In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. At least two of the flat surfaces must have an angle between them; the exact angles between the surfaces depend on the application. The traditional geometrical shape is that of a triangular prism with a triangular base and rectangular sides, in colloquial use "prism" refers to this type; some types of optical prism are not in fact in the shape of geometric prisms. Prisms can be made from any material, transparent to the wavelengths for which they are designed. Typical materials include glass and fluorite. A dispersive prism can be used to break light up into its constituent spectral colors. Furthermore, prisms can be used to reflect light, or to split light into components with different polarizations. Light changes speed; this speed change causes the light to enter the new medium at a different angle. The degree of bending of the light's path depends on the angle that the incident beam of light makes with the surface, on the ratio between the refractive indices of the two media.
The refractive index of many materials varies with the wavelength or color of the light used, a phenomenon known as dispersion. This causes light of different colors to be refracted differently and to leave the prism at different angles, creating an effect similar to a rainbow; this can be used to separate a beam of white light into its constituent spectrum of colors. A similar separation happens with iridescent materials, such as a soap bubble. Prisms will disperse light over a much larger frequency bandwidth than diffraction gratings, making them useful for broad-spectrum spectroscopy. Furthermore, prisms do not suffer from complications arising from overlapping spectral orders, which all gratings have. Prisms are sometimes used for the internal reflection at the surfaces rather than for dispersion. If light inside the prism hits one of the surfaces at a sufficiently steep angle, total internal reflection occurs and all of the light is reflected; this makes a prism a useful substitute for a mirror in some situations.
Ray angle deviation and dispersion through a prism can be determined by tracing a sample ray through the element and using Snell's law at each interface. For the prism shown at right, the indicated angles are given by θ 0 ′ = arcsin θ 1 = α − θ 0 ′ θ 1 ′ = arcsin θ 2 = θ 1 ′ − α. All angles are positive in the direction shown in the image. For a prism in air n 0 = n 2 ≃ 1. Defining n = n 1, the deviation angle δ is given by δ = θ 0 + θ 2 = θ 0 + arcsin − α If the angle of incidence θ 0 and prism apex angle α are both small, sin θ ≈ θ and arcsin x ≈ x if the angles are expressed in radians; this allows the nonlinear equation in the deviation angle δ to be approximated by δ ≈ θ 0 − α + = θ 0 − α + n α − θ 0 = α
An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, moons and galaxies – in either observational or theoretical astronomy. Examples of topics or fields astronomers study include planetary science, solar astronomy, the origin or evolution of stars, or the formation of galaxies. Related but distinct subjects like physical cosmology. Astronomers fall under either of two main types: observational and theoretical. Observational astronomers analyze the data. In contrast, theoretical astronomers create and investigate models of things that cannot be observed; because it takes millions to billions of years for a system of stars or a galaxy to complete a life cycle, astronomers must observe snapshots of different systems at unique points in their evolution to determine how they form and die. They use these data to create models or simulations to theorize how different celestial objects work.
Further subcategories under these two main branches of astronomy include planetary astronomy, galactic astronomy, or physical cosmology. Astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using physical laws. Today, that distinction has disappeared and the terms "astronomer" and "astrophysicist" are interchangeable. Professional astronomers are educated individuals who have a Ph. D. in physics or astronomy and are employed by research institutions or universities. They spend the majority of their time working on research, although they quite have other duties such as teaching, building instruments, or aiding in the operation of an observatory; the number of professional astronomers in the United States is quite small. The American Astronomical Society, the major organization of professional astronomers in North America, has 7,000 members; this number includes scientists from other fields such as physics and engineering, whose research interests are related to astronomy.
The International Astronomical Union comprises 10,145 members from 70 different countries who are involved in astronomical research at the Ph. D. beyond. Contrary to the classical image of an old astronomer peering through a telescope through the dark hours of the night, it is far more common to use a charge-coupled device camera to record a long, deep exposure, allowing a more sensitive image to be created because the light is added over time. Before CCDs, photographic plates were a common method of observation. Modern astronomers spend little time at telescopes just a few weeks per year. Analysis of observed phenomena, along with making predictions as to the causes of what they observe, takes the majority of observational astronomers' time. Astronomers who serve as faculty spend much of their time teaching undergraduate and graduate classes. Most universities have outreach programs including public telescope time and sometimes planetariums as a public service to encourage interest in the field.
