Cosmic rays are energetic particles originating from space that impinge on Earth's atmosphere. Almost 90% of all the incoming cosmic ray particles are protons, about 9% are helium nuclei (alpha particles) and about 1% are electrons. Note that the term "ray" is a misnomer, as cosmic ray particles arrive individually, not in the form of a ray or beam of particles. See wave-particle duality.
The kinetic energies of cosmic ray particles span over fourteen orders of magnitude, with the flux of cosmic rays on Earth's surface falling approximately as the inverse-cube of the energy. The wide variety of particle energies reflects the wide variety of sources. Cosmic rays originate from energetic processes on the Sun all the way to the farthest reaches of the visible universe. Cosmic rays can have energies of over 10

Cosmic ray sources
Solar cosmic rays are cosmic rays that originate from the Sun, with relatively low energy (10-100 keV or 1.6 - 16 fJ per particle). The average composition is similar to that of the Sun itself.
The name solar cosmic ray itself is a misnomer because the term cosmic implies that the rays are from the cosmos and not the solar system, but it has stuck. The misnomer arose because there is continuity in the energy spectra, i.e., the flux of particles as a function of their energy, because the low-energy solar cosmic rays fade more or less smoothly into the galactic ones as one looks at increasingly higher energies.

Galactic cosmic rays
See Extragalactic cosmic ray.

Extragalactic cosmic rays
See Ultra-high-energy cosmic ray.

Ultra-high-energy cosmic rays
Anomalous cosmic rays (ACRs) are cosmic rays with unexpectedly low energies. They are thought to be created near the edge of our solar system, in the heliosheath, the border region between the heliosphere and the interstellar medium. When electrically neutral atoms are able to enter the heliosheath (being unaffected by its magnetic fields) subsequently become ionized, they are thought to be accelerated into low-energy cosmic rays by the solar wind's termination shock which marks the inner edge of the heliosheath. It is also possible that high energy galactic cosmic rays which hit the shock front of the solar wind near the heliopause might be decelerated, resulting in their transformation into lower-energy anomalous cosmic rays.
The Voyager 1 space probe crossed the termination shock on December 16, 2004, according to papers published in the journal Science. Readings showed particle acceleration, but not of the kind that generates ACRs. It is unclear at this stage (September 2005) if this is typical of the termination shock (requiring a major rethink of the origin of ACRs), or a localised feature of that part of the termination shock that Voyager 1 passed through. Voyager 2 is expected to cross the termination shock during or after 2008, which will provide more data.

Anomalous cosmic rays
Cosmic rays may broadly be divided into two categories, primary and secondary. The cosmic rays that arise in extrasolar astrophysical sources are primary cosmic rays; these primary cosmic rays can interact with interstellar matter to create secondary cosmic rays. The sun also emits low energy cosmic rays associated with solar flares. The exact composition of primary cosmic rays, outside the Earth's atmosphere, is dependent on which part of the energy spectrum is observed. However, in general, almost 90% of all the incoming cosmic rays are protons, about 9% are helium nuclei (alpha particles) and about 1% are electrons. The remaining fraction is made up of the other heavier nuclei which are abundant end products of star's nuclear synthesis. Secondary cosmic rays consist of the other nuclei which are not abundant nuclear synthesis end products, or products of the big bang, primarily lithium, beryllium and boron. These light nuclei appear in cosmic rays in much greater abundance (about 1:100 particles) than in solar atmospheres, where their abundance is about 10

Composition
The flux (flow rate) of cosmic rays incident on the Earth's upper atmosphere is modulated (varied) by two processes; the sun's solar wind and the Earth's magnetic field. Solar wind is expanding magnetized plasma generated by the sun, which has the effect of decelerating the incoming particles as well as partially excluding some of the particles with energies below about 1 GeV. The amount of solar wind is not constant due to changes in solar activity over its regular eleven-year cycle. Hence the level of modulation varies in autocorrelation with solar activity. Also the Earth's magnetic field deflects some of the cosmic rays, which is confirmed by the fact that the intensity of cosmic radiation is dependent on latitude, longitude and azimuth. The cosmic flux varies from eastern and western directions due to the polarity of the Earth's geomagnetic field and the positive charge dominance in primary cosmic rays; this is termed the east-west effect. The cosmic ray intensity at the equator is lower than at the poles as the geomagnetic cutoff value is greatest at the equator. This can be understood by the fact that charged particle tend to move in the direction of field lines and not across them. This is the reason the Aurorae occur at the poles, since the field lines curve down towards the Earth's surface there. Finally, the longitude dependence arises from the fact that the geomagnetic dipole axis is not parallel to the Earth's rotation axis.
This modulation which describes the change in the interstellar intensities of cosmic rays as they propagate in the heliosphere is highly energy and spatial dependent, and it is described by the Parker's Transport Equation in the heliosphere. At large radial distances, far from the Sun ~ 94 AU, there exists the region where the solar wind undergoes a transition from supersonic to subsonic speeds called the solar wind termination shock. The region between the termination shock and the heliospause (the boundary marking the end of the heliosphere) is called the heliosheath. This region acts as a barrier to cosmic rays and it decreases their intensities at lower energies by about 90% indicating that it is not only the Earth's magnetic field that protect us from cosmic ray bombardment. For more on this topic and how the barrier effects occur the agile reader is referred to Mabedle Donald Ngobeni and Marius Potgieter (2007), and Mabedle Donald Ngobeni (2006). From modelling point of view, there is a challenge in determining the Local Interstellar spectra (LIS) due to large adiabatic energy changes these particles experience owing to the diverging solar wind in the heliosphere. However, significant progress has been made in the field of cosmic ray studies with the development of an improved state-of-the-art 2D numerical model that includes the simulation of the solar wind termination shock, drifts and the heliosheath coupled with fresh descriptions of the diffusion tensor, see Langner et al. (2004). But challenges also exist because the structure of the solar wind and the turbulent magnetic field in the heliosheath is not well understood indicating the heliosheath as the region unknown beyond. With lack of knowledge of the diffusion coefficient perpendicular to the magnetic field our knowledge of the heliosphere and from the modelling point of view is far from complete. There exist promising theories like ab initio approaches, but the drawback is that such theories produce poor compatibility with observations (Minnie, 2006) indicating their failure in describing the mechanisms influencing the cosmic rays in the heliosphere.

