Canes Venatici, a pair of hunting dogs held on a leash by Boötes, seen in the
Atlas Coelestis of John Flamsteed (1729). The dogs are greyhounds,
which hunt in pairs. Click here for the original depiction by Hevelius.

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 (1495–1552) (also known as Petrus Apianus) 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. (This chart was reissued with hand colouring in Apian's book Astronomicum Caesareum of 1540.) In neither case was any attempt made to connect the dogs with charted stars, nor were they named.

However, in 1602 the Dutch cartographer Willem Janszoon Blaeu (1571–1638) produced a globe in which Boötes holds two dogs that are following the Great Bear. They face the same way as the modern hunting dogs although they occupy only the space filled by Hevelius’s southern dog, Chara. This was the first attempt to incorporate the two brightest stars in this area into a pair of dogs, so it would seem that Blaeu deserves at least a share of the credit for the invention of Canes Venatici.

Cor Caroli, a star named for a king

In the modern constellation, the ring attaching the southern dog’s lead to its collar is marked by the star Alpha Canum Venaticorum, popularly known as Cor Caroli, meaning Charles’s Heart, in honour of King Charles I of England who was beheaded by parliamentarians in 1649. This name arose over a decade before Canes Venatici was formed. The writer and ardent royalist Edward Sherburne tells us in his translation of Manilius published in 1675 that the name was given by Sir Charles Scarborough (1615–94), physician to King Charles I’s son, Charles II. Why Scarborough chose to name this particular star was not explained — perhaps it was because it lies close to the Plough, which was popularly known in England as Charles’s Wain, or wagon.

The name first appeared in 1673 on the northern half of a pair of celestial hemispheres that accompanied a book called Astroscopium by the English cartographer Francis Lamb. He labelled the star Cor Caroli Regis Martyris, a reference to the fact that King Charles I was beheaded, or ‘martyred’, as Lamb loyally put it (Charles had declared himself ‘martyr of the people’ at his execution). Lamb and others, such as Edward Sherburne in his translation of Manilius in 1675, John Seller in his Atlas Caelestis of 1677, and Seller again on a reprint of Edmond Halley’s chart of 1678 (below), drew a heart around the star surmounted by a crown, turning it into a mini-constellation that neatly filled the gap between Ursa Major, Boötes, and Coma Berenices.

Cor Caroli on a reprint of Edmond Halley’s northern hemisphere chart of 1678, issued
by the London map-maker John Seller (the first edition of the chart does not show
it). The star lies at the centre of a mini-constellation depicting a heart surmounted
by a crown. Ursa Major is above left, Coma Berenices to the right, and Boötes below.
This chart was a companion to Halley’s southern hemisphere chart, compiled after
his return from observing the southern skies on St Helena.

Unfortunately in 1844 the English astronomer William Henry Smyth started a long-running confusion when he wrote in his Bedford Catalogue that the star had been named by Edmond Halley after King Charles II, a mistake originally due to Bode in his star catalogue of 1801. According to Smyth’s account, Scarborough supposedly saw the then-unnamed star shining particularly brightly on the night of 1660 May 29, coincidentally when Charles II returned to London at the Restoration of the Monarchy. Smyth gave no source for this statement, and in reality such a brightening would be extremely unlikely, so the story can only be apocryphal. 

Despite this, the American historian R. H. Allen unquestioningly repeated Smyth’s tall story in his classic book Star Names and it has been widely requoted. As a result there has been much uncertainty over which King Charles the star is supposed to commemorate, but Sherburne made clear that it referred to the first King Charles. (Charles II was later commemorated by Halley’s southern constellation Robur Carolinum of 1678, although that invention did not last.)

When Hevelius introduced Canes Venatici in 1687 he incorporated this star into his new constellation, but without a name or the surrounding heart. Johann Bode, in his Uranographia atlas of 1801, retained the heart and crown on the collar of the southern dog, but erred by calling the star Cor Caroli II, wrongly thinking it referred to the second King Charles. Despite its overtly nationalistic nature, the name has stuck.

Other stars, and a Whirlpool

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. Bode in his Uranographia drew the dogs with their names engraved on their collars.

Alpha and Beta CVn are the only two stars in the constellation with Greek letters; they were given these identifiers by the English astronomer Francis Baily in his British Association Catalogue of 1845.

Another remarkable star in Canes Venatici is the 5th-magnitude red giant variable Y Canum Venaticorum, one of the reddest stars known. In 1868 the pioneering Italian spectroscopist Angelo Secchi (1818–78) described its spectrum as ’superba’. In 1876 the Irish astronomer John Birmingham (1816–84) took this description and turned it into the name La Superba, which is now the official name for this star.

Spiral structure of M51, the Whirlpool Galaxy, drawn in March 1848 by William Parsons,
third Earl of Rosse, from a series of observations made through his 72-inch (1.8-m)
reflector at Birr Castle in Ireland. This sketch was published in 1850 in Philosophical
Transactions of the Royal Society. The spiral structure had originally been detected by
Rosse through the same telescope in April 1845.