Saturn's rings are not just beautiful to look at; it turns out they are also responsible for rain falling on the planet.

Using data collected from the Keck Observatory in Hawaii, scientists found that the amount of "ring rain"--when water particles fall from Saturn's rings onto the planet below--is significantly more than previously thought, and may be responsible for the pattern of dark bands or shadows that appear on the planet's surface.

James O'Donoghue, the lead author on the paper which appeared in Nature and a postgraduate researcher at the University of Leicester in England, told Space.com that about "one Olympic-sized swimming pool of water is falling on Saturn per day."

Ring rain is not like regular rain, of course--the water is not coming over in big gushes or even in droplets.

Instead, O'Donoghue surmised that tiny charged water particles are moving from Saturn's rings--which are made up almost entirely of ice--along magnetic pathways between the rings and the planet. Once they hit Saturn, they neutralize glowing triatomic hydrogen ions in the planet's upper atmosphere.

Those areas where the ions are neutralized appear darker than other parts of the planet in infrared images, leaving "shadows" on Saturn in a pattern that mimics the rings themselves.

"It's like a shadow map of the rings has imprinted itself on the planet," said Kevin Baines of the Jet Propulsion Laboratory in La Canada Flintridge, a coauthor on the paper.

"Saturn is the first planet to show significant interaction between its atmosphere and ring system," O'Donoghue said in a statement. "The main effect of ring rain is that it acts to 'quench' the ionosphere of Saturn, severely reducing the electron densities in regions [where] it falls."

The discovery leads to more scientific questions, especially how  ring rain affects the rings. Also: Will the ring rain ultimately lead to the wasting away of Saturn's picturesque rings? And, can further analysis of the rate of ring rain help scientists figure out the age of the rings?

The paper describing the ring rain appeared in the journal Nature this week.

Pakistan Wednesday conducted a successful launch of the Intermediate Range Ballistic Missile Hatf IV Shaheen-1 Weapon System.According to Inter Services Public Relations (ISPR), the missile incorporates series of improvements in range and technical parameters of the existing missile. It is capable of carrying nuclear and conventional warheads to a range of 900 Kms.
Wednesday’s launch, whose impact point was at sea, was witnessed by Director General Strategic Plans Division Lieutenant General (Retired) Khalid Ahmed Kidwai, Chairman NESCOM Mr Muhammad Irfan Burney and other senior military officers, scientists and engineers.
Director General Strategic Plans Division Lieutenant General (Retired) Khalid Ahmed Kidwai congratulated all scientists and engineers on the successful launch. He said that the improved version of Shaheen-1 has consolidated and strengthened Pakistan’s deterrence abilities manifold. He appreciated the efforts of all personnel for their dedication and professionalism.

WASHINGTON: The U.S. Navy is preparing to deploy an experimental laser weapon to the Persian Gulf, where it could be used to deter Iran from using small boats to attack American warships.

Adm. Jonathan Greenert, the U.S. chief of naval operations, on Monday unveiled plans to place the laser cannon aboard a U.S. ship in the Gulf, where swarms of Iranian attack boats have posed a worrisome challenge for the American military.

The $40 million system will be installed aboard the USS Ponce, an amphibious assault ship used in the Gulf for mine clearance and humanitarian operations.

While still in development, the laser system has succeeded in destroying all 12 of its drone and small boat targets in testing, officials said. To bolster its capabilities, the Navy released a video of the laser weapon setting an aerial drone aflame and forcing it to crash into the water.

"It's kind of amazing," Adm. Greenert said in announcing the deployment plans at a convention outside Washington, D.C.

The Laser Weapon System uses directed energy to disable sensors or burn holes through a plane or ship. Because of its limited range, the weapon won't be able to target incoming missiles or jets, but it could be effective in combating Iranian fast boats and any drones the Gulf nation is developing, officials said.

The Pentagon has struggled for years to develop effective laser weapons systems, including ones mounted on planes intended to shoot down missiles. The Naval version, the first of its kind to be dispatched to the field, has more modest ambitions.

Military officials said the Persian Gulf was also an important testing ground because of its harsh physical environment.

"If it can stand up to the weather and rugged nature it can do it anywhere," said one Navy official.

The U.S. military is wary of the threat posed by small attack boats. In 2000, a small boat filled with explosives hit the USS Cole in Yemen, killing 17 sailors.

Last year, a U.S. Navy supply ship opened fire on what was described as a fast-approaching boat off the United Arab Emirates coast. That craft turned out to be an Indian fishing boat, and the shooting killed an Indian fisherman. On Monday, the U.S. Navy cleared the sailors of any wrongdoing in the incident and said that they had acted properly when they opened fire.

The US navy has used a powerful laser cannon to shoot down drone aircraft and will start deploying the weapon on its ships, saying it represents the future of warfare.

"The future is here," said Peter Morrison at the Office of Naval Research's Solid-State Laser Technology Maturation Programme.

The weapon, known as the Laser Weapon System or Laws, has so far only been used to shoot down drones in testing areas but is being billed as a step towards transforming warfare. Since it runs on electricity it can fire as long as there is power at a cost of less than US$1 dollar per shot, says the navy.

"Compare that to the hundreds of thousands of dollars it costs to fire a missile and you can begin to see the merits of this capability," said Rear Admiral Matthew Klunder, chief of naval research.

The prototype, which one official said cost between US$31m and $32m to make, will be installed aboard the USS Ponce, which is being used as a floating base in the Middle East, sometime after October 2013.

Klunder said the navy expected that someday incoming missiles would not be able to "simply outmanoeuvre" a highly accurate laser beam fired at the speed of light.

A report from the Congressional Research Service praised the laser technology but noted drawbacks, including the potential it could accidentally hit satellites or aircraft. Weather also affects lasers.

"Lasers might not work well, or at all, in rain or fog, preventing lasers from being an all-weather solution," it said in a report issued on 14 March.

SINGAPORE: Oil was up in Asia on Monday, buoyed by strong Japanese equities as the market recovered from a downbeat US jobs report, analysts said.

New York's main contract, light sweet crude for delivery in May added 14 cents to $92.84 a barrel and Brent North Sea crude for May delivery increased 32 cents to $104.44.

"The oil market is moving in sync with the Japanese stock market. Oil is also recovering from the selling that came after the US jobs report," Victor Shum, managing director at IHS Purvin and Gertz in Singapore, told AFP.

Tokyo stocks soared three percent in opening trade Monday as the yen plunged further following the Bank of Japan's sweeping monetary easing last week.

Investors are cheering the weakening yen and its obvious impact on future corporate earnings, market players said.

The BoJ on Thursday embarked on a new era of huge spending by releasing a flood of easy money, in its boldest attempt to drag the Japanese economy out of decades of crushing deflation.

But a dismal US jobs report released Friday that fell far short of market expectations continued to weigh on sentiment.

