THE STARS, CHARACTERISTICS
On a clear, dark night,if you lookup into the sky you might see as many as 3000 stars. With a large telescope, you can see billions of individual stars. Astronomers estimate that more than 100 billion trillion stars shine in the observable universe.
The stars we see sparkling in the night sky are actually jaint balls of glowing gas. Stars are born from vast clouds of dust and gas such as the Orient Nebula. Some stars die in a violent explosion called a supernova.
Like the sun each star is an enormous ball of glowing gas, chiefly hydrogen and helium. But the stars vary immensely in distance from Earth, size, temparature, colour and brightness.
Distance: Our solarsystem is in a region of the Milky Way galaxy where stars lie about 4-5 light years apart. Elsewhere in the milky way, distance between the stars can be greater or smaller. In certain group of stars, stars can be less than 0.01 light year apart.
The stars farthest away from earth but still in the milky way are about 80000 light years away. The nearest stars in other galaxies are about 200,000 light years away. And the farthest known stars are billions of light years distant.
Size: The size of stars varies from a diameter of about 16 kilometers to a diameter far larger than the sun's. Some of the largest stars have diameters 1,000 times the size of Earth's.Antars is about 600 times the size of the sun.
TEMPERATURE AND COLOUR: A star's surface temperature and its colour are directly linked.The coolest stars have temperatures less than 3,000 degre C. These stars are red. the hottest stars have temperatures that soar above 50,000 derge C.These stars are blue. The stars with more moderate temperatures can be white, such as Polaris(The Norath Star),or yellow, such as the sun.Some stars have in-between colours.Arcturus glows orange-red.Sirius is blue-white.
BRIGHTNESS. During most of a star's life, it shines because of a nuclear reaction that take place deep within it. During the reaction, some of the star's hydrogen changes in to helium and some changes in to energy.This energy eventually escapes as light, heat and other forms of electromagnetic radiation. A star's brightnes depends on how much light energy it sends out
A star's brightness is related to its temperature and colour because temperature affects how much light energy is emitted.A star also may look bright or dim to observers on earth depending on its size and its distance from earth.
HOW STARS ARE FORMED:Stars may seem unchanging to us, but they pass through a life cycle in which they form, age, and then die. These stages of stellar evolution are similar for all stars.
Astronomers believe that stars are born in groups , not singly.They form out of nebulae, which are large clouds of hydrogen gas, dust and other interstellar material.A nebula may be formed by material thrown off the surface of gaint stars.
HOW STARS DIE: Whatever the speed at which a star burns its hydrogen fuel, eventually its supply of hydrogen drops below a certain level.when this happens , the stars fusion and energy production fall off , and the core stars to collapse slowly. As the pressure in the core increases, temperature rises.At the same time,the outer layers of the stars gases expand greatly, then cool off. Depending on the mass of the original star, the star then becomes either a gaint or super gaint.Red gaints and super gaints are aging stars. A star may remain at this stage for several milion years before all nuclear reactions cease.
When nuclear fusion no longer occures, there is nothing to stop gravitational collapse. If the Star has about the same mass as the sun, it probably will contract to become a white dwarf.With the passage of time the remaining heat and light will all radiate away. When there is no energy left, the star will become a black dwarf, a dead star.