Big Dipper

The asterism of the Big Dipper (shown in this star map in green) lies within the constellation of Ursa Major.

The Big Dipper (US) or The Plough (UK)^[1][2] is an asterism consisting of the seven brightest stars of the constellation Ursa Major;^[3][4][5][6] 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 Big Dipper seen from Kauai.

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.^{[7] [8][9]}

Western astronomy

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".^[10] In Latin, these seven stars were known as the "Seven Oxen" (septentriones, from septem triōnēs).^[11] 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. Former names include the Great Wain (i.e., wagon) or Butcher's Cleaver. The terms Charles's Wain and Charles his Wain are derived from the still older Carlswæn.^[12] 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).^[13][14] An older "Odin's Wain" may have preceded these Nordic designations.^[12]

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" as well, 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.^[15] 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.^[16][17]

Asian traditions

The Hall of the Big Dipper in a Taoist temple, Wuhan

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.^[18] 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).^[19]

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.

The Big Dipper's bowl and part of the handle photographed from the International Space Station. Mizar and Alcor are at the upper right.

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).

4D proper moving in -/+ 150 000 years. 3D red cyan glasses are recommended to view this image correctly.

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

Guide to using Big Dipper to locate Arcturus, Spica, and Polaris

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.

Cultural associations

The "Starry Plough", used by Irish nationalists and leftists.

The "Seven Stars" referenced in the Bible's Book of Amos^[20] may refer to these stars or, more likely, to the Pleiades.

In addition, the constellation has also been used in corporate logos^[21] and the Alaska flag.

See also

• Abenaki mythology
• Amenominakanushi
• Apkallu
• Saptarishi
• Seven Sages of Greece
• Swastika symbols
• Taidi

References