The Labor Department said the United States added just 88,000 jobs in March. The unemployment rate dipped to 7.6 percent from 7.7 percent in February, but only because people dropped out of the workforce.

Shum said the latest rise in oil prices should be viewed with caution "as the latest jobs data indicates that the US economy may be entering a soft patch of slower recovery".

The health of the US economy, which is the world's biggest oil consumer, affects global oil prices. (AFP)

Freezing Mixture: In a freezing mixture like ice and salt, the sa’11 dissolves and lowers the temperature of the solution (acieing a substance to a solvent also lowers the freezing point of the mixture); salt water, for example, freezes below 0°C.During winter season when there is snow fall, salt is spread on the roads. This lowers the freezing point and thus snow does not make ice on the road and the road remains open for safe traffic
An lee cream maker uses a mixture of ice and salt to cool down his ice cream. The salt lowers the freezing point (melting point) and causes more cooling. The temperature is lowered and ice cream is formed easily.
Joule-Kelvin Effect: If a stream of gas is made to flow through a small aperture into a larger container so that its pressure falls, then its temperature usually decreases too. This phenomenon is called the Joule-Kelvin (or Joule-Thomson) effect. It occurs because moving the molecules farther apart requires
energy to overcome the attractive intermolecular forces. The energy comes from the gas molecules themselves and the temperature of the gas therefore falls. If the larger container is not insulated (or if the gas merely expands into normal air, as when using an aerosol spray), then, the gas quickly absorbs heat from its surroundings and warms up again. If, however, the expansion container is very well insulated, so that only negligible amount of heat can enter or leave it, then the expanded gas remains at the lower temperature. This method is widely used to liquefy gases and to produce very low temperatures.
An aerosol spray demonstrates the Joule-Kelvin effect, in which the rapid expansion of a gas through a small jet results in a short fall in temperature. The liquid droplets quickly evaporate, producing a further lowering of temperature. Both effects can be felt when an aerosol is sprayed onto the skin.
.1 rail.
Thus an aerosol spray applied to the forehead of a person with fever causes lowering of body temperature and produces soothing effect.
A pitcher with pores keeps water at a temperature lower than that of the environment or ambient air. Water oozes out of the pores and evaporates. Evaporation requires heat energy. This energy is derived from water itself and thus temperture of the water in pitcher is lowered. The effect keeps the water at lower temperature than that of environmental temperature.
During hot weather we perspire. Sweating followed by evaporation causes lowering of body temperature and cooling. This is a physiological phenomenon to keep human body temperature constant in hot weather.
Dogs do not have sweat glands, so they pant with their drooping tongue. Evaporation from the surface of tongue causes lowering of temperature. This is a physiological phenomenon in dogs to keep body temperature low during hot summer days.

chemical element is characterized and identified by thermodynamical (Z) thermoplastic infrared_protean_Lolita nucleus. As every atom is electrically neutral because it has electrons equal in number to that of protons so Z also equals the number ca. electrons.

The electrons are orbiting around the nucleus. The mass number of an atom (A) is the _sum of number of_protons and neutrons in the _ nucleus (in this way A-Z is the number of neutrons.) Hydrogen has only one proton in its nucleus and only one electron revolving around it, so hydrogen has an atomic number of one and also a mass number of one.

The element helium has an atomic number of 2 and mass number of 4. Thus hydrogen is written as 1111 and helium as 42He. The fissile (undergoing fission reaction) isotope of uranium is 23892U. It has 92 protons, 143 neutrons, and 92 electrons.

inS

Science may be broadly defined as systematic or formulated knowledge of anything. Popularly, however, science means:
“experimentally verifiable knowledge learnt through an intelligent and systematic observation of the universe and the phenomena of nature.”
The word Islam means man’s complete submission to Allah complete submission and obedience to Allah not merely in belief and mode of worship but in ethics and morality, in culture and social behaviour, in politics and law, in economic and social set-up, and in all the individual, national and international affairs of man alike.
Islam is a scientific religion in the sense that it is rational, logical, realistic and practical. There is no room for shirk, superstition and dogma in Islam. Allah’s revealed Book the Quran    makes and appeal to the human intellect and commonsense and its principles, knowledge and wisdom can be tested and verified by means of scientific inquiry. To elucidate this point let us take examples. The Muslims believe in Tauheed (Unity of God or Oneness of God). The Qiiran testifies this truth in 67:3-4 as follows:
“Allah created the seven heavens in harmony. You do not see any incongruity in the creation of the Rahman. Then look again, can you see any flaw? And then look again and yet again, your sight will come back to you confused and fatigued”.
In these Ayat (verses) an open challenge is thrown to mankind to ‘find any inconsistency and disorder in the heavens. Because man finds order and completion in every little detail of the nature; he concludes that the universe must have been created by One Supreme Being Who is All-Powerful and All- Perfect. So this is how the Qiu-an explains the principles of Islam.

