from the Sun, but 4 light years between them. Don't worry: the apparent inconsistency between the distances is due to approximations. What is valid is the concept that these two stars are in space spaced out like the Sun and the three nearest stars, Proxima Centauri and the Alpha Centauri pair.

In fact there is a third component: Mizar is a double physical star where the secondary component (Mizar B) is even bigger (3.7 times the Sun) than the main component (Mizar A, 2 times the Sun). This time, to better see the stellar trio, we placed ourselves at 1 UA from component A and from here we can see the largest component B and Alcor further away. From this distance Mizar A is brighter than our Sun, but even brighter is component B: a hypothetical planet rotating around component A could see two suns in the sky (as in Star Wars Tatooine, but this is science fiction) of which the least bright is the one around which it orbits. From there the star Alioth shines like Venus from us, Alcor is -2.5, so brighter than all our stars and Benetnasch is as bright as our Sirius. I add that both Mizar A and Mizar B and Alcor are all three double stars: in total then this system is six times as bright. I think that the astronomers on that planet that revolves around Mizar A have a lot to study...

Comparative analysis

We have already talked before about the two monsters with two curious exotic names, among the stars of the Big Dipper: now we can compare the sizes of the main stars with some of the stars we have encountered so far in the analysis of the constellations. In the diagram I started to eliminate other stars to make room for the new ones, but I left the two monsters Antares and Betelgeuse and other stars encountered so far in the previous episodes.

Known, curious and mysterious names


In the Big Dipper several stars have received a name (and in some cases more than one), most of the time from the Arabs: let's see the various meanings, although in some cases they are quite mysterious. In any case we can choose to use either the proper name or the acronym, which in any case is universally recognized.

  • Dubhe UMa): Arabic word meaning bear
  • Merak UMa): Arabic word meaning the side of the largest bear
  • Phecda UMa): from Arabic, the thigh of the largest bear
  • Megrez UMa): from the Arabic, the root of the tail of the largest bear
  • Alioth UMa): strangely enough it means the black horse
  • Mizar UMa): this strangely enough means the groin
  • Alcor (80 UMa): from Arabic, the neglected
  • Benetnasch UMa): from the ancient name of the constellation among the Bedouins
  • Alkafzah UMa): from the Arabic the second vertebra
  • Ta Tsun UMa): from the Chinese name of the constellation
  • Tania Australis UMa): from Arabic the second jump, austral
  • Tania Borealis UMa): from Arabic the second jump, boreal
  • Muscida (ο UMa): from late Latin, muzzle
  • Al Haud UMa): from Arabic the pond
  • Talitha Borealis UMa): from Arabic the third leap, boreal
  • Talitha Australis UMa): from Arabic the third jump, austral
  • Alula Australis UMa): from Arabic the first jump, austral
  • Alula Borealis UMa): from Arabic the first jump, boreal

Always with us

I have already said that the Big Dipper is a circumpolar constellation: for those who are at the beginning and are approaching Astronomy, it is better to get familiar with the shape of the constellation, look for it in the sky looking north, between NE and NW, and you will find it immediately, surely turned around than we expect. I, too, more than 40 years ago started out this way..
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Audio Video The constellation Big Beard (Ursa Major -Uma)
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