http://www.daviddarling.info/images/Ursa_Major.png
http://www.daviddarling.info/images/Ursa_Major.png
Ursa Major




Ursa Major, also known as the Great Bear, is a constellation that is visible anytime during the year in the Northern Hemisphere. This constellation is a good starting point when trying to locate other stars and constellations. There are many great legends and myths from various cultures that are associated with Ursa Major.

Important Features



Ursa Major is a circumpolar boreal constellation; meaning, this constellation remains above the horizon at all times and it is located in the Northern hemisphere. During the springtime, the constellation is at its highest point in the sky. Consequently, during the autumn the constellation is at its lowest point in the sky. Because this constellation is circumpolar, it travels closely around Polaris (the North Star) never rising or setting, it can be seen during all times during the year.

Of the eighty-eight constellations, Ursa Major is the third largest. It is surrounded by a number of other constellations: to the North, Camelopardalis and Draco; to the East, Bootes and Draco; to the South, Canes Venatici, Coma Berenices, Leo, Leo Minor, and Lynx; and to the West, Camelopardalis and Lynx. The seven brightest stars in this constellation create an asterism (a familiar group of stars) known as the Big Dipper. The Big Dipper makes up the bear's hindquarters. With the exceptions of Dubhe and Alkaid, the stars in the Big Dipper all have proper motions (measurement of its change in position in the sky after all improper motions have been accounted for) heading in a path toward the constellation of Sagittarius. With the discovery of a few other stars moving in this direction, this moving group of stars is known as the Ursa Major Moving Group.

Additionally, Ursa Major houses another asterism, The Leaps of the Gazelle. It is located around the bear's toes, the southwest boarder. The Leaps of the Gazelle is a series of three pairs of stars. Alula Borealis and Australis are the first leap, Tania Borealis and Australis are the second leap, and third lead is Talitha Borealis and Australis.

Main Stars and Other Objects


http://www.astro.wisc.edu/~dolan/constellations/gif/UMA.jpg
http://www.astro.wisc.edu/~dolan/constellations/gif/UMA.jpg

Dubhe: This star is a class K orange giant with a temperature of roughly 4500 K. Its luminosity is 300 times that of the Sun, and it is the only star in the constellation that is involved in the long processes of dying. Although, the star has temporarily stabilized the fusion of helium at its core. Debhe is denoted as the alpha star (α), simply because when Johann Bayer letter the Big Dipper's star, he did it simply by moving West to East. This star is not the brightest star, but the second brightest star in the constellation. It has a magnitude of 1.82. With the beta star (β), Dubhe comprises the famous "Pointer" stars to Polaris. In the other direction, these stars point to Regalus and Leo.

Merak: This is the beta (β) star. It is a standard hot white class A (A1) "main sequence" dwarf star. Its temperature is around 9000 K. Merak has a magnitude of 2.37 and is the fifth brightest star in the Big Dipper. Again, Merak was denoted as the beta star due to Bayer's lettering from West to East. Merak's luminosity is approximately 60 times solar, and its mass is nearly triple that of the sun. Like the sun, Merak fuses hydrogen to helium at its core. This star is unique in that it is considered a Vega-like star; it radiates extra infrared light that creates a disk-like shroud of heated dust. The size of this disk is close the orbit of Saturn and it is unknown if Merak has any planets.

Phecda: This star is the most southern of the Big Dipper's "bowl stars." The star is the sixth brightest of the Big Dipper, with a magnitude of 2.44. Again, due to Bayer's lettering from West to East, Phecda was denoted at the gamma star (γ). The star is a class A (A0) main sequence dwarf star with a temperature of approximately 9500 K. It is a white colorless star. Phecda rotates at 168 km per second, which consequently is eighty-four times faster than the sun. There is a cloud or a disk of spinning gas surrounding this star, this is known due to the emission from hydrogen circulating.