Modulation
The nuclei that make up cosmic rays are able to travel from their distant sources to the Earth because of the low density of matter in space. Nuclei interact strongly with other matter, so when the cosmic rays approach Earth they begin to collide with the nuclei of atmospheric gases. These collisions, in a process known as a shower, result in the production of many pions and kaons, unstable mesons which quickly decay into muons. Because muons do not interact strongly with the atmosphere and because of the relativistic effect of time dilation many of these muons are able to reach the surface of the Earth. Muons are ionizing radiation, and may easily be detected by many types of particle detectors such as bubble chambers or scintillation detectors. If several muons are observed by separated detectors at the same instant it is clear that they must have been produced in the same shower event.

Detection
When cosmic ray particles enter the Earth's atmosphere they collide with molecules, mainly oxygen and nitrogen, to produce a cascade of lighter particles, a so-called air shower. The general idea is shown in the figure which shows a cosmic ray shower produced by a high energy proton of cosmic ray origin striking an atmospheric molecule.

This image is a simplified picture of an air shower: in reality, the number of particles created in an air shower event can reach in the billions, depending on the energy of the primary particle. All of the produced particles stay within about one degree of the primary particle's path. Typical particles produced in such collisions are charged mesons (e.g. positive and negative pions and kaons); one common collision is:

Cosmic rays are also responsible for the continuous production of a number of unstable isotopes in the Earth's atmosphere, such as carbon-14, via the reaction:

Cosmic rays have kept the level of carbon-14 in the atmosphere roughly constant (70 tons) for at least the past 100,000 years. This an important fact used in radiocarbon dating which is used in archaeology.

Interaction with the Earth's Atmosphere
There are a number of cosmic ray research initiatives. These include, but are not limited to:

CHICOS
PAMELA
Alpha Magnetic Spectrometer
MARIACHI
Pierre Auger Observatory
Spaceship Earth Research and experiments
After the discovery of radioactivity by Henri Becquerel in 1896, it was generally believed that atmospheric electricity (ionization of the air) was caused only by radiation from radioactive elements in the ground or the radioactive gases (isotopes of radon) they produce. Measurements of ionization rates at increasing heights above the ground during the decade from 1900 to 1910 showed a decrease that could be explained as due to absorption of the ionizing radiation by the intervening air. Then, in 1912, Victor Hess carried three Wulf electrometers (a device to measure the rate of ion production inside a hermetically sealed container) to an altitude of 5300 meters in a free balloon flight. He found the ionization rate increased approximately fourfold over the rate at ground level. He concluded "The results of my observation are best explained by the assumption that a radiation of very great penetrating power enters our atmosphere from above." In 1913-14, Werner Kolhörster confirmed Victor Hess' results by measuring the increased ionization rate at an altitude of 9 km. Hess received the Nobel Prize in Physics in 1936 for his discovery of what came to be called "cosmic rays".
For many years it was generally believed that cosmic rays were high-energy photons (gamma rays) with some secondary electrons produced by Compton scattering of the gamma rays. Then, during the decade from 1927 to 1937 a wide variety of experimental investigations demonstrated that the primary cosmic rays are mostly positively charged particles, and the secondary radiation observed at ground level is composed primarily of a "soft component" of electrons and photons and a "hard component" of penetrating particles, muons. The muon was initially believed to be the unstable particle predicted by Hideki Yukawa in 1935 in his theory of the nuclear force. Experiments proved that the muon decays with a mean life of 2.2 microseconds into an electron and two neutrinos, but that it does not interact strongly with nuclei, so it could not be the Yukawa particle. The mystery was solved by the discovery in 1947 of the pion, which is produced directly in high-energy nuclear interactions. It decays into a muon and one neutrino with a mean life of 0.0026 microseconds. The pion→muon→electron decay sequence was observed directly in a microscopic examination of particle tracks in a special kind of photographic plate called a nuclear emulsion that had been exposed to cosmic rays at a high-altitude mountain station. In 1948, observations with nuclear emulsions carried by balloons to near the top of the atmosphere by Gottlieb and Van Allen showed that the primary cosmic particles are mostly protons with some helium nuclei (alpha particles) and a small fraction heavier nuclei.
In 1934 Bruno Rossi reported an observation of near-simultaneous discharges of two Geiger counters widely separated in a horizontal plane during a test of equipment he was using in a measurement of the so-called east-west effect. In his report on the experiment, Rossi wrote "...it seems that once in a while the recording equipment is struck by very extensive showers of particles, which causes coincidences between the counters, even placed at large distances from one another. Unfortunately, he did not have the time to study this phenomenon more closely." In 1937 Pierre Auger, unaware of Rossi's earlier report, detected the same phenomenon and investigated it in some detail. He concluded that extensive particle showers are generated by high-energy primary cosmic-ray particles that interact with air nuclei high in the atmosphere, initiating a cascade of secondary interactions that ultimately yield a shower of electrons, photons, and muons that reach ground level.
Homi Bhabha derived an expression for the probability of scattering positrons by electrons, a process now known as Bhabha scattering. His classic paper, jointly with W. Heitler, published in 1937 described how primary cosmic rays from space interact with the upper atmosphere to produce particles observed at the ground level. Bhabha and Heitler explained the cosmic ray shower formation by the cascade production of gamma rays and positive and negative electron pairs. In 1938 Bhabha concluded that observations of the properties of such particles would lead to the straightforward experimental verification of Albert Einstein's theory of relativity.
Measurements of the energy and arrival directions of the ultra-high-energy primary cosmic rays by the techniques of "density sampling" and "fast timing" of extensive air showers were first carried out in 1954 by members of the Rossi Cosmic Ray Group at the Massachusetts Institute of Technology. The experiment employed eleven scintillation detectors arranged within a circle 460 meters in diameter on the grounds of the Agassiz Station of the Harvard College Observatory. From that work, and from many other experiments carried out all over the world, the energy spectrum of the primary cosmic rays is now known to extend beyond 10 eV (past the GZK cutoff, beyond which very few cosmic rays should be observed). A huge air shower experiment called the Auger Project is currently operated at a site on the pampas of Argentina by an international consortium of physicists. Their aim is to explore the properties and arrival directions of the very highest energy primary cosmic rays. The results are expected to have important implications for particle physics and cosmology.
Three varieties of neutrino are produced when the unstable particles produced in cosmic ray showers decay. Since neutrinos interact only weakly with matter most of them simply pass through the Earth and exit the other side. They very occasionally interact, however, and these atmospheric neutrinos have been detected by several deep underground experiments. The Super-Kamiokande in Japan provided the first convincing evidence for neutrino oscillation in which one flavour of neutrino changes into another. The evidence was found in a difference in the ratio of electron neutrinos to muon neutrinos depending on the distance they have traveled through the air and earth.

