While Ptolemy described the stars of modern-day Canes Venatici as “informes”, or the “unformed” [stars] of Ursa Major, the constellation proper was only introduced to the world in the late 1600’s by the Polish astronomer Hevelius, when he published his magnum opus, Firmamentum Sobiescianum. Along with Canes Venatici, Hevelius also created the constellations, Lacerta, Leo Minor, Lynx, Scutum, Sextans and Vulpecula.
Location
Canes Venatici is the 38th largest of the 88 recognized constellations, taking up an area of 465 square degrees of the northern sky. The constellation is visible for observers located between latitudes +90° and -40°, and can be found tucked under Ursa Major’s tail, where Ptolemy originally included it in the main formation of the Great Bear’s stars.
Best Seen
The constellation is best observed in the northern hemisphere during spring and summer, but note that Canes Venatici never sets for observers north of latitude 43° N. Look for the constellation where it is situated between Ursa Major to the east, and Bootes to the west. The galaxy M94 is directly above, and about halfway along the line formed between the stars that define the constellation.
Historical Background
Canes Venatici is generally taken to represent Asterion and Chara, the two hunting dogs of the neighboring constellation of Bootes (the Herdsman), although the association comes only through a series of mistakes in translation. As mentioned, Ptolemy included Canes Venaticids as part of Ursa Major, and after he published his Almagest some of the stars he referred to as the ‘club’ of Boötes were later mistranslated by first Arabic and then Medieval translators into “canes”, meaning “dogs” in Latin.
Notable Stars
Although Canes Venatici takes up a great deal of space, the constellation proper consists of nothing more than a straight line between Cor Caroli (Alpha Canum Venaticorum) and Chara (Beta Canum Venaticorum), the two bright stars that represent the dogs of Bootes, the Herdsman. The constellation also has several stars that are remarkable for the fact that they are the prototypes of entire classes of stars, and below are brief descriptions of some of the principal stars in the constellations:
– Cor Caroli (Alpha Canum Venaticorum), the constellation’s brightest star, is binary system located about 110 light years away of magnitude 2.81, although being a variable type star its brightness can vary between 2.84 and 2.98. Its primary component called Alpha-2 CVn is a blue star that contains an overabundance of certain metals; in this case, the metals europium, mercury and silicon. Cor Caroli is remarkable for the fact that its magnetic field is about 5,000 times as powerful as the Earth’s. It is also the prototype of the Alpha-2 Canum Venaticorum variables, a class of variable stars that produce star spots so large that they can influence the star’s overall luminosity.
– Chara (Beta Canum Venaticorum) is a G-type main sequence star, and the second-most luminous star in the constellation with an apparent visual magnitude of 4.26. It is located about 27 light years away, making it one of the closest stars to the Sun that is similar in terms of composition, age, and mass. In fact, the star is so similar to our sun that it is referred to as a “solar analogue” or sometimes as the Sun’s Twin.
– La Superba (Gamma Canum Venaticorum), the third brightest star in Canes Venatici, is a red variable star located 711 light years from our solar system. It has a magnitude of 5.42, although this can vary from 4.8 and 6.3 over a 160 day period.
– AM Canum Venaticorum (AM CVn) is a cataclysmic variable star, and the prototype of a class of variable stars known as AM CVn stars. This class of variable star consists of binary systems in which both stars are white dwarfs, enveloped by an accretion disc made up of mostly helium. “Normal” cataclysmic variable star systems usually consist of a white dwarf and a relatively normal star, from which the white dwarf pulls matter first into an accretion disc, and then onto itself.
Notable Deep Sky Objects
Canes Venatici contains a number of notable deep sky objects, including five Messier objects, four of which are galaxies.
– Messier 3 (NGC 5272) may not be a galaxy, but it is one of the oldest, brightest, and biggest globular star clusters ever discovered, containing about half a million stars. It is located about 34,000 light years away, has an apparent visual magnitude of 6.2, and is estimated to be about 8 billion years old.
– The Whirlpool Galaxy (Messier 51, NGC 5194) is a classic example of a grand design spiral galaxy, and no doubt the most photographed, and therefore the best known galaxy in the entire observable universe, even though it is all of 31 million light years away. Also known as Messier 51a, this galaxy is in the opening stages of a destructive interaction with the smaller background galaxy, Messier 51b, also in Canes Venatici. M51 has a huge central disc spanning about 76,000 light years, which makes it an easy target for binoculars even from urban observing sites. With a magnitude of 8.4, M51 is the most luminous galaxy in the M51 Group, a small group of galaxies in Canes Venatici that has about half-a-dozen members.
– The Whale Galaxy (NGC 4631, Caldwell 32, Arp 281, PGC 42637) somewhat resembles a blue whale, with the distorted shape of this galaxy thought to be the result of a very high rate of star formation taking place in its central parts. The high rate of star formation is causing intense X-ray emissions that are thought to be re-emitted by a cloud of gas surrounding the entire galaxy, hence the blue light in its enhanced images.
Other deep sky objects of interest in Canes Venatici includes the beautiful spiral galaxies of the Sunflower Galaxy (M63), the Whale Galaxy (NGC 4631), M94, M106, NGC 5033, NGC 5005, NGC 5371, and NGC 4183. Amongst the numerous other varieties of galaxies in the constellation is the intermediate spiral NGC 4151; the dwarf galaxy NGC 4618 and NGC 4625; the dwarf barred irregular galaxy NGC 4214; the barred spiral galaxy called the Cocoon Galaxy (NGC 4490); the irregular galaxies IC 883 and NGC 4449; and interacting galaxies NGC 4656 and NGC 4657, which are also referred to as the Hockey Stick Galaxies.
Meteor Showers
Although there is some doubt about the existence of a meteor stream from Canes Venatici, an official research program, the Radio Meteor Project, has confirmed the existence of the Canes Venaticids, a shower that runs from January 13th to January 30th as long ago as 1965. The shower seems to peak around January 24th, but with an uncertain average meteor count, since the radio equipment was not operational during a part of the research program.
Planets: 2 Planets
As of 2016, the constellation has only two stars with one planet each, one being a gas giant orbiting a cool red dwarf star.