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Big Dipper Constellation

Big Dipper Constellation (Ursa Major) — Ursa Major is a constellation visible throughout the year in the northern hemisphere. Its name means “Great Bear” in Latin, and is derived from the legend of Callisto. Its seven brightest stars form a famous asterism known in the United States as the Big Dipper, because the major stars can be seen to follow the rough outline of a large ladle, or dipper.

The Big Dipper is recognized as a grouping of stars in many cultures and eras. In the United Kingdom it is commonly known as the Plough, and was sometimes formerly called King Charles’s Wain (where wain means “wagon”).

From the bowl to the handle, the stars in the Big Dipper are called Dubhe, Merak, Phecda, Megrez, Alioth, Mizar, and Alkaid (or Benetnash), and are given Bayer designations of Alpha to Eta Ursae Majoris, in that order. Mizar has a companion star called Alcor, just visible to the naked eye, that served as a traditional test of sight. Both stars are actually multiple in and of themselves, including the first telescopic and spectroscopic binaries.

The star Polaris, the Pole Star, can be found by measuring a line five times the angular distance between the two pointer stars Dubhe and Merak forming the end of the dipper cup, through those stars and up and away from the dipper. The dipper also points the way to other stars, for instance by sweeping down from the handle one reaches Arcturus (α Botis) and Spica (α Virginis). A mnemonic for this is “Follow the arc to Arcturus, and speed on to Spica.”.

In 1869, R. A. Proctor noticed that, except for Dubhe and Alkaid, the stars of the Big Dipper all have proper motions heading towards a common point in Sagittarius. This group, of which a few other members have been identified, formed an open cluster at some distant point in the past. Since then the sparse group has been scattered over a region about 30 by 18 light-years, centered some 75 light-years away, making it the closest cluster-like object. About 100 other stars, including Sirius, form a stream sharing approximately the same proper motion as the ex-cluster, but the exact relationship is unclear. Our solar system is in the outskirts of this stream, but is not a member, being about 40 times older.

Notable deep sky objects

Several galaxies are found in Ursa Major, including the pair M81 (one of the brightest galaxies in the sky) and M82 above the bear’s head, and M101, a beautiful spiral northwest of η Ursae Majoris. The constellation contains about 50 galaxies, most of which are below 10th magnitude.

History

It was one of the 48 constellations listed by Ptolemy.

This is one of the most widely-known constellations, having been mentioned by such poets as Homer, Spenser, Shakespeare, and Tennyson. The Finnish epic Kalevala mentions them, and Vincent Van Gogh painted them.

Mythology

Many distinct civilizations have seen this figure as a bear. In classical mythology, one of Artemis’ companions, Callisto, lost her virginity to Zeus, who had come disguised as Artemis. Enraged, Artemis changed her into a bear. Callisto’s son, Arcas, nearly killed his mother while hunting, but Zeus or Artemis stopped him and placed them both in the sky as Ursa Major and Ursa Minor.

Hera was not pleased with the placement of Callisto and Arcas in the sky, so she asked her nurse, Tethys, to help. Tethys, a marine goddess, cursed the constellations to forever circle the sky and never drop below the horizon, hence explaining why they are circumpolar. To observers above 41N, these stars never seem to set.

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Abbreviation: UMa
Genitive: Ursae Majoris
Meaning in English: the Great Bear
Right ascension: 10.67 h
Declination: 55.38
Visible: to latitude Between 90 and -30
On meridian: 9 p.m., April 20
Area – Total: Ranked 3rd 1,280 sq. deg.
Number of stars with apparent magnitude < 3: 6
Brightest star – Apparent magnitude: Dubhe (α UMa) 1.8

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Big Dipper Constellation


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