The Milky Way
Our own galaxy consists of about 200
billion stars, with our own Sun being a fairly typical specimen. It is a fairly
large spiral galaxy and it has three main components: a disk, in
which the solar system resides, a central bulgeat the core, and an
all encompassing halo.
Disk:
The disk of the Milky Way has four
spiral arms and it is approximately 300pc thick and 30kpc in diameter. It is
made up predominantly of Population I stars which tend to be blue and are
reasonably young, spanning an age range between a million and ten billion
years.
Bulge:
bulge, at the centre of the galaxy, is a flattened spheroid of dimension
1kpc by 6kpc. This is a high density region where Population II stars
predominate---stars which tend toward red and are very old, about 10 billion
years. There is growing evidence for a very massive black hole at its centre.
Halo:
The halo, which is a diffuse spherical region, surrounds the disk. It
has a low density of old stars mainly in globular clusters (these consist of between
10,000 - 1,000,000 stars).The halo is believed to be composed mainly of dark
matter which may extend well beyond the edge of the disk.
Major components of Milky
Way
1. Star
clusters and stellar associations - Though most of the stars in our Milky Way exists as either a
single star (the Sun), but there are a number of well defined groups and
clusters of stars, which has thousands of member stars. This type of formation
of stars in a galaxy can be subdivided into three main categories-globular,
open and stellar associations, moving groups-age and numbers are the main
distinguished parts of star sub division system.
2.
Emission nebulas- Emission Nebulous
are mainly a kind of cloud-like objects consists or bright and diffusive gases
and stars
3. Planetary
nebulas- nebulas are
gaseous clouds. They are so called because they almost resemble disk shaped
planets when you look at them with telescope. This type of nebula represents
the end stage of stellar life cycle. So, far over 1,000 planetary nebulas have
been identified in our Galaxy.
- Supernova remnant- They are another
form of nebulous objects found in our galaxy, in the form of gas. The main
reason of their existence is because of the forming of super massive stars
or supernova. Though they almost look like planetary nebulas, but they
have three distinguished characteristics that make them differ from other
types of nebulas-they have larger mass, higher velocity, short life-time.
5. Dust clouds-
They are located, mainly,
to the Milky Way Plane and they are very conspicuous in the region of spiral
arms of our galaxy. Dust clouds over 2000 light years distant from our Sun are
not detectable with any optical telescope. Dust clouds can have masses over
several hundred of solar masses and their maximum size can be about 200 light
years.
- Interstellarmedium-
CONSTELLATIONS
1.
Andromeda,
the princess- Andromeda was an ancient princess who was saved from being sacrificed
to the sea monster Cetus by the hero Perseus.
- Antlia,
the air pump-
Originally called AntliaPneumatica, it was one of several constellations
created to represent newly invented machines of the era.
3.
Apus, the bird of paradise- It is a
constellation of the Southern Hemisphere, created to honor the new types of
birds discovered by European explorers in the Americas.
4.
Aquarius, the water bearer- Aquarius is located
in a part of the sky known as "the Water" that is full of
water-related constellations. Aquarius represents the youthful shepherd boy
Ganymede who was abducted by the Greek god Zeus and brought to Olympus to serve
as cupbearer to the gods.
5.
Aquila, the eagle- Aquila is the eagle
that was the symbol of the ancient god Zeus. Aquila was known to carry Zeus's
thunderbolts, and was sent to bring the youth Ganymede to Olympus to serve as
cupbearer to the gods.
6.
Ara, the altar- It represents the altar created by the
Olympian gods after they defeated the Titans. It can be found below Scorpius,
located near the constellations of Lupus and Centaraus.
7.
Aries, the ram- Aries represents the golden ram whose
fleece Jason and Argonauts sought.
8.
Auriga, the charioteer- One of the earliest
constellations to be recognized.Auriga may represent the lame Greek god
Hephaestus or his son, each one is credited with inventing the chariot.
9.
Bootes, the bear-driver- The word Bootes means
"ox driver" and the constellation is said to be a farmer using the
the plough (the Big Dipper) to plough his fields.
10.
Caelum, the chisel- It is meant to
represent the tool used by engravers.
- Camelopardalis,
the giraffe- It
was created to fill a region of the sky devoid of constellations. It is
surrounded by the Ursa Major, Auriga, Perseus, Ursa Minor, and others. It
contains no bright stars, and is a challenge to find from any area that
does not have a totally darkened sky.