Those who become astronomers have a broad background in maths and computing in high school. Taking courses that teach how to research and present papers are invaluable. In college/university most astronomers get a Ph. D. in astronomy or physics. While there is a low number of professional astronomers, the field is popular among amateurs. Most cities have amateur astronomy clubs that meet on a regular basis and host star parties; the Astronomical Society of the Pacific is the largest general astronomical society in the world, comprising both professional and amateur astronomers as well as educators from 70 different nations. Like any hobby, most people who think of themselves as amateur astronomers may devote a few hours a month to stargazing and reading the latest developments in research. However, amateurs span the range from so-called "armchair astronomers" to the ambitious, who own science-grade telescopes and instruments with which they are able to make their own discoveries and assist professional astronomers in research.
List of astronomers List of women astronomers List of Muslim astronomers List of French astronomers List of Hungarian astronomers List of Russian astronomers and astrophysicists List of Slovenian astronomers Dallal, Ahmad. "Science and Technology". In Esposito, John; the Oxford History of Islam. Oxford University Press, New York. ISBN 0-300-15911-0. Kennedy, E. S.. "A Survey of Islamic Astronomical Tables. 46. Philadelphia: American Philosophical Society. Toomer, Gerald. "Al-Khwārizmī, Abu Jaʿfar Muḥammad ibn Mūsā". In Gillispie, Charles Coulston. Dictionary of Scientific Biography. 7. New York: Charles Scribner's Sons. ISBN 0-684-16962-2. American Astronomical Society European Astronomical Society International Astronomical Union Astronomical Society of the Pacific Space's astronomy news
Caen, is a commune in northwestern France. It is the prefecture of the Calvados department; the city proper has 108,365 inhabitants, while its urban area has 420,000, making Caen the largest city in former Lower Normandy. It is the third largest municipality in all of Normandy after Le Havre and Rouen and the third largest city proper in Normandy, after Rouen and Le Havre; the metropolitan area of Caen, in turn, is the second largest in Normandy after that of Rouen, the 21st largest in France. It is located 15 kilometres inland from the English Channel, 200 kilometres north-west of Paris, connected to the south of England by the Caen--Portsmouth ferry route. Caen is located in the centre of its northern region, it is a centre of political and cultural power. Located a few miles from the coast, the landing beaches, the bustling resorts of Deauville and Cabourg, Norman Switzerland and Pays d'Auge, Caen is considered the archetype of Normandy. Caen is known for its historical buildings built during the reign of William the Conqueror, buried there, for the Battle for Caen—heavy fighting that took place in and around Caen during the Battle of Normandy in 1944, destroying much of the city.
The city has now preserved the memory by erecting a memorial and a museum dedicated to peace, the Mémorial de Caen. Current arms: Gules, a single-towered open castle Or, windowed and masoned sable. Under the Ancien Régime: Per fess and azure, 3 fleurs de lys Or. During the First French Empire: Gules, a single-towered castle Or, a chief of Good Imperial Cities. Today, Caen has no motto; as a result, its spelling has not been updated: Un Dieu, un Roy, une Foy, une Loy. This motto is reflected in a notable old Chant royal. Caen's home port code is CN. In 1346, King Edward III of England led his army against the city, it was expected that a siege of several weeks would be required, but the army took the city in less than a day, on 26 July 1346, storming and sacking it, killing 3,000 of its citizens, burning much of the merchants' quarter on the Ile Ste-Jean. During the attack, English officials searched its archives and found a copy of the 1339 Franco-Norman plot to invade England, devised by Philip VI of France and Normandy.
This was subsequently used as propaganda to justify the supplying and financing of the conflict and its continuation. Only the castle of Caen held out, despite attempts to besiege it. A few days the English left, marching to the east and on to their victory at the Battle of Crécy, it was captured by Henry V in 1417 and treated harshly for being the first town to put up any resistance to his invasion. During the Battle of Normandy in the Second World War, Caen was liberated from the Nazis in early July, a month after the Normandy landings those by British I Corps on 6 June 1944. British and Canadian troops had intended to capture the town on D-Day; however they were held up north of the city until 9 July, when an intense bombing campaign during Operation Charnwood destroyed 70% of the city and killed 2,000 French civilians. The Allies seized the western quarters, a month than Field Marshal Montgomery's original plan. During the battle, many of the town's inhabitants sought refuge in the Abbaye aux Hommes, built by William the Conqueror some 800 years before.