History

Effects
Cosmic rays constitute a fraction of the annual radiation exposure of human beings on earth. For example, the average radiation exposure in Australia is 0.3 mSv due to cosmic rays, out of a total of 2.3 mSv.[1]

Role in Ambient Radiation
Understanding the effects of cosmic rays on the body will be vital for assessing the risks of space travel. R.A. Mewaldt estimated humans unshielded in interplanetary space receive annually roughly 400 to 900 mSv (compared to 2.4 mSv on Earth) and that a 30 month Mars mission might expose astronauts to 460 mSv (at Solar Maximum) to 1140 mSv (at Solar Minimum).
Due to the potential negative effects of astronaut exposure to cosmic rays, solar activity may play a role in future space travel via the Forbush decrease effect. Coronal mass ejections (CMEs) can temporarily lower the local cosmic ray levels, and radiation from CMEs is easier to shield against than cosmic rays.

Significance to Space Travel
Cosmic rays have been implicated in the triggering of electrical breakdown in lightning. It has been proposed (see Gurevich and Zybin, Physics Today, May 2005, "Runaway Breakdown and the Mysteries of Lightning") that essentially all lightning is triggered through a relativistic process, "runaway breakdown", seeded by cosmic ray secondaries. Subsequent development of the lightning discharge then occurs through "conventional breakdown" mechanisms.

Role in climate change
Because of the metaphysical connotations of the word "cosmic", the very name of these particles enables their misinterpretation by the public, giving them an aura of mysterious powers. Were they merely referred to as "high-speed protons and atomic nuclei" this might not be so.
In fiction, cosmic rays have been used as a catchall, mostly in comics (notably the Marvel Comics group the Fantastic Four), as a source for mutation and therefore the powers gained by being bombarded with them.

Sharbat Gula (Pashto: شربت ګله"flower-juice girl") (Sharbat is pronounced /ˈʃaɾ.bat/) (born ca. 1972) is an Afghan woman of Pashtun ethnicity. Forced to flee Afghanistan to a Pakistan refugee camp she was photographed by journalist, Steve McCurry. The image made her famous when it was featured on the June 1985 cover of National Geographic Magazine. Gula was known throughout the world simply as the Afghan Girl until she was formally identified in 2002.

1984 photograph
The identity of the Afghan Girl remained unknown for over 15 years; Afghanistan remained largely closed to Western media until after the overthrow of the Taliban government in 2001. Although McCurry made several attempts during the 1990s to locate her, he was unsuccessful.
In January 2002, a National Geographic team travelled to Afghanistan to locate the subject of the now-famous photograph. McCurry, upon learning that the Nasir Bagh refugee camp was soon to close, inquired of its remaining residents, one of whom knew Gula's brother and was able to send word to her hometown. However, there were a number of women who came forward and identified themselves erroneously as the famous Afghan Girl. In addition, after being shown the 1984 photo, a handful of young men questioned falsely claimed Gula as their wife.
The team finally located Gula, then around the age of 30, in a remote region of Afghanistan; she had returned to her native country from the refugee camp in 1992. Her identity was confirmed using biometric technology which matched her iris patterns to those of the photograph with virtual certainty. She vividly recalled being photographed – it was the first and only time she had ever had her picture taken. The fame and symbolic character of her portrait were completely unknown to her.
Modern pictures of her were featured as part of a cover story on her life in the April 2002 issue of National Geographic and was the subject of a television documentary, entitled Search for the Afghan Girl, which aired in March 2002. In recognition of her, National Geographic set up the Afghan Girls Fund, a charitable organization with the goal of educating Afghan women.

In probability theory the expected value (or mathematical expectation, or mean) of a discrete random variable is the sum of the probability of each possible outcome of the experiment multiplied by the outcome value (or payoff). Thus, it represents the average amount one "expects" as the outcome of the random trial when identical odds are repeated many times. Note that the value itself may not be expected in the general sense - the "expected value" itself may be unlikely or even impossible.
For example, the expected value from the roll of an ordinary six-sided die is 3.5, found by,
which is not one of the possible outcomes.
A common application of expected value is in gambling. For example, an American roulette wheel has 38 equally likely outcomes. A winning bet placed on a single number pays 35-to-1 (this means that you are paid 35 times your bet and your bet is returned, so you get 36 times your bet). So considering all 38 possible outcomes, the expected value of the profit resulting from a $1 bet on a single number is:

which is about −$0.0526. Therefore one expects, on average, to lose over five cents for every dollar bet, and the expected value of a one dollar bet is $0.9474. In gambling or betting, a game or situation in which the expected value of the profit for the player is zero (no net gain nor loss) is commonly called a "fair game."