12.
Cancer, the crab- Cancer represents the crab that Hera sent to distract the hero Hercules
as he was fighting the sea serpent Hydra. The constellation of Cancer contains
no bright stars so it is one of the hardest of the zodiac constellations to
find.
13.
Canes Venatici, the hunting dogs- This constellation is
said to represent the two hunting dogs of the nearby constellation, Bootes.
14.
Canis Major, the large dog- Within the
constellation can be found the brightest star in the night sky Sirius, also
known as the "Dog Star".
- Canis Minor, the little dog- The constellation is one of
the smallest in the sky and is composed primarily by only two bright
stars.
16.
Capricornus, the sea-goat- Capricornus is one of
the ancient constellations of the zodiac. Although it is a fairly large
constellation, its stars are dim and it is difficult to see unless the sky is
completely dark. Capricornus represents the Greek god Pan who was often
represented as partially being a goat. In order to escape the monster Typhon,
Pan dived into a river and attempted to change himself into a fish.
17.
Carina, the keel- Carina represents the
keel of the ship. The constellation is difficult to see from most of the United
States.
18.
Cassiopeia, the queen- An ancient
constellation that is part of the story of Perseus and Andromeda. Cassiopeia
was the mother of Andromeda, and because of her boasting that she was more
beautiful than the sea nymphs, the Nereids, she was forced by the god Poseidon
to sacrifice her daughter to the sea monster Cetus. Also as punishment the
image of Cassiopeia was placed in the sky in such a way that during part of the
year the queen appears upside down.
19.
Centaurus, the centaur- According to legend
Centaurus is supposed to represent, Chiron a gentle and intellectual centaur.
He was the teacher of many of the heroes of ancient legends, including
Hercules, Achilles, and Jason.
20.
Cepheus, the king- An ancient
constellation that is part of the story of Perseus and Andromeda.Cepheus is the
father of Andromeda and the husband to Cassiopeia. He was forced to stand back
and watch as his wife's boasting resulted in misfortune and almost the death of
their daughter.
21.
Cetus, the whale or sea-monster- An ancient
constellation that is part of the story of Perseus and Andromeda.Cetus was the
monster that Andromeda was to be sacrificed to in order to ease the anger of
the sea god Poseidon. Cetus is an extremely large constellation that has been
represented as both a sea-monster or as simply a whale.
- Chamaeleon,
the chameleon- A
modern constellation created by Johann Bayer in 1603. It is found close
the south celestial pole, so it is impossible to see from the United
States and Canada.
- Chamaeleon,
the chameleon- A
modern constellation created by Johann Bayer in 1603. It is found close
the south celestial pole, so it is impossible to see from the United
States and Canada.
24.
Columba, the dove- The constellation can
be found directly south of the constellation of Orion. A southerly
constellation, it can be seen by those living in the southern United States.
25.
Delphinus, the dolphin- A small but ancient
constellation that is easily located in the night sky. Delphinus represents the
dolphin that helped the sea god Poseidon win the heart of his wife, the mermaid
Amphitrite. In another story Delphinus is the dolphin that helped the musician
Arion escape from sailors who attempted to throw him overboard and steal his
belongings. The god Apollo was so moved by Arion's music, he sent the dolphin
to carry him to the shore.
26.
Dorado, the goldfish- Dorado represents not
the goldfish kept as pets, but a type of fish that can be found in the seas of
the Southern Hemisphere.
27.
Gemini, the twins- ancient constellation
of the zodiac and one of the only that resembles its namesake. The twins of
Gemini, Castor and Pollux, were sons of Zeus and the mortal woman Leda. They
were brothers of Helen of Troy. The twins were said to spend all there time
together, and were part of the crew of the Argo with Jason when he attempted to
retrieve the Golden Fleece. The twins were considered protectors of sailors.
28.
Hercules, the strongman- One of the most
ancient constellations in the night sky. This group of stars has been
recognized as a hero for millennia. Once the story of Hercules become popular
this constellation was given his name. Hercules was the son of Zeus and the
mortal woman Alcmene. He exhibited enormous strength since childhood and was
constantly being challenged by the wife of Zeus, Hera. Because of Hera,
Hercules had become indentured to King Eurystheus and had to perform his famous
Twelve Labors, most of which can be found in other constellations (Hydra,
Cancer, Draco). The stars of the constellation are not very bright and Hercules
is usually pictured upside-down in the sky.