Megrez: The Big Dipper's delta (δ) star, although it is one of the Big Dipper's fainter stars. When the Big Dipper's stars were letter, Bayer designated the letter based on the order from West to East, not on their brightness. Megrez has a magnitude of 3.31, It is an ordinary class A (A3) dwarf star glowing white at a temperature of 8630 K. Megrez is 81 light years away and has a luminosity of 23 solar. Its radius is about double the sun's. Megrez is approximately 50 million years old and it is thought that is has grown fainter over time.

Alioth: This is the brightest of Ursa Major's stars having a magnitude of 1.77. It is the 32nd brightest star in the sky. Alioth represents the tail of the bear. As previously mentioned, Bayer letter the stars from West to East, denoting Alioth as the epsilon star (ε). It is a white class A (A0) star. Its temperature is measured at 9400 K. Alioth is 81 light years away, and its luminosity is 108 times than that of the Sun. Its mass is three times as large as the Sun's. Alioth is the brightest of the peculiar "Ap" stars. These are magnetic stars where its chemicals are either depleted or enhanced depending on the regularity of the star's rotation.

Mizar: This is the zeta (ζ) star. With a magnitude of 2.06, Mizar is the fourth brightest star in the Big Dipper. It is 78 light years away. It is a white class A (A2) dwarf star. This star has odd chemical abundances due to its slow rotation. Mizar is most famous because it is the first known double star. A double star consists of a pair of stars that orbit each other.

Alkaid: This is the third brightest of the the Big Dipper Stars. It has a magnitude of 1.85, and is the 35th brightest star in the sky. Due to Bayer's lettering the stars in the Big Dipper from West to East, Alkaid is the eta (η) star. It is almost exactly 100 light years away. Like the Sun, Alkaid is a main sequence star that fuses hydrogen to helium in its core. It is on the hotter stars and can been seen with the naked eye. With a surface temperature of approximately 20,000 K, this stars glows a soft blue-white. The star's mass is sex times larger than the Sun's, and it is 700 times more luminous.

Theta Uma: The theta (θ) star of Ursa Major, this star has no proper name. However, it does share one with five other stars; the Arabs refer to this grouping of stars as the Throne of Mourners. Theta Uma has a magnitude of 3.20 and it is one of the brighter stars in the sky. The star is 44 light years away, and is unfortunately coming to the end of its 3 billion year lifetime.

Talitha: It is a cooler class A (A7) star with a temperature of 8165 K. It has a magnitude of 3.14, and is denoted by Bayer as the iota (ι) star in Ursa Major. Talitha is a member of three pairs of stars that make up the bear's feet. This star is 48 light years away, and its luminosity is nine times that of the Sun.

Kappa Uma: With Talitha, these two stars make up the eastern paw of the Great Bear. Kappa Uma is a white class A (A1) star, with a surface temperature of 9,600 K. It has a magnitude of 3.60. Kappa Uma is not one star, it is really two stars that are seemingly close to one anoter. Kappa A shines with the light os 290 Suns, and Kappa B shines with the light of 250 Suns. Its total mass is 11 times that of the Sun. Both of these stars are rare class A emission (Ae) stars. These are stars that radiate energy from hydrogen fusion. Kappa Uma is the kappa (κ) star in the Ursa Major constellation.

Tania Borealis: This is Ursa Major's lambda (λ) star. Its magnitude is 3.45, and it is a class A (A2) sub-giant with a surface temperature of 8,930 K. Tania Borealis is 134 light years away and is roughly 480 million years old. It radiates at a rate 59 times greater than the Sun. It is a mid-metallic line star; it is enriched in zinc and other rare earths, but is lacks calcium. It is paired with Tania Australis to create one of the bear's paws.

Tania Australis: This star is a rare class M (M0) giant. It is the mu (μ) star in the Ursa Major constellation. Its magnitude is 3.05, and has a surface temperature of 3,950 K. This star is 205 light years away and its luminosity is 850 times that of the Sun.

