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
Friday, June 8, 2007
Thursday, May 31, 2007
The Wonderous Caterpillar (Science sains)
Caterpillar colors and body shapes are as diverse as the butterflies that they will eventually become. They range from small brown almost maggot-like larvas to huge, fat, alien-like creatures that can reach over 4 inches in length.
The anatomy of a caterpillar is comprised of jointed body segments like that of the common earthworm. They have three sets of legs (true legs) used for walking and also posses fleshly appendages called pro-legs that end in tiny hooks that allow them to grasp the edges of leaves. Like all other butterfly catepillars, beathing is accomplished by intaking air through small openings located between segments of the catepillars body. They have the highest number of muscles in their small body of any animal on the planet. Comparative studies show that humans only have 792 distinct muscles, whereas grasshoppers have 900, and caterpillars may have as many as 4,000 separate muscles.
Most are vegetarians and usually eat only a small number of plants called their host plants where they will later after metamorphosis lay eggs as an adult butterfly if female. Caterpillars are voracious eaters. One species, the Polyphemus larva, also the worlds largest at nearly 4 inches in length, can eat over 86,000 times its body weight in less than 2 months before pupating. They have strong jaws and eat leaves in a top-down fashion usually going from left to right along the leaf edge and working its way down to the stem.
Not the push-overs that they would seem to be adult caterpillars have an arsenal to help protect them from preditors. Some have poisonous spike-like appendages on the top of their segments that when touched produce a irritating toxin that can cause major irritation of the skin when handled. Others rely on the production of toxins built-up from the plants that they consume to dissuade enemies from eating them. The toxins, although not usually fatal, will give pause to birds that are thinking of eating another of the species after their first experience. Members of the swallowtail family have another weapon at their disposal. Theses caterpillars posses two long horn like structures, called an Osmeterium that they can extend from the top of the head that emit a noxious odor that gives the impression to preditors that they will get a very bad taste in their mouth if they try for a quick snack.
Some moths and butterflies remain caterpillars for two or three months, others for about 10 months, hibernating through the winter in this stage. In the Arctic are some forms that require two or three years to develop from egg to adult.
by Tim Willbanks
The anatomy of a caterpillar is comprised of jointed body segments like that of the common earthworm. They have three sets of legs (true legs) used for walking and also posses fleshly appendages called pro-legs that end in tiny hooks that allow them to grasp the edges of leaves. Like all other butterfly catepillars, beathing is accomplished by intaking air through small openings located between segments of the catepillars body. They have the highest number of muscles in their small body of any animal on the planet. Comparative studies show that humans only have 792 distinct muscles, whereas grasshoppers have 900, and caterpillars may have as many as 4,000 separate muscles.
Most are vegetarians and usually eat only a small number of plants called their host plants where they will later after metamorphosis lay eggs as an adult butterfly if female. Caterpillars are voracious eaters. One species, the Polyphemus larva, also the worlds largest at nearly 4 inches in length, can eat over 86,000 times its body weight in less than 2 months before pupating. They have strong jaws and eat leaves in a top-down fashion usually going from left to right along the leaf edge and working its way down to the stem.
Not the push-overs that they would seem to be adult caterpillars have an arsenal to help protect them from preditors. Some have poisonous spike-like appendages on the top of their segments that when touched produce a irritating toxin that can cause major irritation of the skin when handled. Others rely on the production of toxins built-up from the plants that they consume to dissuade enemies from eating them. The toxins, although not usually fatal, will give pause to birds that are thinking of eating another of the species after their first experience. Members of the swallowtail family have another weapon at their disposal. Theses caterpillars posses two long horn like structures, called an Osmeterium that they can extend from the top of the head that emit a noxious odor that gives the impression to preditors that they will get a very bad taste in their mouth if they try for a quick snack.
Some moths and butterflies remain caterpillars for two or three months, others for about 10 months, hibernating through the winter in this stage. In the Arctic are some forms that require two or three years to develop from egg to adult.
by Tim Willbanks
Sunday, May 27, 2007
Sunday, May 20, 2007
Science Definations (science Sains)
Definitions by goal and process:
1. the systematic observation of natural events and conditions in order to discover facts about them and to formulate laws and principles based on these facts.
2. the organized body of knowledge that is derived from such observations and that can be verified or tested by further investigation.
3. any specific branch of this general body of knowledge, such as biology, physics, geology, or astronomy.
Academic Press Dictionary of Science & Technology
Science is an intellectual activity carried on by humans that is designed to discover information about the natural world in which humans live and to discover the ways in which this information can be organized into meaningful patterns. A primary aim of science is to collect facts (data). An ultimate purpose of science is to discern the order that exists between and amongst the various facts.
Dr. Sheldon Gottlieb in a lecture series at the University of South Alabama
Science involves more than the gaining of knowledge. It is the systematic and organized inquiry into the natural world and its phenomena. Science is about gaining a deeper and often useful understanding of the world.
from the Multicultural History of Science page at Vanderbilt University.
Science consists simply of the formulation and testing of hypotheses based on observational evidence; experiments are important where applicable, but their function is merely to simplify observation by imposing controlled conditions.
Robert H. Dott, Jr., and Henry L. Batten, Evolution of the Earth (2nd edition)
Science alone of all the subjects contains within itself the lesson of the danger of belief in the infallibility of the greatest teachers in the preceeding generation . . .As a matter of fact, I can also define science another way: Science is the belief in the ignorance of experts.
Richard Feynman, Nobel-prize-winning physicist,
in The Pleasure of Finding Things Out
as quoted in American Scientist v. 87, p. 462 (1999).
1. the systematic observation of natural events and conditions in order to discover facts about them and to formulate laws and principles based on these facts.
2. the organized body of knowledge that is derived from such observations and that can be verified or tested by further investigation.
3. any specific branch of this general body of knowledge, such as biology, physics, geology, or astronomy.
Academic Press Dictionary of Science & Technology
Science is an intellectual activity carried on by humans that is designed to discover information about the natural world in which humans live and to discover the ways in which this information can be organized into meaningful patterns. A primary aim of science is to collect facts (data). An ultimate purpose of science is to discern the order that exists between and amongst the various facts.
Dr. Sheldon Gottlieb in a lecture series at the University of South Alabama
Science involves more than the gaining of knowledge. It is the systematic and organized inquiry into the natural world and its phenomena. Science is about gaining a deeper and often useful understanding of the world.
from the Multicultural History of Science page at Vanderbilt University.
Science consists simply of the formulation and testing of hypotheses based on observational evidence; experiments are important where applicable, but their function is merely to simplify observation by imposing controlled conditions.
Robert H. Dott, Jr., and Henry L. Batten, Evolution of the Earth (2nd edition)
Science alone of all the subjects contains within itself the lesson of the danger of belief in the infallibility of the greatest teachers in the preceeding generation . . .As a matter of fact, I can also define science another way: Science is the belief in the ignorance of experts.
Richard Feynman, Nobel-prize-winning physicist,
in The Pleasure of Finding Things Out
as quoted in American Scientist v. 87, p. 462 (1999).
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