29.
Leo, the lion- One of the most ancient constellations
in the night sky, and one of the most recognizable. The stars that make up this
constellation easily form the outline of a lion. According to legend, Leo is
the fierce Nemean lion that originated on the moon. The lion could not by
killed by weapons, and as such terrorized the city of Nemea in ancient Greece.
As one of his Twelve Labors, Hercules defeated the lion by strangling the beast
with his bare hands. Zeus then returned the lion to space by placing his image
among the stars.
- Libra,
the scales- Libra
became a separate constellation with the Romans. During that time the sun
entered this constellation during the Autumnal equinox, a time of year
when day and night are nearly equal, or balanced. Libra can be found to
the immediate west of Scorpius.
31.
Orion, the hunter- Orion is one of the
most ancient, and most recognized constellations in the night sky. According to
mythology, Orion was the son of the sea god Poseidon. He was so skilled at
hunting that he boasted that he could kill every animal on the Earth. The
goddess of the earth, Gaia, was so offended by his boast she sent a tiny
scorpion to stop him. Orion was stung by the insect and eventually died. Both
his image and that of the scorpion were placed in the sky. They are on opposite
sides of the sky, so when one is above the horizon, the other is below. The
constellation of Orion is large and easy to find.
- Pegasus,
the flying horse- An ancient constellation who was part of the
story of Andromeda and Perseus. It was told that Pegasus was born when the
hero Perseus cut off the head of Medusa and some of the blood fell into
the sea. Out of the seafoam flew the mythical horse Pegasus. Pegasus was
then ridden by Perseus as he rescued Andromeda. Later Pegasus became part
of the legend of the hero Bellerophon, who attempted to fly him to
Olympus. Zeus was offended by his actions and sent a gadfly to sting
Pegasus, who bucked, thus throwing the hero off. The constellation of
Pegasus is composed primary of the four stars known as the "Great
Square", these stars comprise the body of the horse. Other stars
extend off of the square creating the neck and head, and front legs. Most
pictures of the constellation show only the front part of the horse and he
is pictured upside down in the sky. Pegasus can be found south the the
bright constellation of Cassiopeia, and east of the asterism known as the
"Summer Triangle".
33.
Phoenix, the phoenix- The phoenix is a
mythical bird who lived for 500 years. At the end of its life it would build a
nest of spices, twigs, and fragrances.
34.
Pisces, the fish- While it is one of
the largest and most ancient constellations, Pisces is also one of the most
difficult to see. According to legend the constellation is composed of two fish
who are connected together by a ribbon. The fish are the goddess Aphrodite and
her son Eros (Roman: Venus and Cupid). They turned themselves into fish in order
to escape from the monster Typhon. They then connected themselves together with
a ribbon in order not to be separated. The constellation is located in an area
of the sky known as "the Sea" or "the Water", which is full
of water related constellations. Pisces contains only faint stars, the stars
however do seem to form two small circlets connected together by a string.
35.
Sagittarius, the centaur, the archer- An ancient
constellation and one of the twelve constellations of the Zodiac. Sagittarius
is the second constellation that is depicted as a centaur, a creature that is
half-horse and half-man. The other constellation is Centaurus. Often the
mythology of the two constellations is confused, Centaurus is supposed to be
the wise and benevolent centaur Chiron, while Sagittarius is a more aggressive
and warlike archer centaur. The shape of the centaur is difficult to see in
Sagittarius, however the main stars do create the pattern of a teapot.
36.
Scorpius, the scorpion- Scorpius is one of
the most ancient and the most recognizable constellations in the night sky. The
pattern of stars that create this constellation can easily be imagined as a
scorpion. According to mythology, Scorpius is the scorpion that the earth
goddess Gaia sent to attack and kill the hunter Orion.
37.
Taurus, the bull- The mythology of the
constellation is complex and varied. In Roman mythology the bull of Taurus
represents the god Jupiter who turned himself into a bull in order to kidnap
the maiden Europa, who he took to the island of Crete.
38.
Virgo, the maiden- Virgo is an ancient
constellation, that is easily located by using its brightest member, the star
Spica. Throughout history this group of stars has been pictured as a women.
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