Cygnus the Swan sometimes known as the northern cross is a majestic constellation in the summer skies, its brightest star Deneb is one of the three stars that form the summer triangle. The other two are Altair in the constellation of Aquila the Eagle and Vega in Lyra the Lyre.
In ancient Greece the constellation was sometimes referred to
as a bird or on some occasions a hen. Today we call the constellation a swan
and this probably due to Aratos the Greek poet and philosopher who saw the
group as a ‘quickly flying swan’.
When the Romans adopted the title we have now, our
constellation became the mythical swan identified with Cycnus, the son of Mars,
or the brother of Phaethon, transformed at the river Padus and transported to
the sky. The constellation was also identified with Leda, the friend of Jupiter
and mother of Castor, Pollux and Helena.
The modern-day Cygnus may have originated on the Euphrates,
for the tablets show a stellar bird of some kind, perhaps Urakhga, the original
of the Arabs’ Rukh, the Roc, that Sinbad knew well.
At all events its present figuring did not originate with
the Greeks, for the history of the constellation had been entirely lost to
them, suggesting that they were not the inventors of at least some of the star
groups attributed to them.
In Arabia although occasionally known as Al Ta’ir al Arduf
the Flying Eagle it is usually known as Al Dajajah, the Hen.
Cygnus is usually shown in full flight down the Milky Way,
‘The Steam of Heaven’, but old drawings show it apparently just springing from
the ground.
Christian astronomers of the Middle Ages see the Cross of
Calvary, or Christi Crux in the sky these descend today when we see the
Northern Cross in Cygnus.
The brightest star in Cygnus is alpha or Deneb, which comes from the Arabic Al Dhanab or Hen’s Tail. The star has also been called by other Arabic names such as Arided or the Follower and Aridif the Hindmost. Deneb is part of the summer triangle it does appear the faintest of the stars compared to Altair and Vega. However, appearance can be deceptive because although Deneb appears the faintest it is in fact the brightest. This is because it is much further away than the other two stars.
Deneb is an A class supergiant star around 2,600 light years
away with a surface temperature of about 8,700 degrees much hotter than our Sun
which has a surface temperature of around 5,800 degrees.
Albireo of beta this name is used universally today is in no
way associated with the Arab astronomers.
Apparently, the name was first applied due to a misunderstanding as to
the word’s ab ireo in the description of the constellation in the 1515 version
of the Almagest. The Arabs referred to the star as Al Minnar al Dajajah or the
Hen’s Beak.
Albireo to the naked eye appears as one star, it is however
a fantastic double star when viewed through a small telescope. Surprisingly
although labelled as beta, Albireo is fainter than gamma, delta and epsilon
Cygnus.
The star appears as a magnitude 3.2 object and is a K class
giant star making it cooler than the Sun, it lies at around at a distance 395
light years.
Gamma Cygnus or Sadr which is Arabic for the Hen’s Breast
the star has a magnitude of 2.2 and is an F class giant star with a surface
temperature of about 5,800 degrees and is about 1,800 light years away.
Epsilon Cygnus or Gienah to the Arab astronomers which means
the Wing has a magnitude of 2.5 is a K class giant star with a temperature of about
4,500 degrees and is 73 light years away.
The star called P Cygnus was discovered in August 1600
either by either the Dutch map maker Willem Blaeu or the Dutch optician Janson.
It was classified as a nova, the term which was used then to signify any star
which appeared in the sky where previously there had been none. The term nova
is Latin for New; we still use the term today. It was labelled “P” in the star
catalogue Uranometria which was produced by Johannes Bayer in 1603.
It was numbered 27 in Tycho’s catalogue for Cygnus with the
designation ‘nova anni 1600 in pectore Cygni’ Kepler through it worthy of a
monograph in 1606 while Christiaan Huygens in the 17th century called it the
‘Revenante of the Swan’ due to its light changes.
Six years after its discovery it started to fade in
brightness until in 1626 it was below naked eye visibility. It then brightened
again in 1655 but faded somewhat by 1662. There was another outburst in 1665
following this there were numerous fluctuations in brightness. Since 1715 it
has remained fairly constat as 5th magnitude star.
Today the star is classed as a Luminous Blue Variable star
it is a B class giant star around 5,300 light years away and has a surface
temperature of a whooping 18,500 making it much hotter than the Sun.
Between the stars gamma and beta is the variable star chi
which can vary in brightness from magnitude 3.3 when it is easy to see down to
magnitude 14.2 when a large telescope will be needed to see it. Chi is a Mira
type variable star named after omicron ceti or Mira known as the Wonderful the
prototype star of this class of variable stars. It is a M giant class star,
much cooler than the Sun.
61 Cygni has the distinction of being the first star apart
from the Sun to have its distance worked out. In 1838 Frederick Bessel said the
star is 11.4 light years away. It was worked out by using the parallax method.
61 is a K class dwarf star with a magnitude of 5.2.
Sir John Flamsteed 1646 -1719 the first astronomer royal
produced a star atlas, it was published posthumously in 1725. He noted bright
stars tin the various constellations he could see from Britain. The star 61
Cygnus was the 61st star he catalogued in this constellation.
The last bright nova seen in our galaxy was Nova Cygni 1975,
no known as V 1500 Cygnus when at its
brightest it rose to magnitude 1.8. It was discovered by Kentaro Osada in
Japan. We are certainly due for another bright one, so it is always worth while
watching the skies.
There are two Messier objects in Cygnus
Messier 29
An open cluster discovered by Messier in 1764, a young
cluster around 13 million years old lying at a distance of 7,000 light years.
It shines at a magnitude of 7.0 meaning binoculars to find it.
Messier or M39 is another open cluster that can be seen as a
fuzzy light patch of light north of Deneb shining at a magnitude or 4.6. It was
first recorded by Aristotle in 325 BCE as a cometary looking object. M39 lies
about 950 light years away and only contains about 30 stars. It was discovered
by Messier in 1764.
NGC 7000 or the North American Nebula was discovered by
William Herschel in 1786. This nebula is lying close to Deneb. Some people
claim it may be visible to the naked eye under good, dark conditions, and a
preferred object for amateur astrophotographers. Its mag is 4.4 but spread over
a wide area.
It is called the North American nebula because it has the
same shape as North America and is a great favourite with astronomers to
photograph. It was first photographed by
Max Wolf on December 12, 1890.
The distance to the North America Nebula is estimated at
1,600 light years.
Next door to the North American Nebula is the Pelican Nebula
IC 5070 with a magnitude of 8.0 and this cannot be seen with the naked eye.
Both the North American and Pelican are favourite for astrophotographers.
NGC 6992
The Veil nebula a supernova remnant from an explosion
between 10,000 to 20,000 years ago .it lies next to the 4th magnitude star 52
Cygnus. First seen by William Herschel in 1784 with a magnitude of 7.0, a
telescope is needed to see it. Again, it’s a favourite of astrophotographers
www.theramblingastronomer.co.uk
No comments:
Post a Comment