How life been created?
Lets assume, in now a days war is covering some regions in the middle east, such war takes time to heal up for peaceful life to take over again after earning form previous pasts & history to call. The question is why there has to be a war once there is history?
1st world war, then 2nd & let's assume the 3rd on the way! In this time with so much new modern technologies can make nations to disappear & many nationalities to evacuate to survived nations & to live with. Let's assume this what has already happened. Some nation's remains, then another war starts & few nations remain. Then another war for 2 nations to remain. Then to bring more population (reproduction) to start newer generations & so on till war starts again. Just imagine Adam & Eve. And life to go on. Keep in mind that there is natural & artificial for almost everything. Death caused by any of them too.
Natural is always & much better than artificial. But the good natural is much better than the bad natural. Good or bad artificial is not logic in-compare to natural.
Huge explosion that took over to create this galaxy of our & us to live on earth is how life was created. Let's assume this explosion is war between galaxies & our galaxy survived for us to remain on this planet earth. Space Explorations of NASA has a point that something might go wrong in the universe or some space invasion from another planet. God knows what's there in deep space.
For some reason, life was created for this entire universe, galaxies, planets, mankind & creatures. The reason is, all are living on each others. Believe it or not! & beyond all is the inventor creator. For life is to go on. Explosions of planets (SUN) & new born planets. Think about GOD always. God is the secret for all living beings.
Where is the administration system of control to stop wars, terrorists & control number of population in a single nation or nations to have a better way of livings & peace?
At first God is there, Start from there please.
By: Nabil Z.K.K Polaski
Background
Globally, the 20th century was marked by: (a) two devastating world wars; (b) the Great Depression of the 1930s; (c) the end of vast colonial empires; (d) rapid advances in science and technology, from the first airplane flight at Kitty Hawk, North Carolina (US) to the landing on the moon; (e) the Cold War between the Western alliance and the Warsaw Pact nations; (f) a sharp rise in living standards in North America, Europe, and Japan; (g) increased concerns about the environment, including loss of forests, shortages of energy and water, the decline in biological diversity, and air pollution; (h) the onset of the AIDS epidemic; and (i) the ultimate emergence of the US as the only world superpower. The planet's population continues to explode: from 1 billion in 1820, to 2 billion in 1930, 3 billion in 1960, 4 billion in 1974, 5 billion in 1988, and 6 billion in 2000. For the 21st century, the continued exponential growth in science and technology raises both hopes (e.g., advances in medicine) and fears (e.g., development of even more lethal weapons of war).
Overview
Global output rose by 3.7% in 2003, led by
Now a day's with new modern technology, there are different types of telescopes invented to scan the universe which has billions of living stars & galaxies. Scanning from earth & from space. Such telescopes have reached to many stars that are so much far from our planet with thousand lighting years.
Telescopes with different ray's & different waves (secret weapons)
Some used over a human body & brain. Some used over a location.
Different Gas with different ray's & mainly gamma are also there. Such weapons can start a massive biological war other than an Electronic or Chemical ones. Ozone layer also infected by such natural & artificial different rays other than the moving air from country to country that can carry viruses from location to another.
Science has approached to this already in our existing time & invented fields of magnetic radiation over living beings that have living brains to suffer.
Nation can fall as Babylon people before when they starts so much different thinking with brains attached to each others in one time which makes lot of talk unnecessarily to have an existence (brains in a circle that learning from each others other than amusing or blaming or abusing or opening each others secrets to the public & to pick victims to victimize more victims & madness to take over in a social life of families. Those who whishes to understand suffers from limited miner brains & have hard tuff time even to concentrate on a normal living & to feel under attack from neighbors that scans & sucks information's from a suffering brain. They take what they want from & give so much pain in return. All of this caused by satellites & who's using such satellites in space? Satellite station people on ground from different locations on earth. Those I call behind the shadows are Satanism, Zionism, thieves, murderers, killers, terrorists & corrupting all believes assuming that they are the law & forgetting human rights & giving nothing in return but shit to all since the year of 2000 & still running over man kind & giving no medical insurance or a peace home or a peace mind to live at home. Slavery time to inner conscious to mankind & they are hunting to make budgets out of human suffering). Such technology sold to terrorists. Nice international business between many satellites. Where is justice? Or God?
United international case 11th sept, 2001 between Al Qeada & America Transport Information Technology. This what terror is.
Some telescopes can also have waves of rays which can vibrate an entire location, building, or human skull (knock knock system) other than radiation entering the human body which cause pain & sickness. & there are different types of waves. (Artificial Tsunami & Artificial Earth Quakes for an example).
God, a being in a religion. Especially in monotheisms, a single God is considered the creator or source of everything that exists and is spoken of in terms of perfect attributes-for instance, infinitude, immutability, eternity, goodness, knowledge (omniscience), and power (omnipotence). Most religions traditionally ascribe to God certain character traits that can be understood either literally or metaphorically, such as will, love, anger, and forgiveness.
Conceptions of God
Many religious thinkers have held that God is so different from finite beings that he must be considered essentially a mystery beyond the powers of human conception. Nevertheless, most philosophers and theologians have assumed that a limited knowledge of God is possible and have formulated different conceptions of him in terms of divine attributes and paths of knowledge.
Philosophical and Religious Approaches
The philosophical and religious conceptions of God have at times been sharply distinguished. In the 17th century, for instance, the French mathematician and religious thinker Blaise Pascal unfavourably contrasted the "God of the philosophers", an abstract idea, with the "God of faith", an experienced, living reality. In general, mystics, who claim direct experience of the divine being, have asserted the superiority of their knowledge of God to the rational demonstrations of God's existence and attributes propounded by philosophers and theologians. Some theologians have tried to combine philosophical and experiential approaches to God, as in the 20th-century German theologian Paul Tillich's twofold way of speaking of God as the "ground of being" and "ultimate concern". A certain tension is probably inevitable, however, between the way that theologians speak of God and the way most believers think of and experience him.
Primary Attributes
God may be conceived as transcendent ("above" the world), emphasizing his otherness, his independence from and power over the world order; or as immanent ("indwelling" in the world), emphasizing his presence and participation within the world's process. He has been thought of as personal, by analogy with human individuals; some theologians, on the other hand, have maintained that the concept of personality is inadequate to God and that he must be conceived as impersonal or suprapersonal. In the great monotheistic religions, God is worshipped as the One, the supreme unity that embraces or has created all things; but polytheism, the belief in many gods, has also flourished throughout history.
These contrasts are sometimes dialectically combined. Thus, while theism emphasizes divine transcendence and pantheism identifies God with the world order, in panentheism God is understood as both transcendent and immanent. The Christian doctrine of the Trinity and similar doctrines in other religions acknowledge both the unity and the inner diversity of God. Christianity is a form of monotheism in which the stark unity of God has been modified. It has also been argued that God has both personal and impersonal aspects, or even that he alone is truly personal and that at the finite level there is only an imperfect approximation of personal being. These attempts to unite dialectically in God seemingly opposite characteristics are common in religious and mystical writers and are intended to do justice to the variety and complexity of religious experience. The 15th-century German philosopher Nicholas of Cusa, for instance, believing that God can be apprehended only through mystical intuition, stressed the "coincidence of opposites" in God; the 19th-century Danish philosopher Søren Kierkegaard insisted on the parodoxical nature of religious faith. These formulations suggest that the logic of discourse about God is necessarily different from the logic that applies to finite entities.
Judaism, Christianity, and Islam
In Judaism, Christianity, and Islam, the three religions rooted in the biblical tradition, God is conceived primarily in terms of his transcendence, personality, and unity.
