Hampshire is a county on the southern coast of England. The county town is the city of Winchester, its two largest cities and Portsmouth, are administered separately as unitary authorities. First settled about 14,000 years ago, Hampshire's history dates to Roman Britain, when its chief town was Winchester; when the Romans left Britain, the area was infiltrated by tribes from Scandinavia and mainland Europe, principally in the river valleys. The county was recorded in the 11th century Domesday Book, divided into 44 hundreds. From the 12th century, the ports grew in importance, fuelled by trade with the continent and cloth manufacture in the county, the fishing industry, a shipbuilding industry was established. By the 16th century, the population of Southampton had outstripped that of Winchester. By the mid-19th century, with the county's population at 219,210 in more than 86,000 dwellings, agriculture was the principal industry and 10 per cent of the county was still forest. Hampshire played a crucial military role in both World Wars.
The Isle of Wight left the county to form its own in 1974. The county's geography is varied, with upland to 286 metres and south-flowing rivers. There are areas of downland and marsh, two national parks: the New Forest, part of the South Downs, which together cover 45 per cent of Hampshire. Hampshire is one of the most affluent counties in the country, with an unemployment rate lower than the national average, its economy derived from major companies, maritime and tourism. Tourist attractions include the national parks and the Southampton Boat Show; the county is known as the home of writers Jane Austen and Charles Dickens, the childhood home of Florence Nightingale and the birthplace of engineer Isambard Kingdom Brunel. Hampshire takes its name from the settlement, now the city of Southampton. Southampton was known in Old English as Hamtun meaning "village-town", so its surrounding area or scīr became known as Hamtunscīr; the old name was recorded in the Domesday book as Hantescire, from this spelling, the modern abbreviation "Hants" derives.
From 1889 until 1959, the administrative county was named the County of Southampton and has been known as Southamptonshire. Hampshire was the departure point of some of those who left England to settle on the east coast of North America during the 17th century, giving its name in particular to the state of New Hampshire; the towns of Portsmouth, New Hampshire and Portsmouth, Virginia take their names from Portsmouth in Hampshire. The region is believed to have been continuously occupied since the end of the last Ice Age about 12,000 BCE. At this time, Britain was still attached to the European continent and was predominantly covered with deciduous woodland; the first inhabitants were Mesolithic hunter-gatherers. The majority of the population would have been concentrated around the river valleys. Over several thousand years, the climate became progressively warmer, sea levels rose. Notable sites from this period include Bouldnor Cliff. Agriculture had arrived in southern Britain by 4000 BCE, with it a neolithic culture.
Some deforestation took place at that time, although during the Bronze Age, beginning in 2200 BCE, this became more widespread and systematic. Hampshire has few monuments to show from these early periods, although nearby Stonehenge was built in several phases at some time between 3100 and 2200 BCE. In the late Bronze Age, fortified hilltop settlements known as hillforts began to appear in large numbers in many parts of Britain including Hampshire, these became more and more important in the early and middle Iron Age. By this period, the people of Britain predominantly spoke a Celtic language, their culture shared much in common with the Celts described by classical writers. Hillforts declined in importance in the second half of the second century BCE, with many being abandoned. Around this period, the first recorded invasion of Britain took place, as southern Britain was conquered by warrior-elites from Belgic tribes of northeastern Gaul - whether these two events are linked to the decline of hillforts is unknown.
By the Roman conquest, the oppidum at Venta Belgarum, modern-day Winchester, was the de facto regional administrative centre. Julius Caesar invaded southeastern England in 55 and again in 54 BCE, but he never reached Hampshire. Notable sites from this period include Hengistbury Head, a major port; the Romans invaded Britain again in 43 CE, Hampshire was incorporated into the Roman province of Britannia quickly. It is believed their political leaders allowed themselves to be incorporated peacefully. Venta became the capital of the administrative polity of the Belgae, which included most of Hampshire and Wiltshire and reached as far as Bath. Whether the people of Hampshire played any role in Boudicca's rebellion of 60-61 CE is not recorded, but evidence of burning is seen in Winchester dated to around this period. For most of the next three centuries, southern Britain enjoyed relative peace; the part of th
Ministry of Defence (United Kingdom)
The Ministry of Defence is the British government department responsible for implementing the defence policy set by Her Majesty's Government and is the headquarters of the British Armed Forces. The MOD states that its principal objectives are to defend the United Kingdom of Great Britain and Northern Ireland and its interests and to strengthen international peace and stability. With the collapse of the Soviet Union and the end of the Cold War, the MOD does not foresee any short-term conventional military threat; the MOD manages day-to-day running of the armed forces, contingency planning and defence procurement. During the 1920s and 1930s, British civil servants and politicians, looking back at the performance of the state during the First World War, concluded that there was a need for greater co-ordination between the three services that made up the armed forces of the United Kingdom—the Royal Navy, the British Army and the Royal Air Force; the formation of a united ministry of defence was rejected by David Lloyd George's coalition government in 1921.
