It has often been said that “The female of the species is more deadly than the male”. In the case of this constellation and with the story of the Cassiopeia legend, the female of the species is certainly the more conspicuous than the male, since King Cepheus cannot be compared with his wife Cassiopeia.
Cepheus is not particularity easy to identify since he is
faint. However the constellation takes the form of a large rather faint diamond
which is in the area between the North Star, Cassiopeia and Deneb in Cygnus one
of the stars in the summer triangle.
Cepheus is a circumpolar constellation as seen from Britain
which means it can be seen all year round.
Cepheus seems to have attracted interest almost from the
beginning of recorded history. It relates to the story of Jason and the
Argonauts. Cepheus is married to Queen Cassiopeia who’s the person who manages
to upset the water nymphs and Neptune who was god of the sea then sends a sea
monster the Cetus to attack her land.
To only way to save their land is to have their daughter
Andromeda chained to a rock waiting for the sea monster to attack her, but at
the very last minute our hero Perseus riding the winged horse Pegasus arrives
on the scene. He has just killed the Medusa a creature with her hair made of
snakes and just to glance at her one would be turned to stone. Perseus rescues
Andromeda, hey are married and live happily ever after. All the characters
including Cephus can be seen in the sky. If you have ever seen the film, the
Clash of the Titans can see the story.
Most ancient civilization seemed to refer to Cepheus by that
name, the Persian astronomers had several variations to that name the main one
would be Phicarus or the Fire Kindler. The Hindus knew Cepheus as Kapi the Ape
god. The Chinese believed that within the constellation was the Inner Throne of
the Five Emperors.
The Arabic astronomer Al Ferghani called the constellation
Al Radif the Follower. This may have come from some misunderstanding from the
nearby Al Ridf in the tail of Cygnus the Swan, for the name Cepheus does not
seem to ever to have been known by any such title in Arabic astronomy.
The brightest star in Cepheus is alpha or Alderamin which originally meant the right arm but today is the right shoulder. The star has a brightness of magnitude 2.5 it’s an A class star meaning it’s hotter than our Sun. It also is close to us being only 49 light years away. In around the year 7,500 it will become the North Star. This is due to a process called precession or the wobbling on the Earth on its axis.
Beta or Alfirk which to the Arabic astronomers means the
Flock is a B class star with a surface temperature of around 23,600 degrees
much hotter than our Sun which has a surface temperature of around 5,800
degrees. Alfirk is around 690 light years away and has a magnitude which varies
very slightly from 3.1 to 3.3.
To the Arab astronomer’s gamma or Arrai means the Sheppard.
While the Chinese astronomers called the star Shaou Wei or the Minor Guard.
With a magnitude of 3.2 it’s a K class giant star cooler the Sun and can be
found 45 light years away.
Delta, which has no name is the famous variable star
discovered by the deaf astronomer John Goodricke in York in 1784. It is the
prototype Cepheid type variable which astronomers use today to work out how far
away galaxies are. There is something called the period luminosity law. A Cepheid's luminosity is directly related to
its period of variation. The longer the pulsation period, the more luminous the
star. This relationship was discovered by Miss Henrietta Leavitt at Harvard in
1912.
The importance of this discovery to astronomers was of
course unknown to Goodricke but cepheid type variables are of immense
importance to astronomers today trying to work out how far away galaxies and
clusters are.
This would be John Goodricke’s last astronomical discovery
of his very short life at the age of just 22.
Delta varies between magnitude 3.6 and 4.3 every 5 days and
9 hours. If you can locate delta try to watch it change in brightness as it
goes through its cycle. Delta is about 887 light years away, it varies from a F
supergiant to a G supergiant class star, with a surface temperature which changes from 5,500’C to 6,800’C during
its cycle.
Mu Cepheus the Garnet Star so named by William Herschel
because of its striking red tint colour. It’s a M2 class red supergiant with a
surface temperature of 3,500’C, mu is 2,800 light years away. Mu is a variable
star it varies in brightness erratically between magnitude 3.4 and 5.1. Many
different periods have been reported, but they are between either 860 days or
4,400 days.
The only star cluster I will mention is NGC 188 it cannot be
seen with the naked eye as its brightness is only magnitude 10, meaning a small
telescope would be needed to see it. NGC 188 is an open cluster and was
discovered in 1825 by John Herschel who was the son of William Herschel who had
discovered the planet Uranus in 1781.
Open clusters are much younger clusters than globular
clusters. The stars of open clusters
usually drift apart after a few million years. However, because NGC188 lies far
above the plane of the Milky Way Galaxy where there is far less gravitational
interaction with the Milky Way the cluster has stayed together.
It appears to be one
of the oldest open clusters being about 6.8 billion years old. It lies at a
distance of around 5,000 light years and is one of the closest clusters located
near the Pole Star.
www.theramblingastronomer.co.uk
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