Incidentally, the above Ayat also show lhow the study of nature strengthens the beliefs of the religion of Islam.
During the past fourteen centuri s, science has not been able to contradict any of the Quranic prin_ciples. In fact, as science progressed, the truth of Islamic laws is b•eing tested and verified. Let us take a few more examples.
The scientific truth embodied in the following Quranic Ayat have recently been established by miodern science:
51-49 “And of everything We have created pairs that you (0 mankind) may be mindful.”
The nutritional and medicinaa value of honey is recognised by all scientists and it is used as food and medicine for the treatment of many diseases. The Quratn speaks of it in 16 : 68- 69 thus:
“And your Rabb taught the bee too build its cells in hills, on trees, and in mankind’s inhabi tations; then you eat (0 mankind) of all the fruits and fallow the ways of your Rabb made most easy. There is.sues film within their (bee’s) bodies a drink of various colours, there is healing for mankind in this, there is surelw a Sign for those people who think over.”
The organs of all living bodies: contain a very large percentage of water. Moreover, the’ biol_ogists believe that life began in the surface water of oceans. The’ uran says:
“And Allah has created from water every living creature; so of them is that which walks upeon its belly and of them is that which walks on two feet wend of them which walks on four. Allah creates what He pleeases, for He has power over all things.”
Islam not only allows the studly of science but also repeatedly urges and exhorts the mankind to study, ponder over and deduce laws from the phenomena of nature. It may be remembered that the Quran describes thee natural phenomena as the “Signs of Allah” which means that they are manifestations of His attributes and qualities. The best waay of knowing Allah is, therefore, to observe the natural phenomema. The people who pass by the natural phenomena without usinig their eyes, ears and mind are violating the following injunctions of the Quran which say:
17 : 20 “Will they not regard the camels, how they are created! and the heavens, how it is raised! and the hills, how they are set up! and the’ earth, how it is spread!
13 : 3 ,”And Allah has spread out the earth and placed therein firm hills and flowing streams. And fruits of all kinds. He placed therein the male and the female. He covers the night with the day. Lo! herein surely are Signs for people who take thought.”
13 : 4 “And in the earth are neighbouring tracts, yineyards and ploughed land, and date palms alike and unlike which are watered with one water. And We have made some of them to excel others in fruit. Lo! herein, verily, are portents who have sense.”
45 : 13 “And He has made of service to you whatsoever is in the heavens and whatsoever is in the earth. It is all from Him. Lo! herein verily, are Signs for people who reflect.”
After reading these Ayat (verses) nobody can deny that Islam does not require us to become scientists. Doubt and wonder are the two important ingredients of Islamic philosophy, because these lead mankind to conclusive proof which is the hall mark of conviction.
Whenever there is seemingly a clash between religion and science, it is due, first, to the limitations of science and, second, to the glaring fact that Islam, though preserved in the Quran, is presented, to us divorced of its scientific spirit and content. Talking of science, one should not forget that it is based on human experience and that human understanding is imperfect. Man is not omniscient and there are regions, viz: the secrets of the creation of the universe, the Unseen (ghaib), the mystery of the soul, the ultimate destiny of death, life after death, etc. which his reason cannot explore. Moreover, science sometimes relies on theories, presumptions and hypotheses which are ever-changing and are subject to modifications. Atom was considered indivisible but later researches showed that it could be split up into protons, electrons, neutrons, etc. Till 16th century, scientists believed that heavier things came down faster than lighter ones.
The early Muslims whose contribution to science is an unchallengeable fact of history, derived inspiration and received encouragement to make systematic inquiry and experimentation from the Quran. They conducted research and formulated
scientific principles as a part of their faith. Their science was centred round the idea of Allah. They had realized that they could know Allah better by studying. His attributes as manifested in the natural phenomena. This not only helped them to excel in science but also confirmed their belief in the Quranic principles. Since their philosophy of science was sound and true, their investigations brought forth accurate results.
The West learnt the scientific method of inquiry, hitherto unknown, from the Muslims, through Spain (Undlus) and Sicily, etc. In fact Europe was also to bring about the Renaissance under the Christian church and science that followed in the West, finally changed the idea underlying the study of science. Unlike Islam, Christianity opposed free thinking and the church persecuted those who offered new ideas. The scientists, hence, regarded religion as an impediment in the way of free and objective scientific activitie‘4 and opposed and discarded everything offered in the name of religion. Having failed to face the ,facts of science, the church receded into the background or its activities were forcibly suppressed with the result that the concept of God altogether disappeared from the realm of science.
The absence of the idea of God has made science meaningless and a mundane activity. Science discovers order and perfection in nature, but is unable to explain as to whose mind is at work behind every little detail. Rightly did Einstein say that science without religion is lame and that religion without science is blind. The conflict between religion and science originated in the West. Otherwise, in all times, in Islam, the two has always co¬existed and have been complementary to each other.
The Muslims all over the world, made progress in the scientific field only so long as they acted in accordance With the injunctions of the Quran and the Hadith. Soon after the “Khulafa¬e-Rashedeen” materialistic forces began to exert themselves and corrode the foundations of the Islamic social structure. The Muslim society lost touch with tru Islam and fell a prey to exploitation, which gave rise to ignorance and oppression. This deviation of the Muslims from the religion of Islam resulted in their political downfall which deprived them of peace and prosperity and ultimately proved to be the death knell of their scientific and educational activities. The fact to be realised is that it was not Islam which failed to meet the demands of the changing times but that the Muslim society had degenerated as a result of certain vicious tendencies.Science may be broadly defined as systematic or formulated knowledge of anything. Popularly, however, science means:
“experimentally verifiable knowledge learnt through an intelligent and systematic observation of the universe and the phenomena of nature.”
The word Islam means man’s complete submission to Allah complete submission and obedience to Allah not merely in belief and mode of worship but in ethics and morality, in culture and social behaviour, in politics and law, in economic and social set-up, and in all the individual, national and international affairs of man alike.
Islam is a scientific religion in the sense that it is rational, logical, realistic and practical. There is no room for shirk, superstition and dogma in Islam. Allah’s revealed Book the Quran    makes and appeal to the human intellect and commonsense and its principles, knowledge and wisdom can be tested and verified by means of scientific inquiry. To elucidate this point let us take examples. The Muslims believe in Tauheed (Unity of God or Oneness of God). The Qiiran testifies this truth in 67:3-4 as follows:
“Allah created the seven heavens in harmony. You do not see any incongruity in the creation of the Rahman. Then look again, can you see any flaw? And then look again and yet again, your sight will come back to you confused and fatigued”.
In these Ayat (verses) an open challenge is thrown to mankind to ‘find any inconsistency and disorder in the heavens. Because man finds order and completion in every little detail of the nature; he concludes that the universe must have been created by One Supreme Being Who is All-Powerful and All- Perfect. So this is how the Qiu-an explains the principles of Islam.

Incidentally, the above Ayat also show lhow the study of nature strengthens the beliefs of the religion of Islam.
During the past fourteen centuri s, science has not been able to contradict any of the Quranic prin_ciples. In fact, as science progressed, the truth of Islamic laws is b•eing tested and verified. Let us take a few more examples.
The scientific truth embodied in the following Quranic Ayat have recently been established by miodern science:
51-49 “And of everything We have created pairs that you (0 mankind) may be mindful.”
The nutritional and medicinaa value of honey is recognised by all scientists and it is used as food and medicine for the treatment of many diseases. The Quratn speaks of it in 16 : 68- 69 thus:
“And your Rabb taught the bee too build its cells in hills, on trees, and in mankind’s inhabi tations; then you eat (0 mankind) of all the fruits and fallow the ways of your Rabb made most easy. There is.sues film within their (bee’s) bodies a drink of various colours, there is healing for mankind in this, there is surelw a Sign for those people who think over.”
The organs of all living bodies: contain a very large percentage of water. Moreover, the’ biol_ogists believe that life began in the surface water of oceans. The’ uran says:
“And Allah has created from water every living creature; so of them is that which walks upeon its belly and of them is that which walks on two feet wend of them which walks on four. Allah creates what He pleeases, for He has power over all things.”
Islam not only allows the studly of science but also repeatedly urges and exhorts the mankind to study, ponder over and deduce laws from the phenomena of nature. It may be remembered that the Quran describes thee natural phenomena as the “Signs of Allah” which means that they are manifestations of His attributes and qualities. The best waay of knowing Allah is, therefore, to observe the natural phenomema. The people who pass by the natural phenomena without usinig their eyes, ears and mind are violating the following injunctions of the Quran which say:
17 : 20 “Will they not regard the camels, how they are created! and the heavens, how it is raised! and the hills, how they are set up! and the’ earth, how it is spread!
13 : 3 ,”And Allah has spread out the earth and placed therein firm hills and flowing streams. And fruits of all kinds. He placed therein the male and the female. He covers the night with the day. Lo! herein surely are Signs for people who take thought.”
13 : 4 “And in the earth are neighbouring tracts, yineyards and ploughed land, and date palms alike and unlike which are watered with one water. And We have made some of them to excel others in fruit. Lo! herein, verily, are portents who have sense.”
45 : 13 “And He has made of service to you whatsoever is in the heavens and whatsoever is in the earth. It is all from Him. Lo! herein verily, are Signs for people who reflect.”
After reading these Ayat (verses) nobody can deny that Islam does not require us to become scientists. Doubt and wonder are the two important ingredients of Islamic philosophy, because these lead mankind to conclusive proof which is the hall mark of conviction.
Whenever there is seemingly a clash between religion and science, it is due, first, to the limitations of science and, second, to the glaring fact that Islam, though preserved in the Quran, is presented, to us divorced of its scientific spirit and content. Talking of science, one should not forget that it is based on human experience and that human understanding is imperfect. Man is not omniscient and there are regions, viz: the secrets of the creation of the universe, the Unseen (ghaib), the mystery of the soul, the ultimate destiny of death, life after death, etc. which his reason cannot explore. Moreover, science sometimes relies on theories, presumptions and hypotheses which are ever-changing and are subject to modifications.