The Jewish Idea of God
The idea of transcendence is introduced in the opening verses of the Hebrew Scriptures, in which God is presented as creator, and this conception impresses itself on all Jewish discourse about God. To say the world is created means that it is not independent of God or an emanation of God, but external to him, a product of his will, so that he is Lord of all the Earth. This explains the Jewish antipathy to idolatry-no creature can represent the Creator, so it is forbidden to make any material image of him. Nonetheless, it is also part of the teaching regarding creation that the human being is made in the image of God. Thus, the Hebrew understanding of God was frankly anthropomorphic. He promised and threatened, he could be angry and even jealous; but his primary attributes were righteousness, justice, mercy, truth, and faithfulness. He is represented as king, judge, and shepherd. He binds himself by covenants to his people and thus limits himself. Such a God, even if anthropomorphic, is a living God. It is true that the name of God, Yahweh, was understood as "I am who I am", but this was not taken by the Hebrews of biblical times in the abstract, metaphysical sense in which it was interpreted later. The Hebrew God was unique, and his command was, "You shall have no other gods beside me!" (although in some biblical passages the Spirit of the Lord and the angel of the Lord and, in later Jewish speculation, the divine wisdom appear to be almost secondary divine beings).
Christian Conceptions
Christianity began as a Jewish sect and thus took over the Hebrew God, the Jewish Scriptures eventually becoming, for Christians, the Old Testament. During his ministry, Jesus was probably understood as a holy man of God, but by the end of the 1st century Christians had exalted him into the divine sphere, and this created tension with the monotheistic tradition of Judaism. The solution of the problem was the development of the doctrine of the triune God, or Trinity, which, although it is suggested in the New Testament, was not fully formulated until the 4th century. The God of the Old Testament became, for Christians, the Father, a title that Jesus himself has applied to him and that was meant to stress his love and care rather than his power. Jesus himself, acknowledged as the Christ, was understood as the incarnate Son, or Word (Logos), the concrete manifestation of God within the finite order. Both expressions, Son and Word, imply a being who is both distinct from the Father and yet so closely akin to him as to be "of the same substance" (Greek, homoousios) with him. The Holy Spirit-said in the West to proceed from the Father and the Son, in the East to proceed from the Father alone (after the filioque controversy)-is the immanent presence and activity of God in the creation, which he strives to bring to perfection. Although Christian theology speaks of the three "persons" of the Trinity, these are not persons in the modern sense, but three ways of being of the one God.
Islam
Islam arose as a powerful reaction against the ancient pagan cults of
Asian and Other Religions
Despite the differences, the conceptions of God in Judaism, Christianity, and Islam bear an obvious "family resemblance". The great religions of
Hinduism
In Hinduism, Holy Being can be understood in several ways. Philosophically, it is understood as Brahma, the one eternal, absolute reality embracing all that is, so that the world of change is but the surface appearance (maya). In popular religion, many gods are recognized, but, properly understood, these are manifestations of Brahma. Each god has his or her own function. The three principal gods, charged respectively with creating, preserving, and destroying, are joined as the Trimurti, or three powers, reminiscent of the Christian Trinity. Strictly speaking, the creator god does not create in the Judaeo-Christian sense, for the world is eternal and he is simply the god who has been from the beginning. In bhakti Hinduism, the way of personal devotion, the god Isvara is conceived as personal and is not unlike the Judaeo-Christian God.
Buddhism and Chinese Religion
It is sometimes said that Buddhism, in its Hinayana form, is atheistic, but this is not so. The gods are real, but they are not ultimate. The ultimate reality, or Holy Being, is the impersonal cosmic order. A similar concept is found in ancient Greek religion, in which cosmic destiny seems to have been superior to even the high gods. In the Mahayana Buddhism of China and
In the indigenous Chinese religions, the pure polytheism of the popular cults was modified by contact with the philosophical traditions developed by the scholarly elite. In these philosophies, the ultimate Holy Being also seems to have been conceived as an impersonal order. In Daoism, it is the rhythm of the universe; in Confucianism, it is the moral law of heaven.
Polytheism and Animism
In polytheism, there are many holy beings, each manifesting some particular divine attribute or caring for some particular aspect of nature or of human affairs. Polytheism was the most common form of religion in the ancient world and was well developed in
Summary of Major Types
A range of types, each shading into the other, can be abstracted from this survey. In the monotheism of Judaism and Islam, Holy Being is conceived at its most transcendent and personal level. In Christian Trinitarianism, an attempt is made to synthesize transcendence and immanence. In the Asian religions considered, the immanence and impersonal nature of Holy Being are stressed (although some forms of Hinduism and Buddhism do not exclude personal aspects of the divine).
Grounds for Belief
Although conceptions of God have varied considerably, depending on historical period, culture, and sect, a belief in Holy Being in some sense has been predominant in almost all societies throughout history. This belief has been challenged, however, since ancient times by scepticism, materialism, atheism, and other forms of disbelief, and the proportion of unbelievers is higher in modern societies than in most societies of the past.
Varieties of Disbelief
Arguments against belief in God are as numerous as arguments for it. Atheists absolutely deny the existence of God. Some, for instance, believe the material universe constitutes ultimate reality; others argue that the prevalence of suffering and evil in the world precludes the existence of a sacred being. Agnostics believe that the evidence for and against the existence of God is inconclusive; they therefore suspend judgement. Positivists believe that rational inquiry is restricted to questions of empirical fact, so that it is meaningless either to affirm or deny the existence of God.
The Nature of Belief
If God is the ground or source of being and not simply another being, even the highest or supreme being, then he does not exist in the sense in which things exist within the world. It may even be misleading to say, "God exists", although this is the traditional way of speaking. To believe in God is to have faith in the ultimate ground of being, or to trust in the ultimate rationality and righteousness of the whole scheme of things. This way of expressing the matter also leaves open the questions of transcendence and immanence, personal being and impersonal being, and so on. The primary basis for belief in God is to be found in experience, especially religious experience. There are many experiences in which people have become aware of Holy Being impinging on their lives-mystical experiences, conversion, a sense of presence, sometimes visions and locutions-which may come with the force of a revelation. Besides specifically religious experiences, there are others in which people become aware of a depth or an ultimacy that they call God-moral experiences, interpersonal relations, the sense of beauty, the search for truth, the awareness of finitude, even confrontation with suffering and death. These are sometimes called limit situations (a term used by the 20th-century German philosopher Karl Jaspers), because those who undergo such experiences seem to strike against the limits of their own being. In so doing, however, they become aware of a being that transcends their own, yet with which they sense both difference and affinity. They become aware of what the 20th-century German Protestant theologian Rudolf Otto, in a classic description, called mysterium tremendum et fascinans, the mystery that at once produces both awe and fascination.
Formal Arguments For the Existence of God
To many people these experiences of Holy Being are self-authenticating, and they feel no need to inquire further. All human experience, however, is fallible. Mistakes of perception are everyday experiences, and false conceptions of the natural world, the Earth, the heavenly bodies, and so forth have prevailed for thousands of years. It is therefore possible that the experience of Holy Being is illusory, and this possibility has led some believers to look for a rational basis for belief in God that will confirm the experiential basis. Numerous attempts have been made to prove the reality of God. The medieval Scholastic theologian St Anselm argued that the very idea of a being than whom no more perfect can be conceived entails his existence, for existence is itself an aspect of perfection. Many philosophers have denied the logical validity of such a transition from idea to factual existence, but this ontological argument is still discussed. The 13th-century theologian St Thomas Aquinas rejected the ontological argument but proposed five other proofs of God's existence that are still officially accepted by the Roman Catholic Church: (1) the fact of change requires an agent of change; (2) the chain of causation needs to be grounded in a first cause that is itself uncaused; (3) the contingent facts of the world (facts that might not have been as they are) presuppose a necessary being; (4) one can observe a gradation of things as higher and lower, and this points to a perfect reality at the top of the hierarchy; (5) the order and design of nature demand as their source a being possessing the highest wisdom. The 18th-century German philosopher Immanuel Kant rejected Aquinas's arguments but argued the necessity of God's existence as the support or guarantor of the moral life. These arguments for the reality of God have all been submitted to repeated and searching criticism, and they continue to be reformulated to meet the criticisms. It is now generally agreed that none of them constitutes a proof, but many believers would say that the arguments have a cumulative force, which, although still short of proof, amounts to a strong probability, especially in conjunction with the evidence of religious experience. Ultimately, however, belief in God is, like many other important beliefs, an act of faith-one that must be rooted in personal experience.