As rearmament became a concern during the 1930s, Stanley Baldwin created the position of Minister for Co-ordination of Defence. Lord Chatfield held the post until the fall of Neville Chamberlain's government in 1940. Winston Churchill, on forming his government in 1940, created the office of Minister of Defence to exercise ministerial control over the Chiefs of Staff Committee and to co-ordinate defence matters; the post was held by the Prime Minister of the day until Clement Attlee's government introduced the Ministry of Defence Act of 1946. The new ministry was headed by a Minister of Defence; the three existing service Ministers—the First Lord of the Admiralty, the Secretary of State for War and the Secretary of State for Air—remained in direct operational control of their respective services, but ceased to attend Cabinet. From 1946 to 1964 five Departments of State did the work of the modern Ministry of Defence: the Admiralty, the War Office, the Air Ministry, the Ministry of Aviation, an earlier form of the Ministry of Defence.
These departments merged in 1964. The Ministers in the Ministry of Defence are as follows: The Chief of the Defence Staff is the professional head of the British Armed Forces and the most senior uniformed military adviser to the Secretary of State for Defence and the Prime Minister; the CDS is supported by the Vice Chief of the Defence Staff who deputises and is responsible for the day-to-day running of the armed services aspect of the MOD through the Central Staff, working alongside the Permanent Secretary. They are joined by the professional heads of the three British armed services and the Commander of Joint Forces Command. All personnel sit at OF-9 rank in the NATO rank system. Together the Chiefs of Staff form the Chiefs of Staff Committee with responsibility for providing advice on operational military matters and the preparation and conduct of military operations; the current Chiefs of Staff are as follows. Chief of the Defence Staff – General Sir Nick Carter Vice-Chief of the Defence Staff – General Sir Gordon Messenger First Sea Lord and Chief of the Naval Staff – Admiral Sir Philip Jones Chief of the General Staff – General Mark Carleton-Smith Chief of the Air Staff – Air Chief Marshal Sir Stephen Hillier Commander of Joint Forces Command – General Sir Christopher Deverell The Chief of Staff is supported by several other senior military personnel at OF-8 rank.
Chief of Defence People – Lieutenant General Richard Nugee Deputy Chief of Defence Staff – Lieutenant-General Douglas Chalmers Deputy Chief of Defence Staff – Lieutenant-General Mark Poffley Chief of Joint Operations - Vice-Admiral Timothy Fraser Defence Senior Adviser Middle East - Lieutenant-General John LorimerAdditionally, there are a number of Assistant Chiefs of Defence Staff, including the Assistant Chief of the Defence Staff and the Defence Services Secretary in the Royal Household of the Sovereign of the United Kingdom, the Assistant Chief of Defence Staff. Permanent Secretary and other senior officials The Ministers and Chiefs of the Defence Staff are supported by several civilian and professional military advisors; the Permanent Under-Secretary of State for Defence is the senior civil servant at the MOD. Their role is to ensure that it operates as a government department and has responsibility for the strategy, reform and the finances of the MOD; the role works with the Chief of the Defence Staff in leading the organisation and supporting Ministers in the conduct of business in the Department across the full range of responsibilities.
