STARS (Science Sains)

What is a star? A star is a big ball of hot gases. The gases are mostly hydrogen and helium. A star emits light and heat which are generated by nuclear reactions. Star is different from a planet because it can give off its own light. The sun is actually one of the stars in the universe. The universe contains billions of galaxies with each galaxy containing billions of stars. Many scientists believe in the theory that the universe begins with a huge explosion, the Big Bang. During the explosion, the universe expended from nothing to become a huge space measuring to billion kilometers in width, in a single second.

The sun is the nearest star in earth. It is located about 150 million kilometers from the Earth It is a stable, medium sized star formed about 4.6 billion years ago. The size of the sun at 1 392 000 km in diameter is 100 times wider than the Earth. However, its density is only a quarter that of the Earth because it is primarily made of gases. The temperatures at its surface which range from 5500 Celsius are hot enough to melt almost anything. Stars are bright in the sky. Stars vary in brightness. The brightness of a star is affected by its distance from Earth. The brightest star seen from the Earth is Sirius. Sirius emits white light. Rigel emits a bluish light.

Stars are formed within large clusters of dust and gases. These clouds of dust and gases are called nebulae. The dust consists of solids such as iron and silicates. The gases are mostly hydrogen and helium. The formations of a star start when a nebula is pulled into its core due to the force of gravity. As the nebula collapses, it starts to spin. The spinning clouds pull in more hydrogen gas over millions of years. Collisions occur between hydrogen atoms in the spinning nebula, producing heat. When the temperature reaches 15000 Celsius, nuclear fusion takes place in the core of the nebula. Hydrogen atoms, releasing a large amount of heat and light energy.

Star have a various types.We can classify stars using it characteristics such as brightness, surface, temperature and colour.The brightness of star depends on its size and temperature and colour.The temperature of stars varies from 3000 Celsius to 50000 Celsius. Star with higher temperature are blue. Stars with lower temperature are red. Astronomers found there are four main groups of stars, namely white dwarf, neutron stars are very dense, small stars. White dwarf is dim, compact stars. Most stars are medium – sized and stable. They neither contract nor expend. The include stars which range from those that are bright and hot to those that are dim and cool. Ninety percent of all stars belong to these groups, including the sun. Giant are large stars. Their diameters are 10 to 100 times that of the sun. Supergiants are even larger than Giants.

A life ends with death. Stars also will death. The lifespan of a star is determined by the original mass of the star. A star with a big mass has a shorter lifespan compared to a star with a small mass. Stars that are 50 times bigger than the sun live for only a few million years. Stars that are smaller than the sun can live more than 10 billion years. A star will be become either are white dwarf, neutron star or black hole when it dies, depending on its size. For medium sized star, the dying star expands to become a red Giant star. The outer layers of a red Giant break up and drift off into space to form a planetary nebula. When the red Giant loses most of its mass to the nebula, it shrinks to become a white dwarf. A white dwarf is a stable star. For large star, the dying star expands to become a red super giant star. The red super giant explodes in an explosion called a supernova. The stars remaining mass become a small neutron star. Then, for super-large star, the dying star expands to become a red super giant star. The red super giant explodes in an explosion called a supernova.
by N.Ezana