Andromeda is an easy constellation to find. It is found in the autumn sky. It is also 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 in the sky 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 years 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.
Although we know the Greek version of the story of andromeda
goes back to the Babylonian Epic of Creation much earlier than the Greeks, this
would probably be the basis of the story of andromeda. In some editions of the
Alfonsine Tables and the Almagest she is Alamac which is the star marked as
gamma on star maps of andromeda. The Alfonsine Tables were produced in Toledo
in Spain under the auspices of Alfonso X of Castile 1221- 1284 CE, the
Almagest was written by the Greek astronomy Ptolemy around 150 CE and recorded
all Greek science and astronomy up to that date. The Almagest is the Arabic
name for Ptolemy’s book.
The idea of using the Greek alphabet to label stars in
constellations was introduced by the German astronomer Johann Bayer in 1603 on
his Uranometria star atlas. The idea was that the brightest star would be alpha
the first letter of the alphabet, then the second brightest star would be beta
all the way down to omega the 24th and last letter of the Greek
alphabet. Sometimes the system works and sometimes it doesn’t. People have
asked me why, I simply don’t know.
Arabic astronomers over a thousand years ago portrayed the
constellation not as a maiden chained to a rock but as a seal chained to a
rock.
We start with something of a mystery in andromeda. Starting with alpha or Alpheratz which is also sometimes called Sirrah which means the Horses Navel. This name clearly has nothing at all to do with a maiden chained to a rock.
Most of the star names you will see on star charts today are
Arabic.
For some reason in 1930 the International Astronomical Union
(IAU) the controlling body of world astronomers decided to standardise the
constellation boundaries which had never been accurately defined. We still use
the constellation borders that were introduced in 1930 today. The IAU decided
to move one of the stars from the square of Pegasus to the neighbouring
constellation of Andromeda.
Therefore, delta
Pegasus whose name is Alpheratz and was the top left-hand star of the square
became alpha Andromedae. This star is
not unique there are many examples of stars getting transfers from one
constellation to another.
The other main stars in Andromeda are marked by a rather
irregular line from the square of the Pegasus pointing from the top left-hand
corner of the square of Pegasus towards the constellation of Perseus. In order
they are alpha or Alpheratz, delta, Mirach or beta, and Almach or gamma.
Alpheratz itself is a double star lying at 97 light years
from Earth. There is a third star that was discovered by William Herschel on
July 21st, 1781. However, this star is not part of the system merely
a line-of-sight effect which makes it look like a companion star to
Alpheratz. Herschel was the astronomer
who discovered the planet Uranus on March 13th March 1781, Its
brightness is ranked as magnitude 2.0 which is the same brightness as the North
Star and therefore can easily be seen with the naked eye.
Alpheratz is much hotter than our Sun, it is a spectral
class B star with a surface temperature of around 11,500 degrees compared to
the 5,800 degrees of our Sun which is a G class star.
If we continue our line of stars that form andromeda from
the square of Pegasus the next star along is the fainter star, delta andromeda.
This star does not have a name, it’s worth pointing out that only the brighter
stars tend to have names.
Delta which is the faintest star in this line of stars only
has a magnitude of 3.3 it appears as
just one star to the naked eye however there are in fact three stars that make
up this system. The other two stars can only be observed by using an instrument
called a spectroscope. The star that we can see with our eyes is 105 light
years away. This star is much cooler than our Sun it is classed as a K class
giant star.
If we continue along this line of stars the next one, we
reach is Beta or Mirach which means a girdle in Arabic and the star’s position
marks the left hip of the princess. A much older Babylonian name for the star
is Kamushikeu which means the Deleter.
Mirach is a single M class red giant star larger but cooler
than the Sun with a surface temperature of around 3,500 degrees. It appears
that from a study in 2023 that there might be a close companion object to
Mirach not a planet but possibly a brown dwarf or a kind of failed star.
Beta or Mirach is also of magnitude 2.0 and can be used as a
guide to find the Andromeda Galaxy. A line drawn upwards and slightly to the
right from the star Mirach leads to the faint star Mu then slightly further
along to Nu Then just to the right of Nu if the night is very clear and you are
away from city light year will be able to see a little smudge of light in the
sky. This is the Andromeda Galaxy. The Arab astronomers 1,000 years ago knew of
the galaxy because in 905 Al Sufi described it as the ‘Little Cloud’ in
Andromeda.
The first record of a telescopic observation we have from Europe is in 1612 from the German astronomer, Simon Marius who described the soft glow to the light of a candle shining through horn.
Until the 1920s it was referred to as the Andromeda Nebula
because it was assumed to be in our galaxy, which we refer to as the Milky Way,
however in 1923 Edwin Hubble after whom the space telescope is named realised
that the Andromeda nebula was another galaxy lying outside our own Milky Way
Galaxy. It was Hubble who made the universe much bigger when he placed the
Andromeda Galaxy not 700,000 light years away but over 2 million light years
away. Today astronomers generally agree that the Andromeda Galaxy lies at
around 2.5 million light years.
In 1885 a nova which is a binary system that throws of shell
of gas into space and brightens up, hence its name nova which is Latin for new
was seen in front of the andromeda galaxy.
Astronomers today realise that this was not a nova but a supernova. This
is a star that destroys itself in a massive explosion. The term supernova was
first used by astronomers Walter Baade and Fritz Zwicky in 1931.
What the astronomers had observed in 1885 was the first ever
telescopic observations of an extra galactic supernova. In 1885 when
astronomers thought it was just an ordinary nova it was given the variable star
designation of S Andromeda.
There has only been one ordinary nova discovered in
andromeda that was discovered in December 1986. It has since been given the
designation of OS Andromeda.
A pair of binoculars will show it easily as a fuzzy patch in
the sky.
The Andromeda Galaxy is the most distant object you can see
with the naked eye at 2.5 million light years away.
Andromeda is larger than our galaxy and in about 3.5 billion
years’ time the two galaxies will pass through each other!
The last star that forms this main line of stars of
andromeda is gamma or Almach which means in Arabic either a small animal or the
left foot of andromeda. It’s a double star with the companion star being
discovered by the German astronomer Johann Tobias Mayer in 1778.
Almach also has a magnitude of 2.0 and is a K class giant star cooler than the Sun
with a surface temperature of 3,900 degrees and is 390 light years away.
There is also a meteor shower associated with andromeda, The
Andromedids. Many people refer to meteors as shooting stars. They have nothing
at all to do with stars they are tiny grains of dust burning up as the meteor
enters the atmosphere of the Earth. A
comet is essentially a giant snowball travelling around the Sun leaving a trail
of dust behind it. If the Earth happens
to pass through the trail of dust left by a comet we see a meteor shower.
This comet was first discovered in 1772 and is the first
comet that allowed us to identify the link between comets and meteors.
In 1845 comet Biela was observed to break up. From that
point on, it could not be observed again. There were then spectacular meteor
outbursts in November1872 when 10,000 meteors per hour were seen and in
November 1885 when 6,000 meteors per hour were seen. Today sadly there are only
a very few Andromedid meteors ween every year.
With the breakup of comet Biela and the massive meteor
showers in 1872 and 1885 astronomers were able to confirm the link between
comets and meteors.
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