One of the most prominent constellations in the northern
sky. Queen Cassiopeia sits in her chair as she goes around the north star. It
used to be known as the Celestial W when below the pole star and the Celestial
M when above it.
Cassiopeia is what is called a northern circumpolar
constellation. This means that it can be seen all year round whether it is
spring, summer, autumn or winter. It is found in the opposite side of the sky
to the Plough, with the North Star in between. Therefore, if Cassiopeia is high
in the sky then the Plough is low and vice versa.
If you have ever seen the film the Clash of the Titans, you
might know her story, she upsets the sea nymphs meaning the Neptune god of the
sea send the sea monster to attack her
land. Her husband King Cepheus consults the oracle and is told the only way to
save their land is to take her daughter Andromeda chain her to a rock so the
monster can eat her. With andromeda chained to a rock the monster appears but
at the last minute our hero Perseus riding the winged horse Pegasus appears on
the scene. Perseus has just killed the Medusa, a creature so horrible that if
you look at you will turn to stone.
Luckily Perseus still has the head of the medusa with him he
points it at the sea monster who turns to stone. Perseus lands rescues
andromeda, they were married and live happily ever after. All these characters
can be seen in the constellations in the sky. Today the Sea Monster has become
a whale.
In her depiction in the sky her chair is titled, it is said
she was so placed by the sea nymphs to give her an effectual lesson in
humility, for a location nearer the equator would have kept her nearly upright.
She is depicted as having her legs outstretched which for a women accustomed to
the fashions of the east must have added to her discomfort.
The Greeks of the 5th century BCE referred to
Cassiopeia as She of the Throne. However, some Greek astronomers knew the
constellation as the Lacoian Key, due to its resemblance to that instrument,
although these Greeks are sometimes credited with the invention of the key they
were used at the siege of Troy and have been found in Egyptian catacombs and
sculptured on the walls of the Great Temple of Karnak.
To the Arab astronomers the group was called Al Dhat al
Kursiyy, the Lady in the Chair. On the other hand, the early Arab astronomers
saw two dogs in Cassiopeia and Cepheus.
In early Chinese astronomy Cassiopeia was called Ko Taou
which translates as a Porch Way.
The five stars that make up the W shape of Cassiopeia are:
Alpha Cassiopeiae or Schedar which means ‘Breast’ is a
magnitude 2.2 star, it is a K class giant star with a surface temperature of
4250`C compared to 5,800`C for our Sun. Schedar is 230 light years away. During
the 19th century it was thought to vary in slightly in brightness, but this has
not been confirmed in recent times.
Beta Cassiopeiae or Caph which means ‘Palm’ is a magnitude
2.3 star, it is a class F class giant star 55 light years away. Its surface
temperature is hotter than the Sun’s.
Gamma Cassiopeiae which has no Arabic name. It’s a B class
star with a surface temperature of an incredible 24,700`C and lies 550 light
years away. It is a variable star its brightness varies between magnitude 1.6
and 3.0. It is the prototype of the Gamma Cassiopeiae type eruptive variable
stars. This group is so rare that there are only about 10 examples which are
known to exist.
Before 1910 gamma appeared constant at magnitude 2.2 then it
made puzzling and a series of unpredictable light variations. In April 1937 it
slowly brightened to magnitude 1.6 then decreasing back to magnitude 3.5 in
1940. When at its brightest it was brighter than both alpha and beta. This
completely changed the appearance of the ‘W’ of Cassiopeia. Gamma then slowly
brightened again so that by 1954 it was back to magnitude 2.5. By 1976 it had
brightened to magnitude 2.2 where it has hovered around ever since, however it
is such an unpredictable star that no one knows what it might do next.
Delta Cassiopeiae or Ruchbar which means ‘Knee’ is an A
class star hotter than the Sun, it is of magnitude 2.7 and is 100 light years
away.
Epsilon Cassiopeiae or Segin the meaning of which is
unknown, lies 410 light years away. It has a brightness of magnitude 3.4 and is
a class B class star much hotter than the Sun.
Slightly to the right of beta or Caph lies rho a peculiar
irregular variable star lying around 3,400 light years away. The light from rho varies between 4.1-6.2,
it’s a yellow hypergiant which varies between a F class and K class star. The
star is so big that if it was placed where our Sun is everything out to the
planet Mars would be inside it. Its temperature varies between about 5,000` to
7,000` C. There are only about 12 known
of these hyper giants known in our galaxy. It is believed that this star is on
its way to becoming a supernova.
There are two messier objects in Cassiopeia,
M 52 an open cluster in the constellation of Cassiopeia.
With a magnitude of 6.9 it cannot be seen with the naked eye; binoculars are
needed to see it. It looks like a large uniform glow. There is nothing special
about it, but it just looks nice. M 52 can be found just below the star 4
Cassiopeia. The cluster is about 20
million years old and contains around 200 stars. Of course, more details of M52
can be seen by using a telescope. In fact, the whole area is very rich in stars
as viewed by using a telescope.
Messier observed it in 1774 and described it as a faint
cluster of stars mingled with nebulosity. Messier saw the cluster while he was
observing a comet in September 1774 which just happened to be close to M 52.
Messier 103 the last object in the original messier
catalogue. Astronomer Harlow Shapley thought that this object was a chance
alignment of stars. However recent data suggests that M103 is a true cluster
with as many as 172 stars located in it.
M103 is another open cluster with a magnitude of 7.4 to
faint to be seen with the naked eye. It lies at 8,100 light years away.
Messier who saw it in 1781 said there is a nebula between
the star’s omicron Bootes and iota Draconis. It is very faint.
Cassiopeia is a very interesting area for supernova; these
are stars that destroy themselves in massive explosions. The most famous was
the supernova of 1572 sometimes called Tycho’s Star
Tycho Brahe 1546-1601 was the last great pre telescope
astronomer he didn’t discover the supernova, but he gave the most accurate
series of observations on the star, which is why the star bears his name. This supernova would become the most
brilliant object in the sky during the last 500 years. It reached around mag -4
roughly the same brightness as the planet Venus.
He first saw the star on November 11th, 1572. For several
weeks it outshone every star in the night sky. It could even be seen in
daylight, when the Sun was low in the sky. The star was visible to the naked
eye (there were no telescopes at this point) for about 16 months fading from
view in March 1574.
The object was known for about 200 years after its
appearance as the stranger or Pilgrim Star or The Star in the Chayre. The word
chayre is an obsolete word for the modern day word chair.
The Chinese astronomers recorded the star as Ko Sing a Guest
Star.
At this time of course people believed that the heavens
never changed so to see a new star suddenly appear certainly caused a massive
amount of interest. At this time there was a very hot debate between science
and the church regarding whether the heavens changed at all.
In 1543 Nicolaus Copernicus had said that the Sun should be
at the centre of the solar system replacing the Earth which the Greek
astronomer Aristotle said was there. The church followed the teaching of
Aristotle for around 1,800 years.
The supernova in 1572 is not the only one seen in
Cassiopeia, there have also been supernovae in 1181 and during the 17th
century although its exact date is uncertain.
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