Secrets in our life:
Bermuda Triangle, also known as the Devil's Triangle and the Limbo of the Lost, a geographical area of about 3,900,000 sq km (1,500,000 sq mi), between Bermuda, Puerto Rico, and Melbourne in Florida (located 55°W to 85°W and 30°N to 40°N), in which there have been numerous unexplained disappearances of ships and aircraft.
The mystery dates back as far as the mid-19th century, with a total of more than 50 ships and 20 aeroplanes having been lost in the Triangle. One of the more notorious cases was the disappearance of Flight 19. Five United States torpedo bombers left Fort Lauderdale on December 5, 1945, on a routine training flight in good conditions. None of them returned. Even the seaplane that was sent out to find them vanished. Other stories about the region include ships found abandoned with warm food left on the tables and planes that disappear without even making a distress call. The absence of wreckage is often cited as proof of the mysterious power of the Triangle.
Explanations are legion, and include death rays from Atlantis and UFO kidnappings. Less fantastic analyses suggest that fierce currents and deep water could explain the lack of wreckage, and point out that several of the losses attributed to the Bermuda Triangle actually occurred as far as 1,000 km (600 mi) outside it. Furthermore, military and civil craft pass through the region every day without mishap. As deep sea diving techniques improve it is likely that more of the lost vessels will be recovered, but it is equally likely that the mystery of the Bermuda Triangle will linger in the imagination for a long while yet.
Unidentified Flying Object (UFO), any object or light in the sky that cannot be immediately explained by the observer. Sightings of unusual aerial phenomena date back to ancient times, but UFOs (sometimes called flying saucers) became widely discussed only after the first widely publicized American sighting in 1947. Many thousands of such observations have since been reported worldwide.
At least 90 per cent of UFO sightings can be identified as conventional objects, although time-consuming investigations are often necessary for such identification. UFOs most often turn out to be bright planets or stars, aircraft, birds, balloons, kites, aerial flares, peculiar clouds, meteors, and satellites. The remaining sightings can probably be attributed to other mistaken sightings or to inaccurate reporting, hoaxes, or delusions, although to disprove all claims made about UFOs is impossible.
From 1947 to 1969 the United States Air Force (USAF) investigated UFOs as a possible threat to national security. A total of 12,618 reports was received, of which 701 reports, or 5.6 per cent, were listed as unexplained. The USAF concluded that “no UFO reported, investigated, and evaluated by the Air Force has ever given any indication of threat to our national security”.
Some people nevertheless believe that UFOs are extraterrestrial spacecraft, even though no scientifically valid evidence supports that belief. The possibility of extraterrestrial civilizations is not the stumbling block; most scientists grant that intelligent life may well exist elsewhere in the universe. A fully convincing UFO photograph of a craft-like object has yet to be taken, however, and the scientific method requires that highly speculative explanations should not be adopted unless all of the more ordinary explanations can be ruled out.
UFO enthusiasts persist, however, and some people even claim to have been abducted and taken aboard UFOs. (A close encounter of the third kind is UFO terminology for an alleged encounter between human beings and visitors from outer space.) No one has produced scientifically acceptable proof of these claims.
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Black Hole,
a hypothetical body with a gravitational field so strong that nothing, including electromagnetic radiation, can escape from its vicinity. The body is surrounded by a spherical boundary, called a horizon, through which light can enter but not escape; it therefore appears totally black. Such a field can belong to a high-density body, of relatively small mass-equal to the Sun's or less-that is compressed into a very small volume; or to a low-density body of very great mass, such as a collection of millions of stars at a galaxy's centre.
Properties
The black-hole concept was developed by the German astronomer Karl Schwarzschild in 1916 on the basis of Albert Einstein's theory of general relativity. The radius of the horizon of a Schwarzschild black hole depends only on the mass of the body: in kilometres it is 2.95 times the mass of the body in solar units-that is, the mass of the body divided by the mass of the Sun. (For the radius in miles, the corresponding factor is 1.83). If a body is electrically charged or rotating, Schwarzschild's results are modified. An "ergosphere" forms outside the horizon, within which matter is forced to rotate with the black hole; in principle, energy can be emitted from the ergosphere.
According to general relativity, gravitation severely modifies space and time near a black hole. As the horizon is approached from outside, time slows down relative to that of distant observers, stopping completely on the horizon. Once a body has contracted within its Schwarzschild radius, it would theoretically collapse to a singularity, that is, a dimensionless object of infinite density.
Formation
Black holes may form during the course of stellar evolution. As nuclear fuels are exhausted in the core of a star, the pressure associated with the heat they produce is no longer available to resist contraction of the core to ever higher densities. Two new types of pressure arise at densities a million and a million billion (1015) times that of water, respectively, and a compact white dwarf or a neutron star may form. If the core mass exceeds about 1.7 solar masses, however, neither of these types of pressure is sufficient to prevent collapse to a black hole.
Astronomers have discovered X-ray emissions from a binary star system, Cygnus X-1, in which the primary is a normal star of about 30 solar masses. Doppler shifts in its spectrum show that a companion object of 10 to 15 solar masses must be in orbit around it; evidence exists that the X-rays originate near the companion (see Doppler Effect). Normally such X-rays are produced by an "accretion disc", a dense, hot disc of gas that forms as the gas from a normal star spirals into a compact object. The companion in Cygnus X-1, because of its massiveness, is thought likely to be a black hole rather than a white dwarf or neutron star. Other potential candidates for a black hole are an X-ray source in a galaxy neighbouring our own, the Large Magellanic Cloud, and another X-ray source located in the constellation Monoceros. Astrophysicists conjecture that many, if not all, galaxies of substantial size may contain black holes at their centres.
In 1994 the Hubble Space Telescope provided strong evidence that a black hole exists at the centre of the galaxy M87. The high acceleration of gases in this region indicates that an object, or group of objects, of 2.5 billion to 3.5 billion solar masses must be present.
The English physicist Stephen Hawking has suggested that many black holes may have formed in the early universe. If this is so, many of these black holes could be too far from other matter to form detectable accretion discs, and they could even compose a significant fraction of the total mass of the universe. In reaction to the concept of singularities, Hawking has also proposed that black holes do not collapse in this manner but instead form "wormholes" to other universes besides our own.
A black hole of sufficiently small mass can capture one member of an electron-positron pair near the horizon, the other escaping (see X Ray: Pair Production). The resulting radiation carries off energy, in a sense evaporating the black hole. Any primordial black holes weighing less than a few billion tonnes would already have evaporated, but heavier ones may remain.
The questions multiply. What will be the next stages? Will old media disappear? For example, what will happen to the book or to the compact disc? How will the newspaper change? Will it ever become completely electronic? Can public broadcasting survive? What is the future of digital terrestrial television? Will we have new business alliances and consortia? They are already forming. At the individual level will E-mail displace letters or fax? Will the relationship between media producers and editors and users (or customers) become more interactive?
At the more fundamental level will digitalization divide the world even more than at present into “haves” and “have nots”—those countries that have the capacity and ability to develop new digitalized networks and those that do not? Will the concentration of economic power in the hands of those who now own quite different segments of media—from books to motion pictures and from cable to satellite—endanger individual freedom? Will the opportunity of choice, offered to individuals, mean that the field of choice will be genuinely widened? May we not have more and more of the same thing?
It is logical to separate out questions relating to technological developments from questions relating to ownership and control, but, in practice, visions of the future world involve bringing them together. It is difficult in present circumstances to avoid the blurring of “image” (seeing the world as it is presented to us or as we present it to ourselves) and “reality.” Can “truth” survive? The media in their mediation can create what has come to be called “virtual reality”; and Internet can offer fantasy ways of escaping from the restraints of life as it is lived to a world of cyberspace. Cyber words have multiplied during the 1980s and 1990s—from “cybernaut” to “cyborg” through a whole new vocabulary.