Permanent Under-Secretary of State – Stephen Lovegrove Director General Finance – Cat Little Director General Head Office and Commissioning Services – Julie Taylor Director General Nuclear – Julian Kelly Director General Security Policy – Peter Watkins MOD Chief Scientific Adviser – Professor Hugh Durrant-Whyte MOD Chief Scientific Adviser – Professor Robin Grimes Lead Non-Executive Board Member – Sir Gerry Gri
Unidentified flying object
An unidentified flying object is an object observed in the sky, not identified. Most UFOs are identified as conventional objects or phenomena; the term is used for claimed observations of extraterrestrial spacecraft. The term "UFO" was coined in 1953 by the United States Air Force to serve as a catch-all for all such reports. In its initial definition, the USAF stated that a "UFOB" was "any airborne object which by performance, aerodynamic characteristics, or unusual features, does not conform to any presently known aircraft or missile type, or which cannot be positively identified as a familiar object." Accordingly, the term was restricted to that fraction of cases which remained unidentified after investigation, as the USAF was interested in potential national security reasons and/or "technical aspects". During the late 1940s and through the 1950s, UFOs were referred to popularly as "flying saucers" or "flying discs"; the term UFO became more widespread during the 1950s, at first in technical literature, but in popular use.
UFOs garnered considerable interest during the Cold War, an era associated with a heightened concern for national security, more in the 2010s, for unexplained reasons. Various studies have concluded that the phenomenon does not represent a threat to national security, nor does it contain anything worthy of scientific pursuit; the Oxford English Dictionary defines a UFO. The first published book to use the word was authored by Donald E. Keyhoe; the acronym "UFO" was coined by Captain Edward J. Ruppelt, who headed Project Blue Book the USAF's official investigation of UFOs, he wrote, "Obviously the term'flying saucer' is misleading when applied to objects of every conceivable shape and performance. For this reason the military prefers the more general, if less colorful, name: unidentified flying objects. UFO for short." Other phrases that were used and that predate the UFO acronym include "flying flapjack", "flying disc", "unexplained flying discs", "unidentifiable object". The phrase "flying saucer" had gained widespread attention after the summer of 1947.
On June 24, a civilian pilot named Kenneth Arnold reported seeing nine objects flying in formation near Mount Rainier. Arnold estimated the speed of discs to be over 1,200 mph. At the time, he claimed he described the objects flying in a saucer-like fashion, leading to newspaper accounts of "flying saucers" and "flying discs". Ufo's were referred to colloquially, as a "Bogey" by military personal and pilots during the cold war; the term "bogey" was used to report anomalies in radar blips, to indicate possible hostile forces that might be roaming in the area. In popular usage, the term UFO came to be used to refer to claims of alien spacecraft, because of the public and media ridicule associated with the topic, some ufologists and investigators prefer to use terms such as "unidentified aerial phenomenon" or "anomalous phenomena", as in the title of the National Aviation Reporting Center on Anomalous Phenomena. "Anomalous aerial vehicle" or "unidentified aerial system" are sometimes used in a military aviation context to describe unidentified targets.
Studies have established that the majority of UFO observations are misidentified conventional objects or natural phenomena—most aircraft, noctilucent clouds, nacreous clouds, or astronomical objects such as meteors or bright planets with a small percentage being hoaxes. Between 5% and 20% of reported sightings are not explained, therefore can be classified as unidentified in the strictest sense. While proponents of the extraterrestrial hypothesis suggest that these unexplained reports are of alien spacecraft, the null hypothesis cannot be excluded that these reports are other more prosaic phenomena that cannot be identified due to lack of complete information or due to the necessary subjectivity of the reports. Instead of accepting the null hypothesis, UFO enthusiasts tend to engage in special pleading by offering outlandish, untested explanations for the validity of the ETH; these violate Occam's razor. No scientific papers about UFOs have been published in peer-reviewed journals. There was, in the past, some debate in the scientific community about whether any scientific investigation into UFO sightings is warranted with the general conclusion being that the phenomenon was not worthy of serious investigation except as a cultural artifact.
