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.
Most of the star names are Arabic which is why they can
sometimes seem strange to us.
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 B class giant star with a whopping surface temperature 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 F
class 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, it’s 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 B class 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 B class 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
O class supergiant star with a surface temperature of an incredible 31,500’C,
it is one of the most luminous supergiant’s known. The cluster is about 5,000
light years in distance from Earth.
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