It may well be that through an effort to chart the words that we use, and the dates when they were first used, we can achieve a greater understanding of a continuing historical process that encompasses the future as well as the past.
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DANGERS TO EARTH FROM GAMMA-RAY BURSTS:
If a GRB occurred close to our solar system, it could pose a major threat to life on Earth. One likely effect would be to strip away our planet’s ozone layer, exposing Earth to dangerous ultraviolet radiation from the Sun. Some scientists think such events may have happened in the past and could explain some mass extinctions recorded in the history of life on Earth. However, a powerful enough GRB might blast away the atmosphere entirely and scorch Earth’s surface, ending all life forever.
Astronomers think that the huge star Eta Carinae is preparing to explode as a supernova sometime in the future, possibly unleashing a GRB. The star appears to be far enough away at 7,500 light-years that only astronauts and spacecraft would be severely affected, but the gamma rays would damage Earth’s ozone layer. Astronomers are also looking for nearby pairs of neutron stars that might collide in the future.
SHORT GAMMA-RAY BURSTS:
Scientists theorize that short-duration bursts result from the collision of two neutron stars or the collision of a neutron star and a black hole. Such events may occur as the catastrophic end of a double-star system in which two very massive stars once orbited together. As each star reached the end of its life cycle and nuclear fusion no longer released energy from the core, the core collapsed and the star exploded as a supernova. In each case the supernova left behind either a neutron star or a black hole.
The two objects in the system continued to orbit a common center of gravity, drawing closer together. In a final act, the two neutron stars collided, forming a black hole, or the neutron star and the black hole collided to create a larger black hole. Both of these events would release an intense, short flash of gamma rays. A system that had two black holes that merged into a single black hole would not give off a similar burst of gamma rays, however. Scientists think that the merger of two black holes would give off gravitational waves, as would the collision of two neutron stars or a neutron star and a black hole. Gravitational waves are ripples in space-time predicted by Einstein’s theory of relativity.
LONG GAMMA-RAY BURSTS:
Long-duration gamma-ray bursts are thought to occur when a star at least 30 times as massive as the Sun reaches the end of its life and the core collapses. A narrow jet of high-energy gamma rays is emitted by the formation of a black hole in the core just before the star explodes as a hypernova. Hypernovas are extremely powerful supernovas. In some cases the star may be so massive that it collapses entirely into a black hole and does not explode. If the jet of energy is directed toward Earth, it is seen as a long-duration gamma-ray burst.
According to some theories, another type of long-duration GRB may result from the collision of a white dwarf star and a black hole, similar to the events thought to cause short-duration gamma-ray bursts.
Gamma-ray bursters are staggeringly powerful but short-lived events which astronomers detect regularly from earth. In 1997 astronomers first determined the location of such an event, finding that it originated well outside our galaxy. The following article from the Encarta Yearbook relates how astronomers made this discovery.
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Electromagnetic Radiation, waves produced by the oscillation or acceleration of an electric charge. Electromagnetic waves have both electric and magnetic components. Electromagnetic radiation can be arranged in a spectrum that extends from waves of extremely high frequency and short wavelength to extremely low frequency and long wavelength. Visible light is only a small part of the electromagnetic spectrum. In order of decreasing frequency, the electromagnetic spectrum consists of gamma rays, hard and soft X-rays, ultraviolet radiation, visible light, infrared radiation, microwaves, and radio waves.
Properties
Electromagnetic waves need no material medium for their transmission. Thus, light and radio waves can travel through interplanetary and interstellar space from the Sun and stars to the Earth. Regardless of their frequency and wavelength, electromagnetic waves travel at the same speed in a vacuum. The value of the metre has been defined so that the speed of light is exactly 299,792.458 km (approximately 186,282 mi) per second in a vacuum. All the components of the electromagnetic spectrum also show the typical properties of wave motion, including diffraction and interference. The wavelengths range from billionths of a centimetre to many kilometres. The wavelength and frequency of electromagnetic waves are important in determining their heating effect, visibility, penetration, and other characteristics.
Theory
The British physicist James Clerk Maxwell laid out the theory of electromagnetism in a series of papers published in the 1860s. He deduced that electromagnetic waves must exist and stated that visible light consisted of such waves.
Physicists had known since the early 19th century that light travels as a transverse wave (a wave in which the vibrations move in a direction perpendicular to the direction of the advancing wave front). They assumed, however, that the wave required some material medium for its transmission, so they thought that there was an extremely diffuse substance, called ether, which was the unobservable medium. Maxwell's theory made such an assumption unnecessary, but the ether concept was not abandoned immediately, because it fitted in with the Newtonian concept of an absolute space-time frame for the universe. A famous experiment conducted by the American physicist Albert Abraham Michelson and the American chemist Edward Williams Morley in the late 19th century undermined the ether concept and was important in the development of the theory of relativity. This work led to the realization that the speed of electromagnetic radiation in a vacuum is the same, regardless of the velocity of the source or the observer.
Quanta of Radiation
At the beginning of the 20th century, however, physicists found that the wave theory did not account for all the properties of radiation. In 1900 the German physicist Max Planck demonstrated that the emission and absorption of radiation occur in finite units of energy, known as quanta. In 1905, Albert Einstein was able to explain some puzzling experimental results concerning the photoelectric effect by suggesting that electromagnetic radiation can behave like a particle.
Other phenomena that occur in the interaction between radiation and matter can also be explained only by the quantum theory. Thus, modern physicists were forced to recognize that electromagnetic radiation can behave sometimes like a particle and sometimes like a wave. The parallel concept-that matter also exhibits particle-like and wave-like characteristics-was developed in 1925 by the French physicist Louis de Broglie. See Wave-Particle Duality.
Electromagnetic Radiation, energy waves produced by the oscillation or acceleration of an electric charge. Electromagnetic waves have both electric and magnetic components. Electromagnetic radiation can be arranged in a spectrum that extends from waves of extremely high frequency and short wavelength to extremely low frequency and long wavelength (see Wave Motion). Visible light is only a small part of the electromagnetic spectrum. In order of decreasing frequency, the electromagnetic spectrum consists of gamma rays, hard and soft X rays, ultraviolet radiation, visible light, infrared radiation, microwaves, and radio waves.
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Radiation Effects, Biological, effects observed when ionizing radiation interacts with living tissue by transferring energy to molecules of cellular matter. Cellular function may be temporarily or permanently impaired as a result of such interaction, or the cell may be destroyed. The severity of the injury depends on the type of radiation, the absorbed dose, the rate at which the dose was absorbed, and the radiosensitivity of the tissues involved. The effects are the same, whether from a radiation source outside the body or from material within.
The biological effects of a large dose of radiation delivered rapidly differ greatly from those of the same dose delivered slowly. The effects of rapid delivery are due to cell death, and they become apparent within hours, days, or weeks. Protracted exposure is better tolerated because some of the damage is repaired while the exposure continues, even if the total dose is relatively high. If the dose is sufficient to cause acute clinical effects, however, repair is less likely and may be slow even if it does occur. Exposure to doses of radiation too low to destroy cells can induce cellular changes that may be detectable clinically only after some years.
Acute Effects
High whole-body doses of radiation produce a characteristic pattern of injury. Doses are measured in grays, 1 gray (Gy) being equal to an amount of radiation that releases 1 joule of energy per kilogram of matter. Doses of more than 40 Gy severely damage the human vascular system, causing cerebral oedema, which leads to profound shock and neurological disturbances; death occurs within 48 hours. Whole-body doses of 10 to 40 Gy cause less severe vascular damage, but they lead to a loss of fluids and electrolytes into the intercellular spaces and the gastrointestinal tract; death occurs within ten days as a result of fluid and electrolyte imbalance, severe bone-marrow damage, and terminal infection. Absorbed doses of 1.5 to 10 Gy cause destruction of human bone marrow, leading to infection and haemorrhage; death, if it occurs, can be expected about four to five weeks after exposure. Currently only the effects of these lower doses can be treated effectively; but if untreated, half the people receiving as little as 3 to 3.25 Gy to the bone marrow will die.
