Nothing But the Facts About the Big Dipper (Ursa Major)
written by: slight_underweft•edited by: RC Davison•updated: 5/24/2011
Although the Big Dipper and Ursa Major are used synonymously much of the time, there is a difference: The Big Dipper is a popular name for an asterism in Ursa Major, Ursa Major being an official constellation, and the third largest. Both are part of mythologies worldwide.
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The Big Dipper Asterism Facts
General: Composed of seven of the brightest stars in the constellation Ursa Major. These seven stars form the rump and tail of The Great Bear, or Ursa Major.
Names: The Big Dipper (North America), The Plough (British Isles), Sapta Rishi (Hindu Astronomy),
Star Information: (Western name first, Indian name in parenthesis)
Merak (Pulaha): 79 ly from Earth; 2.4 apparent magnitude
Phecda (Pulastya): 84 ly from Earth; 2.4 apparent magnitude
Megrez (Atri): 81 ly from Earth; 3.3 apparent magnitude
Alioth (Angiras): 81 ly from Earth; 1.8 apparent magnitude
Mizar (Vasishtha): 78 ly from Earth; 2.1 apparent magnitude
Alkaid (Bhrigu): 101 ly from Earth; 1.9 apparent magnitude
Mythology: Much of the mythology concerning the Big Dipper is relative to the myths about the Great Bear, which can be found in the next page about the mythology of Ursa Major; however, there is some mythology concerned wholly with the Big Dipper itself. In Hindu astronomy, the name for the asterism is Sapta Rishi; the seven stars of the asterism are said to represent the seven rishis, or poet-sages, seers, who were mediums or conduits for the Vedic texts.
Interesting Facts: In roughly 50,00 years, the Big Dipper will no longer be visible in its current shape. All of the stars except for Dubhe and Alkaid are part of the Ursa Major Moving Group, and so the members of the asterism are shifting incongruously with one another as a whole. The Ursa Major Moving Group is a group of stars which are all moving toward the same point in Sagittarius.
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Ursa Major Facts
Right Ascension: 10.67h
Brightest Star: Alioth
Latitudes Visible at: +90° and -30°
Best Visible at: 21:00, April
Messier Objects: 7
M40: Not really a Messier object, although still catalogued as one: A mistaken nebulosity is actually two ninth-magnitude binary stars
M81: A spiral galaxy, one of the densest known with 250 billion suns
M82: A galaxy with more of a spindle shape, possibly caused by an explosion at its center approximately one and a half million years ago
M97: The "owl nebula," named so because of two dark areas resembling owl's eyes
M101: An expansive galaxy, one of the largest known
Stars of Note:
47 Ursae Majoris: Within the last 15 years there was discovered orbiting the star two Jupiter sized planets (there may be more in the system), one of which has a region that could possibly support water.
Groombrage 1830: Has the third largest proper motion known: 7.050 arc seconds.
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Roman and Greek Mythology
Ursa Major is Latin for The Great Bear. The stories vary in particulars, especially the cast, though each version appears to essentially share the same tale. Either Jupiter (Roman) or Zeus (Greek) either falls in love, or becomes infatuated with a mortal women, Callisto (same name in the Roman or Greek).
In some tales (Roman for one) she is a wood-nymph, others a huntress, andthe deity either forces himself upon her, or they make love, and she gives birth to a child, Arcas. So, Juno (Roman) or Hera (Greek), the respective wives of Jupiter and Zeus,become vengefully jealous (the women in either version have tendency to become especially jealous), and turn Callisto into a bear. Then, one day Arcas either went hunting or searching for his mother and ran across her in bear form, and of course did not recognize her. in the hunting version, Acras is going to shoot his mother, the bear, but Jupiter takes mercy, stops him, and turns Arcas into a smaller bear. In the searching version, his mother in bear form runs at him and Arcas gets scared, gets ready to shoot an arrow at his mother, but Zeus saves Callisto by turning Arcas into a small bear. In both stories, the all-mighty god (Jupiter or Zeus) tossed both of them into the night sky, where they would remain safe forever. So the Great Bear is Callisto. The Little Dipper is Arcas. The Big Dipper is the tail of the Great Bear, Callisto.
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The Native American Myth About the 'Great Bear'
However, the Greeks and Romans were not the only ones who saw a bear in the same segment of stars. The Iroquois, among other Native American tribes, also saw a "great bear."
The myth of the Iroquois tells of three or four hunters--though most stories hold that there were four brothers, excellent hunters, one of which was fat and lazy however--and a dog chasing a great bear(called so, both because of it's size, and because it had very powerful magic), named Nyah-gwaheh (monsterbear), which had been terrorizing their village. They attempt to hunt down the great bear with the aid of their dog; the fat and lazy brother wants to stop and eat often, and eventually becomes tired, saying he turned his ankle, and asks the brothers to carry him, which they assent to, and are consequently slowed down, but continue to chase fiercely. The dog is on the heels of the bear, and about to be struck down when, now rested, the fat and lazy brother jumps out of his brothers' arms and catches up to the bear and shoots it, killing it. The other three brothers catch up as the fat and lazy one is cooking the bear in preparation for meal. When they looked down from the hill they thought they were on and saw white lights below them, they realized that they were in the sky.
They realized that the great bear had worked it's magic, and was arising and organizing it's bones to run again, and so the brothers gave chase. Thus the brothers and their dog form the "handle" of the Big Dipper chasing the bear. Although there appears to be only three stars forming the handle (Alkaid, Mizar, Alioth--The three hunters in some legend), Mizar does have a subtle optical binary, Alcor, who seems to be the best candidate for the fourth hunter.
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Star Chart: http://en.wikipedia.org/wiki/Big_dipper