|Pronunciation||/ /, genitive //|
|Symbolism||The Northern Crown|
|Right ascension||15h 16m 03.8205s–16h 25m 07.1526s|
|Area||179 sq. deg. (73rd)|
|Stars with planets||4|
|Stars brighter than 3.00m||4|
|Stars within 10.00 pc (32.62 ly)||0|
|Brightest star||α CrB (Alphecca or Gemma) (2.21m)|
|Nearest star||HD 144579
(46.86 ly, 17.25 pc)
|Visible at latitudes between +90° and −50°.
Best visible at 21:00 (9 p.m.) during the month of July.
Corona Borealis / / is a small constellation in the northern sky. Its name is Latin for "northern crown", a name inspired by its shape; its main stars form a semicircular arc. One of the 48 constellations listed by the 2nd-century astronomer Ptolemy, it remains one of the 88 modern constellations.
The brightest star is the 2.2-magnitude Alpha Coronae Borealis. Four star systems have been found to have exoplanets to date; three of these are orange giants, while the fourth—Rho Coronae Borealis—is a solar twin, very like our own Sun. Abell 2065 is a highly concentrated galaxy cluster located one billion light-years from our Solar System containing over 400 members, the brightest of which are 16th magnitude.
Covering 179 square degrees and hence 0.433% of the sky, Corona Borealis ranks 73rd of the 88 constellations in area. It is bordered by Bootes 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. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 15h 16.0m and 16h 25.1m, while the declination coordinates are between 39.71° and 25.54°. Its position in the Northern Celestial Hemisphere means that the whole constellation is visible to observers north of 50°S.[a]
Johann Bayer gave twenty stars in Corona Borealis Bayer designations from Alpha to Upsilon in his 1603 star atlas Uranometria. The components of the double star Zeta have since been designated Zeta1 and Zeta2, and John Flamsteed equated his 20 and 21 Coronae Borealis with Nu1 and Nu2.
The seven stars that make up the constellation's figure are all 4th-magnitude stars, except for the constellation's brightest star, Alpha Coronae Borealis. This blue-white main-sequence star, also called Alphekka and Gemma, is of magnitude 2.2, though it is an Algol-type eclipsing binary. It varies by 0.1 magnitude with a period of 17.4 days. Lying 75 light-years distant from Earth, Alphekka is believed to be a member of the Ursa Major Moving Group of stars that have a common motion through space.
Corona Borealis is home to several binary and double stars. Beta Coronae Borealis or Nusakan is a spectroscopic binary system located around 114 light-years away. The two components are separated by 10 astronomical units and orbit each other every 10.5 years. Zeta Coronae Borealis is a double star divisible in small telescopes. It has two blue-white components, 470 light-years from Earth. The primary is of magnitude 5.0 and the secondary is of magnitude 6.0. Another double star is Nu Coronae Borealis; both components are 550 light-years from Earth but have different radial velocities and are assumed to be unrelated. The primary, Nu1 Coronae Borealis, is a red-hued giant star of magnitude 5.2; the secondary, Nu2 Coronae Borealis is an orange-hued giant star of magnitude 5.4. Sigma Coronae Borealis, on the other hand, is a true binary star. Both components are yellow and orbit each other every 1000 years. The system, 71 light-years from Earth, has a primary of magnitude 5.6 and a secondary of magnitude 6.6. Sigma Coronae Borealis is divisible by small amateur telescopes. ADS 9731 is a system composed of six stars, two of which are spectroscopic binaries.
Corona Borealis is home to two remarkable variable stars. T Coronae Borealis is an exploding variable star also known as the Blaze Star. Normally placid around magnitude 10—it has a minimum of 10.2 and maximum of 9.9—it brightens to magnitude 2 in a period of hours, caused by a nuclear chain reaction and the subsequent explosion. T Coronae Borealis is one of a handful of stars called recurrent novae, which include RS Ophiuchi, T Pyxidis, V1017 Sagitarii, and U Scorpii. An outburst of T Coronae Borealis was first recorded in 1866; its most recent outburst was in February 1946. T Coronae Borealis is a binary star with a red-hued giant primary and a small blue secondary; its period is approximately 8 months. R Coronae Borealis is a yellow-hued variable supergiant star, over 7000 light-years from Earth, and prototype of a class of stars known as R Coronae Borealis variables. Normally of magnitude 6, its brightness periodically drops as low as magnitude 15 and then slowly increases over the next several months. Though small dips in brightness occur sporadically, extreme decreases happened most recently in 1962, 1972, and 1977. Small carbon particles building up in the stellar atmosphere may be responsible.
S Coronae Borealis is a Mira-type long period variable that ranges between magnitudes 5.8 and 14.1 over a period of 360 days. RR Coronae Borealis is a M3-type semiregular variable star that varies between magnitudes 7.3 and 8.2 over 60.8 days.
