Perseus was the hero of Greek mythology who rescued Andromeda who was chained to a rock waiting to be eaten by the Kraken Sea monster.
Andromeda’s mother Cassiopeia had upset Neptune god of the
sea who then sent a monster the Kraken to attack her land. She was told the
only way to save her land as to chain her daughter Andromeda to the Rocks and
let the Kraken eat her.
Andromeda was chained to the rocks the monster appeared
everything appeared lost but at the last-minute Perseus appeared riding the
winged horse Pegasus. He had just killed the Medusa, a monster so horrible that
anyone who looked at it would turn to stone. The medusa’ s hair was made of
snakes. Perseus still had the head of the monster, he showed it to the Kraken
which turned to stone. Perseus landed rescued Andromeda. They were married and
lived happily ever after.
The Arab astronomers sometimes referred to Perseus as Hamil
Ra’s al Ghul or the Bearer of the Demon’s Head.
The brightest star alpha has two given names Algenib which means Side or which can mean Elbow. It has a magnitude of 1.8 and is a F class supergiant with a surface temperature of 6,300 degrees and is 510 light years away.
Beta marks the eye of the medusa and its name is Algol which
means the Winking Demon. It’s not one star but two which are eclipsing each
other. This causes the brightness of the star to change. Astronomers call stars
that change in brightness Variable Stars. This variability can be caused by
several factors. The name Algol is interesting because the name might suggest
that Arab astronomers 1,000 year ago knew it changed in brightness or winked in
the sky. Sadly, we have no proof for this idea, yet.
This change in brightness of Algol was noted by the Italian
astronomer Montanari in 1669. It would however not be until 1782 that the cause
of the variability of Algol would be explained. It was the deaf astronomer John
Goodricke who lived in York and who
explained what was happening to Algol.
Although he was deaf there was nothing wrong with his brain,
he was very clever. He worked with another astronomer in York, Edward Pigott
between 171-1786 when Goodricke died, they discovered and suggested what was
causing light variations in some stars. They were literally hundreds of years
ahead of their time with some of their thinking and ideas. When I was Curator
of Astronomy at the Yorkshire Museum in York, I christened these two as the
Fathers of Variable Star Astronomy.
John Goodricke suggested that the two stars were eclipsing
each other in a regular period causing the light variations. He was right and
his ideas of objects eclipsing stars and causing changes of light in stars is
still used today as astronomers use the same theory and principals to find
planets orbiting other stars.
The eclipse occurs every 2.8 days and the magnitude varies
between 2.2 – 3.5. Algol lies at a distance of 90 light years and has a surface
temperature of 13,000’C and is a B class star. The star which is eclipsing
Algol cannot be seen with the eye.
Zeta has a magnitude of 2.9 and is a B class supergiant with
a temperature of 20,500’C and is 750 light years away. There does not appear to
be a name for this star.
Epsilon also has a magnitude of 2.9 and like zeta does not
appear to have a name. Epsilon is also a B class star, with a temperature of
26,000’C and is 640 light years away.
NGC 869 and NGC 884 both with a magnitude of 3.7 and 3.8
respectively form the famous double cluster. They mark the sword of Perseus
These are open clusters with 350 and 300 stars respectively, lying about 7,600
light years away and about 300 light years apart. They are both visible to the naked eye but
seen through binoculars they are spectacular.
Each cluster contains over 300 blue, white super giant stars. They are
about 7,500 light years away.
One of the most spectacular meteor showers of the year is the Perseids which can be seen around the 12th/13th of August each year. Usually around 80 meteors per hour can be seen. The meteors or shooting stars as some people call them are small grains of dust left behind by a comet as it travels around the Sun. There are several important meteor showers throughout the year. The comet connected with the Perseid meteor shower is comet Swift – Tuttle.
While it was curious that Messier overlooked the double
cluster maybe it was too obviously not a comet, he did however discover another
open cluster in Perseus, this is M34 glimmering at mag 5.5 just visible to the
naked eye to the right of Algol.
www.theramblingastronomer.co.uk
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