Atom was considered indivisible but later researches showed that it could be split up into protons, electrons, neutrons, etc. Till 16th century, scientists believed that heavier things came down faster than lighter ones.
The early Muslims whose contribution to science is an unchallengeable fact of history, derived inspiration and received encouragement to make systematic inquiry and experimentation from the Quran. They conducted research and formulated
scientific principles as a part of their faith. Their science was centred round the idea of Allah. They had realized that they could know Allah better by studying. His attributes as manifested in the natural phenomena. This not only helped them to excel in science but also confirmed their belief in the Quranic principles. Since their philosophy of science was sound and true, their investigations brought forth accurate results.
The West learnt the scientific method of inquiry, hitherto unknown, from the Muslims, through Spain (Undlus) and Sicily, etc. In fact Europe was also to bring about the Renaissance under the Christian church and science that followed in the West, finally changed the idea underlying the study of science. Unlike Islam, Christianity opposed free thinking and the church persecuted those who offered new ideas. The scientists, hence, regarded religion as an impediment in the way of free and objective scientific activitie‘4 and opposed and discarded everything offered in the name of religion. Having failed to face the ,facts of science, the church receded into the background or its activities were forcibly suppressed with the result that the concept of God altogether disappeared from the realm of science.
The absence of the idea of God has made science meaningless and a mundane activity. Science discovers order and perfection in nature, but is unable to explain as to whose mind is at work behind every little detail. Rightly did Einstein say that science without religion is lame and that religion without science is blind.

The conflict between religion and science originated in the West. Otherwise, in all times, in Islam, the two has always co¬existed and have been complementary to each other.
The Muslims all over the world, made progress in the scientific field only so long as they acted in accordance With the injunctions of the Quran and the Hadith. Soon after the “Khulafa¬e-Rashedeen” materialistic forces began to exert themselves and corrode the foundations of the Islamic social structure. The Muslim society lost touch with tru Islam and fell a prey to exploitation, which gave rise to ignorance and oppression. This deviation of the Muslims from the religion of Islam resulted in their political downfall which deprived them of peace and prosperity and ultimately proved to be the death knell of their scientific and educational activities. The fact to be realised is that it was not Islam which failed to meet the demands of the changing times but that the Muslim society had degenerated as a result of certain By reviving the pristine glory of Islam and infusing its scientific spirit into the study of science, Muslims always lead the world. By Allah’s grace, the Muslims all over the, world, have again clung and are rapidly clinging to the cord of Allah, and are making great progress in the field of science.
To sum up, Islam is the only religion that recommends research, discoveries and stupendous progress of science. It claims that more the scientific knowledge expands, the more are we constrained to admit the truth of the Quranic revelations and the confess that Islam is the only true religion of mankind and, indeed, the more astounding its achievements, the more do we and more than the layman, the scientists, stand in awe of Allah Who created the vast universe. And the more do we acknowledge as divine that Book which draws our attention to material truths which modern science is beginning to prove to us only today.
vicious tendencies.

Evolution of Stars: Stars are believed to be born in groups from the collapse of large, cold clouds of interstellar material composed chiefly of hydrogen gas. Whenever the mass of such a cloud exceeds the Jeans mass (named after the British astrophysicist James Jeans), the gravitational force within it is greater than any outward thermal pressure and causes the cloud to collapse.
Protestors: If the Jeans mass of a cloud is equal to many solar masses, the collapse of the cloud leads to the formation of the same number of stars as there are solar masses, each star having approximately one solar mass. These stars are then part of a star cluster. As the whole cloud collapses, regions within it undergo their own localized contraction in a process called fragmentation.

The temperature of these regions starts to rise because their density is so high that heat cannot escape. Eventually, the temperature rises far enough for outward thermal prmaire to halt the collapse of the localized regions and hammentaion ends. These now stable, non-collapsing regions of
(111ir;ily and temperature are called protostars.
Thv next stage in the evolution of a star depends on its mass. lithe mass of the protostar is similar to that of the sun, collapse of cloud leads to a hot central region. This core contracts to form the nucleus of the future star. The outer region draws closer to the nucleus. About 60 million years after the start of collapse, the temperature become very high and nuclear fusion reactions begin which then become source of energy of the star for next many million years.
If the mass of the protostar is more than one solar mass, the initial nucleus expands quickly, and thermonuclear reactions begin much more rapidly.

As a result nucleus becomes very bright and radiation pressure prevents outer part from moving inward. Thus only one-third of the initial mass burns by hydrogen conversion. The corresponding stages of a star of 10 solar masses may last only 200,000 years.
Main-Sequence Stars and Supergiants: When the hydrogen burning reactions begin in a newly-born star, the star is at the Zero-Age Main Sequence (ZAMS) stage. A star of one solar mass burns its hydrogen for about 10 billion years and for this remains on the main sequence.

According to this analysis, the sun, which is about 4.6 billion years old is a middle aged star.
As the hydrogen fuel is used up in a star’s core, its energy production decreases and the core slowly collapses. The unburnt hydrogen in the shell outside the helium-filled core is gradually converted to helium. When this process continues the core starts contracting under its own weight and weight of outer layers. The core contracts rapidly and the surrounding envelope expands. Now the star becomes a Red Jiant. Over period of a few tens of million of years the star grow to an enormous size, very luminous but relatively cold red giant. Our sun will reach this stage after 5 million years from now.