Both the cathedral and the university were destroyed by the British and Canadian bombing. Post-Second World War work included the reconstruction of complete districts of the city and the university campus, it led to the current urbanization of Caen. Having lost many of its historic quarters and its university campus in the war, the city does not have the atmosphere of a traditional Normandy town such as Honfleur, Cabourg and Bayeux; the Canadian Army Film and Photo Unit filmed the D-Day offensive and Orne breakout several weeks then returned several months to document the city's recovery efforts. The resulting film, is preserved in the National Archives of Canada; the first mentions of the name of Caen are found in different acts of the dukes of Normandy: Cadon 1021/1025, Cadumus 1025, Cathim 1026/1027. Year 1070 of the Parker manuscript of the Anglo-Saxon Chronicle refers to Caen as Kadum, year 1086 of the Laud manuscript gives the name as Caþum. Despite a lack of sources as to the origin of the settlements, the name Caen would seem to be of Gaulish origin, from the words catu-, referring to military activities and magos, hence meaning "manoeuvre field" or "battlefield".
In Layamon's Brut, the poet asserts. Caen is in an area of high humidity; the Orne River flows through the city, as well as small rivers known as les Odons, most of which have been buried under the city to improve urban hygiene. Caen has a large flood zone, named "La prairie", located around the hippodrome, not far from the River Orne, submerged. Caen is 10 km from the Channel. A canal parallel to the Orne was built during the reign of Napoleon III to link the city to the sea at all times; the canal reaches the English Channel at Ouistreham. A lock keeps the tide out of the canal and lets large ships navigate up the canal to Caen's freshwater harbours. Caen has an oceanic climate, somewhat ameliorated due to its inland position. In spite of this, summers are still cool by French standards and the climate is maritime in terms of high precipitation modest
The Paris Observatory, a research institution of PSL Research University, is the foremost astronomical observatory of France, one of the largest astronomical centres in the world. Its historic building is to be found on the Left Bank of the Seine in central Paris, but most of the staff work on a satellite campus in Meudon, a suburb southwest of Paris. Administratively, it is a grand établissement of the French Ministry of National Education, with a status close to that of a public university, its missions astrophysics. It maintains a radio astronomy observatory at Nançay, it was the home to the International Time Bureau until its dissolution in 1987. The Paris Observatory Library, founded in 1785, provides the researchers with documentation and preserves the ancient books and heritage collections of the institution. Many collections are available on the Paris Observatory digital library, its foundation lies in the ambitions of Jean-Baptiste Colbert to extend France's maritime power and international trade in the 17th century.
Louis XIV promoted its construction, started in 1667 and completed in 1671. It thus predates by a few years the Royal Greenwich Observatory in England, founded in 1675; the architect of the Paris Observatory was Claude Perrault whose brother, was secretary to Colbert and superintendent of public works. Optical instruments were supplied by Giuseppe Campani; the buildings were extended in 1730, 1810, 1834, 1850, 1951. The last extension incorporates the spectacular Meridian Room designed by Jean Prouvé; the world's first national almanac, the Connaissance des temps, was published by the observatory in 1679, using eclipses in Jupiter's satellites to aid sea-farers in establishing longitude. In 1863, the observatory published the first modern weather maps. In 1882, a 33 cm astrographic lens was constructed, an instrument that catalysed what proved to be the over-ambitious international Carte du Ciel project. In November 1913, the Paris Observatory, using the Eiffel Tower as an antenna, exchanged sustained wireless signals with the United States Naval Observatory to determine the exact difference of longitude between the two institutions.
The Paris Observatory library preserves a great number of original works and letters of the Observatory and well known astronomers. The entire collection - archives, iconography - has been inventoried on Alidade; some of the work is now digitized on the digital library such as Hevelius, Lalande or Delisle letters. Among other, are to be found: Administrativ documents Scientific observations Scientifc work of Giovanni Domenico Cassini Scientific work of Jacques Cassini Scientific work of Charles Messier Annual reports from 1878 to 1940 Numerous images of instruments and persons The Meudon great refractor was a 83 cm aperture refractor, which with September 20, 1909 observations by E. M. Antoniadi helped disprove the Mars canals theory, it was a double telescope completed in 1891, with secondary having 62 cm aperture lens for photography. It was one of the largest active telescopes in Europe; the title of Director of the Observatory was given for the first time to César-François Cassini de Thury by a Royal brevet dated November 12, 1771.
However, the important role played by his grandfather and father in this institution during its first century gives them somewhat the role of director. Solar Observatory Tower Meudon Chateau de Meudon LESIA space and astrophysics instrumentation research laboratory Nançay radio telescope Also known as the Observatoire du Pic de Château Renard, the Observatoire de Saint-Véran was built in 1974 on top of the Pic de Château Renard, on the commune of Saint-Véran in the Haut Queyras. A coronograph was in operation there for ten years. Nowadays, the AstroQueyras amateur astronomy association operates the facility, using a 60 cm telescope on loan from the Observatoire de Haute Provence. Numerous asteroids have been discovered there. "Paris Observatory", Encyclopædia Britannica, Deluxe CDROM edition Aubin, D.. "The fading star of the Paris Observatory in the nineteenth century: astronomers' urban culture of circulation and observation". Osiris. 18: 79–100. Doi:10.1086/649378. Guinot, B.. "History of the Bureau International de l'Heure".