UFOs have been the subject of investigations by various governments who have provided extensive records related to the subject. Many of the most involved government-sponsored investigations ended after agencies concluded that there was no benefit to continued investigation; the void left by the lack of institutional or scientific study has given rise to independent researchers and fringe groups, including the National Investigations Committee on Aerial Phenomena in the mid-20th century and, more the Mutual UFO Network and the Center for UFO Studies. The term "Ufology" is used to describe the collective efforts of those who study reports and associated evidence of unidentified flying objects. UFOs have become a prevalent theme in modern culture, the social phenomena have been the subject of academic research in sociology and psychology. Unexplained aerial observations have been reported throughout history; some were undoubtedly astronomical in nature: comets, bright meteors, one or more of the five planets that can be readily
University of Oxford
The University of Oxford is a collegiate research university in Oxford, England. There is evidence of teaching as early as 1096, making it the oldest university in the English-speaking world and the world's second-oldest university in continuous operation, it grew from 1167 when Henry II banned English students from attending the University of Paris. After disputes between students and Oxford townsfolk in 1209, some academics fled north-east to Cambridge where they established what became the University of Cambridge; the two'ancient universities' are jointly called'Oxbridge'. The history and influence of the University of Oxford has made it one of the most prestigious universities in the world; the university is made up of 38 constituent colleges, a range of academic departments, which are organised into four divisions. All the colleges are self-governing institutions within the university, each controlling its own membership and with its own internal structure and activities, it does not have a main campus, its buildings and facilities are scattered throughout the city centre.
Undergraduate teaching at Oxford is organised around weekly tutorials at the colleges and halls, supported by classes, lectures and laboratory work provided by university faculties and departments. It operates the world's oldest university museum, as well as the largest university press in the world and the largest academic library system nationwide. In the fiscal year ending 31 July 2018, the university had a total income of £2.237 billion, of which £579.1 million was from research grants and contracts. The university is ranked first globally by the Times Higher Education World University Rankings as of 2019 and is ranked as among the world's top ten universities, it is ranked second in all major national league tables, behind Cambridge. Oxford has educated many notable alumni, including 27 prime ministers of the United Kingdom and many heads of state and government around the world; as of 2019, 69 Nobel Prize winners, 3 Fields Medalists, 6 Turing Award winners have studied, worked, or held visiting fellowships at the University of Oxford, while its alumni have won 160 Olympic medals.
Oxford is the home of numerous scholarships, including the Rhodes Scholarship, one of the oldest international graduate scholarship programmes. The University of Oxford has no known foundation date. Teaching at Oxford existed in some form as early as 1096, but it is unclear when a university came into being, it grew from 1167 when English students returned from the University of Paris. The historian Gerald of Wales lectured to such scholars in 1188 and the first known foreign scholar, Emo of Friesland, arrived in 1190; the head of the university had the title of chancellor from at least 1201, the masters were recognised as a universitas or corporation in 1231. The university was granted a royal charter in 1248 during the reign of King Henry III. After disputes between students and Oxford townsfolk in 1209, some academics fled from the violence to Cambridge forming the University of Cambridge; the students associated together on the basis of geographical origins, into two'nations', representing the North and the South.
In centuries, geographical origins continued to influence many students' affiliations when membership of a college or hall became customary in Oxford. In addition, members of many religious orders, including Dominicans, Franciscans and Augustinians, settled in Oxford in the mid-13th century, gained influence and maintained houses or halls for students. At about the same time, private benefactors established colleges as self-contained scholarly communities. Among the earliest such founders were William of Durham, who in 1249 endowed University College, John Balliol, father of a future King of Scots. Another founder, Walter de Merton, a Lord Chancellor of England and afterwards Bishop of Rochester, devised a series of regulations for college life. Thereafter, an increasing number of students lived in colleges rather than in halls and religious houses. In 1333–34, an attempt by some dissatisfied Oxford scholars to found a new university at Stamford, was blocked by the universities of Oxford and Cambridge petitioning King Edward III.