It will expand about 48-64 million km to reach the planet Mercury. The earth’s temperature will rise so drastically that life will cease to exist.
White Dwarf: A star may remain giant or supergiant for several million years before all its nuclear fuel exhausts. Gravitation collapse will change it into a white dwarf. Such a star is small (like the size of earth) but very dense (1 million times than water). If the core of such a star has a final mass at this time of less than 1.4 solar masses, then the collapse stops at white dwarf stage. With the passage of time, the remaining heat will be radiated away, so that the star eventually becomes a black dwarf.
Stars from four to eight solar masses become red supergiant and eventually explode in a supernova explosion. After the75
supernova explosion the remaining mass of the star becomes so condensed that electrons combine with protons to form neutrons. As the matter consists mostly of neutrons, the object is called a neutron star. If condensation continues then the star becomes a black hole.
Pulsar: Pulsar is a neutron star which produces regular pulses of electromagnetic radiation. The pulses are very short and are produced by the effect of magnetic field of the object. The light looks like that of a light house beam.

Nova: The sudden increase in the brightness of a star, probably as a result of its interaction with another, very close star, forming a binary system.

The brightness increase is due to the blowing off of a large amount of hydrogen gas from the star’s surface, the star probably being a white dwarf.

Supernova: The sudden, temporary and enormous increase in brightness of a star resulting from the blowing off of most of its constituent material in its death throes.

Such an event occurs for stars only about six times more massive than the sun, the result being a white dwarf.

The age of the universe has been estimated from the pace of the receding galaxies and the theory of big bang. How does one prove that something was hot many thousand million years ago? Well, how can you tell if there has been a fire in a fireplace recently? Coals that glow red hot indicate there has been a fire not too long ago. Coals that are dull orange suggest that more time has passed since the flame died down. The duller the glow, the longer the time interval. Even if the coals were not glowing, one could feel heat. A physicist would speak of detecting the radiation emitted by the coals as they cooled of. A glow would mean that the radiation being emitted was ordinary visible light. Heat alone would mean that now the radiation was infrared rather than visible.
The radiation emitted by the big bang is no longer even in the infrared, but consists of microwaves. IA, 1964-65, two physicists at the Bell Laboratories in New Jersey,-Arno Penzias and Robert. Wilson, first detected the radiation, left by the big bang. Other scientists also got similar results.
On the basis of these kind of experiments the estimated age of the universe starting from big bang has been found to be between 10 and 20 billion years. Or on the average it is 15 billion years (15 x 10-9).
RED SHIFT
Q.    What is red shift and what is its significance in determining behaviour of galaxies?
Ans.
Red shift is the observed shift of the characteristic spectral lines of (for example of a galaxy or a star) toward the red, longer wavelength, end of the spectrum as a result of the galaxy’s recession from us.
The movement of stars is revealed by the Doppler shift of their spectral lines. When a star moves toward the earth in its orbit, its spectral lines shift toward the blue end of the spectrvm. As the star reaches a point where it is neither approaching nor receding, the spectral lines remain in their current normal position. Continuing on its orbit, when the star moves away from the earth the spectral lines shift toward the red end of the spectrum.
Similarly the movements of a galaxy — whether it is rotating and whether it is approaching the earth or receding — are revealed by its spectrum. The farther a galaxy is from the earth, the faster it appears to recede (as described by Hubble’s law).
Doppler effect is demonstrated in the spectral shift of galaxies. The wavelength of light emitted by a receding source becomes redder as it lengthens. The wavelength of an approaching source of light becomes shorter and is seen to shift toward the blue end of the spectrum.

AIDS, the Acquired Immune Deficiency Syndrome, is the result of infection by a virus known as HIV (Human Immunodeficiency Virus), which was formerly called HTLV (111).
History
The disease seems to have spread to man in Africa and then to the rest of the world via Haiti. It was fast recognised in 1981 and is now reaching epidemic proportions. By 1991, more than 200,000 cases in over 150 countries had been reported. Contact with the virus, which is spread primarily by blood and semen, may result in–
(1)    The disease AIDS. The virus damages the T- lymphocytes which play an important part in the normal defence system. As a result the normal immune response is suppressed so that the AIDS victim is affected by illnesses which are usually quite rare e.g. Karposi sarcoma, rare lymphomas and lung infections (pneumocystis penumonia). Lethargy, weight loss and glandular swelling may herald its onset. As yet there is no effective vaccine and the mortality rate is over 50%. However, drugs such as Zidovudine (AZT) may help some patients and delay the progression of the disease. Trials are still continuing.
(2)    A carry state. Such people have antibodies to the AIDS virus and may transmit it to others but they themselves seem perfectly well.
It is much more difficult to estimate the percentage of people carrying the virus in the general population (perhaps up to 10 million or more worldwide). Nor is it certain how many of those with AIDS antibodies will eventually develop the disease. Recent evidence suggests approximately 30% will do so over a 5 year period.
The virus is transmitted as follows:–
(a)    By sexual intercourse with an infected person; penetrative anal intercourse seems to carry the greatest risk especially to the recipient partner. In Europe and USA, therefore, the majority of victims have been homosexual males.
(b)    By contaminated blood products and equipment. Drug
abusers -Who share hypodermic needles are another high risk category. Many haemophiliacs were the unfortunate victims of the first onslaught of the disease. This was because they received contaminated factor V111, which had been concentrated from the serum of many donors. However, proper screening and testing has now brought this problem under control.
(c)    From mother to child via the placenta.
It is a matter of grave concern that the drug menace is plaguing the whole world and thus making the younger generation totally unproductive, dependent and deviant. Coupled with this grave problem, the AIDS menace is also on the increase. People are infected with AIDS through several sources and one major source is the use of syringes for injecting drugs by drug addicts. If the syringes are contaminated there is every chance of a person becoming an AIDS victim.
In a global survey which was conducted on the problems of AIDS in the year 1992, it was estimated that almost 10 per cent of AIDS victims were drug addicts who used syringes to inject drugs into their bodies. In Thailand, in the year 1990, there were more than 50,000 ADDS victims and out of them 50 per cent were drug addicts. Hence, it is evident that drug abuse and AIDS go together, thus giving rise to more health problems which will have serious effects on the population.
More than 14,000 people attended the 9th International Conference on AIDS, which opened in Berlin, June, 7, 1993. Reports indicated that the number of people infected with the AIDS virus continued to rise worldwide, with especially sharp increases in Africa and Southeast Asia. Confirming a report first published in April, scientists said, June 8, that the antiviral drug AZT provided no long-term benefit in delaying the onset of symptoms and the death of AIDS patients. A research team headed by Dr. Jonas Salk said, June 9, that use of an experimental AIDS vaccine, on which much hope had been focused, had not slowed the course of the disease or lessened its severity.
It is a matter of grave concern that the drug menace is plaguing the whole world and thus making the younger generation totally unproductive, dependent and deviant. Coupled with this grave problem, the AIDS menace is also on the increase. People are infected with ADDS through several sources and one

