Canes Venatici or the Hunting Dogs is a modern constellation, created by the Polish astronomer Johannes Hevelius 1611-1687 who introduced this constellation to the star maps in the 1680s. He introduced 9 new constellations of which 8 are surprisingly still used today. Although most are faint groups that fit in-between the ancient classical constellations. Canes Venatici is probably one of the brighter examples.
This constellation is what is known as a northern
circumpolar constellation. This means that we can see it all year round. It
does not matter what season we are in. If we think about Earth in space in a
3-dimensional way, then whichever season we are in we see those stars in the
night sky. There are stars in the daytime sky, which we can’t see because the
Sun is so bright we can’t see behind it. These stars are from the opposite
season. To give an example if we are looking at stars in the autumn the stars that
we would see in spring night sky would be in the daytime sky.
However, as we are thinking three dimensionally there will
be stars above and below the Earth. These are the circumpolar stars, northern
for the northern hemisphere and southern for the southern hemisphere. This
means it does not matter where the Earth is in its orbit around the Sun whether
it be spring, summer, autumn or winter we will always see the circumpolar
stars.
The stars that form Canes Venatici were once part of Ursa Major the Great Bear. They can be found under the handle of the Plough. The Plough is an asterism of 7 stars which is part of a much larger group called Ursa Major or the Great Bear.
Most civilisations
seem to regard that these stars were part of Ursa Major certainly this was the general belief of the Greek
Chinese and Arab astronomers.
According to Greek myths the hunting dogs were being held by
Bootes the Herdsman, and it is suggested that this may be to prevent them from
chasing the two bears around the sky. There are only two stars of any note in
the constellation alpha or Asterion and beta or Chara.
The story now becomes a little confusing because when
Hevelius created the constellation Asterion which means Starry changed its name
to Cor Caroli which is still used today. Cor Caroli means Charles’ Heart. Some
sources suggest it was named in honour of King Charles I who was executed in
1649 while some suggest that it was named in honour of King Charles II when he
became king in 1660. It has been suggested that it shone brightly when he
returned to England.
The Chinese regarded Asterion and two faint nearby stars as
San Kung, the Three Honorary Guardians of the heir Apparent. However, the Arab
astronomers saw an extra faint star in this group and called it Al Karb al Ibl,
The Camel’s Burden.
Cor Caroli itself is a star with a magnitude of 2.9 lying at
110 light years. It varies slightly in brightness and is the prototype star for
the alpha Canes Venatici type variable stars. It’s an A class star meaning that
it is hotter than the Sun
Just to keep the confusion going beta or Chara which means
the Southern Dog is the name that is still used today. Chara is a fainter magnitude 4.3 star lying
at a distance of 27 light years and it’s a G class star slightly hotter than
our Sun.
There is one variable star I would like to mention and that
is Y Canes Venatici or to give it its name La Superba. It varies in brightness
between magnitudes 4.3 to 7.8 so at its brightest it can be seen with the naked
eye but when it is at its faintest a pair of binoculars will be need to see.it.
Astronomers refer to this star as a semi regular variable star reaching its
brightest every 160 or so days.
It is known as La Superba because it is one of a rare group
of stars that astronomers refer to as carbon stars, these are stars very close
to the end of their lives, La Superba only has a temperature of around 2,700
degrees making it one of the coolest known true stars. La Superba lies at about
1,000 light years away and is in the process of becoming a planetary nebula
leaving behind its core which is a white dwarf. This is the eventual fate of
our own Sun.
The name La Superba was given to the star in 1866 by the
Italian Catholic Priest astronomer Father Secchi 1818 – 1878 due to its very
deep red colour.
There are no less than 5 messier objects in Canes Venatici.
M3
Oddly enough, when
Charles Messier first noticed this object on May 3rd, 1764, it was only the
76th Deep Sky Object ever seen by human eyes (with the assistance of
telescopes, that is). Although Messier had logged his previous two discoveries
M1 The Crab Nebula and the globular cluster M2 it was this third object that
prompted him to begin his now famous catalogue of ‘objects that are not
comets’.
Messier Object 3 a globular cluster. Since it was first
observed, this globular star cluster has gone on to become one of the
best-studied objects in the night sky and is considered by many amateur
astronomers to be one of the finest visible clusters.
Globular clusters are densely packed collections of ancient
stars. Roughly spherical in shape, they contain hundreds of thousands, and
sometimes millions, of stars.
M3 is one of the largest and brightest and most splendid
star clusters and is made up of around 500,000 stars. It is located at about
33,900 light-years from Earth, the cluster spans about 220 light-years. It is
estimated to be 8 billion years old, making M3 one of the oldest formations in
our galaxy. It has a magnitude of 6.2 which means it is invisible to the naked
eye, a pair of binoculars would be needed to find it.
M51
The famous Whirlpool Galaxy. Once believed to be a great
swirling nebula in our galaxy M51 is now known to be the finest example of a
face on spiral galaxy. A near neighbour at only 15 million light years away
this graceful pinwheel of stars and gas is about 500,000 light years across.
Binoculars are needed to find it as it has a magnitude of 8.4.
Lord Rosse in Ireland at Birr Castle in 1845 used his
72-inch telescope which at the time was the largest telescope in the world to
study M51, he was the first person to see the spiral structure with the stars.
Some astronomers of the time after seeing these drawings believed that M51 was
a stellar universe like the one in which we live. This was of course based on
knowledge of the day; astronomers didn’t realise that there are billions of
other galaxies they assumed that our galaxy was the universe.
There is a small satellite galaxy located at the end of one
of its spiral arms.
Messier discovered M51 in 1773 and described it a s a nebula
without stars near the northerly ear of Canes Venatici below the second
magnitude star (Eta end star) in the tail of Uma. He said it was only seen with
difficulty with his simple telescope.
M63
The Sunflower Galaxy in photographs looks like a spiral
galaxy that has lost control of its gravity, and we are catching a rare sight
of its arms being tossed into space.
This spiral galaxy is a prime example of a type of galaxy
that displays a lack of cohesion between its inner and outer arms The inner
region of M63's is 86,000 light year wide disk is ringed by a strong spiral
structure and the plentiful outer arms appear loose, patchy and haphazard. Not
surprisingly M63 is nicknamed the Sunflower Galaxy because of its resemblance
to that towering plant whose dense seedy head is ringed with an abundance of
bright overlapping petals. M63 lies at around 29 million light years and at
magnitude 8.6 is below naked eye visibility and can be seen by binoculars or
small telescopes
Charles Messier observed M63 on June 14th, 1779, who
described it as faint and does not contain any stars. It is close to a 8th mag
star.
M94
The Croc’s Eye Galaxy despite its placid appearance, may
have experienced an explosion only 10 million years ago, a cleansing event that
disgorged millions of solar masses of material out of its disk or nucleus. The
galaxy lies at 16 million light years and has a magnitude of 8.2.
Messier observed M94 in 1781 as a nebula without a star
above Cor Caroli. The centre is bright and the nebulosity not very diffuse.
M106
Another spiral galaxy this time it does not appear to have a
name. It looks like M94 and appears odd shaped suggesting that it also survived
some violent upheavals in the past. Like most galaxies we see there appears to
be a black hole at its centre, this was discovered in 1994.
Lying at 22 million lights and shinning at magnitude 8.3 it
can be just seen through binoculars as a faint spot but really binoculars will
be needed to see it.
Messier leaves no notes to this galaxy.
www.theramblingastronomer.co.uk
No comments:
Post a Comment