Thereafter, until the 1820s, no new universities were allowed to be founded in England in London. The new learning of the Renaissance influenced Oxford from the late 15th century onwards. Among university scholars of the period were William Grocyn, who contributed to the revival of Greek language studies, John Colet, the noted biblical scholar. With the English Reformation and the breaking of communion with the Roman Catholic Church, recusant scholars from Oxford fled to continental Europe, settling at the University of Douai; the method of teaching at Oxford was transformed from the medieval scholastic method to Renaissance education, although institutions associated with the university suffered losses of land and revenues. As a centre of learning and scholarship, Oxford's reputation declined in the Age of Enlightenment. In 1636 William Laud, the chancellor and Archbishop of Canterbury, codified the university's statutes. These, to a large extent, remained its gove
Nazi Germany is the common English name for Germany between 1933 and 1945, when Adolf Hitler and his Nazi Party controlled the country through a dictatorship. Under Hitler's rule, Germany was transformed into a totalitarian state that controlled nearly all aspects of life via the Gleichschaltung legal process; the official name of the state was Deutsches Reich until 1943 and Großdeutsches Reich from 1943 to 1945. Nazi Germany is known as the Third Reich, meaning "Third Realm" or "Third Empire", the first two being the Holy Roman Empire and the German Empire; the Nazi regime ended. Hitler was appointed Chancellor of Germany by the President of the Weimar Republic, Paul von Hindenburg, on 30 January 1933; the NSDAP began to eliminate all political opposition and consolidate its power. Hindenburg died on 2 August 1934 and Hitler became dictator of Germany by merging the offices and powers of the Chancellery and Presidency. A national referendum held 19 August 1934 confirmed Hitler as sole Führer of Germany.
All power was centralised in Hitler's person and his word became the highest law. The government was not a coordinated, co-operating body, but a collection of factions struggling for power and Hitler's favour. In the midst of the Great Depression, the Nazis restored economic stability and ended mass unemployment using heavy military spending and a mixed economy. Extensive public works were undertaken, including the construction of Autobahnen; the return to economic stability boosted the regime's popularity. Racism antisemitism, was a central feature of the regime; the Germanic peoples were considered by the Nazis to be the master race, the purest branch of the Aryan race. Discrimination and persecution against Jews and Romani people began in earnest after the seizure of power; the first concentration camps were established in March 1933. Jews and others deemed undesirable were imprisoned, liberals and communists were killed, imprisoned, or exiled. Christian churches and citizens that opposed Hitler's rule were oppressed, many leaders imprisoned.
Education focused on racial biology, population policy, fitness for military service. Career and educational opportunities for women were curtailed. Recreation and tourism were organised via the Strength Through Joy program, the 1936 Summer Olympics showcased Germany on the international stage. Propaganda Minister Joseph Goebbels made effective use of film, mass rallies, Hitler's hypnotic oratory to influence public opinion; the government controlled artistic expression, promoting specific art forms and banning or discouraging others. The Nazi regime dominated neighbours through military threats in the years leading up to war. Nazi Germany made aggressive territorial demands, threatening war if these were not met, it seized Austria and Czechoslovakia in 1938 and 1939. Germany signed a non-aggression pact with the USSR, invaded Poland on 1 September 1939, launching World War II in Europe. By early 1941, Germany controlled much of Europe. Reichskommissariats took control of conquered areas and a German administration was established in the remainder of Poland.
Germany exploited labour of both its occupied territories and its allies. In the Holocaust, millions of Jews and other peoples deemed undesirable by the state were imprisoned, murdered in Nazi concentration camps and extermination camps, or shot. While the German invasion of the Soviet Union in 1941 was successful, the Soviet resurgence and entry of the US into the war meant the Wehrmacht lost the initiative on the Eastern Front in 1943 and by late 1944 had been pushed back to the pre-1939 border. Large-scale aerial bombing of Germany escalated in 1944 and the Axis powers were driven back in Eastern and Southern Europe. After the Allied invasion of France, Germany was conquered by the Soviet Union from the east and the other Allies from the west, capitulated in May 1945. Hitler's refusal to admit defeat led to massive destruction of German infrastructure and additional war-related deaths in the closing months of the war; the victorious Allies initiated a policy of denazification and put many of the surviving Nazi leadership on trial for war crimes at the Nuremberg trials.