Mathematical definition
And so on.

When one speaks of the "expected price", one means the expected value of a random variable that is a price.
When one speaks of the "expected height", one means the expected value of a random variable that is a height.
When one speaks of the "expected number of attempts needed to get one successful attempt," one might conservatively approximate it as the reciprocal of the probability of success for such an attempt. Conventional terminology

Properties
Expected value of a constant is equal to that constant or If c is a constant, E(c) = c

Constants
If X and Y are random variables so that almost surely, then .

Monotonicity
The expected value operator (or expectation operator) is linear in the sense that



Combining the results from previous three equations, we can see that -


for any two random variables X and Y (which need to be defined on the same probability space) and any real numbers a and b.

Linearity

Iterated expectation
For any two discrete random variables X,Y one may define the conditional expectation:

which means that is a function on y.
Then the expectation of X satisfies

Hence, the following equation holds:

The right hand side of this equation is referred to as the iterated expectation and is also sometimes called the tower rule. This proposition is treated in law of total expectation.

Iterated expectation for discrete random variables
In the continuous case, the results are completely analogous. The definition of conditional expectation would use inequalities, density functions, and integrals to replace equalities, mass functions, and summations, respectively. However, the main result still holds:


Iterated expectation for continuous random variables
If a random variable X is always less than or equal to another random variable Y, the expectation of X is less than or equal to that of Y:
If , then .
In particular, since and , the absolute value of expectation of a random variable is less or equal to the expectation of its absolute value:


Inequality
The following formula holds for any nonnegative real-valued random variable X (such that ), and positive real number α:


Representation
In general, the expected value operator is not multiplicative, i.e. is not necessarily equal to . If multiplicativity occurs, the X and Y variables are said to be uncorrelated (independent variables are a notable case of uncorrelated variables). The lack of multiplicativity gives rise to study of covariance and correlation.

Non-multiplicativity
In general, the expectation operator and functions of random variables do not commute; that is

A notable inequality concerning this topic is Jensen's inequality, involving expected values of convex (or concave) functions.

Uses and applications of the expected value
If X is an matrix, then the expected value of the matrix is defined as the matrix of expected values:

This is utilized in covariance matrices.

Computation

Conditional expectation;
An inequality on location and scale parameters;
Expected value is also a key concept in economics and finance;
The general term expectation;
Pascal's Wager;
Moment (mathematics);
Expectation value (quantum mechanics).

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Part of a series on the Islamic Jurisprudence – a discipline of Islamic studies
A caliphate (from the Arabic خلافة or khilāfah), is the Islamic form of government representing the political unity and leadership of the Muslim world. The head of state (Caliph) has a position based on the notion of a successor to Muhammad's political authority; according to Sunnis ideally elected by the people or their representatives,

Economical
Political

• Political Aspects
  Caliphate
  Imamah
  Wilayat al-faqih
  Bay'ah
  Dhimmi
  Marital
  Criminal
  Etiquette
  Theological
  Hygiene
  Military History
  
  
  Main articles: Rashidun and Muslim conquests Rashidun
  
  

  Main article: Umayyad Umayyads, 7th-8th century
  
  

  Main article: Caliph of Córdoba The Caliphate in Spain
  
  

  Main article: Abbasid Abbasids, 8th-13th century
  1258 saw the conquest of Baghdad and the execution of Abbasid caliph al-Musta'sim by Mongol forces under Hulagu Khan. A surviving member of the Abbasid House was installed as Caliph at Cairo under the patronage of the Mamluk Sultanate three years later; however, the authority of this line of Caliphs was confined to ceremonial and religious matters, and later Muslim historians referred to it as a "shadow" Caliphate.
  
  Shadow Caliphate, 13th century
  
  

  Main article: Ottoman Caliphate Ottomans, 15th-20th century
  
  

  Main article: Khilafat Movement Khilafat Movement, 1920
  Further information: Atatürk's Reforms
  On March 3, 1924, the first President of the Turkish Republic, Gazi Mustafa Kemal Atatürk, as part of his reforms, constitutionally abolished the institution of the Caliphate. Its powers within Turkey were transferred to the Turkish Grand National Assembly (parliament) of the newly formed Turkish Republic and the title has since been inactive. Though the Turkish Republic still retains the right to reinstate the Caliphate, it currently seems improbable that it will ever choose to do so.
  Scattered attempts to revive the Caliphate elsewhere in the Muslim World were made in the years immediately following its abandonment by Turkey, but none were successful. Hussein bin Ali, a former Ottoman governor of the Hejaz who aided the British during World War I and revolted against Istanbul, declared himself Caliph two days after Turkey relinquished the title. But his claim was largely ignored, and he was soon ousted and driven out of Arabia by the Saudis, a rival clan that had no interest in the Caliphate. The last Ottoman Sultan Mehmed VI made a similar attempt to re-establish himself as Caliph in the Hejaz after leaving Turkey, but he was also unsuccessful. A summit was convened at Cairo in 1926 to discuss the revival of the Caliphate, but most Muslim countries did not participate and no action was taken to implement the summit's resolutions.
  Though the title Ameer al-Mumineen was adopted by the King of Morocco and Mullah Mohammed Omar, former head of the now-defunct Taliban regime of Afghanistan, neither claimed any legal standing or authority over Muslims outside the borders of their respective countries. The closest thing to a Caliphate in existence today is the Organization of the Islamic Conference (OIC), an international organization with limited influence founded in 1969 consisting of the governments of most Muslim-majority countries.
  
