On a clear night, only a few hundred stars can be seen without the use of any astronomical instruments. The Milky Way Galaxy consists of at least 200 billion stars. Stars are huge balls of hot gases. The sun is a star, but it is not the largest star; it is only the nearest star. A star has three recognizable stages: its birth; the years in which it exists; and its death. Its formation and its life expectancy have captured the curiosity of astronomers for centuries.

Astronomers from the past have devoted their entire lives to the studying of the formation of stars. Gases make up 99 percent of the materials in the galaxy. These gases in space gather together to form clouds of gas, known as nebulae. Millions of years later, "the temperature of the cloud climbs until it becomes hot enough to radiate light. It is then no longer a gas cloud; it is a star" [1] (Asimov 182). New stars are formed when nuclear reactions occur in these concentrated clouds of gas.

Stars are made of 60 different elements, all of which are found on Earth. Elements such as hydrogen, helium, iron, and calcium. The average star's atmosphere consists of 87% hydrogen, 10% helium, and 3% of other elements. Each star has its own motion, but it is not obvious.

Although the sun appears to be huge, many stars are bigger than it. Our sun's diameter is 864,000 miles. Betelgeuse, a red supergiant, has a diameter 500 times bigger than the sun: 500 million miles. Betelgeuse, though, is not the biggest star. Epsilon Auriga e is close to one billion miles in diameter and VV Cepheid has a diameter of two billion miles, known as the super-supergiants. There are also stars that are small.

One of the smallest is the Whale and it has a diameter of 1, 60 kilometres. Small stars are known as white dwarfs. Stars also have different temperatures. Temperatures ranging from 2,100 C to 50,000 C. The temperature of the stars is indicated by the colour of the stars. The blue colour stars are the hottest and usually the brightest stars, the yellow stars are medium hot, and the red stars are coolest and the most dim. Over time, there have been many questions concerning the supply of gas clouds in our galaxy.

Some people concluded that there will be only enough to fuel the creation of stars for another 200 million years. Due to this immature hypothesis, astronomers investigated and came to the conclusion that there will be materials enough for the creation of new stars for at least another 10 billion years. Other questions asked were: will there be new stars being born after 10 billion years and how long will the stars last The question concerning new stars being born after 10 billion years is still left unanswered. Certain stars will last for a very long time because "stars with masses from one-quarter to one-tenth that of the sun burn long and slow, some lasting more than 10 trillion years before finally sputtering out" [2] (Adams and Laughlin). Nothing in the universe seems to last forever. From studies, astronomers predict that "by 10 trillion years from now, the last stars will have winked out.

The sky, containing the darkened and collapsed corpses of a trillion trillion once brilliant suns, will finally fade to black" [3] (Adams and Laughlin). Stars seem enduring, but eventually die out. Stars die out when they have used up all their hydrogen fuel. The hottest stars actually have the shortest lifetimes, usually 100,000 years. The life expectancy of our sun is about 12 billion years. It has already lived half of its lifetime, and in about 6 billion years the sun will begin to "die".

By that time, the sun will have used up most of its energy fuel and will start releasing its gases into space. Some stars die quietly and some stars explode. Before dying out, stars go through processes of expansion and contraction. When a star has used up all its hydrogen supply, the helium in the core begins to fuse into carbon which causes the star to expand and become a red giant for many thousands of years. After thousands of years, the star will collapse and shrink to the size of a white dwarf star. This entire process of expansion and contraction will take about 100,000 years.

When our sun expands and becomes a red giant, "its hot surface gases will swallow up Mercury, the planet closest to the Sun, and vaporize the plane tOur planet's climate will have grown warmer The oceans will heat up until life on Earth surface will be impossible. Earth will become a molten dead planet" [4] (Gallant 63). Centuries later, the sun will collapse. It will shrink and the Earth will begin to cool. There will be oceans again because: the huge stores of water vapour in the atmosphere will condense and fall as rain Earth will grow colder and colder. The centuries-long rains will turn to snow, and the oceans will freeze.

It will snow for thousands of years until the last parcel of water vapour is wrung out of the atmosphere. Earth will become locked in a planet-wide ice age that will last forever. [5] (Gallant 64) The sun will end up being 100 times smaller than it originally was; it will be a white dwarf star. Huge stars end their lives differently. They explode with a bang, producing very bright light. These violent explosions are known as supernovae.

A supernova can only be seen once every few hundred years. Astronomers believe that "their explosions are the most violent events since the Big Bang with which the universe began in a single second, a supernova releases as much energy as the Sun does over a period of about 60 years". [6] (Gallant 87) The mysterious life of the star can be explained by the examination of the relationship between the star, its surrounding atmosphere, and the individual elements that make up the star itself. Although astronomers now, have resolved many questions concerning the stars, they are still continuing on the studies of the stars and the hidden nature of the universe. The universe is huge and mysterious. Our Earth is just a small dot in it.

Perhaps most of its riddles will never be solved. The exploration of the stars and the universe seems to be an endless journey, resulting in astronomy as a lifetime hobby. Asimov, Isaac. The Exploding Suns: The Secrets of the Supernovas. New York: Nightfall, 1985.

Branley, Franklyn M. Star Guide: A Voyage into Space Book. New York: Harper & Row, 1987. Dickinson, Terence. "Astronomers predict date the last stars will wink out".

The Toronto Star 2 Feb. 1997: F 8. Gallant, Roy A. Private Lives of the Stars. New York: Macmillan, 1986. Pasachoff, Jay M., and Menzel Donald H. Stars and Planets.

3rd ed. New York: Houghton Mifflin, 1992.

Bibliography

Appel, Ne cia H. Nebulae: The Birth & Death of Stars. New York: Lothrop, Lee & Shepard, 1988.
Asimov, Isaac. Dickinson, Terence. 3rd ed. Simon, Seymour. Look To The Night Sky: An Introduction to Star Watching. New York: Penguin, 1979.
Simon, Seymour. Stars. New York: William Morrow, 1986.
Whitney, Charles A. Whitney's Star Finder. New York: Alfred A. Knopf, 1989.