Alula Borealis: A class K (K3) giant with a surface temperature of 4,100 K is Ursa Major's nu (ν) star. At approximately 100 million years old, the star is 421 light years away. Its luminosity is 1,355 times that of the Sun. Alula Borealis has a star companion that is a G1 dwarf.

Alula Australis: This star is a double star; it has a twin class G hydrogen fusing dwarf. The star has a magnitude of 3.78, and is 27 light years away. Alula Australis is denoted as the xi (ξ) star in Ursa Major.

Muscida: Although not one of the Big Dipper stars in Ursa Major, Muscida is the star that leads the Great Bear around the North Pole. It a unique star in the Ursa Major constellation; it is a yellow class G (G5) giant with a surface temperature of 5,157 K. It has a magnitude of 3.36, and is 185 light years away. The star is denoted as the constellation's omicron (ο) star. The star is approximately 360 million years old. It spins slowly at only 3 kilometers per second taking is 250 to complete one full rotation.


To learn more about these stars and other stars in the Ursa Major cluster, visit STARS.


Mythological Background


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http://www.hubbletelescope.btinternet.co.uk/ursamajor.jpg

In many cultures there is a reoccurring theme of a kinship between humans and bears. As Ursa Major moves through the sky it can be observed as being a quadrupedal, on all four paws, or a bipedal, on its hind-legs. Many believe that this continual changing of position reflects the bear's running on all fours across the horizon, and its rising to ascend back into the sky. In many cultures bears are revered as god, and many stories have been written about humans taking the form of bears.


Greek Mythology


Greek mythology incorporates both Ursa Major and Ursa Minor into its story. According to the myth, the God Zeus fell in love with Callisto, a beautiful nymph. Callisto was one of the virgin followers of the virgin goddess Dianna, the huntress. In order to approach her, Zeus tricked Callisto into believing he was Dianna by taking her form. While Zeus was pretending to be Dianna, he managed to make love to her. When Dianna found out about what happened, she sent Callisto away. At the same time, Zeus' wife, Hera, had just given birth to a baby boy, Arcas, and became filled with jealousy. In her jealous rage, Hera turned Callisto into a bear.

Years later, the son, Arcas, met Callisto, still in her bear form, and out of fright tried to kill her. Zeus, who saw this tragedy about to unfold, tried to undo Hera's curse and turn Callisto back into her human form. But he was unsuccessful. In order to keep the two safe, he turn Arcas into a smaller bear, and made them immortal by placing them in the sky.


Roman Mythology


Like the Greek myth, the Roman myth also involves both of the bear consteallations. According to the Roman myth, Callisto grew tired while hunting in the forest and decided to lay down to rest. Infatuated by her beauty, the god Jupiter took a liking to this beautiful maiden. Juno, Jupiter's wife, became very jealous of Callisto. Some time had passed, Callisto had given birth to a baby boy. When Juno learned of this news, she decided that Jupiter must have been the father. In her rage, Juno turned Callisto into a bear so she would no longer be beautiful. Arcas, Callisto's son, was adopted and became a hunter. One day while Arcas was out hunting Callisto saw him. Overjoyed to see her son and forgetting that she was a bear, Callisto ran over to him. Arcas believing that he was being attacked, shot an arrow at Callisto. Jupiter, who was watching this scene unfold, was able to stop the arrow from hitting Callisto and he turned Arcas into a bear as well. In order to save the two of them from any further punishment from Juno, Jupiter grabbed the two bears by their tails and swung them both into the heavens.

The strength of the throw caused the usually short tails of the bears to become elongated. When Juno learned of what Jupiter had done for Callisto and Arcas, she was able to persuade the gods of the sea to never allow the two bears wade in their water or their streams. Seemingly, the bears never dip below the horizon and continue on their endless journey around Polaris.