major source is the use of syringes for injecting drugs by drug addicts. If the syringes are contaminated there is every chance of a person becoming an AIDS victim.
Acquired Immune Deficiency Syndrome (AIDS) is probably the most acknowledged health problem in the world today. Concern with AIDS is due to a number of unique features. Among these features are the long period which elapses between infection with the cause of AIDS, the Human Immunodeficiency Virus (HIV) and the possibility of detecting the infection; the permanence of such infection; the potentially explosive rates of growth in prevalence of HIV infection among vulnerable populations; the near 100 per cent mortality rate; the concentration of AIDS in the most productive age groups; and the fact that the forms of behaviour which. spread AIDS, namely, intravenous abuse of illicit drugs, are extremely difficult to change.
Intravenous drug abuse and promiscuous sexual behaviour are two of the main sources of HIV transmission. Drug abuse and dangerous sexual practices are closely linked. Those whose life styles are associated with drug abuse, of any kind, are also more prone to engage in the kinds of sexual behaviour which are most conducive to HIV transmission. There is, for instance, a high correlation between alcohol use and dangerous sexual practices and this is a major reason why alcohol cannot logically be excluded from policies which are concerned with both drug abuse and AIDS.
AIDS awareness has to be integrated with drug abuse awareness programmes so that people are aware of the consequences of AIDS. While planning awareness programmes on ADDS the target groups have to be families of drug addicts, cured addicts and general population with special extphasis on the young generation in the crucial age group of 15-25 years.
There is now preponderant evidence to suggest that over the years the proportion of drug users, who have developed AIDS has increased dramatically, with the result that at present the global AIDS epidemic is threatening to soar out of control, not only because of complacency, but also due to lack of coordination in national and international efforts to fight the disease.
It is now an established fact that developing an effective vaccine to prevent the spread of the fatal disease is expected to take long time, and until a vaccine is developed, the only means

to prevent the spread of ADDS is through behavioural change. It is, therefore, crucial that effective AIDS prevention programmes on such lines be initiated throughout the world to prevent further spread of HIV in high-prevalence areas and to prevent initial spread in low-prevalence areas of the world.
It is also a fact, universally acknowledged, that drug abusing behaviours, most specifically the use of needle, are among those behaviours, that have proved difficult to modify because drug dependence is a chronic mental disorder and not a temporary condition. Overcoming drug dependence always requires an extensive lifestyle change and a long-term abstinence which is difficult to achieve without help. Even IV drug abusers required repeated and prolonged treatment to overcome drug dependence. Short of abstinence from drugs, behaviour change to reduce the risk of HIV transmission is also difficult to achieve. However, the only redeeming feature in the present situation is the fact that IV drug abusers are generally concerned about their risk for AIDS and many are also taking steps to reduce their risks. It is also quite apparent that risk reduction efforts by drug abusers are often incomplete and inconsistently applied and many such drug abusers continue to regularly engage in high risk behaviours. Considering the urgency of this need, it is essential that AIDS prevention initiatives be designed for maximum effectiveness, all over the world.
The NGO’s from all parts of our country, working for betterment of drug addicts must include AIDS information as an integral component for awareness programmes.
Experiences with other behaviours, such as dietary modification, smoking cessation and performance of regular exercise have shown that both the initiative and maintenance of behavioural change can be successfully achieved within the context of the target group’s enviranment. In fact, community prevention approaches are largely designed for specific target groups, and are mostly delivered by individuals and organisations that have credibility and are also trusted within the target groups, and in corporate social support within the community to reinforce behavioural change. Thus, rather relying on a single intervention strategy, community prevention approach are multiple sources to encourage, support and reinforce change. Based on the success of community prevention in changing selected healthy behaviours, this approach provides possible models for designing programmes to prevent the spread of AIDS

prevention of 11W all over the world.
In fact, preventing the AIDS epidemic associated with IV drug abuse requires a broad programme that includes multiple strategies. The effort must include interventions designed to alter high risk behaviours among IV drug abusers and to educates the public about the infection so that when a vaccine becomes available mechanisms are in place to reach those who are in the greatest need.
Risk-reduction programming also needs to extend beyond medical and drug abusers who are not in treatment. It is quite apparent that AIDS prevention programmes should separate components that disseminate information from those that are designed to change behaviours. Each of these approaches addresses different objectives but they are also interdependent, one approach reinforcing the other.
For the first approach, factual information about infection with the IIW and AIDS is provided through one or more channels, such as electronic media, written materials or information sessions. For some people information dissemination is sufficient to alter attitudes and behaviours. Usually, these are individuals who hold values and beliefs that are compatible with the message being transmitted to them. The social networks of these individuals also support these individuals also support these messages and the associated behaviours, therefore, change. In most cases, those most readily affected by media messages are highly educated and mainstream members of the society.
For harder-to-reach populations, particularly those not in the mainstream of the society, such as addicted, needle using persons, additional strategies are necessary. These parameters include perceptions of AIDS, its transmission, and its relative importance in the lives of the population, as well as existing levels of involvement in high risk behaviours.
However, we will have no hope of saving those who are drug addicts today or our children tomorrow if we don’t do something to prevent death from AIDS.

Stars: A star is a body, such as the sari, that produces energy by means of nuclear reactions taking place within it. The star is held in a stable state by .balancing the outward adiation pressure by the inward gravitational force.
Difference between stars and planets: Stars and planets
SOLAR SYSTEM
How many planets and moons are there in the solar system? How the planets move?
Ans.
Solar System: There are nine planets in the solar system, the sun being at the centre of the solar system and the planets revolving around the sun. Up till now 67 satellites (moons) of the planets have been discovered. The solar system also contains asteroids, meteors and visiting comets. Starting from the sun the planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.
Virtually all the different theories about the formation of the solar system agree on two facts. One is the age of the solar system — about 4.5 billion years. This age is determined from examination of certain types of meteorites. Particular radioactive elements like uranium and thorium decay into element lead with the passage of time. The scientist can deduce the age of the material by comparing the relative amount of the element decaying and the elements formed by decay:
The second point of agreement is that the planets were formed from gas and dust, in the vicinity of the sun. Opinions vary on the origin of this material, ranging from gaseous rings thrown off by the sun to matter pulled from a passing star by the sun’s gravity. The gas and dust seem to have condensed into tiny bodies, or planetesimals, which eventually built up the planetary system we know today. This formative sequence would explain the presence of asteroids, which are, planetesimals (tiny planets) that never accreted (grew) into a planet, possibly because of the gravitational influence of the giant planet Jupiter.
Motion of the Planets: The planets. perform two types of motions; one called rotation on their axis and the second revolution or the orbital motion along their orbits around the sun. The orbits of the inner planets are almost circular but the orbits of the outer planets are highly. elliptical. All the planets except Mercury and Pluto orbit the sun in more or less the plane of elliptic which means that planet remain in one plane not many planes.
It is accepted that most of the planets in the solar system have, or have had, rotation periods of about 10 hours. Both Jupiter and Saturn maintain this average. Other planets have47
changed their period by gravitational interference. The effects of moon’s gravity have contributed greatly toward the lengthening of the day of the earth from 10 hours (that it was originally) to the present 24 hours.