Exposure of small areas of the body—the most frequent kind of radiation accident—leads to localized tissue damage. Damage to the blood vessels in exposed areas causes disturbed organ function and, at higher doses, necrosis (localized tissue death) and gangrene.
Injury from internally deposited radiation sources is not likely to cause acute effects but, rather, delayed phenomena, depending on the target organ and on the half-life, radiation characteristics, and biochemical behaviour of the radiation source. Consequences may include degeneration or destruction of the irradiated tissue and the initiation of cancer.
Late Effects
Nonmalignant delayed effects of ionizing radiation are manifested in many organs—particularly bone marrow, kidneys, lungs, and the lens of the eye—by degenerative changes and impaired function; these are largely secondary to radiation-induced damage to blood vessels. The most important late effect of radiation exposure, however, is an increased incidence of cancers and leukaemia of the types that occur naturally in unexposed individuals. Statistically significant increases in leukaemia and of cancers of the thyroid, the lung, and the female breast have been demonstrated unequivocally only in populations exposed to relatively high doses (greater than 1 Gy). Non-specific life-shortening effects suggested by animal experiments have not been demonstrated in humans as yet, however.
Nonionizing Radiation
The radio-frequency radiation from sources such as power lines, radar, communications networks, and microwave ovens is nonionizing, and for many years only high doses of such radiation were known to be harmful, causing burns, cataracts, temporary sterility, and other effects. In recent years, however, with the proliferation of such devices, the possible effects of long-term exposure to low levels of nonionizing radiation began to be a matter of scientific concern. Subtle biological effects have been observed, but their health significance is thus far not certain.
Radiation Sickness, illness caused by exposure of the body or part of the body to high doses of ionizing radiation (radiation that alters atoms that it strikes). The symptoms normally arise from high exposure to external radiation, such as that from X-rays or gamma rays, but may arise from internal absorption of radioactive materials (such as radiocaesium) or from both.
Radiation sickness is characterized by a sudden sensation of anorexia (loss of appetite) or nausea and is soon followed by vomiting and sometimes diarrhoea. It extends beyond these early symptoms to more serious conditions, as damage to other tissues, such as the bone marrow, progressively causes lowering of blood cell counts, thereby leaving the body vulnerable to infections. High radiation doses can also lead to permanent sterility resulting from damage to reproductive organs; to serious damage to other organs of the body; and to death-with or without medical treatment. Many other symptoms may arise which depend on the dose, the dose rate, and the area of the body affected. These may include, in the short term, loss of hair, skin burns, or haemorrhages, and, in the long term, increased risk of cancer.
Acute Radiation Sickness
In an acute exposure (measured in seconds, minutes, hours) death may occur; the main biological effect is cell damage, the severity depending on the tissue type. In the sensitive lining stem cells of the gastrointestinal tract, in particular in the stomach and small intestine, the compound serotonin, or 5-hydroxytryptamine (5HT3) is released into the bloodstream. This stimulates the nausea and vomiting centres in the brain and other 5HT3 receptors in the body. There is an accompanying increase in bowel motility (movement) which may be caused by bile salts acting on the damaged mucosa. These symptoms may vary according to individual susceptibility, and because in most uncontrolled situations not everyone is exposed to equal amounts of radiation. In radiotherapy, where exposures are controlled and planned in sessions to enable normal sensitive tissues to recover between treatments, nausea and vomiting usually occur only where there is a high-dose total-body irradiation, for example, in the ablation (surgical removal) of bone marrow for subsequent bone marrow transplantation. It is normal for patients to be given anti-emetics such as ondansetron, which, by counteracting the effects of 5HT3, reduce such side effects. All these effects are exacerbated by radiation damage to other cell types, particularly the bone marrow.
The gray (Gy) is the unit of absorbed dose, when the energy per unit mass imparted to matter by ionizing radiation is 1 joule per kilogram. The previously used unit, the rad, is equivalent to 10-2 Gy. At doses greater than 1 Gy significant reductions in blood cell counts follow depletion of the bone marrow, and can lead to reduced resistance to infections, haemorrhages, and anaemia. Where there is significant direct exposure or surface contamination with radioactive materials, skin burns may occur, leading to further fluid loss and danger of infections. The acute symptoms are sometimes grouped together and known as acute radiation syndrome. Combined injuries have a worse prognosis and this is important in medical management. Without medical treatment an acute dose of approximately 4 Gy is likely to lead to death within 60 days in 50 per cent of those exposed. Doses in excess of 10 Gy are likely to result in earlier death even with treatment. Similar doses over longer periods (days, weeks) may cause a variety of symptoms, but death is less likely as the cells and tissues have time to repair damage.
Experience from the Hiroshima and Nagasaki atomic bomb explosions, and from other accidents with radiation sources, nuclear weapon tests, and nuclear power plants, has provided important findings. The time from exposure to onset of symptoms, the incidence rates, and the duration of radiation sickness can now be estimated. However, in most situations it has been extremely difficult to reconstruct the doses accurately.
The following figures are given as guidelines for adults. Anorexia may be seen in 5 per cent of those exposed at 0.4 Gy and 95 per cent at 3 Gy; nausea in 5 per cent at 0.5 Gy and 95 per cent at 4.5 Gy; vomiting in 5 per cent at 0.6 Gy and 100 per cent at 7 Gy; and diarrhoea in 5 per cent at 1 Gy and over 20 per cent at 8 Gy. If the time from exposure to onset of any of the above symptoms is less than one hour, the dose is likely to be more than 3 Gy; if more than three hours, less than 1 Gy; and if more than 24 hours, the dose is likely to be more than 6 Gy. These general findings can be helpful to doctors as an aid to medical triage (prioritizing treatment for different casualty levels) before more refined estimates can be made.
Fall-out from a thermonuclear test explosion carried out by the United States in the Marshall Islands in 1954 drifted over local inhabitants, who received estimated average whole-body doses of 1.75 Gy. There were no deaths, but there was a degree of illness, with early sickness and diarrhoea in some 10 per cent of the inhabitants, and a fall in blood cell counts. Body surface contamination from the fallout caused skin ulceration in about 20 per cent of those affected.
At the nuclear plant disaster which took place at Chernobyl' in Ukraine in 1986, a total of 203 people involved with the accident were found to be suffering from acute radiation sickness. In the highest exposure group (6 to 16 Gy) the first symptom was vomiting, occurring within 15 to 30 minutes of exposure, followed by profuse diarrhoea. This group, which included firemen, was also affected acutely by inhalation of radioactive materials and toxic substances, as well as being victims of conventional injuries. Despite sophisticated treatment at specialist centres, 20 of 22 members of this group died. The other radiation effects on the bone marrow and the external radiation burns resulting from skin contamination with beta-emitting radioactive isotopes also contributed to these deaths. As doses decreased, the symptoms and signs were less severe. In those victims with doses in the 1 to 2 Gy range vomiting occurred later and, although some individuals also suffered skin contamination, none in this group died.
Chronic Radiation Sickness
Following a chronic exposure (measured in days, weeks, months) the symptoms are usually more subtle. The usual feature is of general malaise, with symptoms similar to flu, fever, and possibly diarrhoea and vomiting. These cases are extremely difficult to unravel and have arisen from inadvertent exposure to an industrial radiation source or to medical therapy equipment, sometimes discarded or procured illegally. In a case in Estonia, where a radiation source had been taken into a house, it was only after an elderly member of the household died and others started to suffer from general malaise that radiation exposure was suspected.