Four star systems have been found to have exoplanets to date. Kappa Coronae Borealis is an orange subgiant of spectral type K0III-IV that has a dust debris disk and one confirmed and one possible planet. Omicron Coronae Borealis is another K-type clump giant with one confirmed planet., believed to be, like HD 100655 b, one of the two least massive planets known around clump giants. Rho Coronae Borealis is a Solar twin, yellow dwarf around 57 light-years distant. It has a planet around the size and mass of Jupiter orbiting it every 40 days. HD 145457 is an orange giant of spectral type K0III found to have one planet.
Corona Borealis contains no bright deep-sky objects. Abell 2065 is a highly concentrated galaxy cluster containing over 400 members, the brightest of which are 16th magnitude. The cluster is more than one billion light-years from Earth. Abell 2142 is a huge, X-ray luminous galaxy cluster that is the result of a still ongoing merger between two galaxy clusters. The combined cluster is six million light years across, contains hundreds of galaxies and enough gas to make a thousand more. It has a heliocentric redshift of 0.0909 (meaning it is moving away from us at 27,250 km/s) and a visual magnitude of 16.0. It is about 1.2 billion light years (380 Mpc) away. Another galaxy cluster in the constellation, RX J1532.9+3021, is located approximately 3.9 billion light years from Earth. At the cluster's center is a large elliptical galaxy containing the supermassive black hole.
In November 2013 astronomers discovered the largest structure in the universe ever found—the Hercules–Corona Borealis Great Wall, which lies partly within this constellation's borders. The structure is a galaxy filament, or a huge group of galaxies assembled by gravity. It is about 10 billion light-years (3 Gpc) at its longest dimension, which is approximately 1/9 (10.7%) of the diameter of the observable universe, 7.2 billion light-years (2.2 Gpc; 150,000 km/s in redshift space) wide, but only 900 million light-years (300 Mpc) thick, and is the largest known structure in the universe. It is at redshift 1.6–2.1, corresponding to a distance of approximately 10 billion light-years away from Earth.
History and mythology
In Greek mythology, Corona Borealis was sometimes considered to represent a crown that was given by Dionysus to Ariadne, the daughter of Minos of Crete. When she wore the crown to her wedding, where she married Dionysus, he placed her crown in the heavens to commemorate the wedding. In Welsh mythology, it was called Caer Arianrhod, "the Castle of the Silver Circle", and was the heavenly abode of the Lady Arianrhod.
The Arabs called the constellation Alphecca (a name later given to Alpha Corona Borealis), which means "separated" or "broken up" (الفكة al-Fakkah), a reference to the resemblance of the stars of Corona Borealis to a loose string of jewels. Among the Bedouins, the constellation was known as qaṣʿat al-masākīn (قصعة المساكين), or "the dish/bowl of the poor people", since the stars form an unsymmetrical pattern with an indent in one side.
In Australian Aboriginal astronomy, the constellation is called womera ("the boomerang") due to the shape of the stars. The Wailwun people of northwestern New South Wales saw Corona Borealis as mullion wollai "eagle's nest", with Altair and Vega—each called mullion—the pair of eagles accompanying it.
Polynesian peoples often recognized Corona Borealis; it was likely called Te Hetu in the Tuamotus, whose people called the constellation Na Kaua-ki-tokerau. In Hawaii, the constellation was likely called Kaua-mea; it was called Rangawhenua in New Zealand. The figure of Corona Borealis was called Te Wale-o-Awitu in Pukapuka. Its name in Tonga was unsure; it was either called Ao-o-Uvea or Kau-kupenga.
The Cheyenne nation of Native Americans called the main stars of this constellation the "Camp Circle", as they arranged their camps in a semicircle. Native Americans also used stars to make designs in the ground at the Medicine Wheel in Bighorn National Forest, Wyoming, USA.
- While parts of the constellation technically rise above the horizon to observers between the 50°S and 64°S, stars within a few degrees of the horizon are to all intents and purposes unobservable.
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- Ian Ridpath. "Constellations: Andromeda–Indus". Star Tales. self-published. Retrieved 9 September 2014.
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- Distance calculated from redshift.
- "NASA/IPAC Extragalactic Database". Results for Abell 2142. Archived from the original on 16 December 2008. Retrieved 11 Nov 2008.
- "RX J1532.9+3021: Extreme Power of Black Hole Revealed". Chandra X-ray Center. January 23, 2014. Retrieved 27 January 2014.
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|Wikimedia Commons has media related to Corona Borealis.|
- The Deep Photographic Guide to the Constellations: Corona Borealis
- Star Tales – Corona Borealis
- Corona Borealis at Constellation Guide