The Polish astronomer Johannes Hevelius formed this constellation in 1687 from a scattering of faint stars beneath the tail of Ursa Major. Canes Venatici represents a pair of hounds held on a lead by Boötes, snapping at the heels of the Great Bear. The constellation’s two brightest stars, Alpha and Beta Canum Venaticorum, lie in the southern dog. Ptolemy had listed both these stars in the Almagest as among the “unformed” stars outside the figure of the Great Bear, not belonging to any particular constellation, so they were free to be used in a new figure.
The idea of dogs being held by Boötes was not original to Hevelius. On a star chart published in 1533 the German astronomer Peter Apian showed Boötes with two dogs at his heels and holding their leash in his right hand. On another chart published by Apian three years later the number of dogs had grown to three and the leash had moved to the left hand, but they were still following Boötes and not the bear. In neither case was any attempt made to connect the dogs with charted stars, nor were they named, so the credit for showing the dogs in their current position and for making them a separate constellation remains with Hevelius.
Canes Venatici, two hunting dogs held on a leash by Boötes, seen in the Atlas Coelestis of John Flamsteed (1729). For the original depiction by Hevelius, click here.
Charles’s Heart, and a Whirlpool
Where the southern dog’s lead is attached to its collar lies the star Alpha Canum Venaticorum, known as Cor Caroli, meaning Charles’s Heart, in honour of King Charles I of England. It was given this title by Sir Charles Scarborough, physician to King Charles II, before Canes Venatici was formed. Scarborough reputedly said that this star shone particularly brightly on the night of 1660 May 29, when King Charles II returned to London at the Restoration of the Monarchy. Because of this there has been much confusion over which King Charles the star is supposed to commemorate, but it definitely refers to the first King Charles.
The name first appeared on a chart of 1673 by the English cartographer Francis Lamb, who labelled it Cor Caroli Regis Martyris, a reference to the fact that King Charles I was beheaded (or ‘martyred’, as Lamb loyally put it). Lamb and others, such as the Englishman Edward Sherburne in 1675, drew a heart around the star surmounted by a crown, turning it into a mini-constellation. Johann Bode, in his Uranographia atlas, retained the heart and crown on the neck of the southern dog, but erred by calling the star Cor Caroli II.
Beta Canum Venaticorum, on the dog’s snout, is called Chara, from the Greek for ‘joy’, also the name that Hevelius gave the southern dog. The northern dog, which Hevelius called Asterion (‘little star’), is marked only by a scattering of faint stars. In Bode’s Uranographia, the names of the dogs are engraved on their collars.
Canes Venatici contains a globular cluster of stars, M3, and a beautiful spiral galaxy, M51, called the Whirlpool. M51 was the first galaxy in which spiral form was noticed, by the Irish astronomer Lord Rosse in 1845. It consists of a large galaxy in near-collision with a smaller one.
The stars 21 and 24 Canum Venaticorum plus a fainter, unnumbered star were known to the Chinese as Sangong, ‘three excellencies’, representing the Emperor’s closest and most trusted aides. Changchen was a group of seven stars representing a contingent of palace guards, stretching from Alpha via Beta CVn and ending just across the border at 67 Ursae Majoris.
One individual star was named Xiang, ‘prime minister’. It is usually identified as 5 Canum Venaticorum, although Sun and Kistemaker think it is not in Canes Venatici at all but actually the star Chi Ursae Majoris.
© Ian Ridpath. All rights reserved