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Corona Borealis
Corona Borealis is a small constellation in the Northern Celestial Hemisphere. It is one of the 48 constellations listed by the 2nd-century astronomer Ptolemy, and remains one of the 88 modern constellations. Its brightest stars form a semicircular arc. Its Latin name, inspired by its shape, means "northern crown". In classical mythology Corona Borealis generally represented the crown given by the god Dionysus to the Cretan princess Ariadne and set by him in the heavens. Other cultures likened the pattern to a circle of elders, an eagle's nest, a bear's den, or even a smokehole. Ptolemy also listed a southern counterpart, Corona Australis, with a similar pattern.
The brightest star is the magnitude 2.2 Alpha Coronae Borealis. The yellow supergiant R Coronae Borealis is the prototype of a rare class of giant stars—the R Coronae Borealis variables—that are extremely hydrogen deficient, and thought to result from the merger of two white dwarfs. T Coronae Borealis, also known as the Blaze Star, is another unusual type of variable star known as a recurrent nova. Normally of magnitude 10, it last flared up to magnitude 2 in 1946. ADS 9731 and Sigma Coronae Borealis are multiple star systems with six and five components respectively. Five star systems have been found to have Jupiter-sized exoplanets. Abell 2065 is a highly concentrated galaxy cluster one billion light-years from our Solar System containing more than 400 members, and is itself part of the larger Corona Borealis Supercluster.
== Characteristics ==
Covering 179 square degrees and hence 0.433% of the sky, Corona Borealis ranks 73rd of the 88 modern constellations by area.〔 Its position in the Northern Celestial Hemisphere means that the whole constellation is visible to observers north of 50°S. It is bordered by Boötes to the north and west, Serpens Caput to the south, and Hercules to the east. The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is 'CrB'. The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of eight segments (''illustrated in infobox''). In the equatorial coordinate system, the right ascension coordinates of these borders lie between and , while the declination coordinates are between 39.71° and 25.54°. It has a counterpart—Corona Australis—in the Southern Celestial Hemisphere.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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