  End of Caliphate, 1924
  Once the subject of intense conflict and rivalry amongst Muslim rulers, the caliphate has lain dormant and largely unclaimed since the 1920s. In recent years though, interest among Muslims in international unity and the Caliphate has grown. For many ordinary Muslims the caliph as leader of the community of believers, "is cherished both as memory and ideal", though "not an urgent concern" compared to issues such as Israeli-Palestinian conflict.
  Tight restrictions on political activity in many Muslim countries, coupled with the obstacles to uniting over 50 nation-states under a single institution, have prevented efforts to revive the caliphate. Popular apolitical Islamic movements such as the Tablighi Jamaat identify a lack of spirituality and decline in personal religious observance as the root cause of the Muslim world's problems, and claim that the caliphate cannot be successfully revived until these deficiencies are addressed. No attempts at rebuilding a power structure based on Islam were successful anywhere in the Muslim World until the Iranian Revolution in 1979, which was based on Shia principles and whose leaders did not outwardly call for the restoration of a global Caliphate.
  
  Reestablishment
  A number of Islamist political parties and Islamist guerrilla groups have called for the restoration of the caliphate by uniting Muslim nations, either through peaceful political action (e.g., Hizb ut-Tahrir) or through force (e.g., al-Qaeda).
  
  Islamist call
  United States President George W. Bush has warned repeatedly in speeches on the War on Terror that the Caliphate is at the heart of radical Islamic ideology. President Bush has said Iraq is a pivotal battleground in a larger conflict between advocates of freedom and radical Islamists.
  Bush said that Al Qaeda terrorists and those that share their ideology
  "hope to establish a violent political utopia across the Middle East, which they call caliphate, where all would be ruled according to their hateful ideology...This caliphate would be a totalitarian Islamic empire encompassing all current and former Muslim lands, stretching from Europe to North Africa, the Middle East and Southeast Asia."
  
  Position of George W. Bush
  
  Political system
  Fred M. Donner, in his book The Early Islamic Conquests (1981), argues that the standard Arabian practice during the early Caliphates was for the prominent men of a kinship group, or tribe, to gather after a leader's death and elect a leader from amongst themselves, although there was no specified procedure for this shura, or consultative assembly. Candidates were usually from the same lineage as the deceased leader, but they were not necessarily his sons. Capable men who would lead well were preferred over an ineffectual direct heir, as there was no basis in the majority Sunni view that the head of state or governor should be chosen based on lineage alone.
  This argument is advanced by Sunni Muslims, who believe that Muhammad's companion Abu Bakr was elected by the community and that this was the proper procedure. They further argue that a caliph is ideally chosen by election or community consensus, even though the caliphate soon became a hereditary office, or the prize of the strongest general.
  Al-Mawardi has written that the caliph should be Qurayshi. Abu Bakr Al-Baqillani has said that the leader of the Muslims simply should be from the majority. Abu Hanifa also wrote that the leader must come from the majority against Ali and that the 3 caliphs before ˤAlī were usurpers. ˤAlī and his descendents are believed to have been the only proper leaders, or imams regardless of Democracy and what the majority wanted, in the Shia's point of view. This matter is covered in much greater detail in the article Succession to Muhammad, and in the article on Shi'a Islam, although it is worth mentioning that ˤAlī himself did not rebel against the majority choosing Abu Bakr though he may have disagreed. Some shia's argue that in the absence of a Caliphate headed by their Imams, the system termed Vilayat-e Faqih suffices.
  Contrary to the Shia, Sunni Muslims believe that the caliph has always been a merely temporal political ruler, appointed to rule within the bounds of Islamic law (Shariah), and not necessarily the most qualified in Islamic law. The job of adjudicating orthodoxy and Islamic law (Shariah) was left to Islamic lawyers, judiciary, or specialists individually termed as Mujtahids and collectively named the Ulema. The first four caliphs are called the Rashidun meaning the Rightly Guided Caliphs, because they are believed to have followed the Qur'an and the sunnah (example) of Muhammad in all things.
  
  Electing or appointing a Caliph
  
  

  Main article: Shura Majlis al-Shura: Parliament
  Sunni Islamic lawyers have commented on when it is permissible to disobey, impeach or remove rulers in the Caliphate. This is usually when the rulers are not meeting public responsibilities obliged upon them under Islam.
  Al-Mawardi said that if the rulers meet their Islamic responsibilities to the public, the people must obey their laws, but if they become either unjust or severely ineffective then the Caliph or ruler must be impeached via the Majlis al-Shura. Similarly Al-Baghdadi believed that if the rulers do not uphold justice, the ummah via the majlis should give warning to them, and if unheeded then the Caliph can be impeached. Al-Juwayni argued that Islam is the goal of the ummah, so any ruler that deviates from this goal must be impeached. Al-Ghazali believed that oppression by a caliph is enough for impeachment. Rather than just relying on impeachment, Ibn Hajar al-Asqalani obliged rebellion upon the people if the caliph began to act with no regard for Islamic law. Ibn Hajar al-Asqalani said that to ignore such a situation is haraam, and those who cannot revolt inside the caliphate should launch a struggle from outside. Al-Asqalani used two ayahs from the Quran to justify this:
  "...And they (the sinners on qiyama) will say, 'Our Lord! We obeyed our leaders and our chiefs, and they misled us from the right path. Our Lord! Give them (the leaders) double the punishment you give us and curse them with a very great curse'...".
  
