Download Winter Night Sky - transcript

The Winter Night Sky – current.
When we try to find our way around the constellations of the night sky it is easy to
become frustrated at the countless stars we see, but if you persist, not only will you
find it much easier than you first thought, you will also be rewarded with a wealth of
knowledge that will grow and grow every time you look to the heavens.
Planets, nebulae, Galaxies and star clusters as well as the ability to identify
constellations, will all be within your grasp just by following a few simple steps. Firstly
consult a Star map, which will give you names and shapes of constellations; (one of
our monthly night watch sheet’s will get you started). Find one of the most prominent
of these shapes in the sky, for instance the Plough then draw an imaginary line to
the next constellation find out what this constellation is on your star map, and repeat
this process over and over and soon you will be immersed in a world of modern fact
and ancient myth.
As we move around the Sun, the tilt in the Earth’s axis causes our seasonal
changes, and we see different constellations in the night sky throughout these
seasons. For instance during the summer months the constellation Cygnus is directly
overhead but during winter it is nowhere to be seen. Cygnus is still overhead during
winter only now it is daytime and so it is drowned out by the daylight.
There are always fascinating things to see in the seasonal night sky, but winter is
particularly rich and diverse with interesting objects for us to see. Let us look at some
of these objects as we take a journey of wonder and imagination around the winter
night sky.
We start off with a constellation that most people know, the Plough. Some people
think the Plough looks like an old saucepan; here is the curved handle and here is
the pan. It is called a circumpolar constellation, which means that it never sets below
the horizon for us Northern hemisphere observers. If you look closely at this star in
the handle of the Plough, you will see that it is actually two stars which orbit around
each other called Mizar and Alcor and this type of star is called a binary or double
star.
These two stars are called the pointers because if we draw an imaginary line this
way, we come to the North Star; this Star always points in the direction north.
If we continue our line this way we come to another star pattern, Cassiopeia, who in
Greek myth was said to be a powerful but vain Queen of Ethiopia who was punished
for comparing her beauty to that of the Gods. This constellation is easy to recognise
as it looks like a “W” shape.
If we come back to the pointers and strike a line in the opposite direction from
Polaris, we eventually come to the constellation Leo.
Leo, meaning “Lion” is one of the few constellations that actually resembles its
description. Greek myth tells us that Leo represents the Nemean Lion from the story
of Hercules, who had the unenviable task of destroying the creature with his bare
hands, as its skin was impervious to weapons.
Eventually after fighting a terrible battle with the Lion, Hercules managed to wrap his
enormous arms around the throat of the Lion and finally slay the beast. Afterwards
Hercules skinned the Lion and wore the skin like a suit of armour in future battles.
This star called Regulus is the brightest star in Leo and is spinning so fast that it is
wider at its equator than at its poles. If it were to rotate just 16% faster, the force of
gravity would not be able to keep it from tearing itself apart.
Let us continue our imaginary line this way until we come to these two bright stars
called Castor & Pollux in the constellation of Gemini. Castor and Pollux are the two
"heavenly twin" stars giving the constellation Gemini its name. Ironically the two are
nothing alike, while Castor is a hot white star in a group of six; Pollux is a single
cooler yellow/orange giant. In Greek mythology Castor and Pollux were the offspring
of the beautiful mortal Leda, and the God Zeus who was disguised as a swan and as
a result the twins sprang from an egg. Helen of Troy, famous as the cause of the
Trojan War, was their sister, and the twins engaged in many adventures, including
becoming two of the Argonauts, who led by Jason, went in search of the famed
Golden Fleece.
Now can anyone guess which constellation this is? Of course, this is “Orion, the
hunter”.
Orion’s brilliant stars are found on the celestial equator and are visible throughout
the world, making this constellation globally recognized. These are his shoulders,
these are his feet and these three stars make up the famous Orion’s belt.
This Star called Betelgeuse, meaning “armpit of the giant” in Arabic, is a red giant so
large that if put in place of our sun, it would almost reach the orbit of Jupiter, but the
brightest star in this constellation is Rigel at the left foot of Orion. Rigel shines with
the brightness of 40,000 Suns and is a blue supergiant in the process of dying, fated
to explode in a huge supernova. Stars like Rigel live fast and die young and the
saying “the light that burns twice as bright burns half as long” couldn’t be more
appropriate. Orion was said to be the powerful son of Neptune, God of the sea and
was known for his hunting prowess. He would boast that he could hunt and kill any
creature along with his favourite hunting dog, Sirius.
Follow a line down from Orion’s belt and we come to Sirius. Sirius is the brightest
star in the whole night sky and belongs to the constellation Canis Major, meaning
“Great dog”.
If we follow the line of Orion’s belt upwards, we come to another supergiant star
Aldebaran, which marks the eye of Taurus the bull. Aldebaran is an old star that has
burnt up its hydrogen and is now fusing Helium to make heat and light. The word
Aldebaran comes from the Arabic word meaning “the follower” and refers to the way
the star follows the Pleiades around the night sky. This faint patch of stars at the
shoulder of Taurus is the Pleiades cluster, or the seven sisters and people with good
eyesight can usually make out seven stars with the naked eye, but if we look closely,
there are actually hundreds in this patch of sky. According to the ancient Greeks, the
Pleiades were seven sisters, daughters of Pleione and Atlas who was condemned by
Zeus to support the world on his shoulders.
If the sky is dark enough and you are away from city lights, you may just be able to
make out a misty faint band of stars extending across the sky this is our home
galaxy, the Milky Way. The Milky Way is a spiral galaxy with over 100 billion stars
and the Sun and its retinue of planets are in one of the outer spiral arms of our
galaxy. It takes the Sun roughly 200 million years to complete a single orbit around
the Milky Way galaxy.
Occasionally you may see a streak of light flash through the sky; this is a Meteor or
shooting star. Meteors are mostly no bigger than a grain of sand, and while they are
travelling through space at incredible speeds they come into contact with our
atmosphere which causes friction which in turn heats up the tiny rock until it starts to
burn. Periodically we have meteor showers, with hundreds of meteors emanating
from the same apparent point in the sky. These showers typically last from a few
hours to several days and are caused by debris being expelled by a comets tail.
Each day as many as 4 billion meteors, mostly miniscule in size, fall from space.
Occasionally, one of these Meteors will survive to hit the ground. These are called
Meteorites. You can see some meteorites on the space gallery after the show.
The night makes way for the daytime and the only star we can see now is our life
giving Sun. The Sun will one day run out of fuel then start to expand so much that it
will swallow up the inner planets including the Earth; but don’t worry, this won’t occur
for a couple of billion years. Who knows, before that happens humans may have
colonised dozens of worlds in a fraction of that time, especially when you consider
how far we have come in the past fifty years.
Don’t forget to pick up one of our monthly night watch sheets on your way out which
will not only show you where and when you can see passing planets but also show
you which constellations you can expect to see amongst “The Winter night sky”.