Canes Venatici lies in the northern hemisphere. Its name means “hunting dogs” in Latin. The constellation represents the hunting dogs of Boötes the Herdsman, a neighboring constellation.
The Greek astronomer Ptolemy included the stars of Canes Venatici in the constellation Ursa Major as informes (unformed), but the constellation was not introduced until 1687, when the Polish astronomer Johannes Hevelius created it from the faint stars located under the bear’s tail.
Canes Venatici contains the famous stars Cor Caroli and La Superba as well as a number of interesting deep sky objects, among them the globular cluster Messier 3, the famous Whirlpool Galaxy (Messier 51), the Sunflower Galaxy (Messier 63), the spiral galaxies Messier 94 and Messier 106, the Whale Galaxy and the Hockey Stick Galaxies (also known as the Crowbar Galaxy).
FACTS, LOCATION & MAP
Canes Venatici is the 38th largest constellation in the sky, occupying an area of 465 square degrees.
It is located in the third quadrant of the northern hemisphere (NQ3) and can be seen at latitudes between +90° and -40°.
Canes Venatici contains five Messier objects: M3 (NGC 5272), the Whirlpool Galaxy (M51, NGC 5194, NGC 5195), the Sunflower Galaxy (M63, NGC 5055), M94 (NGC 4736), and M106 (NGC 4258). The constellation does not have any stars with known planets.
The brightest star in Canes Venatici is Cor Caroli, Alpha Canum Venaticorum.
There is one meteor shower associated with the constellation, the Canes Venaticids.
In the Middle Ages, Canes Venatici was identified with the two dogs held on a leash by Boötes, the Herdsman, because there was a mistake in the translation of Ptolemy’s Almagest from Greek to Arabic. In Ptolemy’s text, some of the stars in Boötes represent the Herdsman’s club. The translator loosely translated the Greek word for “club” (Κολλοροβος ) as “the spearshaft with a hook” (“al-`aşā dhāt al-kullāb”). When the Arabic phrase he used was later translated to Latin, the translator mistook one of the words for kilāb, which means “dogs.”
Boötes was depicted with two dogs in 1533 on a map by the German astronomer Peter Apian, and Hevelius decided to define the dogs’ position in the night sky in the 17th century. Hevelius named the northern dog Asterion (“little star” in Greek) and the southern one Chara (“joy”). The name Chara later started to be used specifically to refer to the star Beta CVn.
MAJOR STARS IN CANES VENATICI
Cor Caroli – α Canum Venaticorum (Alpha Canum Venaticorum, α CVn)
Cor Caroli is the brightest star in the constellation, with an apparent visual magnitude varying between 2.84 and 2.98. It is approximately 110 light years distant. Its name means “Charles’ heart.”
The star was named by Sir Charles Scarborough, mathematician and physician to Charles II, in honour of Charles I, the king executed after the English Civil War, whose son was restored to the throne shortly after his death. Alpha CVn was originally named Col Caroli Regis Martyris.
Cor Caroli is a binary star composed of two stars separated by 19.6 arcseconds in the sky. The brighter component, Alpha-2 CVn, is a chemically peculiar star that belongs to the spectral class A0 and is classified as an Ap/Bp star (one showing an overabundance of certain metals). The star has an unusually strong magnetic field, one 5,000 times as strong as the Earth’s, and its atmosphere has overabundances of europium, mercury and silicon.
Cor Caroli’s brighter component is a prototype of a class of variable star, the Alpha-2 Canum Venaticorum variables. These stars are notable for strong magnetic fields which are believed to produce enormous starspots which, in turn, cause the luminosity to vary significantly during the stars’ rotation.
The companion star, Alpha-1 CVn, is an F-type main sequence star with an apparent magnitude of 5.60.
Alpha CVn is part of the Great Diamond (or Diamond of Virgo) asterism, marking its northern vertex. Other stars forming the asterism are Denebola (Beta Leonis) in Leo, Spica (Alpha Virginis) in Virgo and Arcturus (Alpha Boötis) in Boötes.
Chara – β Canum Venaticorum (Beta Canum Venaticorum, β CVn)
Beta CVn is the second brightest star in Canes Venatici. It is a G-type main sequence dwarf approximately 27.4 light years from Earth. The name Chara, which was originally used for the southern dog, means “joy” in Greek. The star has an apparent visual magnitude of 4.26. It is similar to the Sun in terms of age, mass and stage of evolution, and it has been called a solar analogue or solar twin.
La Superba – Y Canum Venaticorum (Gamma Canum Venaticorum, Y CVn)
La Superba is a well known star in Canes Venatici and one of the reddest stars in the sky. It was named La Superba by 19th century Italian astronomer Angelo Secchi because of its striking appearance.