Dose Controls at Work
In Britain, companies and organizations which employ people to work with radiation (hospital radiologists, industrial radiographers, and nuclear industry workers) are required to comply with statutory requirements under the Ionising Radiations Regulations passed in 1985. These regulations set a maximum dose limit for radiation workers of 50 millisievert (mSv) per annum. (The sources of radiation, gamma rays and X-rays, are about equal numerically to the exposure measurement units, sievert and gray.) This maximum dose limit may be compared with the average background radiation dose in Britain of 2.4 mSv per annum. The National Radiological Protection Board has recommended that the occupational dose limit should be reduced to 20 mSv per annum. Any worker deemed likely to exceed a 15 mSv dose is subjected to medical surveillance and dose assessment by dosimetry (constant dose monitoring) and are required to wear film badges. Most radiation workers in Britain receive an average dose of 1.4 mSv and annual doses well below 15 mSv. Employers are required to keep doses as low as reasonably achievable and to report any cases of overexposure to the Health and Safety Executive, the statutory body enforcing the regulations. These and other regulations also impose strict controls on the procurement, use, storage, and disposal of all radioactive sources or materials.
ABSORPTION OF ELECTROMAGNETIC RADIATION
Electromagnetic radiation is the transfer of energy by waves travelling at the speed of light (300,000km/s) in a vacuum. These waves are transverse waves and have both and electric and a magnetic component to them. There is a spectrum of electromagnetic radiation from high energy waves (short wave lengths) such as gamma rays and x-rays, through ultraviolet, visible light and infra-red radiation to lower energy waves such as microwaves and radio waves (long wavelengths).
Radiation may be absorbed by many types of materials. It turns out that all objects are able to emit radiation at all wavelengths and similarly absorb all types of radiation. In fact good emitters are also good absorbers of radiation. However, the intensity of the radiation emitted or absorbed will vary enormously with different wavelengths of radiation.
Dark coloured objects tend to absorb the thermal energy from radiation more efficiently than light coloured or white objects. Light coloured materials are more likely to reflect the radiation away from them. The rate of absorption of radiation depends strongly on the temperature difference between the absorbing material and the emitter of the radiation. In fact it varies with the fourth power of T, where T is the temperature difference (T4). The rate of absorption is also dependent on the amount of exposed surface area – the larger the area, the greater the absorption.
As radiation is absorbed, its energy is transferred to the materials constituent atoms and molecules. This energy transfer depends on the wavelength or energy of the incoming radiation. Microwave radiation, for example, will be absorbed in such a way that the bonds between molecules in the material will vibrate and the temperature of the body will rise. Some of the energy, however, may be re-emitted. For example when a poker is placed in a fire, it absorbs infrared radiation and stores part of it as heat and re-emits part as light as it glows.
III. SOUND ABSORPTION
Energy can take the form of sound. A sound wave is produced from a vibrating object such as a string or a drill where the energy of some of the vibrations is transmitted to its surroundings. The molecules of the surrounding medium (such as the air) then start vibrating. This leads to a series of compressions and expansions in the medium- a sound wave. The frequency of the wave is given by the number of compressions and expansions passing a given point per second.
Sound waves will be gradually absorbed by the medium through which they are travelling. This is because the wave causes several types of vibrations in the material, including rotation of the molecules. This rotation means that the material has an increase in its internal energy, which is not given back to the travelling sound wave and so the sound is absorbed. The amount of absorption is dependent on the frequency of the sound wave, with higher frequencies being absorbed faster than lower sounds. The humidity and temperature of the material also plays a part – in a fog, sound will diminish rapidly. Warning fog horns use a low frequency sound for transmission as this will be absorbed less than a high frequency siren.
Sound absorption is much less in water than in air. This is because the molecules are closer together and so the vibrational sound wave is able to pass faster through water than in air and so the fall off in sound intensity is not so apparent.
In solids sound absorption varies greatly. Carpets, for example, absorb sound well because they have many pockets of trapped air effectively absorbing noise. Other surfaces such as ceramic tiles, will reflect sound waves back into the atmosphere and will not muffle or absorb sound well.
Remote Sensing, process of obtaining information about land, water, or an object, without any physical contact between the sensor and the subject of analysis. The term remote sensing most often refers to the collection of data by instruments carried aboard aircraft or satellites. Remote sensing systems are commonly used to survey, map, and monitor the resources and environment of Earth. They also have been used to explore other planets (see Space Exploration).
Global Greenness Image
The United States NOAA-11 meteorological satellite carries an instrument called the Advanced Very High Resolution Radiometer (AVHRR) that senses the earth’s environmental makeup. Scientists use AVHRR images to observe the entire globe, and they analyze images compiled over the years for evidence of global climate changes. This AVHRR chart integrates images acquired between June 21 and 30, 1992, and transforms the data into a “greenness index.” Colors on the map signify areas of differing photosynthetic activity, including dense vegetation (dark green); less vegetation (lighter green and yellow); snow, ice, or clouds (white); water (blue); and barren terrain (brown).
There are several different types of remote sensing devices. Many systems take photographs with cameras, recording reflected energy in the visible spectrum. Other systems record electromagnetic energy beyond the range of human sight, such as infrared radiation and microwaves (see Electromagnetic Radiation). Multispectral scanners produce images across both the visible and the infrared spectrum.
II. SENSORS
The most familiar form of electromagnetic energy is visible light, which is the portion of the electromagnetic spectrum to which human eyes are sensitive (see Color). When film in a camera is exposed to light, it records electromagnetic energy. For more than 50 years, photographic images obtained from airborne cameras have been used in urban planning, forest management, topographic mapping, soil conservation, military surveillance, and many other applications (see Aerial Survey; Photogrammetry; Photography).
Infrared sensors and microwave sensors record invisible electromagnetic energy. The heat of an object, for example, can be measured by the infrared energy it radiates. Infrared sensors create images that show temperature variations in an area—a difficult or impossible task using conventional photography. Thermal infrared sensors can be used to survey the temperatures of bodies of water, locate damaged underground pipelines, and map geothermal and geologic structures.
Microwave sensors, such as radar, transmit electromagnetic energy toward objects and record how these objects reflect the energy. Microwave sensors operate at very long electromagnetic wavelengths capable of penetrating clouds, a useful feature when cloud cover prohibits imaging with other sensors. By scanning an area with radar and processing the data in a computer, scientists can create radar maps. The surface of Venus, which is entirely shrouded by dense clouds, has been mapped in this way. Radar imagery is also used in geologic mapping, estimating soil moisture content, and determining sea-ice conditions to aid in ship navigation.
Multispectral scanners provide data electronically for multiple portions of the electromagnetic spectrum. Scientists often use computers to enhance the quality of these images or to assist in automated information-gathering and mapping. With computers, scientists can combine several images obtained by multispectral scanners operating at different frequencies.
III. SATELLITES
Satellites have proved extremely useful in the development of remote sensing systems. In 1972 the United States launched Landsat 1, the first in a series of satellites designed specifically for remote sensing. Beginning in 1999, Landsat 7 produced images of most of Earth’s surface every 16 days. Each Landsat image covers more than 31,000 sq km (11,970 sq mi). Objects as small as 230 sq m (2,500 sq ft) can be seen in the images produced by Landsat's Enhanced Thematic Mapper Plus, a type of multispectral scanner. Landsat data are used for applications such as mapping land use, managing forested land, estimating crop production, monitoring grazing conditions, assessing water quality, and protecting wildlife.
Between 1990 and 1996 almost 50 remote sensing satellites were placed into orbit. Since 1986 France's SPOT satellites have provided images showing objects as small as 100 sq m (1,076 sq ft) and have produced stereoscopic images useful for topographic mapping. Earth-observing satellites have also been launched by the European Space Agency and by Japan, Russia, India, and other nations.
Meteorological satellites, such as those operated by the U.S. National Oceanic and Atmospheric Administration, provide images for use in weather forecasting (see Meteorology), as well as in oceanic and terrestrial applications. Remote sensors on weather satellites can track the movement of clouds and record temperature changes in the atmosphere.
IV. OUTLOOK
Remote sensing is changing rapidly. Some satellites carry instruments that can provide images of objects as small as an automobile and constantly improving technology promises even better resolution in the near future. Computer-assisted image-analysis techniques are leading to many new applications for remote sensing. In the late 1990s and the early 21st century, the U.S. National Aeronautics and Space Administration was scheduled to launch the Earth Observing System, a key program in its Mission to Planet Earth, which involves launching a series of satellites to study environmental changes on the planet.
