Annotations of elementary astronomical observation


The Great Bear

Posted by: bitacoradegalileo on: August 27, 2011


This is a beautiful constellation, the most famous in the Northern Hemisphere, and also the best reference to find the North Star, we will see the appropriate method for this. It is a circumpolar constellation, therefore visible during the entire year, even at latitudes near 20 ° S, and even more southern, as Argentina’s northern border with Bolivia and the Chilean regions of Tarapaca and Antofagasta. Boreal dwellers, as stated above, we have vision at any time of year.

Its asterism (the set of stars that seem to form a shape characteristic of each constellation) is undoubtedly the most famous, and its shape makes it known by various names such as Plough or Big Dipper although the stars that are reminiscent of these shapes are only part of the constellation, albeit they are the most visible to the naked vision due to their size. The main stars of the Dipper, except Dubhe and Benetnash, have a common proper motion, and constitute what is called Ursa Major Moving Group.

Ursa Major, is surrounded by Lynx, Bootes (Arcturus) and Dragon, among other constellations.

    The Big Dipper, photographed from Kahului, Hawaii, 19 degrees North latitude.


Here we find three first-magnitude stars (Alioth, Dubhe, and Benetnash or Alkaid), and three second-magnitude (Mizar, Merak and Phekda), plus Megrez, of third magnitude which are the seven that make up the asterism of the Plough.

We will stop briefly at each one, from right to left, according to their Bayer designation (the Greek letter that precedes the Latin genitive of the constellation):

Dubhe (Alpha Ursae Majoris), which we see in the picture on the right, is a multiple star system that is 124 light years from us. With +1.8, is the second brightest star in the constellation after Alioth.

Merak (Beta UMa) has a magnitude of +2.34 and is just the fifth brightest. It will be important, along with Dubhe, as it helps us find the North Star.

Gamma UMa is Phekda, a white star situated 84 light years away and with a magnitude of +2.4.

Megrez (Delta UMa) is, with magnitude +3.32, the weakest of the seven that form The Plough.

To the left as we observe a photography of Alioth (Epsilon Ursae Maioris), wich is the most luminous in the constellation, with a magnitude of +1.76. It’s located at about 82 light-years of distance and it is a white star, slightly variable.

Mizar (Zeta UMa) is a very peculiar double star, known because it poses an acid test for visual acuity, since those who enjoy this advantage can separate it at a glance from its companion, Alcor (80 UMa, doesn’t have a Bayer designation). I am not among the lucky ones, although it is the mother of my children, that perfectly describes the situation of both in a direct observation. If you turn turn your attention to the photos above again, now that you know the location of Mizar, you may perceiving this circumstance.

Benetnash or Alkaid (Eta Ursae Majoris), lastly, is a blue-white star of +1.85 in magnitude, the third brightest of the Great Bear.


The two stars opposing the handle of the Dipper, ie, Dubhe and Merak, will help us to find the North Star very easily. Effectively, extending the line joining the two stars towards Dubhe, the brighter of the two, about five times, we get to Polaris without difficulty. This resource will be useful for excursionists who are disoriented at night, easily providing the situation of the North.

This star chart is nothing new. It’s reproduced on the state flag of Alaska in the United States of America. The high latitude of this country justifies the presence of the Great Bear below, whose stars pointers indicate the position of Polaris, top right, on the blue background that symbolizes the northern sky.

On the other hand, the Polar Star On the other hand, the Polar Star is a center of radial symmetry between the Great Bear and the constellation Cassiopeia, that in the figure we observe has the shape of a “W” or an “M” and both will forever be at opposite situations with respect to the North Celestial Pole, represented by

Polaris, the pivot around which they revolve counterclockwise.


In the constellation of Ursa Major we find more than fifty of these objects, among which we have galaxies, nebulae and star clusters. So we limit ourselves to four of them, the best known, all members of Charles Messier’s Catalog.

Bode’s Galaxy (M81), in the picture with the smaller Cigar Galaxy (M82) is a spiral galaxy distant from us in about 12 million light-years. It contains about 250,000 stars and can be seen with binoculars. Its companion, M82, is also a spiral but we see its edge, so that its elongated aspect resembles a cigar.

The Pinwheel Galaxy (M101) is around 27 million light-years afar from our Solar System. Is a barred spiral with obvious asymmetry because of its off-center core of the disc. It is one of the most prominent spirals in heaven, and can also be seen with binoculars if the conditions of darkness and clean air are conducive to observation.

Finally, the Owl Nebula ( M97 ), gets its name for having two dark spots on the gaseous disk of the nebula, which resemble the eyes of this animal. It is a planetary nebula and we still do not know well its distance, though there are different estimations of about 2,600 light-years.


This constellation is identified with the Great Bear from the time of Homer, who already quoted it in his major works, The Iliad and The Odyssey calling it Bear and Cart. In Higinio we read one of the most popular names of the Great Bear, Triones, ie oxen. As there are seven brightest stars of the asterism, it was customary precede seven to the name, hence septem triones (seven oxen) or septentrion, name that received the northerly wind.

Different cultures have associated the constellation figure from Siberian Yakut to diverse North American Indian tribes, including Iroquois. It also appears in Pyrenean myths and in northern regions. It can be recognized easily in Egyptian texts, along with Orion and Sirius. It currently receives the names of The Plough in European countries, and The Big Dipper in America.


The great Zeus fell madly in love with Callisto, the beautiful huntress nymph inhabitant of the forests of Arcadia. The father of the gods seduced the nymph, and she became pregnant. Upon learning what happened Hera, wife of Zeus, prey of jealousy, turned Calisto into a bear.

Over time, Arkas, the son of Calisto, also a hunter, one day came across a bear and wanted to kill it, not knowing it was his mother. Zeus intervened and revealed the truth. For that not to happen again, Zeus took Callisto, turned into a bear, from her tail and threw her into the sky, also transformed Arkas into a bear and put him in heaven with her ​​mother to keep her company. Arkas is the constellation of Ursa Minor (the Little Bear).

But Hera, wife of Zeus, was not happy and asked her brother, Poseidon, to not allow the heavenly bears, Calisto and Arkas, to approach to his marine domains. Then, The Great Bear and the Little Bear never disappear beneath the sea.

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