The official name of the state was Deutsches Reich from 1933 to 1943 and Großdeutsches Reich from 1943 to 1945, while common English terms are "Nazi Germany" and "Third Reich". The latter, adopted by Nazi propaganda as Drittes Reich, was first used in Das Dritte Reich, a 1923 book by Arthur Moeller van den Bruck; the book counted the Holy Roman Empire as the German Empire as the second. Germany was known as the Weimar Republic during the years 1919 to 1933, it was a republic with a semi-presidential system. The Weimar Republic faced numerous problems, including hyperinflation, political extremism, contentious relationships with the Allied victors of World War I, a series of failed attempts at coalition government by divided political parties. Severe setbacks to the German economy began after World War I ended because of reparations payments required under the 1919 Treaty of Versailles; the government printed money to make the payments and to repay the country's war debt, but the resulting hyperinflation led to inflated prices for consumer goods, economic chaos, food riots.
When the government defaulted on their reparations payments in January 1923, French troops occupied German industrial areas along the Ruhr and widespread civil unrest followed. The National Socialist German Workers' Party (National
A chemist is a scientist trained in the study of chemistry. Chemists study the composition of its properties. Chemists describe the properties they study in terms of quantities, with detail on the level of molecules and their component atoms. Chemists measure substance proportions, reaction rates, other chemical properties; the word'chemist' is used to address Pharmacists in Commonwealth English. Chemists use this knowledge to learn the composition and properties of unfamiliar substances, as well as to reproduce and synthesize large quantities of useful occurring substances and create new artificial substances and useful processes. Chemists may specialize in any number of subdisciplines of chemistry. Materials scientists and metallurgists share skills with chemists; the work of chemists is related to the work of chemical engineers, who are concerned with the proper design and evaluation of the most cost-effective large-scale chemical plants and work with industrial chemists on the development of new processes and methods for the commercial-scale manufacture of chemicals and related products.
The roots of chemistry can be traced to the phenomenon of burning. Fire was a mystical force that transformed one substance into another and thus was of primary interest to mankind, it was fire. After gold was discovered and became a precious metal, many people were interested to find a method that could convert other substances into gold; this led to the protoscience called alchemy. The word chemist is derived from an abbreviation of alchimista. Alchemists discovered many chemical processes. Chemistry as we know it today, was invented by Antoine Lavoisier with his law of conservation of mass in 1783; the discoveries of the chemical elements has a long history culminating in the creation of the periodic table by Dmitri Mendeleev. The Nobel Prize in Chemistry created in 1901 gives an excellent overview of chemical discovery since the start of the 20th century. Jobs for chemists require at least a bachelor's degree, but many positions those in research, require a Master of Science or a Doctor of Philosophy.
Most undergraduate programs emphasize mathematics and physics as well as chemistry because chemistry is known as "the central science", thus chemists ought to have a well-rounded knowledge about science. At the Master's level and higher, students tend to specialize in a particular field. Fields of specialization include biochemistry, nuclear chemistry, organic chemistry, inorganic chemistry, polymer chemistry, analytical chemistry, physical chemistry, theoretical chemistry, quantum chemistry, environmental chemistry, thermochemistry. Postdoctoral experience may be required for certain positions. Workers whose work involves chemistry, but not at a complexity requiring an education with a chemistry degree, are referred to as chemical technicians; such technicians do such work as simpler, routine analyses for quality control or in clinical laboratories, having an associate degree. A chemical technologist has more education or experience than a chemical technician but less than a chemist having a bachelor's degree in a different field of science with an associate degree in chemistry or having the same education as a chemical technician but more experience.
There are degrees specific to become a chemical technologist, which are somewhat distinct from those required when a student is interested in becoming a professional chemist. A Chemical technologist is more involved in the management and operation of the equipment and instrumentation necessary to perform chemical analyzes than a chemical technician, they are part of the team of a chemical laboratory in which the quality of the raw material, intermediate products and finished products is analyzed. They perform functions in the areas of environmental quality control and the operational phase of a chemical plant. In addition to all the training given to chemical technologists in their respective degree, a chemist is trained to understand more details related to chemical phenomena so that the chemist can be capable of more planning on the steps to achieve a distinct goal via a chemistry-related endeavor; the higher the competency level achieved in the field of chemistry, the higher the responsibility given to that chemist and the more complicated the task might be.
