Canis Major The Greater Dog
Canis Major is a
stunning constellation with many bright stars and clusters,
unfortunately for observers in Britain it is always low in the sky so
we never see it at its best. It represents one of the two dogs the
other being Canis Minor that follows at the heels of Orion the
Hunter.
The brightest star
in Canis Major, Sirius is also the brightest star in the sky. This is
the dog star and sometimes known as the scorching one or the Nile
star. Although low down in winter skies it is easy to find. If you do
need a guide to find Sirius you can use the stars of Orion’s belt
and draw a line down and to the left this will lead you to Sirius.
At magnitude -1.4
(it has a minus sign in front of the magnitude number because it is
so bright, there are 3 stars with minus magnitudes in the night sky)
Sirius outshines all the other stars in the sky but appearances can
be deceptive because Sirius is very close to us being only 8.6 light
years away. It is an A class star which means it is hotter than the
Sun with a temperature of 9,500’C compared to 5,800’C of the Sun.
Sirius was very
important in ancient Egypt because astronomers/priests would wait to
see Sirius rise just before the Sun rose in the morning sky. They
knew this meant the river Nile was about to flood, it was at this
point that farmers had to make sure their fields were ready for the
inrush of water and sediment that would help their crops to grow.
This astronomical event is known as the Helical Rising.
Sirius has a
companion star a white dwarf which was discovered by the American
telescope maker Alvan Clark in 1862 when he was testing a 15 inch
refractor. A white dwarf is a small, faintly lit object made of super
dense stuff called degenerate matter. It is thought that most stars,
including the Sun, will end their days as white dwarfs. A teaspoon
full of white dwarf material would weigh many tons.
As Sirius is the Dog
Star it seems appropriate that the small companion star which is
officially known as Sirius B should be known unofficially as ‘The
Pup’
We know that the
brightest stars in a constellation are allocated a letter from the
Greek alphabet with the brightest being alpha then beta etc., and we
have also seen that the system often does not work, well here we go
again.
The second brightest
star is epsilon (5th letter of the Greek alphabet) or
Adhara which means ‘Virgins’ and has a magnitude of 1.5 it is a
B2 giant star with a whopping surface temperture of 22,500’C which
makes our Sun seem very cool by comparison. Adhara is 440 light years
away.
A line drawn down
from Sirius and slightly to the left leads to delta or Wezen which
means ‘Weight’ which has a magnitude of 1.8 and is a F8
supergiant and is slightly hotter than the Sun, Wezen lies about 1600
light years away. It is thought that in the next 100,000 years Wezen
could destroy itself in a supernova explosion.
To the right of
Sirius is beta or Murzim which means ‘Announcer’ and should be
the 2nd brightest star in this constellation however it is
in fact the 4th. Murzim is a magnitude 2.0 blue giant
class star lying 500 light years away, its another very hot star with
a surface temperature of 22,750’C.
Below Wezen and to
the left is eta or Aludra the meaning is unknown and is B5 supergiant
of magnitude 2.4 , with a temp of 14,750`. Aludra is about 2,000
light years away. It will also become a Supernova in the next few
million years.
A line drawn to the
right from epsilon will lead to zeta or Phurud meaning the ‘Bright
Single Ones’. This is a magnitude 3.0 star, 362 light years away.
Another B class star this time a B2 with a temperature of 18,400’
C.
To the left of
Sirius is gamma or Muliphein whose meaning is unknown. Gamma is of
magnitude 4.1 and is a B8 giant with a surface temperature of
13,100’C and lies 440 light years away. There is a mystery here
because Gamma appears to have varied over a period of many 100s of
years. It is recorded that in 1670 the Italian astronomer Montanari
said that it disappeared from view. It was not observed for another
23 years.
Below Sirius is an
open cluster, M41 which contains about 80 stars and shines at a
magnitude of 4.5 it is about 2,100 light years away it was recorded
as far as back as 325 BCE by Aristotle in Greece. In ‘modern time’
it was reported by the Italian astronomer Hodierna in 1654 and
recorded by Messier in 1765.
NGC 2362
An open star cluster
NGC 2362 was discovered by Hodierna in 1654 this cluster was not
reported again until it was eventually found by William Herschel
(discoverer of the planet Uranus in 1781) on March 4, 1783
NGC 2362 contains about 60 stars, and is of mag 4.1 and is only about
25 million years old. The brightest star in this cluster is tau
which is of magnitude 4.39 and is a class O9 supergiant star with a
surface temperature of an incredible 31,500’C, it is one of the
most luminous supergiants known. The cluster is about 5,000 light
years in distance from Earth.
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