In the south quite low down in the sky in the south in late summer and early autumn is one of the constellations that form the zodiac. This is Capricornus the Sea Goat. Although there are no particularly bright stars in Capricorn it has some of the oldest mythological legends attached to it.
Normally associated with a sea goat by Aratus 315 – 240 BCE
the Greek poet who drew the pictures we recognise as the 48 classical
constellations it was a Horned Goat, while Eratosthenes 276 – 194 BCE he was
the Greek astronomer and mathematician who measured the circumference of the
Earth thought that Capricorn was half fish who jumped into the river Nile to
escape the monster the Typhon.
In Persia, it was Bushgali, in Syria it was Gadjo, in Turkey
it was Ughlak while to the Arabian astronomers it was Al Jady, all these names
refer to a goat. In Egypt it was Chnum or the God of the Waters, this would I
assume be associated with the rising of the river Nile.
In Asia Capricorn was sometimes known as The Southern Gate
of the Sun, this would almost certainly be because Capricorn is the
constellation where the Sun is at its lowest in the sky, and this is when the
winter solstice occurs. The Tropic of Capricorn is the position at
approximately south 23 degrees where around December 21st the Sun
will be directly overhead. Although it is still referred to as the Tropic of
Capricorn the position has moved and is now moved into the neighbouring
constellation of Sagittarius. This is due to a very long-term effect called
Precision or the wobbling of the Earth.
The second mythical
king of Rome Numa Pompilius c715 BCE – 673 BCE began the year when the Sun was
in the middle of Capricorn and when the day lengthened after the winter
solstice.
Today we see Capricorn as the sea goat, but some Greek and
Arabic astronomers saw it as just goat like.
Early Hindu names were Mriga and Makara, while the Tamils
saw it as Makaram an antelope. It was sometimes shown with the head of a goat
upon the body of a hippopotamus indicating some kind of amphibious creature.
In China it was the zodiacal bull or Ox that would later
become Mo Ki the Goat Fish. Sometimes the Chinese grouped some of the stars of
Capricorn and Sagittarius together to form Sing Ki the Starry Record. Very
early in astronomy in China it was known as the Dark Warrior.
The brightest star in Capricorn is not alpha but delta. I have mentioned before that in 1603 the German astronomer Johann Bayer introduced a system on his Uranometria star atlas using the 24 letters from the Greek alphabet. Whereby the brightest star is labelled alpha followed by beta then gamma and all the way down to omega which is the 24th and last letter of the Greek alphabet. It does not always follow that this system works. It doesn’t in Capricorn. I don’t know why this situation sometimes occurs.
Delta or Deneb Algedi which is Arabic and means The Tail of
the Goat, it has a magnitude of 2.9 and is 39 light years away. It is an
eclipsing binary system of the Algol type. The prototype for this class of
variable star was discovered in 1669 by the Italian astronomer Montanarri and
explained by John Goodricke the deaf astronomer and Edward Pigott in York in
1782. I called these two astronomers the Fathers of Variable Star Astronomy
because of the work they did together between 1781 -1786 observing and explaining
the changing light of some of the stars they observed. This partnership went on
until the untimely death of John Goodricke at the age of just 22. The magnitude
of delta varies between 2.8 -3.0 over a period of just over one day.
It was close to delta that the planet we now call Neptune as
discovered in 1846 through the calculations of the astronomers Urbain Le
Verrier in France and John Couch Adams in Great Britain. Neptune was discovered at the Berlin
Observatory.
The next brightest star in beta or Dabih the meaning of
which is uncertain it’s another double star. The brighter component has a
magnitude of 3.1 and its companion star has a magnitude of 6.1, the pair can be
seen with binoculars. The system is 340 light years away.
Alpha or Al Sa’d al Dhabih, the Lucky one of the
Slaughterers this name appears to refer to the sacrifice of animals by the
Arabs at the time of the heliacal rising of Capricorn. Another double star, the
two components can be seen with the naked eye under the very best of
conditions. The brighter star has a magnitude of 3.1 the other star has a
magnitude of 4.3. The system lies at 690 light years away.
The last star I will mention here is gamma or Nashira which
means the fortunate one or the bringer of good tidings. It has magnitude of
3.7, it’s an A class star meaning it’s hotter than our Sun and is 139 light
years away.
There is one messier object in Capricorn this is Messier 30,
it is known as the jellyfish cluster. It’s a globular cluster and was
discovered by Charles Messier in 1764 who described it as a circular nebula
without a star. Globular clusters are
old clusters of stars compared to open clusters which are formed of young
stars. M30 lies close to a 5th magnitude star labelled as 41
Capricorn. This was the 41st star catalogued by John Flamsteed in
Capricorn as part of his survey of the stars in the night sky. He was the first astronomer royal in the late
17th century. His project was
to record the bright stars in all the constellations visible from London.
Today astronomers
refer to M30 as a remarkably bright, large and a slightly oval cluster. It lies
at around 27,100 light years and is about 93 light years across, this gives
some idea of just how big some of these globular clusters can be. M30 is
believed to be about 12.9 billion years old. With a magnitude of 7.2 it can
just be glimpsed as a spot of light through a pair of binoculars.
www.theramblingastronomer.co.uk
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