The star is believed to be in the last stages of fusing its secondary fuel, helium, into carbon. It is losing mass at a relatively fast rate and is surrounded by a disk of ejected material. Most likely, Y CVn will eject its outer layers (relatively) soon to form a nebula and become a white dwarf.
La Superba is a semi-regular variable star, with an apparent magnitude varying between 4.8 and 6.3 over a period of 160 days. It is the brightest J-star known. (J-stars are the rare carbon stars that contain an abundance of carbon-13.) The star lies about 711 light years from Earth.
AM Canum Venaticorum (AM CVn)
AM CVn is classified as a cataclysmic variable star, one that irregularly has dramatic increases in luminosity and then drops back to a quiescent state. Cataclysmic variables are typically binary stars, composed of a white dwarf and a mass transferring secondary star. The gravity of the white dwarf distorts the other star and the white dwarf accretes matter from it. The material falling from the donor star usually forms an accretion disc around the white dwarf.
AM CVn is a prototype of a class of variables known as the AM CVn stars. These stars are cataclysmic variables consisting of two white dwarfs, with the accretion disc composed mainly of helium. The stars are also interesting as a source of gravitational waves.
AM Canum Venaticorum has an apparent magnitude of 14.18 and is approximately 2,000 light years distant.
RS Canum Venaticorum (RS CVn)
RS Canum Venaticorum is another star in Canes Venatici that serves as a prototype for a class of variable stars.
The RS Canum Venaticorum variables are close binary stars with variations in luminosity caused by the stars’ active chromospheres. The period of variations typically mirrors the orbital period of the star system. The stars’ luminosity typically fluctuates by 0.2 magnitudes.
DEEP SKY OBJECTS IN CANES VENATICI
Messier 3 (NGC 5272)
Messier 3 is a globular cluster about 33,900 light years from Earth. It is one of the largest, brightest globular clusters known, containing about 500,000 stars. It was discovered by William Herschel in 1784. The cluster has an apparent magnitude of 6.2. Its estimated age is 8 billion years.
Whirlpool Galaxy – Messier 51 (NGC 5194)
The Whirlpool Galaxy is one of the best known galaxies in the night sky. It is a grand design spiral galaxy located about 31 million light years from the Milky Way.
The galaxy, which is also known as Messier 51a, is interacting with NGC 5195 (Messier 51b), a dwarf galaxy, also in Canes Venatici. The galaxies are connected by a tidal bridge which is full of interstellar dust. The dust can be seen silhouetted against the center of the dwarf galaxy. NGC 5195 is highly distorted in shape because of its interaction with the Whirlpool Galaxy.
The Whirlpool Galaxy has an apparent magnitude of 8.4 and can even be seen with binoculars, along with its companion galaxy. M51 has a bright circular disk with a radius of 38,000 light years.
The galaxy was first discovered by Charles Messier in 1774, while the dwarf galaxy NGC 5195 was discovered in 1781 by the French astronomer Pierre Méchain. In 2005, a supernova (SN 2005cs) peaked at apparent magnitude 14 in the direction of the Whirlpool Galaxy.
M51 never sets for observers north of 43°. It can easily be found by moving 3.5° to the southeast from Alkaid (Eta Ursae Majoris), the easternmost star in the Big Dipper asterism and the tip of the tail of Ursa Major.
Whirlpool is the brightest galaxy in the M51 Group, a group of galaxies in Canes Venatici that also includes the Sunflower Galaxy (M63), M51’s companion galaxy NGC 5195, and also NGC 5023, NGC 5229, UGC 8313, and UGC 8331.
Sunflower Galaxy – Messier 63 (NGC 5055)The Sunflower Galaxy is the second brightest member of the M51 Group, after the Whirlpool Galaxy. It has an apparent magnitude of 9.3. It is a spiral galaxy with an apparent magnitude of 9.3, approximately 37 million light years from Earth.
The galaxy was discovered by Pierre Méchain in 1779 and then included in the Messier Catalogue by Charles Messier as M63. A supernova was observed in the galaxy in 1971.
Messier 94 (NGC 4736)
Messier 94 is another spiral galaxy in Canes Venatici, also discovered by Pierre Méchain and catalogued by Messier. It has an apparent magnitude of 8.99 and is approximately 16 million light years distant.
The galaxy is notable for its two ring structures. The inner ring is sometimes referred to as the starburst ring. It has a diameter of 70’’ and is a site of strong star formation activity. The outer ring has a diameter of 600’’ and is not a closed stellar ring, but has a complex structure of spiral arms.
M94 is one of the brightest galaxies in the M94 Group (Canes Venatici I Group), which contains between 16 and 24 galaxies that all lie within the Virgo Supercluster in the constellations Canes Venatici and Coma Berenices.
