Constellations: Corona Borealis 'the Northern Crown' Content from the guide to life, the universe and everything

Constellations: Corona Borealis 'the Northern Crown'

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The shield of the Science, Mathematics and Engineering faculty of the h2g2 University.Constellations: Overview | Andromeda | Antlia | Apus | Aquarius | Aquila | Ara | Aries | Auriga | Boötes | Caelum
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Telescopium | Triangulum | Triangulum Australe | Tucana | Ursa Major | Ursa Minor | Vela | Virgo | Volans | Vulpecula
Corona Borealis 'the Northern Crown'.
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

StarDesignationName or
catalogue number
Brightness (m)Distance
(light years)
Spectral Classification
and/or comments
α CrB Alpha Gemma+2.2 to 2.375EA variable
β CrB Beta Nusaken+3.7114F0
γ CrB Gamma 8 Coronae Borealis+3.8 and 6.0145B9 (A3)
δ CrB Delta 10 Coronae Borealis+4.6165G3
ε CrB Epsilon 13 Coronae Borealis+4.1230K2
ζ CrB Zeta-2
Zeta-1
Struve 1965+5.0 and 6.0114B8 (K0)
η CrB Eta 2 Coronae Borealis+5.050G2
θ CrB Theta 4 Coronae Borealis+4.1311B6
ρ CrB Rho 15 Coronae Borealis+5.456.8G0
κ CrB Kappa 11 Coronae Borealis+4.79101.5K1
R CrB Alchin HR5880+5.71 to +14.86037C0 (Nova)
T CrB Blaze HR5958+2.0 to +10.8323M3 (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 circum-stellar 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.

  • 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.

1The current convention of the International Astronomical Union (IAU) is to use a plus sign (+) for northern constellations and a minus sign (-) for southern ones.2A light year is the distance light travels in one year, roughly 5.88 trillion miles or 9.46 trillion kms.3Ref: I Hachisu and M Kato - Astrophysical Journal 1999.4 Astronomical Units.5 D Trilling, R Brown and A Rivkin.

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