One of the oldest sky figures Hercules is in a very confusing part of the sky there are no bright marker stars but essentially it is made up of a quadrilateral of stars between Vega and Corona Borealis. Hercules is the 5th largest constellation and because of the legends associated with Hercules it should be a very prominent constellation sadly its not.
Hercules was not known by this name to the early Greek
astronomers, but he was seen as the Phantom or Kneeling One. Around 700 BCE his
12 labours were seen to refer to the Sun’s journey through the 12 signs of the
zodiac. Around 500 BCE Hercules was introduced in the heavens as a member of
the crew of the Argo. It was only around
200 BCE that the Greek astronomer Eratosthenes is said to have described the
Hercules and his 12 labours that we recognise today.
The image we see today of Hercules kneeling and holding a
club dates to the Farnese Globe which was made around 150 CE and shows Atlas
holding a celestial globe. Although it probably was a copy of an earlier piece
of work produced in Greece around 150 BCE by Hipparchus..
In ancient Phoenicia the constellation was said to represent
the great sea god Melkarth.
The Arab astronomers saw Hercules as either Al Rakis the
Dancer or Al Jathiyy a’la Rukbataihi the One who Kneels on Both Knees.
The brightest star alpha is known by it Arabic name as Ras
Algethi of The Kneeler’s Head. Nomadic Arabs knew is as Al Kalb al Ra I, The
Shepherd’ s Dog.
The Chinese knew the star as Ti Tso or the Emperor’s Seat.
Ras Algethi is a semi regular variable star varying in
brightness between magnitude 2.7-4.0 these changes can be followed with the
naked eye in a period of between 80-140 days. It is a M red supergiant star
lying at a distance of 360 light years.
Beta or Korneforos which means ‘Club Bearer’ this term is
often given to the whole figure of Hercules. The star lies at a distance of 139
light years. The star is a G giant star and has a magnitude of 2.8.
To the Chinese this star was Ho Chung which means in the
River.
Nova 1934 discovered by English amateur JPM Prentice on
December 13th, 1934, at mag 3.0 and reached its peak brightness on December
22nd, 1934, at mag 1.5. It remained visible to the naked eye for several months.
There are two Messier objects to look for in Hercules. Located below the star eta is Messier 13 which
is probably the finest globular cluster in the northern hemisphere. Globular
Clusters are groups of very old stars. M13 can just be seen with the naked eye
if the sky is very clear when it is high up in the summer months. It is very
easy to find in binoculars M13 has a magnitude 5.8 and was discovered in 1764
M13 contains anywhere from 300,000 to 500,000 stars spread
out over 140 light years. It is relatively close to us at around 23,000 light
years
M13 is sometimes called the Great Globular Cluster in
Hercules If you have a small telescope M13 is fantastic to look at. It is
always a target for astro- photographers.
Messier 92
A globular cluster only slightly inferior to M13, Messier 92
discovered in 1781 it lies at a distance of 26,700 light years magnitude 6.3.
It contains about 330,000 stars. You will need at least a pair of binoculars to
see M92
No comments:
Post a Comment