Neptune is the outermost of the four giant planets (Jupiter, Saturn, Uranus) and is called a twin of Uranus due to their similarity of size, mass and composition. It was discovered in 1848, surprisingly not by observation through a telescope but by theoretical prediction of the position (mathematically), keeping in, view the principle of celestial mechanics and disturbances it was causing in the path of Uranus. The mean distance of the planet from the sun is 4.5 billion kilometres (4.497 x 109 km). The period of rotation is 16.1 hour and that of revolution around the sun is 164.8 years. The diameter of the planet is 49100 kin, density is 1.6 times that of water and mass is 17.2 times that of the earth. The temperature of the planet at cloud top is —200°C. Neptune is denser than Uranus but both are composed primarily of hydrogen and helium. Through a telescope, Neptune appears as tiny greenish disc. Great Da,* Spot: Voyager cameras discovered the huge stormy vortex in the atmosphere of Neptune. Other turbulences discovered in the planet’s atmosphere are a small dark spot and a fast moving white spot nicknamed the Scooter. The Great Dark Spot is of the size of earth and is a countercyclone. It is a high pressure system and changes shape as it contracts and relaxes. Winds present in the atmosphere of the planet are deflected by the storm. Neptune’s observed temperature is 60K (-214°C) and is closer to that of Uranus, although Neptune is 1.6 billion kilometres farther from sun than Uranus. This shows that Neptune (like Jupiter and Saturn) has an internal source of energy. Neptune’s deep atmosphere is composed mainly of hydrogen with 15 percent helium. Methane is also present perhaps 2% with small amount of ethane. Neptune’s interior is thought to be formed of rocks and ice. The riiost fascinating character of N ptune is its blue colour which results from light being filtered though a veil of methane. Voyager discovered 3 prominent charcoal dark rings of Nept:une. The ring particles are darker than charcoal and are difficult to image as Neptune receives only one thousandth as rnucn solar radiation as the earth receives. Before Voyager 2 mission only 2 moons of Neptune were known. Voyager discovered six more small moons of Neptune. Most astonishing features were observed on Triton (Neptune’s largest moon). It revolves 354,800 km from Neptune. Triton has a thin atmosphere and a magnetic field. Triton’s tortured surface appeared to have craters, smooth plains and vast ice basins. Farthest Planet: Pluto (along most of its orbit) is the planet farthest from the sun. But Pluto’s path is not rounded but stretched out elliptical. At its closest approach it is 2.74 billion miles away from the sun, but at its farthest it is 4.57 billion miles distant. As a result of Pluto’s eccentric orbit, Neptune becomes farthest planet, whenever Pluto’s path crosses inside Neptune’s. From 1979 to 1999 Neptune is the farthest planet. Then for the next 228 years Pluto will be the farthest planet.

The present rate of literacy is estimated at 36.8 % which was the lowest amongst the developing countries . The proportion of primary enrolment was 70.8 % . Out of this the proportion of boys was.86.2 % while of girls it was 54.9 %. In 1992 — 93 Rs 29.9 billion were spent on education while Rs 34.8 billion were spent on education which are 2.2 % of GNP. In the coming days, such ratio will be enhanced to 3%. Under SAP, attention will be paid to enhance primary education, particularly amongst girls .
After coming into power, Benazir Bhotto took steps to promote privatisation de-regulation, and market friendly atmosphere. Again, the concept of Public-Private Partnership was put forward whereby the private sector will be made capable enough to ply its role in Social Sector Development and Labor-Intensive Industrial Development. The process of privatisation will be made transparent, rapid and in accordance with the principle whereby the general public could take part in it and purchase the units privatised.
In order to promote domestic and foreign investments so many steps were taken and different controls on investment were abolished. Board of Investment was set up by merging National Investment Council, Pakistan, Investment Board and Investment Council. Different Funds were set up at world level with the view of raising investment in Pakistan like emerging markets. These Funds are financed by Citi Bank an a French Bank working in Hong Kong. The Asian Development Bank (ADB) with the assistance of Morgan, Stainly established 'Pakistan Investment Fund' which was listed in New York Exchange Market. Different steps were made to reduce unproductive expenditures so that the size of fiscal deficits could come down. Again, emphasis was laid upon reducing imports and increasing imports. Following such steps the performance of the economy during 1995 — 96 remained as :
1.    In 1994 — 95, the GDP growth rate was 4.4% which went to 6.1% in 1995
— 96. The cotton production was 10.6 million bales. Growth rate in manufacturing sector was 2.9% which went to 4.8% in 1995 — 96.
2. In 1995— 96, govt. revenues were estimated at Rs. 386.5 billion while the expenditures were projected at Rs. 495 billion with the budget deficit of Rs.108.5 billion. Such deficit was 5% of the GDP. In 1994 — 95, inflation rate was 10.81% on the basis of CPI, while it decreased to 9.77% in 1995 96.
3 In January, 1996 domestic population was estimated at 131.63 million and the population growth rate was 2.8%. Labor force was estimated at .31.70 million out of which the employed labor force was 34.92 million. Hence the unemployment rate was 4.84%. The literacy rate in the country was 37.9%, out of which male literacy rate was 50% while female literacy rate was 25.3%. Urban literacy rate was 58.3% and the rural literacy rate was 28.3%. Expenditures on education remained 2.5% of GNP
4. The deficit in BOP could not be decreased as exports could not be increased to the desirable extent while imports went on rising. Moreover, govt. liberal import policy remained operative whereby the maximum tariff rate was decreased to 65% from 70%. During the period of 1995 — 96, foreign aid worth $3243 became available.

Conductor is a substance that readily permits the passage of heat, electricity (electric current) or charge.
Metals are good conductors of heat and electric current. Metals have free 'electrons which can carry electric current. Gold, silver, copper, aluminum and tin are good conductors. Silver is the best conductor. Copper is used in electrical wires. Similarly aluminum is used in high voltage transmission because it is very light weight. Metals are also used to make utensils for cooking because they are good constructors of heat.