Chemistry, as a field, have so many applications that different tasks and objectives can be given to workers or scientists with these different levels of education or experience. The specific title of each job varies from position to position, depending on factors such as the kind of industry, the routine level of the task, the current needs of a particular enterprise, the size of the enterprise or hiring firm, the philosophy and management principles of the hiring firm, the visibility of the competency and individual achievements of the one seeking employment, economic factors such as recession or economic depression, among other factors, so this makes it difficult to categorize the exact roles of these chemistry-related workers as standard for that given level of education; because of these factors affecting exact job titles with distinct responsibilities, some chemists might begin doing technician tasks while other chemists might begin doing more complicated tasks than those of a technician, such as tasks th
An octane rating, or octane number, is a standard measure of the performance of an engine or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating. In broad terms, fuels with a higher octane rating are used in high performance gasoline engines that require higher compression ratios. In contrast, fuels with lower octane numbers are ideal for diesel engines, because diesel engines do not compress the fuel, but rather compress only air and inject fuel into the air, heated by compression. Gasoline engines rely on ignition of air and fuel compressed together as a mixture, ignited at the end of the compression stroke using spark plugs. Therefore, high compressibility of the fuel matters for gasoline engines. Use of gasoline with lower octane numbers may lead to the problem of engine knocking. In a normal spark-ignition engine, the air-fuel mixture is heated because of being compressed and is triggered to burn by the spark plug. During the combustion process, if the unburnt portion of the fuel in the combustion chamber is heated too much, pockets of unburnt fuel may self-ignite before the main flame front reaches them.
Shockwaves produced by detonation can cause much higher pressures than engine components are designed for, can cause a "knocking" or "pinging" sound. Knocking can cause major engine damage; the most used engine management systems found in automobiles today have a knock sensor that monitors if knock is being produced by the fuel being used. In modern computer-controlled engines, the ignition timing will be automatically altered by the engine management system to reduce the knock to an acceptable level. Octanes are a family of hydrocarbons, they are colorless liquids that boil around 125 °C. One member of the octane family, isooctane, is used as a reference standard to benchmark the tendency of gasoline or LPG fuels to resist self-ignition; the octane rating of gasoline is measured in a test engine and is defined by comparison with the mixture of 2,2,4-trimethylpentane and heptane that would have the same anti-knocking capacity as the fuel under test: the percentage, by volume, of 2,2,4-trimethylpentane in that mixture is the octane number of the fuel.
For example, gasoline with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90. A rating of 90 does not mean that the gasoline contains just iso-octane and heptane in these proportions but that it has the same detonation resistance properties; because some fuels are more knock-resistant than pure iso-octane, the definition has been extended to allow for octane numbers greater than 100. Octane ratings are not indicators of the energy content of fuels.. They are only a measure of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner. Where the octane number is raised by blending in ethanol, energy content per volume is reduced. Ethanol BTUs can be compared with gasoline BTUs in heat of combustion tables, it is possible for a fuel to have a Research Octane Number more than 100, because iso-octane is not the most knock-resistant substance available. Racing fuels, avgas, LPG and alcohol fuels such as methanol may have octane ratings of 110 or higher.
Typical "octane booster" gasoline additives include ETBE, isooctane and toluene. Lead in the form of tetraethyllead was once a common additive, but its use for fuels for road vehicles has been progressively phased-out worldwide, beginning in the 1970s; the most common type of octane rating worldwide is the Research Octane Number. RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, comparing the results with those for mixtures of iso-octane and n-heptane. Another type of octane rating, called Motor Octane Number, is determined at 900 rpm engine speed instead of the 600 rpm for RON. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 octane lower than the RON, but there is no direct link between RON and MON.
Pump gasoline specifications require both a minimum RON and a minimum MON. In most countries in Europe the "headline" octane rating shown on the pump is the RON, but in Canada, the United States and some other countries, the headline number is the average of the RON and the MON, called the Anti-Knock Index, written on pumps as /2, it may sometimes be called the Posted Octane Number. Because of the 8 to 12 octane number difference between RON and MON noted above, the AKI shown in Canada and the United States is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel; this difference between RON and MON is known as the fuel's Sensitivity, is not published for those countries that use the Anti-Knock Index labelling system. See the table in the following section for a comparison. Another type of octane rating, called Observed Road Octane Number, is derived from testing gasolines in real world multi-cylinder engines at wide open throttle, it is still reliable today. The ori