Interference (wave motion), effect that occurs when two or more waves overlap or intersect. When waves interfere with each other, the amplitude of the resulting wave depends on the frequencies, relative phases (relative positions of the crests and troughs), and amplitudes of the interfering waves (see Wave Motion). For example, constructive interference occurs at a point where two overlapping or intersecting waves of the same frequency are in phase—that is, where the crests and troughs of the two waves coincide. In this case, the two waves reinforce each other and combine to form a wave that has an amplitude equal to the sum of the individual amplitudes of the original waves. Destructive interference occurs when two intersecting waves of the same frequency are completely out of phase—that is, when the crest of one wave coincides with the trough of the other. In this case, the two waves cancel each other out. Intersecting or overlapping waves that have different frequencies or that are not entirely in or out of phase with each other have more complex interference patterns.
Visible light is made up of electromagnetic waves that can interfere with each other. For example, interfering light waves are responsible for the colors occasionally seen in soap bubbles. White light is made up of light waves of different wavelengths; the light waves that reflect off the inner surface of the bubble interfere with light waves of the same wavelength that reflect off the outer surface of the bubble. Some of the wavelengths interfere constructively, and other wavelengths interfere destructively. Since different wavelengths of light correspond to different colors, the light reflecting off the soap bubble appears colored. The phenomenon of interference between visible light waves is exploited in holography and in interferometry (see Interferometer).
Interference can occur with all types of waves, not only with light waves. Radio waves interfere with each other when they bounce off buildings in cities, distorting radio signals. Sound-wave interference must be taken into account when constructing concert halls, so that destructive interference does not result in areas in the hall where the sounds produced on stage cannot be heard. The interference of water waves can be observed by dropping objects in a still pool of water and watching how the overlapping waves interfere constructively at some points and destructively at others.
Holography, method of obtaining three-dimensional photographic images. These images are obtained without a lens, so the method is also called lensless photography. The records are called holograms (Greek holos, “whole”; gram, “message”). The theoretical principles of holography were developed by the British physicist Dennis Gabor in 1947. The first actual production of holograms took place in the early 1960s, when the laser became available. By the late 1980s the production of true-color holograms was possible, as well as holograms ranging from the microwave to the X-ray region of the spectrum. Ultrasonic holograms were also being made, using sound waves.
Microwave Relay Transmission
Microwave relay stations are tall towers that receive television signals, amplify them, and retransmit them as a microwave signal to the next relay station. Microwaves are electromagnetic waves that are much shorter than normal television carrier waves and can travel farther. The stations are placed about 50 km (30 mi) apart. Television networks once relied on relay stations to broadcast to affiliate stations located in cities far from the original source of the broadcast. The affiliate stations received the microwave transmission and rebroadcast it as a normal television signal to the local area. This system has now been replaced almost entirely by satellite transmission in which networks send or uplink their program signals to a satellite that in turn downlinks the signals to affiliate stations.
Satellite Transmission
Communications satellites receive television signals from a ground station, amplify them, and relay them back to the earth over an antenna that covers a specified terrestrial area. The satellites circle the earth in a geosynchronous orbit, which means they stay above the same place on the earth at all times. Instead of a normal aerial antenna, receiving dishes are used to receive the signal and deliver it to the television set or station. The dishes can be fairly small for home use, or large and powerful, such as those used by cable and network television stations.
Satellite transmissions are used to efficiently distribute television and radio programs from one geographic location to another by networks; cable companies; individual broadcasters; program providers; and industrial, educational, and other organizations. Programs intended for specific subscribers are scrambled so that only the intended recipients, with appropriate decoders, can receive the program.
Direct-broadcast satellites (DBS) are used worldwide to deliver TV programming directly to TV receivers through small home dishes. The Federal Communications Commission (FCC) licensed several firms in the 1980s to begin DBS service in the United States. The actual launch of DBS satellites, however, was delayed due to the economic factors involved in developing a digital video compression system. The arrival in the early 1990s of digital compression made it possible for a single DBS satellite to carry more than 200 TV channels. DBS systems in North America are operating in the Ku band (12.0-19.0 GHz). DBS home systems consist of the receiving dish antenna and a low-noise amplifier that boosts the antenna signal level and feeds it to a coaxial cable. A receiving box converts the superhigh frequency (SHF) signals to lower frequencies and puts them on channels that the home TV set can display.
Federal Communications Commission (FCC), independent agency of the United States government created in 1934, with jurisdiction over communications in the 50 states, Guam, Puerto Rico, and the Virgin Islands. The function of the commission is to regulate interstate and foreign radio, television, wire, and cable communications; to provide for orderly development and operation of broadcasting services; to provide for rapid, efficient nationwide and worldwide telegraph and telephone service; to promote the safety of life and property through the use of wire and radio communications; and to employ communications facilities for strengthening national defense.
In the field of radio, the FCC regulates amplitude modulation (AM) and frequency modulation (FM) broadcasting and other kinds of radio services. It issues construction permits and licenses for all nongovernmental radio stations. It also assigns frequencies, operating power, and call signs; inspects transmitting equipment, and regulates the use of such equipment. Television broadcasting is regulated by the FCC in the same manner. The commission also regulates the use of cable channels and the quality of service delivered by cable television.
In common-carrier operations, which include telephone, telegraph, radio, and satellite communications, the FCC issues regulations and supervises service. The FCC is responsible for domestic administration of the telecommunications provisions of treaties and international agreements, and licenses radio and cable circuits from the United States to foreign points. The Emergency Broadcast System, which alerts and instructs the public in the event of enemy attack, is supervised by the FCC; the system is regularly used for broadcasting weather warnings and may also be used in local emergencies.
The FCC is administered by five commissioners appointed by the president, with approval of the Senate, to five-year terms.
Wave Aspect of Electrons
This pattern is produced when a narrow beam of electrons passes through a sample of titanium-nickel alloy. The pattern reveals that the electrons move through the sample more like waves than particles. The electrons diffract (bend) around atoms, breaking into many beams and spreading outward. The diffracted beams then interfere with one another, cancelling each other out in some places and reinforcing each other in other places. The bright spots are places where the beams interfered constructively, or reinforced each other. The dark spots are areas in which the beams interfered destructively, or cancelled each other out.
Electron, negatively charged particle found in an atom. Electrons, along with neutrons and protons, comprise the basic building blocks of all atoms. The electrons form the outer layer or layers of an atom, while the neutrons and protons make up the nucleus, or core, of the atom. Electrons, neutrons, and protons are elementary particles—that is, they are among the smallest parts of matter that scientists can isolate. The electron carries a negative electric charge of –1.602 x 10-19 coulomb and has a mass of 9.109 x 10-31 kg.
Scientists cannot simultaneously measure both the exact location of an electron and its precise speed and direction, so they cannot measure the path a specific electron takes as it orbits the nucleus. The law of physics governing this phenomenon is called the uncertainty principle. Scientists can, however, determine the area an electron will probably occupy, and the probability of finding the electron at some place inside this area. A map of this area and its probabilities forms a cloud like pattern known as an orbital. Each orbital can contain two electrons, but these electrons can not have identical properties, so they must spin in opposite directions. Orbitals are grouped into shells, like the layers of an onion, around the nucleus. Each shell can contain a limited number of orbitals, which means that each shell can contain a limited number of electrons. Each shell corresponds to a certain level of energy, and all the electrons in the shell have this same level of energy. As the shells get farther from the nucleus, they can contain more electrons, and the electrons in the shells have higher energy.
The Electron Cloud
Electron Density and Orbital Shapes
Atomic orbitals are mathematical descriptions of where the electrons in an atom (or molecule) are most likely to be found. These descriptions are obtained by solving an equation known as the Schr?dinger equation, which expresses our knowledge of the atomic world. As the angular momentum and energy of an electron increases, it tends to reside in differently shaped orbitals. The orbitals corresponding to the three lowest energy states are s, p, and d, respectively. The illustration shows the spatial distribution of electrons within these orbitals. The fundamental nature of electrons prevents more than two from ever being in the same orbital. The overall distribution of electrons in an atom is the sum of many such pictures. This description has been confirmed by many experiments in chemistry and physics, including an actual picture of a p-orbital made by a Scanning Tunneling Microscope.