(ii) Resistor
Resistor is defined as as substance that resist the flow of electric current. All conductors have at least some resistance. The resistance of a resistor is measured in ohms. All conductors, however, do not obey Ohm's law. For example the .filament in an ordinary light bulb heats up when electric current passes through it. Heating causes an increase in resistance. The resistance of a piece of material. depends on its composition and its Size. For example, the resistance of a wire depends on its composition, length, and thickness. A thick, short wire has a lower resistance (and carries more current for a given potential difference) than a long thin wire Nichrome is a high resistance alloy used in irons, and heaters. Similarly other kinds of resisters are used in heaters.
Semi-conductor:
Semi-conductor is a substance, such as silicon, whose electrical resistance decreases as its temperature increases, unlike normal conductors. These are widely used in electronics as their electrical properties can be finely controlled by including small aniounts of impurities.
Semi-conductors have electrical resistance which lies between that of conductors and insulators. They have a few free electrons that can drift from atom to atom --- unlike conductors, which have many free electrons, and unlike insulators, which have none.
The semi-conductors used in electric devices are 'doped' to change their electrical properties. Doping involves introducing minute traces of other elements into the semi-conductor's crystal lattice. Silicon and germanium each have four outer electrons per atom; doping them with an element with five outer electrons, such as phosphorus, frees the fifth electron so that the semi¬conductor has an electron excess. It is then known as an r-type (negative type); because electrons, have a negative charge.
Thermisior:
Therinistor is a thermally sensitive resistor whose resistance falls -4-apidly with temperature. Thermistors are made from semi-conducting material and are used for measuring small temperature changes (as little as 0.005 °C) controlling output voltage or current, and in compensating systems which normally have positive temperature coefficients to prevent over heating. These are usually thermal sensors. -

It is a nuclear reaction in which the nuclei of a heavy fissile element breaks apart, each producing two smaller nuclei, neutrons and a large amount of energy (nuclear/atomic energy). Nuclear fission is the basis of energy released by an atomic bomb or the energy used at nuclear thermal power stations for generation of electricity.
Nuclear fission is caused when a nucleus is bombarded with high-velocity neutrons. In the best known example, uranium is struck by neutrons, and each uranium nucleus splits into two roughly equal parts, a process accompanied by the release of two or three neutrons and a huge amount of energy.
Above a certain critical mass of such a fissile material (such as U-235), it is possible to ensure that there is always at least one neutron produced by each transformation capable of disrupting another nucleus, and so on in a chain reation. If this is allowed to run away, out of control, the result is a nuclear explosion of vast power; this is the basis of the nuclear bomb. But if the chain reaction is moderated and controlled, the enormous energy produced by the fission process can, for example, be used to heat water and produce steam to drive turbines and then generate electricity. This is the way in which a nuclear power station works.
Fusion Process:
Nuclear fusion is a nuclear reaction in which the nuclei of light elements are forced together to produce the nucleus of a heavier element with the release of a huge amount of energy.
By fusion together the nuclei of two elements, it is possible to form a new nucleus whose mass is slightly less than the original ones. The 'lost' mass appears as energy according to Einstein's relation E=mc2. To be able to fuse, the two nuclei must have sufficient energy to overcome the electrostatic repulsion resulting from their charges. Such energy can be provided only by • temperatures of hundred of millions of degrees. In the stars, however, such temperatures are commonplace, and the fusion of hydrogen to produce helium keeps them shining for thousands of millions of years.
Scientists on the earth have already demonstrated the uncontrolled power of nuclear fusion in the hydrogen bomb. By
contrast, one area of active research in practical nuclear physics is concerned with finding a method of conrtrolling fusion, so that it can be used productively to generate electricity.
Source of Solar Energy:
Our sun is like other stars and produces energy by nuclear reactions. A huge amount of energy is released by the sun in the form of electromagnetic radiation and solar wind. The principle source of solar energy is the fusion reactions going on in the sun. The mass of the sun mainly consists of hydrogen which undergoes nuclear fusion at high temperature.

Exocrine glands are the glands which don't pour their secretions directly into blood (like endocrine glands) but into a duct. These are the glands with ducts and the effect of their secretions is not generalized on all tissios of the body but localized.
Salivary glands, exocrine pancreas, lacrimal, bile producing cells 'of liver and secretory cells of stomach and intestine are the examples of exocrine glands.
Exocrine Pancreas:
Pancreas secrete pancreatic juice which contain a large number of digestive enzymes. Pancreatic juice goes to the .intestine through a pancreatic duct and perform function of digestion inside the intestine.
llfammary Glands:
Mammary glands are also exocrine glands which secrete milk or colostrum. Milk is collected by a series of ducts and secreted outside the body.
Saliva!), Glands: Salivary glands are present inside the jaw. These secrete saliva which comes to the mouth (oral cavity) through salivary duct. Saliva is responsible for lubrication food and early digestion of starch.
Lacrimal:
Lacrimal or lachrymal is the gland which is present in the eye. its secretion the lachrymal secretion form tears. Lachrymal secretion washes the eye and the lysozyme enzyme present in this secretion kill bacteria to protect eye.

The earth revolves around the sun and the moon revolves around the earth. The moon shines due to reflected light of the sun. During this motion when the moon comes between the earth and the sun in such a way that the sun (while seen from the earth) is partially or completely obscured and the rays coming from the sun are hampered by the moon a solar eclipse is caused. Total obscuration is total eclipse while partial obscuration is partial eclipse.

This happen with the new moon when the moon is in conjunction with the sun. This does not happen at every new moon because of the inclination of the orbit of the "noon to the orbit of earth around the sun.

Many great Muslim physicists made • extremely commendable and valuable achievements during the 10th century A.D. These scientists were Al-Beruni. (973-1048), Al-Razi (864- 930), Abu Ali-Ibn Sina (980-1037), Ibn-al-Haitham (965-1039) and Abul Wafa Muhammad Al-Buzjani (940-997). These scientists added extensively to the knowledge of physics.
Abul Wafa worked in the field of trignometry and mathematics and made new discoveries. He developed a new method for constructing sine tables. He investigated movements of moon. He was born in Buzjan (Iran) but migrated to Baghdad in
959.
Ibn-al-Haitham was one of the greatest physicists of all times (Abdus Salam). His masterpiece was his book "Kitab-ul¬Marir" The book deals with optics (a branch of physics) in which he criticized the theories of big philosophers like Ptolemy and Euclid about the nature of light. He described the nature of light and declared it as a form of energy. He 'gave the formal definition of a ray of light. He constructed .a pinhole camera and managed to obtain an image of a "solar eclipse" with his camera. He was the first scientist to give the world two laws of reflection of light. He also carried out research on the formation of image using spherical mirrors. He described luminous, non-luminous, opaque and transparent objects.
Another discovery by his was principle of least time, now called the Fermate principle of least time. According to this principle a ray of light passing through a medium always adopts a path which takes the least time to traverse. He discussed theories of attraction between masses:
-AI-Beruni wrote more than one huncired and fifty books. Al-Beruni determined the radius of the earth as 3938 miles with the help of a sextant and a trignometric theorem he proved. He discussed earth's axial rotation. He also determined the densities of the metals.
Ibn-Sina developed an instrument like vernier for precise measurements. He investigated specific gravity. He used an air thermometer.
Astrolabe was known previously but it was improved greatly by Muslim scientists of 10th century. The earliest dated instrument that has been preserved comes from the Islamic period of 927-928 A.D. It is now one of the treasures of the Kuwait National Museum. It is an instrument which tells positions of stars and sun.