ZODIAC

A band around the sky about 18?wide, centered on the ecliptic, in which the Sun, Moon, and planets move.

The band is divided into 12 signs of the zodiac, each 30° long, that were named by the ancient Greeks after the constellations that used to occupy these positions; "zodiac" means "circle of animals," and only Libra is inanimate. Over the past 2,000 years, precession has moved the constellations eastward by over 30° so that they no longer coincide with the old signs.

The 12 constellations of the zodiac are:

• Aries
• Taurus
• Gemini
• Cancer
• Leo
• Virgo
• Libra
• Scorpio
• Sagittarius
• Capricornus
• Aquarius
• Pisces

FROM: http://www.daviddarling.info/encyclopedia/Z/zodiac.html
             http://journals.jevon.org/zodiac.php

WHAT ARE THE IMPORTANCE OF CONSTELLATIONS

LAST TIME

1. Poets, farmers and astronomers created the named of various constellations over the past 6000 year.Traveller used constellations to map the sky and show direction.

2. Farmers cerated constellation to help them with their crops. They used them as a reminder of planting and harvesting season.

3. Constellations have been used to tell time for hundreds of years.

NOWADAYS

4. The 12 zodiacal constellations are used to symbolize the 12 months in a yearly cycle. 

5. It may lead a person to their position and to use this information in many ways like telling direction.

6. The constellations can be used to determine what month of the year it is as well as the time of night. For  thousands of years the constellations of the stars have shown in the same place in the sky. This constant has lead many to learn their positions and to use this information in many ways.

THE HISTORY OF CONSTELLATION

The current list of 88 constellations recognised by the International Astronomical Union^[1] since 1922^[2] is based on those listed by Claudius Ptolemy, Greek-speaking mathematician, geographer, astronomer, and astrologer who lived in the Hellenistic culture of Roman Egypt. He may have been a Hellenized Egyptian, but he was probably of Greek ancestry, although no description of his family background or physical appearance exists, though it is likely he was born in Egypt, probably in or near Alexandria.
The Bear, Orion and the Pleiades are mentioned in chapters 9 and 38 of the book of Job in the Bible.
Greek astronomy was built on Mesopotamian foundations. They defined the Zodiac and at least another 18 constellations taken over or adapted by the Greeks:

The earliest direct evidence for the constellations comes from inscribed stones and clay writing tablets dug up in Mesopotamia (within modern Iraq)... It appears that the bulk of the Mesopotamian constellations were created within a relatively short interval from around 1300 to 1000 B.C [...]

The Mesopotamian groupings turn up in many of the classical Greek constellations. The stars of the Greek Capricorn and Gemini, for example, were known to the Assyrians by similar names - the Goat-Fish and the Great Twins. A total of 20 constellations are straight copies. Another 10 have the same stars but different names. The Assyrian Hired Man and the Swallow, for instance, were renamed Aries and Pisces.^[3]

The Sumerian constellations were inherited by Babylonian astronomy. There are various Babylonian star catalogues or lists of stars, notably the MUL.APIN, a text dating to the Late Bronze Age, ca. 14th to 12th century BC.
In more recent times, Ptolemy's list has been added to in order to fill gaps between Ptolemy's patterns. Most of the northern sky was filled in by Petrus Plancius and Johannes Hevelius.
The constellations around the South Pole were not observable by the Greeks. Twelve were observed by Dutch navigators Pieter Dirkszoon Keyser and Frederick de Houtman in the end of sixteenth century and depicted by Johann Bayer in his star atlas Uranometria of 1603. Several more were created by Nicolas Louis de Lacaille in his star catalogue, published in 1756.
Other proposed constellations didn't make the cut, most notably Quadrans (now part of between Boötes and Draco) for which the Quadrantid meteors are named. Also the ancient constellation Argo Navis was so big that it was broken up into several different constellations, for the convenience of stellar cartographers.