Most of the physical and chemical properties of atoms, and hence of all matter, are determined by the nature of the electron cloud enclosing the nucleus.
The nucleus of an atom, with its positive electric charge, attracts negatively charged electrons. This attraction is largely responsible for holding the atom together. The revolution of electrons about a nucleus is determined by the force with which they are attracted to the nucleus. The electrons move very rapidly, and determination of exactly where any particular one is at a given time is theoretically impossible (see Uncertainty Principle). If the atom were visible, the electrons might appear as a cloud, or fog, that is dense in some spots, thin in others. The shape of this cloud and the probability of finding an electron at any point in the cloud can be calculated from the equations of wave mechanics (see Quantum Theory). The solutions of these equations are called orbitals. Each orbital is associated with a definite energy, and each may be occupied by no more than two electrons. If an orbital contains two electrons, the electrons must have opposite spins, a property related to the angular momentum of the electrons. The electrons occupy the orbitals of lowest energy first, then the orbitals next in energy, and so on, building out until the atom is complete (see Atom).
The orbitals tend to form groups known as shells (so-called because they are analogous to the layers, or shells, around an onion). Each shell is associated with a different level of energy. Starting from the nucleus and counting outward, the shells, or principal energy levels, are numbered 1, 2, 3, … , n. The outer shells have more space than the inner ones and can accommodate more orbitals and therefore more electrons. The nth shell consists of 2n-1 orbitals, and each orbital can hold a maximum of 2 electrons. For example, the third shell contains five orbitals and holds a maximum of 10 electrons; the fourth shell contains seven orbitals and holds a maximum of 14 electrons. Among the known elements, only the first seven shells of an atom contain electrons, and only the first four shells are ever filled.
Each shell (designated as n) contains different types of orbitals, numbered from 0 to n-1. The first four types of orbitals are known by their letter designations as s, p, d, and f. There is one s-orbital in each shell, and this orbital contains the most firmly bound electrons of the shell. The s-orbital is followed by the p-orbitals (which always occur in groups of three), the d-orbitals (which always occur in groups of five), and finally the f-orbitals (which always occur in groups of seven). The s-orbitals are always spherically shaped around the nucleus; each p-orbital has two lobes resembling two balls touching; each d-orbital has four lobes; and each f-orbital has eight lobes. The p-, d-, and f-orbitals have a directional orientation in space, but the spherical s-orbitals do not. The three p-orbitals are oriented perpendicular to one another along the axis of an imaginary three-dimensional Cartesian (x, y, z) coordinate system. The three p-orbitals are designated px, py, and pz, respectively. The d- and f-orbitals are similarly arranged about the nucleus at fixed angles to one another.
When elements are listed in order of increasing atomic number, an atom of one element contains one more electron than an atom of the preceding element (see Chemical Elements). The added electrons fill orbitals in order of the increasing energy of the orbitals. The first shell contains the 1s orbital; the second shell contains the 2s orbital and the 2p orbitals; the third shell contains the 3s orbital, the 3p orbitals, and the 3d orbitals; the fourth shell contains the 4s orbital, the 4p orbitals, the 4d orbitals, and the 4f orbitals.
After the two innermost shells, certain orbitals of outer shells have lower energies than the last orbitals of preceding shells. For this reason, some orbitals of the outer shells fill before the previous shells are complete. For example, the s-orbital of the fourth shell (4s) fills before the d-orbitals of the third shell (3d). Orbitals generally fill in this order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s.
In a notation frequently used to describe the electron configuration of an element, a superscript after the orbital letter gives the number of electrons in that orbital. Thus, 1s22s22p5 means that the atom has two electrons in the 1s orbital, two electrons in the 2s orbital, and five electrons in the 2p orbitals.
Neutral atoms with exactly eight electrons in the outer shell (meaning the s- and p-orbitals of the outer shell are filled) are exceptionally stable. These neutral atoms are atoms of the noble gases, which are so stable that getting them to chemically react with other elements is very difficult. The unusual stability of the noble-gas electron structures is of great importance in chemical bonding and reactivity. All other elements tend to combine with each other in such a way as to imitate this stable structure. The structure of helium is 1s2; neon adds another stable shell, 2s22p6, to this; argon adds the orbitals 3s23p6; krypton adds the orbitals 4s23d104p6; and xenon adds the orbitals 5s24d105p6 (the s-orbital fills before the d-orbital of the previous shell).
Electron Density and Orbital Shapes
Atomic orbitals are mathematical descriptions of where the electrons in an atom (or molecule) are most likely to be found. These descriptions are obtained by solving an equation known as the Schr?dinger equation, which expresses our knowledge of the atomic world. As the angular momentum and energy of an electron increases, it tends to reside in differently shaped orbitals. The orbitals corresponding to the three lowest energy states are s, p, and d, respectively. The illustration shows the spatial distribution of electrons within these orbitals. The fundamental nature of electrons prevents more than two from ever being in the same orbital. The overall distribution of electrons in an atom is the sum of many such pictures. This description has been confirmed by many experiments in chemistry and physics, including an actual picture of a p-orbital made by a Scanning Tunneling Microscope.
In 1995 American physicists used particle traps to cool a sample of rubidium atoms to a temperature near absolute zero (-273°C, or –459°F). Absolute zero is the temperature at which all motion stops. When the scientists cooled the rubidium atoms to such a low temperature, the atoms slowed almost to a stop. The scientists knew that the momentum of the atoms, which is related to their speed, was close to zero. At this point, a special rule of quantum physics, called the uncertainty principle, greatly affected the positions of the atoms. This rule states that the momentum and position of a particle both cannot have precise values at the same time. The scientists had a fairly precise value for the atom’s momentum (nearly zero), so the positions of the atoms became very imprecise. The position of each atom could be described as a large, fuzzy cloud of probability. The atoms were very close together in the trap, so the probability clouds of many atoms overlapped one another. It was impossible for the scientists to tell where one atom ended and another began. In effect, the atoms formed one huge particle. This new state of matter is called a Bose-Einstein condensate.
Spectroscopes
Electric Discharge in Nitrogen
In this discharge tube filled with nitrogen, an electric current excites the nitrogen atoms. Almost instantaneously, these excited atoms shed their excess energy by emitting light of specific wavelengths. This phenomenon of discrete emission by excited atoms remained unexplained until the advent of quantum mechanics in the early 20th century.
Encarta Encyclopedia
Yoav Levy/Phototake NYC
Spectroscopy is the study of the radiation, or energy, that atoms, ions, molecules, and atomic nuclei emit. This emitted energy is usually in the form of electromagnetic radiation—vibrating electric and magnetic waves. Electromagnetic waves can have a variety of wavelengths, including those of visible light. X rays, ultraviolet radiation, and infrared radiation are also forms of electromagnetic radiation. Scientists use spectroscopes to measure this emitted radiation.
Radiation Released by Radioactivity
Atomic nuclei emit radiation when they undergo radioactive decay, as discussed in the Radioactivity section above. Nuclei usually emit radiation with very short wavelengths (and therefore high energy) when they decay. Often this radiation is in the form of gamma rays, a form of electromagnetic radiation with wavelengths even shorter than X rays. Once again, nuclei of different elements emit radiation of characteristic wavelengths. Scientists can identify nuclei by measuring this radiation. This method is especially useful in neutron activation analysis, a technique scientists use for identifying the presence of tiny amounts of elements. Scientists bombard samples that they wish to identify with neutrons. Some of the neutrons join the nuclei, making them radioactive. When the nuclei decay, they emit radiation that allows the scientists to identify the substance. Environmental scientists use neutron activation analysis in studying air and water pollution. Forensic scientists, who study evidence related to crimes, use this technique to identify gunshot residue and traces of poisons.
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