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.
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.
Names and places
The constellation of Ursa Major has been seen as a bear, a wagon, or a ladle. The "bear" tradition is Greek, but apparently the name "bear" has parallels in Siberian or North American traditions. 
The name "Bear" is Homeric, and apparently native to Greece, while the "Wain" tradition is Mesopotamian. 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. The classical mythographer identified the "Bear" as the nymph Callisto, changed into a she-bear by Hera, the jealous wife of Zeus.
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), but also the "Great Bear" (Stora Björn). 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.
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 the Dipper, proceeding from the handle to the bowl: Alkaid, Mizar, Alioth, Megrez, Phecda, Merak, and Dubhe.
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 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.
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:
- Polaris, the North Star, is found by imagining a line from Merak (β) to Dubhe (α) and then extending it for five times the distance between the two Pointers.
- Extending a line from Megrez (δ) to Phecda (γ), on the inside of the bowl, leads to Regulus (α Leonis) and Alphard (α Hydrae). A mnemonic for this is "A hole in the bowl will leak on Leo."
- Extending a line from Phecda (γ) to Megrez (δ) leads to Thuban (α Draconis), which was the pole star 4,000 years ago.
- Crossing the top of the bowl from Megrez (δ) to Dubhe (α) takes one in the direction of Capella (α Aurigae). A mnemonic for this is "Cap to Capella."
- Castor (α Geminorum) is reached by imagining a diagonal line from Megrez (δ) to Merak (β) and then extending it for approximately five times that distance.
- By following the curve of the handle from Alioth (ε) to Mizar (ζ) to Alkaid (η), one reaches Arcturus (α Boötis) and Spica (α Virginis). A mnemonic for this is "Arc to Arcturus then speed (or spike) to Spica."
Additionally, the Dipper may be used as a guide to telescopic objects:
- The approximate location of the Hubble Deep Field can be found by following a line from Phecda (γ) to Megrez (δ) and continuing on for the same distance again.
- Crossing the bowl diagonally from Phecda (γ) to Dubhe (α) and proceeding onward for a similar stretch leads to the bright galaxy pair M81 and M82.
- Two spectacular spiral galaxies flank Alkaid (η), the Pinwheel (M101) to the north and the Whirlpool (M51) to the south.
- Projecting a line from Alkaid through the pole star will point to Cassiopeia.
- Stern, David P. (23 April 2008). "Finding the Pole Star". Goddard Space Flight Center. Retrieved 31 August 2013.
- Rao, Joe (9 May 2008). "Doorstep Astronomy: See the Big Dipper". space.com. Retrieved 31 August 2013.
- Holbrook, J. C.; Baleisis, Audra (2008). "Naked-eye Astronomy for Cultural Astronomers". African Cultural Astronomy. Astrophysics and Space Science Proceedings. p. 53. doi:10.1007/978-1-4020-6639-9_5. ISBN 978-1-4020-6638-2.
- Olson, R. J. M.; Pasachoff, J. M. (1992). "The 1816 Solar Eclipse and the Comet 1811I in Linnell's Astronomical Album". Journal for the History of Astronomy. 23: 121. Bibcode:1992JHA....23..121O.
- John C. Barentine (4 April 2016). Uncharted Constellations: Asterisms, Single-Source and Rebrands. Springer. pp. 16–. ISBN 978-3-319-27619-9.
- Nemiroff, R.; Bonnell, J., eds. (21 April 2013). "Big Dipper". Astronomy Picture of the Day. NASA.
- "But whence came the same idea into the minds of our North American Indians? Was it by accident? or is it evidence of a common origin in the far antiquity of Asia? The conformation of the seven stars in no way resembles the animal, — indeed the contrary; yet they called them Okuari and Paukunawa, words for a "bear," before they were visited by the white men, as is attested by Le Clercq in 1691, by the Reverend Cotton Mather in 1712, by the Jesuit missionary La Fitau in 1724, and by the French traveler Charlevoix in 1744. And Bancroft wrote in his history of our country: [...] In justice, however, to their familiarity with a bear's anatomy, it should be said that the impossible tail of our Ursa was to them either Three Hunters, or a Hunter with his two Dogs, in pursuit of the creature; the star Alcor being the pot in which they would cook her. They thus avoided the incongruousness of the present astronomical ideas of Bruin's make-up, although their cooking-utensil was inadequate. The Housatonic Indians, who roamed over that valley from Pittsfield through Lenox and Stockbridge to Great Barrington, said that this chase of the stellar Bear lasted from the spring till the autumn, when the animal was wounded and its blood plainly seen in the foliage of the forest." Allen (1899), p. 423. c.f. Gibbon, William B. (1964). "Asiatic parallels in North American star lore: Ursa Major". Journal of American Folklore. 77 (305): 236–250. doi:10.2307/537746. JSTOR 537746.
- Bradley E Schaefer, The Origin of the Greek Constellations: Was the Great Bear constellation named before hunter nomads first reached the Americas more than 13,000 years ago!', Scientific American, November 2006, reviewed at The Origin of the Greek Constellations;[unreliable source?] Yuri Berezkin, The cosmic hunt: variants of a Siberian – North-American myth. Folklore, 31, 2005: 79-100.
- 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" d'Huy Julien, Un ours dans les étoiles: recherche phylogénétique sur un mythe préhistorique, Préhistoire du sud-ouest, 20 (1), 2012: 91-106; A Cosmic Hunt in the Berber sky : a phylogenetic reconstruction of Palaeolithic mythology, Les Cahiers de l'AARS, 15, 2012.
- Homer. "Book XVII". The Iliad. Translated by Samuel Butler.
- In Latin, short vowels often syncopate before -r- in medial syllables.
- Hinckley Allen, Richard (1963). "Star Names: Their Lore and Meaning – "Ursa Major"".
- Bågenholm, Gösta. "Astro ordlista: Karlavagnen" [Astrological glossary: The Big Dipper]. 150 ord och begrepp inom astronomisk navigation (in Swedish). Archived from the original on 3 December 2005.
"Som pendang till Karlavagnen kallas Lilla björn (latin Ursæ Minoris) för kvinnovagnen..." — as an appendix to the Men's Wagon, the Little Bear is called the Women's Wagon
- Hellquist, Elof (1922). Svensk etymologisk ordbok [Swedish etymological dictionary] (in Swedish).
Karlavagnen: "I stället sammansatt" ... – "Instead composed from the appellative karl [man] in opposition to Icelandic kvennavagn [women's wagon]"
- Kaisa, Häkkinen (2007). Nykysuomen etymologinen sanakirja (in Finnish) (4th ed.). WSOY. ISBN 978-951-0-27108-7.
- Hämäläinen, Pirjo (11 November 2013). "Otavassa on orjan merkki". Kansan Uutiset (in Finnish). Retrieved 21 April 2014.
- Mykrä, Sakari. "Kahdensadan nimen kontio". Suurpedot.fi (in Finnish). Archived from the original on 9 February 2013. Retrieved 21 April 2014.
- See their individual pages.
- Amos 5:8.
- Allen P. Adamson; Martin Sorrell (2007). Brandsimple: how the best brands keep it simple and succeed. Palgrave Macmillan. p. 101. ISBN 978-1-4039-8490-6. For an example see Iridium Satellite LLC.