  Accountability of rulers
  The following hadith establishes the principle of rule of law in relation to nepotism and accountability
  Narrated 'Aisha: The people of Quraish worried about the lady from Bani Makhzum who had committed theft. They asked, "Who will intercede for her with Allah's Apostle?" Some said, "No one dare to do so except Usama bin Zaid the beloved one to Allah's Apostle." When Usama spoke about that to Allah's Apostle Allah's Apostle said: "Do you try to intercede for somebody in a case connected with Allah's Prescribed Punishments?" Then he got up and delivered a sermon saying, "What destroyed the nations preceding you, was that if a noble amongst them stole, they would forgive him, and if a poor person amongst them stole, they would inflict Allah's Legal punishment on him. By Allah, if Fatima, the daughter of Muhammad (my daughter) stole, I would cut off her hand.
  Various Islamic lawyers do however place multiple conditions, and stipulations e.g the poor cannot be penalised for stealing out of poverty, before executing such a law, making it very difficult to reach such a stage. It is well known during a time of drought in the Rashidun caliphate period, capital punishments were suspended until the effects of the drought passed.
  
  Rule of Law
  
  

  Main article: Islamic economics Economy and Banking
  The land that the Caliphate was at war with was referred to as Dar al-Harb (Arabic: دار الحرب "land of war") , and only the Caliph could declare war for Muslims if it was considered a just war, or Jihad. Only a Caliph, or one of the provincial governors in a caliphate, can declare an offensive jihad, in order to allow Islam to be practiced in foreign land, to stop persecution, or to protect the interests of Muslims there.
  
  Foreign policy and Jihad
  
  

  Main article: List of caliphs Further reading
  
  Primary Islamic evidence
  To Govern by Islam in the Quran
  Some Sunnis argue that to govern a state by Islamic law (Shariah) is, by definition, to rule via the Caliphate, and use the following verses to sustain their claim.
  "So govern between the people by that which God has revealed (Islam), and follow not their vain desires, beware of them in case they seduce you from just some part of that which God has revealed to you"
  
  The Quran
  It is reported that Abu Huraira narrated that Muhammad said;
  "Beware! every one of you is a shepherd and every one is answerable with regards to his flock. The Caliph is a shepherd over the people and shall be questioned about his subjects (as to how he conducted their affairs). A man is a guardian over the members of his family and shall be questioned about them (as to how he looked after their physical and moral well-being). A woman is a guardian over the household of her husband and his children and shall be questioned about them (as to how she managed the household and brought up the children)..."
  Nafi'a reported saying:
  Umar said to me that he heard [Muhammad] saying: Whoever takes away his hand from allegiance to God will meet Him on the Day of Resurrection without having any proof for him, and whoever dies whilst there was no baya'a on his neck (to a Caliph), he dies a death in the days of ignorance (Jahilliya).
  Hisham ibn Urwa reported on the authority of Abu Saleh on the authority of Abu Hurairah that Muhammad said:
  Leaders will take charge of you after me, where the pious (one) will lead you with his piety and the impious (one) with his impiety, so only listen to them and obey them in everything which conforms with the truth (Islam). If they act rightly it is for your credit, and if they acted wrongly it is counted for you and against them.
  Muslim narrated on the authority of al-A'araj, on the authority of Abu Hurairah, that Muhammad said:
  Behold, the Imam (Caliph) is but a shield from behind whom the people fight and by whom they defend themselves.
  Muslim reported on the authority of Abu Hazim, who said,
  I accompanied Abu Hurairah for five years and heard him talking of Muhammad's saying: The Prophets ruled over the children of Israel, whenever a Prophet died another Prophet succeeded him, but there will be no Prophet after me. There will be Khalifahs and they will number many. They asked: What then do you order us? He said: Fulfil the baya'a to them one after the other and give them their due. Surely God will ask them about what He entrusted them with.
  Ibn 'Abbas narrated that Muhammad said,
  If anyone sees in his Emir something that displeases him let him remain patient, for behold, he who separates himself from the sultan (authority of Islam) by even so much as a hand span and dies thereupon, has died a death of the days of ignorance (jahilliyah).
  Muslim reported that Muhammad said,
  "Whoever pledged allegiance to a leader (Caliph) giving him the clasp of his hand and the fruit of his heart shall obey him as long as he can, and if another comes to dispute his authority (cause division of the nation) you have to strike the neck of that man.
  Imam Ahmed reported on the authority of Abdullah Ibnu Amru that Muhammad said in a Sahih narration,
  It is forbiden even for three persons to be together in a place without appointing one of them as their Emir.
  
  Sayings of Muhammad
  All of Muhammad's disciples agreed (Ijma as-Sahaba) upon the necessity to establish a successor (Caliph) to the his political authority after his death, and they all eventually accepted Abu Bakr, then Umar, Uthman, and Ali after the death of each one of them.
  This consensus manifested itself emphatically when they delayed the burial of Muhammad after his death whilst engaged in appointing a successor to him, despite the speedy burial of the dead being an Islamic obligation (Fard). Sunni lawyers argued this would not be legitimate unless the Caliphate was a higher obligation (Fard) than the burial of the dead, especially for such a man of importance such as their prophet.
  Although they disagreed upon the person to elect as a Caliph, they never disagreed upon the need for appointment.
  Al-Habbab Ibn ul-Munthir said when the Sahaba met in the wake of the death of Muhammad at the Saqifah hall:
  "Let there be one Amir from us and one Amir from you (meaning one from the Ansar and one from the Mohajireen)".
  Upon this Abu Bakr replied:
  "It is forbidden for Muslims to have two Amirs (rulers)..."
  Then he got up and addressed the Muslims.
  
  The consensus of the Sahaba (Companions)
  Al-Mawardi says::
  There is consensus that appointing a Caliph is obligatory. The difference of opinion is on whether the appointment must be by Allah or by his servants, and whether the basis (for appointment) is textual evidence or rational proof. The adoption is that it is obligatory upon the servants by textual evidence because of the saying of the Messenger, "Whoever dies not having known the Imam of his time, dies the death of the days of ignorance." Also, the Ummah agreed that this was the most important duty following the death of the Messenger, so important in fact that they considered it more important than the matter of his burial, and so also has it been after the death of each Imam.
  