FROM: http://en.wikipedia.org/wiki/History_of_the_constellations

SUPER GIANT STAR

A super giant star is the exact same thing as a giant star only much bigger. Remember that as a star gets older it begins to run out of fuel. As the star runs out of fuel, it will start to burn out.

Just like the sun-sized stars, blue giant stars also begin to burn helium.  As they do these stars get much hotter. This extra heat makes the outside of an old blue giant  star stretch out further. Remember how hot air balloons stretch out as the air in them gets hotter?

The only difference between Giant Stars and Super Giant Stars is their size. Super Giant Stars are much bigger.  If the Sun were replaced by a super giant star, it would extend from the center of our Solar System almost all the way out to Uranus.

GIANT STAR

Remember when we talked about sun-sized stars? We said that at the end of their lives these stars expand, taking up much more space than before. This is exactly what a Giant Star is.

As a sun-sized star gets old, it starts to run out of its hydrogen fuel.  When the process of burning hydrogen in the star's core begins to slow down, the core gets more compact and dense. This means all the stuff in the middle of the star gets really close together.  As the center gets smaller and smaller it starts to heat up again. When it gets hot enough it will start to burn a new fuel called helium.

Once ignited, helium burns much hotter than hydrogen. The additional heat pushes the outer layer of the star out much further than it used to be, making the star much larger. Imagine a hot air balloon. As the air inside the balloon gets hotter, it stretches the balloon out further and further. As the giant star gets hotter, its outside stretches out further and further. When our own sun begins to stretch into a giant star, it will engulf Mercury, Venus, Earth and Mars.



BLUE GIANT

Blue stars are large and compact, this causes them to burn their fuel quickly which in turn makes their temperature very hot.  These stars often run out of fuel in only 10,000 - 100,000 years. 

A blue giant is extremely bright.  Like a lighthouse, they shine across a great distance.  Even though blue giant stars are rare, they make up many of the stars we see at night because they shine so brightly.

Blue giant stars die in a spectacular way.  They grow larger just like the sun-sized stars, but then instead of shrinking and forming a planetary nebula, they explode in what is called a supernova. Supernova explosions can be brighter than an entire galaxy, and can be seen from very far away.

YELLLO STAR

Like the Sun, these medium-sized stars are yellow because they have a medium temperature (remember the fire example?).  Their higher temperature causes them to burn their fuel faster. This means they will not live as long, only about 10 billion years or so.  Near the end of their lives these medium-sized stars swell up, becoming very large. When this happens to the Sun, it will grow large enough to engulf even the Earth. Eventually they shrink again, leaving behind most of their gas. This gas forms a beautiful cloud around the star called a Planetary Nebula. 

When will the Sun expand into a giant, and then shrink leaving behind a planetary nebula?
Don't worry, the sun is only about 5 billion years old. It still has another 5 billion years or so before it will expand and turn into a planetary nebula.

RED DWARF

Red Dwarf stars are smaller than our sun. And since they are smaller, they also have less mass. Because of their small size, these stars burn their fuel very slowly, which allows them to live a very long time. This also causes these stars to not shine as brightly as others. Some red dwarf stars will live trillions of years before they run out of fuel.

Why are red dwarf stars red?
Because red dwarf stars only burn a little bit of fuel at a time, they are not very hot compared to other stars. Think of a fire. The coolest part of the fire is at the top of the flame where it glows red, the hotter part in the middle glows yellow, and the hottest part near the fuel glows blue. Stars work the same way. Their temperature determines what color they are. Thus, we can determine how hot a star is just by its color.

Red dwarf stars are by far the most common type of star in outer space. However, very few stars that you see in the sky are red dwarfs. This is because they are so small and make very little light. Imagine standing on a mountain. Pretend that there are one million kids 5 miles away holding flashlights, and 20 miles away there is a lighthouse for ships. You will most likely not see any of the flashlights, while you will very easily see the lighthouse. If the flashlights all glowed as brightly as the lighthouse they would blind you. Likewise, if all the red dwarf stars glowed as bright as the bigger stars, our nighttime sky would be very bright.

THE CONSTELLATION