Native American Myths - The Hunt


Micmac Indians and the Iroquois Indians


These two Native American tribes share the same myth about the Great Bear. The quadrangle of the Big Dipper repsents a bear being pursued by seven hunters. The three closest hunters are the handle of the dipper. As autumn approaches, the four hunters that are the farthest away dip below the horizon and abandon the hunt. The three remaining hunters are left to chase the bear. These three hunters are named after different birds: the one closes to the bear, Robin; the next, Chickadee; and then the farthest, Moose Bird. According to the myth, the second hunter, Chickadee is carrying a pot that is to be used to cook the bear in.

In the autumn the bear attempts to stand up on its hind-legs, Robin hits the bear with an arrow. Blood is sprayed all over Robin. He shakes of the blood, which causes the leaves in the forest to change to red. Some of the blood staind Robin, and henceforth he is called Robin Redbreast. The bear is then eaten and its skeleton remains in the sky, appearing to be laying on its back for the remainder of winter. When the next spring arrives, a new bear leaves its den and the eternal hunt continues once more.

Algonquin Indians


According to the Algonquin myth, there was a large bear, who's only pleasure in life was to destory a village. Everyone in the village was scared of this bear, and each time it would attack the village it caused more damage than the time before. The elders of the village met and decided that something needed to be done about the bear attacks. They decided that each would bring their best and bravest warriors together to hunt the bear.

The three warriors had all proven themselves over time showing how strong and brave they were. The bear, realizing that the village's best warriors were hunting him decided to run away. This bear at heart was really a coward. As the bear fled, the hunters chased after him. This hunt went on for many moons and over time, the bear began to tire. The hunters were relentless and would not stop chasing the bear. In an act of desperation, the bear ran right up into the sky and the hunters followed him. Around and around the bear and the hunters went circling the North Star.

The hunter closest to the bear manage to wound the bear with an arrow, but this bear's magic was very powerful and this wound was not fatal. However, every autumn, when the bear and the hunters are close to the horizon, the bear bleeds a few drops of blood onto the Earth. This spillage of blood is what makes the leaves change color every autumn.

The Arab Myth


Unlike the myths above, this myth associates the constellation with a funeral. According to the myth, the quadrangle represents a coffin and the three handle stars of the Big Dipper are the people following the coffin. The middle star, which is really two stars (Mizar and Alcor), represent the son and the
daughter of al-Naash, the man who has died. Al-Naash was murdered by Al-Jadi, who is the North Star.

References




American Association of Variable Star Observers. "The Myths of Ursa Major, The Great Bear." 23 March 2008.
http://www.aavso.org/vstar/vsots/ursamyth.shtml

Dolan, Chris. "Ursa Major." The Constellations and their Stars. 1995. University of Wisconsin. 23 March 2008. http://www.astro.wisc.edu/~dolan/constellations/constellations/Ursa_Major.html

Kaler, Jim. "Constellations and the Stars." Stars. 2008. University of Illinois. 12 April 2008. http://www.astro.uiuc.edu/~kaler/sow/sowlist.html

Kronberg, C. "Ursa Major." 2005. Students for the Exploration and Development of Space. 28 March 2008. http://seds.org/Maps/Stars_en/Fig/ursamajor.html

Pasachoff, Jay M. A Field Guide to the Stars and Planets. New York: Peterson Field Guides, 2000.

Petrie, R.M. & B.N. Moyls. "Convergent Point and Space Motion of Ursa Major Cluster." Monthly Notices of the Royal Astronomical Society. 113 (1953): 239-250.

Raasch, Rick. "Constellation of the Month / Ursa Major." The Texas Astronomical Society. 1995. University of Wisconsin. 23 March 2008.
http://www.astro.wisc.edu/~dolan/constellations/cotm/uma.hmtl

Raymo, Chet. 365 Starry Nights. New York: Prentice Hall, 1982.

"Ursa Major." Windows to the Universe. 2000. University Coorporation of Atmospheric Research. 26 March 2008. http://www.windows.ucar.edu/tour/link=/the_universe/Constellations/circumpolar/ursa_major.html&edu=high