  See also
  
  

  Saturday, October 27, 2007

  
  "Pistol" redirects here. For other uses, see Pistol (disambiguation).
  A handgun is a firearm designed to be held in the hand when used. This characteristic differentiates handguns as a general class of firearms from their larger cousins: long guns such as rifles and shotguns, mounted weapons such as machine guns and autocannons, and larger weapons such as artillery.
  Some handgun subtypes include single-shot pistols, revolvers, semi-automatic pistols, and fully automatic, or machine pistols.
  The overlapping variations in meaning of the words "pistol" and "handgun" are discussed below.
  
  Multiple senses of the word "pistol"
  The word "pistol" is derived from the French pistole (or pistolet), which has these possible origins:
  
  From the Czech pistole and this one from the Czech píšťala (flute or pipe, referring to the shape of a Hussite firearm).
  From the city of Pistoia, Italy, where perhaps a manufacturer was one Camillio Vettelli in the 1540s.
  That early pistols were carried by cavalry in holsters hung from the pommel (or pistallo in medieval French) of a horse's saddle. Etymology of the word "pistol"
  The general types of handguns are listed below in their order of historical appearance. Each type can be classified into many subtypes. Some of these types can also be differently classified using the general distinction between muzzle-loading firearms (loading from the front of the barrel) and breech-loading firearms (loading from behind the barrel).
  
  Types of handguns
  Single-shot pistols are the theoretically simplest pistols. The earliest handguns were single-shot, muzzle-loading guns with ignition provided by inserting a smoldering match cord into a touch hole. As such, they were essentially nothing more than miniature cannons, small enough to be handheld.
  Improvements followed in subsequent centuries, as various types of locks (ignition devices) were invented. In the matchlock, the separate match cord was affixed to a spring-loaded pivot which could be tripped by a trigger. In the wheellock, a mechanism analogous to that used in today's cigarette lighters replaced the smoldering match cord. In the 17th century, the flintlock, which strikes a flint against steel, appeared. (The flintlock, amazingly, remained state-of-the-art for some two hundred years.) In the 19th century, percussion caps were developed, followed shortly by modern integrated-primer cartridges, and hammers therefore traded their flint for firing pins.
  Single-shot pistols are not completely things of the past, as they have continued to be built (for various reasons) throughout the breech-loading era. However, for most applications, the single-shot handgun has been replaced by revolvers and semi-automatic pistols.
  
  Single-shot pistols
  Not long after the very beginning of firearms, inventors began experimenting with multi-barreled weapons in the quest for the ability to fire more than one shot before needing to reload. Not surprisingly, all types of firearms were included in their efforts, from volley guns to analogously devised handguns. Before anyone developed a practical capability for delivering multiple loads to one barrel in quick succession (which is how repeat fire is usually accomplished today), they were aggregating multiple loaded barrels into one place.
  Some examples of such handguns are:
  
  Duck's-foot pistols
  Derringers
  Pepper-box guns (variously referred to as pepper-box pistols or pepper-box revolvers) Revolvers
  The next development in handgun history after a practical revolver was the development of the semi-automatic pistol, which uses the energy of one shot to reload the chamber for the next (typically by mechanically harnessing the energy of recoil). After a round is fired, the pistol will cycle, ejecting the spent casing and chambering a new round from the magazine, allowing another shot to take place immediately.
  Some terms that have been, or still are, used as synonyms for "semi-automatic pistol" are automatic pistol, autopistol, self-loading pistol and selfloader.
  
  Semi-automatic pistols
  A machine pistol is generally defined as a firearm designed to be fired with one hand, and capable of fully automatic or selective fire. While there are a number of machine pistols such as the Glock 18 and later models of the Mauser C96, these are rare; the light weight, small size, and extremely rapid rates of fire of a machine pistol make them difficult to control, making the larger heavier submachine gun a better choice in cases where the small size of a machine pistol is not needed. Most machine pistols can attach a shoulder stock (the Heckler & Koch VP70 would only fire single rounds at a time unless the stock was attached); others, such as the Beretta 93R, add a forward handgrip. Either of these additions technically create a legal non-pistol under the US National Firearms Act, as pistols are by definition designed to be fired with one hand. The addition of a stock or forward handgrip is considered a design change that creates either a short-barreled rifle or any other weapon, and therefore such additions are generally only found on legal machine guns.
  
  Machine pistols
  Single-action (SA) handguns have a trigger whose sole function is to drop a pre-cocked hammer to discharge a cartridge. For revolvers, the popular Colt Peacemaker of Old West fame is typically thought of. Its hammer must be manually cocked for each shot. For auto-loading pistols the Colt 1911 or Browning Hi-Power are typical examples. They must be cocked for the first shot, but subsequent shots are cocked automatically. These types of guns typically have a very light and crisp trigger pull, making for more accurate target shooting.
  Traditional double-action (DA) handguns have a mechanism that can be either pre-cocked, like the above single-action gun, or can be fired with the gun uncocked. In this case, the gun has an additional mechanism added to the trigger that will cock the gun (and rotate the cylinder in the case of revolvers) as the trigger is pulled. Once the trigger is pulled far enough, the hammer is released and the gun fired. For autoloading pistols the self-loading mechanism will also re-cock the hammer after the first shot is fired so that subsequent shots are fired single-action. For revolvers, each shot is fired with the hammer initially uncocked unless the shooter manually cocked the gun. Popular auto pistols in this category include the Walther P38 and Beretta Model 92. These guns typically have a longer, heavier trigger pull for the first shot then light, crisp pulls for subsequent shots. Popular revolvers include the Ruger Redhawk and Smith & Wesson Model 629. These have comparatively long, heavy trigger pulls for all shots unless the revolver is manually cocked.
  Double-action only (DAO) handguns do not have the ability to be cocked and is usually evidenced by a lack of either the hammer spur or the entire hammer. A typical autopistol in this category is the Ruger KP93DAO and Taurus Millennium, and a typical revolver is the Smith & Wesson Model 642 "Centennial". All pistols in this category have a long, heavy trigger pull for all shots.
  Pre-set triggers are only on autoloading pistols. In this case the pistol mechanism is always partially cocked while being carried and during firing. The partially-cocked firing pin or striker is not cocked enough to cause an accidental release to discharge a cartridge, adding to the safeness of the design, but is cocked enough to remove much of the trigger pull and weight of a purely double-action pistol. These types of pistols do not have external hammers and do not generally have a decock function. Common pistols in the category are the Springfield Armory XD and the various forms of the extremely popular Glock. The trigger pull of these guns is between double-action and single-action pistols. Pre-set triggers may or may not have a second-strike feature on a dud cartridge.
  Some automatic pistol models such as the HK Heckler & Koch USP (Universal Self-loading Pistol) come in a variety of mechanism types and can be easily changed by a gunsmith for both left- and right-handed shooters and for different operating mechanism and safety features.
  
