CORONA BOREALIS "the Northern Crown" and CANES VENATICI "the Hunting Dogs"
(Pronounced koh ROH-nah BOH-ree-AL-liss and KAY-neez veh-NAT-ih-sigh)
Corona Borealis was known to the ancient Greeks as the "wreath". Only later was the adjective "northern" added to distinguish it from its southern counterpart. It represents the jewelled crown given as a wedding present by Bacchus to Ariadne, and cast into the sky by him, upon her death. Another legend has it as the golden crown given to Ariadne by Theseus after the quest in the labyrinth to kill the Minotaur. It is a lovely arc of 4th magnitude stars, with a second magnitude star (Gemma) set as a central gem.
Canes Venatici is a constellation introduced by the Polish astronomer Hevelius in 1690 in his great star atlas Uranometria. The sprinkling of faint stars was taken from the constellation Ursa Major, the Great Bear. It represent the dogs Asterion and Chara held on a leash by Boötes the herdsman as they pursue the Great Bear round the north pole.
To find these constellations look low to the north in the evening sky, find the bright reddish star Arcturus in Boötes and look either side. Canes Venatici is to the left (west) and the more easily seen Corona Borealis is the arc of stars to the right (east).
Chart showing Corona Borealis and Canes Venatici.The chart shows the sky to the north at about 11.30 pm (NZST) in mid May or 9.30 pm mid June. The horizon shown is for central New Zealand.
Some stars and interesting objects in the Constellations
α Coronae Borealis (Gemma or Alphecca) is a magnitude 2.2 blue-white star 75 light years away. It is an eclipsing binary of the Algol type, but it varies only 0.1 in magnitude, which is too slight to be seen visually.
R CrB is a remarkable star. It is hydrogen poor and carbon rich. Its variability was discovered by Pigott in 1795. Violent changes are happening in its corona and chromosphere, and these are reflected in its brightness, which can be between 6th magnitude and 14th magnitude. It is a prototype star for a class of variable stars.
α Canum Venaticorum is popularly called Cor Caroli, meaning Charles' heart. This is a reference to King Charles I of England. It is said to have shone brightly in 1660 on the arrival of Charles II in England at the Restoration of the Monarchy. It is a double star, the brighter having a magnitude of 2.9, with a magnitude 5.5 companion, visible in small telescopes. The brighter star is representative of the a CVn class of variable stars, with strong varying magnetic fields. These are probably evolving away from the main sequence of stars.
β CVn at magnitude 4.2 is the only other prominent star in the constellation. It is a yellow star 27 light years away and has a similar brightness to the Sun.
The two constellations are a long way north of the equator and are low as seen from New Zealand. α CVn is above the horizon for only a little over 6 hours from Wellington, while α CrB is up for just over 8.5 hours.
Canes Venatici rises first and is due north and highest at about 10 pm mid May and 8 pm a month later. From mid New Zealand α CVn has a maximum altitude of about 10°. From Auckland it is rather higher at 15°, but from Invercargill it only rises 5° above the horizon. The constellation is so far north that, for most parts of New Zealand, the lower parts do not rise above the horizon.
Corona Borealis is due north about 150 minutes after Canes Venatici, that is about 10.30 pm mid June and 8.30 pm mid July. The constellation is smaller than Canes Venatici and not as far north. Consequently it rises a little higher in southern skies with α CrB being about 22° above the horizon as seen from Wellington.