The constellation of Bootes is sometimes associated with a
herdsman who was placed in the sky for inventing the plough pulled by two oxen.
It has also been associated as the driver of the wain, which is an old name for
plough. However, he has also seen with the hunting dogs Asterion and Chara
chasing the great bear around the sky. Asterion and Chara are the two old names
for the hunting dogs connected with the constellation of Canes Venatici,
although we still use the name Chara, Asterion has now become Cor Caroli. We
will meet these two stars later when I look at Canes Venatici.
In another version of what the constellation represents is
the idea that Bootes was seen as the shouting of the driver of the oxen or the
shouting of the hunter to the dogs while chasing the bear.
There appears to be some confusion with Egyptian
translations where Bootes sometimes gets confused in translation with Orion in
this case they both can be seen as Horus. To Arabian astronomers like the Greek
astronomers the constellation is seen as a herdsman.
The best way to pronounce Bootes is to think of the word
co-ordinate. Bootes is very prominent in
the spring and early summer skies. It is
always a little bit difficult to work out the best shape to describe Bootes
because it is a large constellation, and it is in a barren part of the sky.
The brightest star alpha or to give its proper name,
Arcturus which is also the brightest
star in the northern hemisphere at magnitude 0. 0 and its name means the ‘Bear
Keeper’. In India it was regarded as
Svati the Good Goer, while the Chinese called the star Ta Kio the Great Horn.
Arcturus is an orange K0 class giant star 37 light years away. It is cooler but
larger than the Sun.
One Arab name for Arcturus was Al Simak which means the leg
of the lance bearer, while Al Biruni one of the great Arab astronomers called
it the Second Calf of the Lion , the first being Spica the brightest star in
Virgo.
Every star has its own story, but some are more curious than
others. The bright orange star Arcturus, which can be found by following the
curve of the handle of the Plough around and down, has an electrifying story
with a twist involving the 1933 ‘Chicago Century of Progress Exposition’ in
America.
Chicago had hosted its first big scientific fair in 1893. At
the time it was believed that Arcturus was forty light years away, so when the
second Exposition was planned for 1933, forty years after the first, it was
decided to use the light from Arcturus to switch on the lights to the
exhibition by hitting a photocell. A photocell is an electronic device that
produces electricity when light falls upon it.
On May 27th, 1933, the light which left Arcturus in 1893,
taking 40 years to reach earth, was channelled through a powerful telescope and
directed on to a photocell to switch on the lights for the Exposition.
Everything worked perfectly, except that today we know that Arcturus is only 37
light years away, not 40. The light had left the star not in 1893 but in 1896!
You might remember that I explained in the introduction to
the constellations that the brightest 24 stars in each constellation have a
Greek letter assigned to it with the brightest being alpha and the 24th or
least bright one being omega. I also said that sometimes this does not follow
and Bootes is another good example of this.
The second brightest star is epsilon which is the 5th letter
of the Greek alphabet and has a magnitude of 2.4. Epsilon or Izar which means
the ‘veil’. Izar is a K0 giant and is cooler than the Sun and is 203 light
years away.
Eta or to give its Arab name Al Mufrid, the Solitary Star of
the Lancer, a name which was given to the star
by the Arab astronomer Ulug Beg,
while another Arabic astronomer Al Kazwini calls it Al Rumh meaning the Lance
of the Lance Bearer. Eta has a magnitude of 2.7 and is a G0 class start just a
little hotter than the Sun and lies just 37 light years away.
Gamma is an A7 class star which is hotter than the Sun, it
has a magnitude of 3.0 and is 87 light years away. Gamma is sometimes known as
Seginus the meaning of which is unknown.
The Chinese refer to this star as Heuen Ko or heavenly spear.
The only other bright stars are Beta or Nekka meaning
‘Herdsman’ which can also refer to the whole constellation and is a magnitude
3.5 star and is 225 light years away. The Chinese called it Chaou Yaou which
means to beckon or move. Nekka is a G8 giant slightly cooler than the Sun.
I will mention one deep sky object which is NGC 5466 a
globular cluster. The NGC stands for New General Catalogue this was introduced
in 1888, although not new today we still use the term. This globular cluster is
approximately 51,800 light years from Earth. The cluster was first discovered
by the British astronomer William Herschel in 1784. Herschel had discovered the
planet Uranus in 1781. At magnitude 9.2 you would need a telescope to be able
to see NGC 5466. This cluster lies about 52,800 light years from the Galactic
centre.
There is one important meteor shower that can be seen coming
from the constellation of Bootes. This is the Quadrantids and is usually seen
around the 4th of January. There can be between 60-100 meteors per hour seen in
the sky, however with this shower the peak of activity will only last for a few
hours rather than the whole night.
If you look up into the sky on any clear night you will be
unlucky not to see at least one meteor or shooting star as some people like to
call them. These meteors have nothing at all to do with stars. They are the
tiny grains of dust that are left behind by a comet or an asteroid as it
travels around the Sun. If the Earth happens to cut across the path of one of
those trails of dust left by comets we see lots of meteors in the sky. This is
called a meteor shower, there are several prominent ones each year. We see the
meteors when they burn up as they enter the atmosphere of the Earth and for
just a moment, we see a streak of light dash across the sky.
The Quadrantids are
associated not with a comet, but an asteroid called 2003 EH1.
The Quadrantids take their name from the now defunct
constellation of Quadrans Muralis the Mural Quadrant, this was an instrument
attached to a wall that would allow astronomers to measure the positions of
stars in the sky. It could measure up to 90 degrees or one quarter of the sky.
The constellation can no longer be seen on modern star maps. It was created by the French astronomer
Jérôme Lalande 1732-1808 in 1795. It was located between the constellations of
Boötes and Draco, near the tail of Ursa Major or Great Bear.
The constellation had ceased to be used by astronomers
towards the end of the 19th century. The Mural Quadrant is the only defunct
constellation referred to by astronomers today, albeit thought the Quadrantid
meteor shower.
Don’t forget if you see a meteor, you must make a wish!!
www.theramblimngastronomer.co.uk