  Operating Mechanisms
  Both revolvers and semiautomatic pistols have prominent places in the world of handgun applications today. For over a century, however, a debate has continued as to which one is better for which particular application and why. Each has its place, although personal preference is as large a factor as the following variables:
  
  reliability (likelihood of jams; how to recover from jams; how to recover from misfires)
  degree of user training needed
  degree and frequency of gun cleaning needed
  "firepower" (usually meaning the number of rounds that can be fired before reloading; not to be confused with "stopping power")
  speed and ease of reloading
  bulkiness with regard to concealment Semiautomatic pistols vs. revolvers
  
  Easier to cycle to next round in the unlikely event of a failure/blockage: all that is needed is a pull of the trigger, while in semi autos one must rack the slide, which takes the pistol out of the shooting position. See Tap Rack Bang.
  Can carry more powerful rounds than most semi autos
  More reliable.
  Easier to aim follow up shots (lack of a recoiling slide results in less perceived recoil).
  More accurate out of the box than semi autos. Advantages of revolvers
  
  Faster firing rate and higher volume of fire.
  Generally has a larger ammo capacity: A Glock 17 carries 17 rounds: while few revolvers can carry more than six.
  Faster to reload: Using magazines is faster than loading individual rounds into a revolver and easier to use and more ergonomic to carry than a speedloader.
  Easier to conceal in certain circumstances due to the flatter profile - there is no cylinder creating a bulge.
  The mainstay cartridge of the semi-auto family, the 9mm, is widely available and inexpensive. Advantages of semiautomatics
  In comparison to longer guns such as shoulder weapons (rifles and shotguns), handguns are smaller, lighter, cheaper, and easier to carry. Since firearms don't rely on the user's strength, they put weaker individuals on an equal defensive footing; when Colt produced the first practical repeating handgun, it gave rise to the saying "God created men, but Colt made them equal".
  
  Advantages of handguns versus shoulder weapons
  Handguns are often considered self-defense weapons for use under 50 meters. While a handgun in the hands of an experienced shooter may be effective at longer ranges than 50 meters, a handgun cartridge is much more limited in its energy capacity than many long gun cartridges. Many rifles are commonly able to achieve bullet velocities of over 3,000 feet per second, whereas handguns are rarely able to achieve velocities over 1,500 feet per second. Thus, long guns are generally more powerful at any range, and especially more effective at longer ranges than handguns.
  A shooter is generally able to achieve considerably greater accuracy with a long gun than with a handgun. This is due partly to the longer distance between the rear and front sights, partly due to a more stable hold attainable with a long gun, and partly due to the higher muzzle velocity, which reduces the bullet travel time and thus reduces external effects on the bullet such as gravitational drop and wind.
  
  Disadvantages of handguns versus shoulder weapons
  Many handgun models are easily concealed on a person—a trait that is useful both to people wishing to bear arms for self-protection and to criminals wishing to carry a handgun for illegal purposes. For these reasons, handguns are a particular focus of debates on gun politics, and in many jurisdictions their ownership is much more heavily regulated than that of long arms.
  In the United States, 48 states allow some form of concealed carry by citizens meeting training or other requirements. 39 of these states, called "shall-issue" states, require issue of a permit if there is no compelling reason not to issue a permit (such as a prior felony conviction, a restraining order, or history of mental illness). Generally, in a shall-issue state, if a person cannot obtain a concealed weapons permit once training requirements are met, that person also cannot lawfully own a firearm. The remaining 9 states, called "may-issue" states, may deny a permit for any reason, usually at the discretion of local law enforcement.
  In the United States, a person must be 21 years of age to purchase a handgun or ammunition intended for a handgun from a federally licensed dealer, which is higher than the age requirement of 18 for rifles and shotguns.
  In the United Kingdom, civilian ownership of almost any handgun has been outlawed since the Dunblane massacre of 1996; the only exclusion were single shot rimfire and muzzleloading pistols; all cartridge firearms were later banned in 1997. Air pistols are still legal, however, those with power levels over 6 foot pounds (half the limit for air rifles) are classified as firearms.
  Civilian ownership of handguns in Australia is legal, but heavily restricted. Handguns may not be owned for self-defence purposes (Target shooting, collecting, and occupational reasons for farmers/gun dealers are, by and large, the only legal reasons for handgun ownership), and anyone wishing to possess a handgun must obtain a firearms licence and observe stringent storage regulations.
  In Israel, handguns are the only type of firearms that most private citizens may own. They are licensed for self-defense purposes to eligible individuals. Current regulations limit licenses to one handgun and 50 cartridges per licensee.
  See the main gun politics article or the article on concealed carry in particular for more details on this debate.
  
  Other related info
  
  Blowback
  Concealed carry
  Gun
  Handgun effectiveness
  Machine-pistol
  Pocket pistol
  Small arms
  Semi-automatic pistol
  Target shooting
  Weapon
  List of pistols

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