Andromeda – autumn sky
We
start our tour of the constellation with a fairly easy one to find
and is involved in probably the most famous mythological story.
Andromeda
is the princess linked with the story of Perseus and the Medusa plus
Cassiopeia, Cepheus and Cetus (Kraken). Andromeda is depicted chained
to a rock, however needless to say the pattern is nothing like a
princess.
In
mythology Andromeda is the daughter of queen Cassiopeia and King
Cepheus, Cassiopeia boasted that her daughter was more beautiful than
the Nereids these were 50 charming daughters of Nereus the wise old
man of the sea. This was a decidedly tactless thing to say, offended
by Cassiopeia’s remarks they complained to their protector the sea
god, Neptune.
In
anger Poseidon struck the water with his trident flooding the lands
of the Palestine coast and calling up from the deep the sea monster
the Kraken or Cetus. (There could be a basis in truth here because
the great flood could have been caused by a meteor strike 3,700 year
ago in the Eastern Mediterranean. The meteor crashed into where
Austria is found but chunks could have fallen off into the sea
causing the flood).
Cepheus
consulted the oracle as to how to save his kingdom and was told that
his land could only be saved if his daughter Andromeda was sacrificed
to the monster. Accordingly Andromeda was chained to rocks near
Joppa. Jaffa is the modern name for (Joppa) The name Joppa appears
for the first time in the list of cities that Thutmose III captured
(15th century BC). The legend of Andromeda being bound to the rock
was first associated with Joppa by Strabo (1st century A.D.).
With
Andromeda chained to the rocks and the monster appearing everything
seemed lost, however at the very last minute Perseus riding the
winged horse Pegasus appeared on the scene. He had just killed the
Medusa. Anyone looking at Medusa would turn to stone. By chance
Perseus still had the head of the medusa with him, he showed it to
the monster who turned to stone. Perseus then landed and rescued
Andromeda. They were married and lived happily ever after. All these
characters can be found in the night sky.
For
some reason in 1930 the International Astronomical Union the
controlling body of world astronomers decided to move one of the
stars from the square of Pegasus to the neighbouring constellation of
Andromeda. Therefore Delta Pegasi whose name is Alpheratz and was the
top left hand star of the square became alpha Andromedae. The other
main stars in Andromeda are marked by a rather irregular line from
the square of the Pegasus pointing towards the left to the
constellation of Perseus. In order they are alpha or Alpheratz,
delta, Mirach or beta, and Alamac or gamma.
Starting
with alpha or Alpheratz or sometimes Sirrah which means the Horses
Navel and clearly has nothing to do with a maiden chained to a rock
is a star of magnitude 2.0 which means it is as bright as the North
Star. The star is a B9 class star which means that with a surface
temperature of around 13,500 degrees it is hotter than the Sun which
has a surface temperature of only around 5,800 degrees, Alpheratz it
lies about 97 light years away.
The
next star on this line moving left from the square of Pegasus is
delta Andromedae, it’s a K3 giant star which means it is not as hot
as Alpheratz , it lies about 105 light years away. The star is
fainter than Alpheratz being of mag 3.3 and its temperature is 4,000
degrees. It looks orange in colour.
Beta
Andromedae or Mirach which means girdle, is next and is at mag 2.0
the same brightness as Alpheratz but at 200 light years away is
actually brighter. It is an M0 giant star with a surface temperature
of around 3,500 degrees which means that it is the coolest stars in
this line. It looks more red than orange.
The
final star in this line is gamma, whose name is Almach which means a
small animal like a badger. Almach is about 350 light years away. It
is at mag 2.1, the main star is K1 giant star with a surface
temperature of 4,200 degrees.
Beta
or Mirach can be used as a guide to find the Andromeda galaxy (M31).
A line drawn upwards and slightly to the right from the star Mirach
leads to the faint star Mu magnitude 3.9 then continue the line
slightly further along to Nu magnitude 4.5. The Andromeda Galaxy is
close to Nu slightly to the right. You will need a very dark site but
it can be seen with the naked eye, if you know where to look. It is
not spectacular with the naked eye but there is always the
satisfaction of seeing the most distant object to be seen without
optical aid. It is about 2.2 million light years away. It is larger
than our galaxy and in about 3.5 billion years’ time the two
galaxies will pass through each other!!.
A
pair of binoculars will show it easily as a fuzzy patch in the sky.
Other
stars you might try to find in Andromeda
Epsilon
Andromedae is just below delta and is magnitude 4.4 and is 155 light
years away. It is a G class giant star our Sun is also a G class
star, however while the Sun is a dwarf star it will be slightly
hotter than epsilon
Continue
the line from delta through epsilon and further downwards and you
will reach zeta Andromedae which is classified as an orange K-type
bright giant with a magnitude of 4.1. It is cooler than our Sun and
zeta is about 180 light years away.
Just
to the left of zeta is eta Andromeda at magnitude 4.4 it is slightly
fainter than zeta. It lies 240 light years away and is another G
class giant star.
Located
just above delta is pi Andromedae at magnitude of 4.4 and is located
approximately 600 light-years from Earth. It is a B class dwarf star
meaning it is much hotter than the Sun.
Groombridge 34 - One of the
closest double stars to Earth at 11.7 light-years distant. Although
not bright or spectacular Groombridge 34 is an interesting double
since it consists of two red dwarf stars in near circular orbit. The
two stars shine at magnitudes +8.1 and +11.1 far too faint to be seen
with the naked eye. They are easily within the range of medium size
telescopes. In August 2014, a planet orbiting Groombridge 34 was
discovered.
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