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The Big Dipper (US) or Plough (UK) is an asterism consisting of the seven brightest stars of the constellation Ursa Major; six of them are of second magnitude and one, Megrez (δ), of third magnitude. Four define a "bowl" or "body" and three define a "handle" or "head". It is recognized as a distinct grouping in many cultures.
Contents
The North Star (Polaris), the current northern pole star and the tip of the handle of the Little Dipper, can be located by extending an imaginary line from Merak (β) through Dubhe (α). This makes it useful in celestial navigation.
Origin
The constellation of Ursa Major has been seen as a bear by many distinct civilizations. This may stem from a common oral tradition stretching back for thousands of years. Using statistical and phylogenetic tools, Julien d'Huy reconstructs the following Palaeolithic state of the story: "There is an animal that is a horned herbivore, probably an elk. One human pursues this ungulate. The hunt proceeds to the sky. The animal is alive when it is suddenly transformed into a constellation-- It forms the Big Dipper".
Canada and United States
In Canada and the United States, the asterism is known as the Big Dipper because the major stars can be seen to follow the rough outline of a spoon or "dipper". There are seven stars in this constellation, such as Alkaid, Mizar, Alioth, Phecda, Megrez, and Dubne, and Mereak.
A widespread Native American figuration had the bowl as a bear. Some groups considered the handle to be three cubs following their mother, while others pictured three hunters tracking the bear. The Anishinaabe or Ojibway First Nation know the Big Dipper as the "Fisher Star" (Ojig-anang) after the small mammal known as the fisher.
Europe
In both Ireland and the United Kingdom, this pattern is known as the Plough. The symbol of the Starry Plough has been used as a political symbol by Irish Republican and left wing movements. Another former name was the Great Wain (i.e., wagon). In northern England, it is occasionally still known as the Butcher's Cleaver, and in the northeast, as Charlie's Wagon. This derives from the earlier Charles's Wain and Charles his Wain, which derived from the still older Carlswæn. A folk etymology holds that this derived from Charlemagne, but the name is common to all the Germanic languages and intended the churls' wagon (i.e., "the men's wagon"), in contrast with the women's wagon (the Little Dipper). An older "Odin's Wain" may have preceded these Nordic designations.
In German, it is known as the "Great Wagon" (Großer Wagen) and, less often, the "Great Bear" (Großer Bär). In Scandinavia, it is known by variations of "Charles's Wagon" (Karlavagnen, Karlsvogna, or Karlsvognen). In Dutch, its official name is the "Great Bear" (Grote Beer), but it is popularly known as the "Saucepan" (Steelpannetje). In Italian, too, it is called the "Great Wagon" (Grande Carro).
In Romanian and most Slavic languages, it is known as the "Great Wagon" but, in Hungarian, it is commonly called "Göncöl's Wagon" (Göncölszekér) or, less often, "Big Göncöl" (Nagy Göncöl) after a táltos (shaman) in Hungarian mythology who carried medicine that could cure any disease. In Finnish, the figure is known as the "Salmon Net" (Otava) and widely used as a cultural symbol. The brown bear in Finnish actually became known as otava, but this is claimed to stem from its resemblance to—and mythical origin from—the asterism rather than vice versa.
Book XVIII of Homer's Iliad mentions it as "the Bear, which men also call the Wain". In Latin, these seven stars were known as the "Seven Oxen" (septentriones, from septem triōnēs). Triōnēs is a hapax legomenon, occurring only in a single passage by Varro, where he glosses it as meaning "plough oxen". The derivation is acceptable but the meaning, if Varro is right that it derives from terō ("thresh grain by rubbing"), is surely "threshing oxen": the seven stars wheel around the pole star like oxen on a threshing floor. The name is the origin of septentriōnēs the Latin word for north, from which came the adjective septentrional ("northern") in English, French, Italian, Portuguese, and Spanish.
Asia
In traditional Chinese astronomy, which continues to be used for throughout East Asia (e.g., in astrology), these stars are generally considered to compose the Right Wall of the Purple Forbidden Enclosure which surrounds the Northern Celestial Pole, although numerous other groupings and names have been made over the centuries. Similarly, each star has a distinct name, which likewise has varied over time and depending upon the asterism being constructed. The Western asterism is now known as the "Northern Dipper" (北斗) or the "Seven Stars of the Northern Dipper" (Chinese and Japanese: 北斗七星; pinyin: Běidǒu Qīxīng; Cantonese Yale: Bak¹-dau² Cat¹-sing¹; rōmaji: Hokutō Shichisei; Korean: 북두칠성; romaja: Bukdu Chilseong; Vietnamese: Sao Bắc Đẩu). The personification of the Big Dipper itself is also known as "Doumu" (斗母) in Chinese folk religion and Taoism, and Marici in Buddhism.
In Malaysian, it is known as the "Dipper Stars" (Buruj Biduk); in Indonesian, as the "Canoe Stars" (Bintang Biduk).
In Hindu astronomy, it is referred to as the "Collection of Seven Great Sages" (Saptarshi Mandal), as each star is named after a mythical Hindu sage.
An Arabian story has the four stars of the Plough's bowl as a coffin, with the three stars in the handle as mourners, following it.
In Mongolian, it is known as the "Seven Gods" (Долоон бурхан). In Kazakh, they are known as the Jetiqaraqshi (Жетіқарақшы) and, in Kyrgyz, as the Jetigen (Жетиген).
Stars
Within Ursa Major the stars of the Big Dipper have Bayer designations in consecutive Greek alphabetical order from the bowl to the handle.
In the same line of sight as Mizar, but about one light-year beyond it, is the star Alcor (80 UMa). Together they are known as the "Horse and Rider". At fourth magnitude, Alcor would normally be relatively easy to see with the unaided eye, but its proximity to Mizar renders it more difficult to resolve, and it has served as a traditional test of sight. Mizar itself has four components and thus enjoys the distinction of being part of an optical binary as well as being the first-discovered telescopic binary (1617) and the first-discovered spectroscopic binary (1889).
Five of the stars of the Big Dipper are at the core of the Ursa Major Moving Group. The two at the ends, Dubhe and Alkaid, are not part of the swarm, and are moving in the opposite direction. Relative to the central five, they are moving down and to the right in the map. This will slowly change the Dipper's shape, with the bowl opening up and the handle becoming more bent. In 50,000 years the Dipper will no longer exist as we know it, but be re-formed into a new Dipper facing the opposite way. The stars Alkaid to Phecda will then constitute the bowl, while Phecda, Merak, and Dubhe will be the handle.
Guidepost
Not only are the stars in the Big Dipper easily found themselves, they may also be used as guides to yet other stars. Thus it is often the starting point for introducing Northern Hemisphere beginners to the night sky:
Additionally, the Dipper may be used as a guide to telescopic objects:
Cultural associations
The "Seven Stars" referenced in the Bible's Book of Amos may refer to these stars or, more likely, to the Pleiades.
In addition, the constellation has also been used in corporate logos and the Alaska flag.