by ANDY FLEMING
The Constellation of Orion the Hunter and to the lower left Sirius, his trusty 'Dog Star'. Sirius is actually a binary star system; Sirius A is the star shown in the photograph and is a much larger than our Sun. Sirius B is a white dwarf at the end of its life and orbits Sirius A. It's nickname is appropriately enough 'the Pup'
If you look to the
southern horizon on a clear late evening from anywhere in the northern hemisphere this month you’ll see
the gorgeous constellation of Orion the Hunter, unmistakable due to the three
bright stars in a diagonal line that constitute his belt.
These are called Alnilam, Alnitak and Mintaka. Look down from the left hand side of the belt
and running down almost vertically is Orion’s sword. A hazy patch around the
middle of the sword reveals itself through binoculars as the Great Nebula in
Orion… a stellar nursery with some new born stars in its centre. This group of stars is called 'The Trapezium'.
Star-hop following a
line straight down from Orion’s Belt and you will find Sirius, easy to locate
as it’s the brightest star in the night sky.
A very hot star and hence a bluish hue, it’s actually part of another
constellation, called Canis Major, or the Greater Dog.
Sirius is bright for two main reasons – it’s much
larger than our Sun and is just 8.6 light years distant.
Sirius is also known
colloquially as the "Dog Star", and was an important object in
antiquity. The heliacal rising of Sirius marked the flooding of the Nile in
Ancient Egypt and the "dog days" of summer for the ancient Greeks,
while to the Polynesians it marked winter and was an important star for
navigation around the Pacific Ocean.
But Sirius has a
secret that wasn’t revealed until as late as 1862. It turned out it wasn’t
alone. Orbiting it was an intensely dense and tiny star at the end of its life,
a cosmic cinder otherwise known as a white dwarf. It was unresolved until
bigger and more powerful telescopes came along, due to the glare from the Dog
Star itself that thereafter was named Sirius A. It orbits Sirius at a distance
much less than the radius of our solar system.
It’s called Sirius B or appropriately enough, the Pup!
Sirius is what
astronomers term a binary star system!
Original source: Andy Fleming, 102.4 Radio Hartlepool
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