Constellations: Corona Borealis 'the Northern Crown'
Created | Updated Nov 22, 2017
Constellations: Overview
| Andromeda
| Antlia
| Apus
| Aquarius
| Aquila
| Ara
| Aries
| Auriga
| Boötes
| CaelumCamelopardalis | Cancer | Canes Venatici | Canis Major | Canis Minor | Capricornus | Carina | Cassiopeia | Centaurus
Cepheus | Cetus | Chamæleon | Circinus | Columba | Coma Berenices | Corona Australis | Corona Borealis | Corvus
Crater | Crux | Cygnus | Delphinus | Dorado | Draco | Equuleus | Eridanus | Fornax | Gemini | Grus | Hercules | Horologium
Hydra | Hydrus | Indus | Lacerta | Leo | Leo Minor | Lepus | Libra | Lupus | Lynx | Lyra | Mensa | Microscopium | Monoceros
Musca | Norma | Octans | Ophiuchus | Orion | Pavo | Pegasus | Perseus | Phoenix | Pictor | Pisces | Piscis Austrinus
Puppis | Pyxis | Reticulum | Sagitta | Sagittarius | Scorpius | Sculptor | Scutum | Serpens | Sextans | Taurus
Telescopium | Triangulum | Triangulum Australe | Tucana | Ursa Major | Ursa Minor | Vela | Virgo | Volans | Vulpecula
Will there be any stars in my crown,
when at evening the sun goeth down
— Eliza E Hewitt
| Name: | Corona Borealis (Latin: 'Northern Crown' |
| Genitive: | Coronae Borealis |
| Short form: | CrB |
| Area: | 179 sq deg |
| Co-ordinates1: | Right Ascension 16h, Declination +30° |
| Origin: | Ancient |
The Northern Crown is quite a small constellation. Typically seen during the spring and summer, its rather characteristic crescent lies between the constellations of Boötes and Hercules.
It has a fainter sibling in the southern hemisphere: Corona Australis 'the Southern Crown'. Corona Borealis also includes a cluster of galaxies (Abell 2065) which average 1,200,000,000 light years2 away.
Mythology
The seven major stars of this group form a recognisable crown shape. The usual story is that the crown was a wedding present to Ariadne, a princess of Crete. Abandoned by her husband Theseus on the island of Naxos, she then married one of the lesser gods Dionysus, who, upon her death, placed her crown in the heavens. You can read more about this Greek myth at Richard Dibon-Smith's website.
A Christian might equate it to the crown of the believer in Heaven rising above Serpens Caput, the head of the snake, as described in Genesis 3:15.
Native Americans of the Cherokee tribe saw it as a camp circle.
Welsh mythology connects it with the palace of Arianrhod, who according to the Mabinogion was the sister of Gwydion and had a castle near Dinas Dinille.
Stars of Corona Borealis
The scientific star names are simpler to understand (if you know your Greek alphabet). For example: 'alpha' means it is the brightest star in that constellation. The next brightest is designated 'beta' etc. Combined with the genitive, this is known as the 'Bayer designation'. Some stars have proper names as well, for example, alpha Coronae Borealis is Gemma. Others are known by their catalogue number.
The brightest star in Corona Borealis, Gemma, is a variable of the Algol (beta Pegasi) type. This is actually a close pair of stars which routinely eclipse one another, causing a decrease in magnitude of about a tenth. They are, however, far enough apart that no matter is physically transferred from one star to another.
However, the star T Coronae Borealis, which lies slightly south-east of Epsilon, regularly receives matter from somewhere over a period of decades. Some speculate that the star is feeding from a white dwarf with an accretion disk.
This periodic interaction with the star results in episodes of Thermo-Nuclear Runaway (TNR) in the star's photosphere3. The change is nothing less than spectacular. At the moment it is only visible with a large telescope, but it has been known to be magnitude +1.35 during eruptions. The last of these were seen in 1866 and 1946. So any time now we might see this nova changing the appearance of the crown.
Star Table
| Star | Designation | Name or
catalogue number | Brightness (m) | Distance
(light years) | Spectral Classification and/or comments |
| α CrB | Alpha | Gemma | +2.2 to 2.3 | 75 | EA variable |
| β CrB | Beta | Nusaken | +3.7 | 114 | F0 |
| γ CrB | Gamma | 8 Coronae Borealis | +3.8 and 6.0 | 145 | B9 (A3) |
| δ CrB | Delta | 10 Coronae Borealis | +4.6 | 165 | G3 |
| ε CrB | Epsilon | 13 Coronae Borealis | +4.1 | 230 | K2 |
| ζ CrB | Zeta-2
Zeta-1 | Struve 1965 | +5.0 and 6.0 | 114 | B8 (K0) |
| η CrB | Eta | 2 Coronae Borealis | +5.0 | 50 | G2 |
| θ CrB | Theta | 4 Coronae Borealis | +4.1 | 311 | B6 |
| ρ CrB | Rho | 15 Coronae Borealis | +5.4 | 56.8 | G0 |
| κ CrB | Kappa | 11 Coronae Borealis | +4.79 | 101.5 | K1 |
| R CrB | Alchin | HR5880 | +5.71 to +14.8 | 6037 | C0 (Nova) |
| T CrB | Blaze | HR5958 | +2.0 to +10.8 | 323 | M3 (Nova) |
Extrasolar Planets in Corona Borealis
Rho: The search for extrasolar planets led to the discovery that this typical star has a solar system of its own. It has a Jupiter-sized planet orbiting it at about 0.22 AU4. The star also has a circumstellar ring similar to our Kuiper Belt, and scientists5 believe there may be more undetected planets hiding here.
Kappa b: discovered in 2007, this planet is 1.8 times the mass of Jupiter and orbits the star every 1,191 days at a distance of 2.7 AU.
Epsilon b: discovered in 2012, this planet is superjovian and orbits its star every 418 days at a distance of 1.3 AU.
Omicron b: a superjovian world which orbits its orange giant star every 188 days at a distance of 0.8 AU.
XO-1: the XO project, headed by David McCulloch, seeks to find stars that are variable due to planets transiting them. The first one it found, XO-1, is 600-650 light years distant and has a planet that is about 0.9 of the mass of Jupiter, orbiting every four days at a distance of 0.0488 AU.
HD 145457 b: a superjovian planet in orbit around an orange giant star, taking 176 days at the distance of 0.76 AU.
