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Canes Venatici is one of those obscure constellations
introduced by Johannes Hevelius in 1690. It represents the two dogs Asterion
and Chara, both held on a leash by Bootes as they apparently chase the Great
Bear around the North
Pole.
With one exception, the constellation's stars are quite faint, fourth- and
fifth-magnitude stars. There are only three Bayer stars, yet several notable binaries can be found,
as well as a famous variable and a number of interesting deep sky
objects as well.
Alpha Canum Venaticorum is popularly called Cor Caroli (Heart of
Charles). Most sources give Edmund Halley the credit, naming it after King
Charles II after the restoration of the monarchy in Britain in 1660. (Some say,
however, that the reference was initially meant to commemorate Charles I, after
his execution.)
The star has a visual magnitude of 2.9 (variable), a distance of 110 light
years, and roughly the same size as our Sun. It is also a splendid
double with, perhaps, a subtle colour contrast (discussed below).
Double stars in Canes Venatici:
Canes Venatici has two attractive binaries: alpha CVn and 25 CVn.
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Alpha2 and alpha1 CVn form a celebrated
fixed double star system. Note that the primary is alpha2,
since it is slightly east of its companion.
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While both stars are usually reported to be blue-white, some find them
slightly different, perhaps soft blue and yellow, or two shades of white.
25 CVn (Struve 1768) is a visual binary with an elegant orbit of 240 years. Presently, the companion is at
near maximum separation, with a PA of 100 degrees and separation 1.8".
Variable stars in Canes Venatici:
The constellation contains one of the more interesting semi-regular
stars, Y CVn, called La Superba by its admirers. One look and you
will understand why: the star is an unusually vivid red.
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Y CVn is classified as an SRb star. Such stars are known to have
several periodic cycles, superimposed on each other. Basically, it changes in
magnitude from 7.4 to 10.0 every 157 days. (However an update published in
Budapest, in the Information Bulletin of Variable Stars, #2271, has
reassessed the period at 251.8 days.)
Alpha2 CVn is the prototype of a class of variables. Such
stars usually have a spectrum from B9 to A5, are unusually abundant in
particular heavy metals and deficient in common elements. Alpha2
has an abundance of silicon, europium, and mercury, and oscillates in
magnitude from 2.84 to 2.98 every 5.5 days.
Deep Sky Objects in Canes Venatici:
There are five Messier objects in this constellation, and many more deep
sky objects worthy of attention.
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M3 (NGC 5272) is a wonderful globular cluster found roughly halfway
between Cor Caroli and Arcturus (in Bootes). Considered one of the finest
globular clusters in the entire heavens, you'll need a large scope to
resolve its individual stars. The cluster is about 45,000 light years away.
M51 (NGC 5194) or The Whirlpool Galaxy is the finest
galaxy in Canes Venatici.
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This spiral, found just southwest from the tip of the Big Dipper's
handle, was the first spiral galaxy to be discovered (in 1845 by Lord
Ross at his castle in Ireland).
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Some say the galaxy is 14 million light years away, others that it is
twice that. In any case, you'll need a large telecope and a fine evening
to enjoy its delicate detail, which includes an appendage system (NGC
5195), another galaxy seemingly hanging onto one of its extended arms.
M63 is sometimes called the Sunflower Galaxy, by its numerous arms,
which Burnham describes as "reminiscent of showers of sparks thrown out
by a rotating fiery pinwheel". Fairly bright, at 8.1 magnitude, it has a
very condensed centre. The galaxy is found five degrees north-northeast
of Cor Caroli.
M94 is another spiral, seen practically face-on, and sometimes
described as "comet-like". This is a very compact circular spiral and very
bright (8.1 magnitude). To find it draw a line between Cor Caroli and
beta CVn, and at the half-way point draw a perpendicular off to
the northeast. About two degrees up this perpendicular is found M94.
M106 (NGC 4258) is another bright spiral. Burnham doesn't list
this object as a Messier, but gives a fine photograph (p 375). The
galaxy is six degrees north north-west of beta CVn.
Below are listed a selected number of galaxies considered the best of
the non-Messiers.
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NGC 4244: a large edge-on spiral, found eight degrees west of
Cor Caroli.
NGC 4485 and NGC 4490 are two splendid galaxies in the same field: 4485 is more compact (this one is sometimes called the Cocoon Galaxy), while 4490 is larger and brighter. Located less than one degree northwest of beta CVn.
NGC 4631: very large and bright, seen edge-on. Found in a rather
barren field, six degrees south of Cor Caroli and two degrees west. In the same field are two more galaxies, NGC 4656 and 4657, just southwest of 4631.
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A printed version of this web site ["The Constellations
Pocket Guide"] is available, covering all 88 constellations and their graphics.
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