The M94 Group includes the barred irregular galaxy NGC 4214, the edge-on spiral galaxy NGC 4244 (Caldwell 26) next to the star Beta CVn, the low surface brightness spiral galaxy NGC 4395, the irregular galaxy NGC 4449 (Caldwell 21), and the dwarf irregular galaxy UGC 8320.
Messier 106 (NGC 4258)
Messier 106 is also a spiral galaxy that was discovered by Pierre Méchain in 1781. Its estimated distance from Earth is between 22 and 25 million light years.
M106 is classified as a Seyfert II galaxy, one that has unusual emission lines and emits x-rays, which is why it is suspected that a part of it is falling into a supermassive black hole at its core. M106 has an apparent visual magnitude of 9.1.
The M51 Group includes several notable galaxies other than the Whirlpool and Sunflower galaxies.
NGC 5023 is relatively isolated from the group, but is considered a member nonetheless. It is a spiral galaxy, 49,000 light years across, seen edge-on. More than 200 stars in the galaxy have an apparent magnitude greater than 23.5. NGC 5023 is between 17.6 and 26.1 million light years distant. It has an apparent magnitude of 12.82.
UGC 8331 is an irregular galaxy between 19.7 and 26.8 million light years distant. It has an apparent magnitude of 14.61.
UGC 8313 is another edge-on spiral galaxy, about 19,000 light years in diameter. It is believed to be a companion of the Sunflower Galaxy. UGC has an apparent magnitude of 14.4.
NGC 5229 is yet another edge-on spiral, also pretty isolated from the rest of the group. Its estimated age is 13.7 billion years. The galaxy is about 23,000 light years in diameter and has an apparent magnitude of 14.3.
Whale Galaxy (NGC 4631, Caldwell 32, Arp 281, PGC 42637)
The Whale Galaxy is an edge-on spiral galaxy approximately 30 million light years from Earth. It has an apparent magnitude of 9.8. It was nicknamed the Whale because it has a slightly distorted shape that resembles a whale or a herring. The galaxy is also notable for its central starburst region and intense star formation, which results in X-ray and spectral line emission. There is a giant diffuse corona of X-ray emitting gas surrounding the entire galaxy.
NGC 5033 is another spiral galaxy in Canes Venatici. It has an apparent magnitude of 10.8. It appears inclined and has a bright nucleus and a relatively faint disk. The galaxy has a Seyfert nucleus (a type of active galactic nucleus) which is believed to contain a supermassive black hole.
The galaxy’s nucleus does not lie at the galaxy’s kinematic centre (that around which the stars rotate), which might indicate that NGC 5033 has undergone a merger with another galaxy.
NGC 5033 is located relatively close to another spiral galaxy, NGC 5005. The two comprise a physical pair and influence each other gravitationally somewhat, but are still distant enough not to be distorted by the tidal forces of the interaction.
NGC 5005 (Caldwell 29)
NGC 5005 is also an inclined spiral galaxy, with a visual magnitude of 10.6. It has a bright nucleus and a bright disk, and can be observed even in large amateur telescopes. The galaxy’s nucleus contains an X-ray source.
NGC 5005 is approximately 65 million light years from Earth.
NGC 4151 is an intermediate spiral Seyfert galaxy with an apparent magitude of 11.5. It is a known X-ray source.
NGC 4618 is a dwarf galaxy with an apparent magnitude of 11.2. It has a distorted shape and a single spiral arm. It is classified as a Sm galaxy and sometimes referred to as a Magellanic spiral.
NGC 5371 is a spiral galaxy seen face-on. It is classified as an Sbc barred spiral galaxy and located about 100 million light years from Earth. Together with Hickson Galaxy Group 68, NGC 5371 makes up the Big Lick Galaxy Group.
NGC 4625 is a dwarf galaxy with an apparent magnitude of 13.2. The galaxy has an asymmetric shape and a single spiral arm. It is classified as a Sm galaxy because its structure somewhat resembles that of a spiral galaxy. NGC 4625 is occasionally referred to as a Magellanic spiral galaxy because its appearance resembles that of the Magellanic clouds (irregular dwarf galaxies in the southern hemisphere, orbiting the Milky Way).
Hockey Stick Galaxies – NGC 4656 & NGC 4657 (Crowbar Galaxy, UGC 7907, PGC 42863)
NGC 4656 and NGC 4657 are interacting galaxies with an apparent magnitude of 11.0. They both belong to the NGC 4631 Group, a group of galaxies approximately 25 million light years from Earth in the constellations Canes Venatici and Coma Berenices. Other than the Whale (NGC 4631) and Hockey Stick Galaxies, the dwarf elliptical galaxy NGC 4627 also belongs to the group.