Polar Motion: Historical and Scientific problems. Pp. 175–184. Bibcode:2000ASPC..208..175G. Paris Observatory Location in Paris Inventory of astronomy heritage Digital library for astronomy archives Publications of the Observatoire de Paris in Gallica, the digital library of the BnF
France the French Republic, is a country whose territory consists of metropolitan France in Western Europe and several overseas regions and territories. The metropolitan area of France extends from the Mediterranean Sea to the English Channel and the North Sea, from the Rhine to the Atlantic Ocean, it is bordered by Belgium and Germany to the northeast and Italy to the east, Andorra and Spain to the south. The overseas territories include French Guiana in South America and several islands in the Atlantic and Indian oceans; the country's 18 integral regions span a combined area of 643,801 square kilometres and a total population of 67.3 million. France, a sovereign state, is a unitary semi-presidential republic with its capital in Paris, the country's largest city and main cultural and commercial centre. Other major urban areas include Lyon, Toulouse, Bordeaux and Nice. During the Iron Age, what is now metropolitan France was inhabited by a Celtic people. Rome annexed the area in 51 BC, holding it until the arrival of Germanic Franks in 476, who formed the Kingdom of Francia.
The Treaty of Verdun of 843 partitioned Francia into Middle Francia and West Francia. West Francia which became the Kingdom of France in 987 emerged as a major European power in the Late Middle Ages following its victory in the Hundred Years' War. During the Renaissance, French culture flourished and a global colonial empire was established, which by the 20th century would become the second largest in the world; the 16th century was dominated by religious civil wars between Protestants. France became Europe's dominant cultural and military power in the 17th century under Louis XIV. In the late 18th century, the French Revolution overthrew the absolute monarchy, established one of modern history's earliest republics, saw the drafting of the Declaration of the Rights of Man and of the Citizen, which expresses the nation's ideals to this day. In the 19th century, Napoleon established the First French Empire, his subsequent Napoleonic Wars shaped the course of continental Europe. Following the collapse of the Empire, France endured a tumultuous succession of governments culminating with the establishment of the French Third Republic in 1870.
France was a major participant in World War I, from which it emerged victorious, was one of the Allies in World War II, but came under occupation by the Axis powers in 1940. Following liberation in 1944, a Fourth Republic was established and dissolved in the course of the Algerian War; the Fifth Republic, led by Charles de Gaulle, remains today. Algeria and nearly all the other colonies became independent in the 1960s and retained close economic and military connections with France. France has long been a global centre of art and philosophy, it hosts the world's fourth-largest number of UNESCO World Heritage Sites and is the leading tourist destination, receiving around 83 million foreign visitors annually. France is a developed country with the world's sixth-largest economy by nominal GDP, tenth-largest by purchasing power parity. In terms of aggregate household wealth, it ranks fourth in the world. France performs well in international rankings of education, health care, life expectancy, human development.
France is considered a great power in global affairs, being one of the five permanent members of the United Nations Security Council with the power to veto and an official nuclear-weapon state. It is a leading member state of the European Union and the Eurozone, a member of the Group of 7, North Atlantic Treaty Organization, Organisation for Economic Co-operation and Development, the World Trade Organization, La Francophonie. Applied to the whole Frankish Empire, the name "France" comes from the Latin "Francia", or "country of the Franks". Modern France is still named today "Francia" in Italian and Spanish, "Frankreich" in German and "Frankrijk" in Dutch, all of which have more or less the same historical meaning. There are various theories as to the origin of the name Frank. Following the precedents of Edward Gibbon and Jacob Grimm, the name of the Franks has been linked with the word frank in English, it has been suggested that the meaning of "free" was adopted because, after the conquest of Gaul, only Franks were free of taxation.
Another theory is that it is derived from the Proto-Germanic word frankon, which translates as javelin or lance as the throwing axe of the Franks was known as a francisca. However, it has been determined that these weapons were named because of their use by the Franks, not the other way around; the oldest traces of human life in what is now France date from 1.8 million years ago. Over the ensuing millennia, Humans were confronted by a harsh and variable climate, marked by several glacial eras. Early hominids led a nomadic hunter-gatherer life. France has a large number of decorated caves from the upper Palaeolithic era, including one of the most famous and best preserved, Lascaux. At the end of the last glacial period, the climate became milder. After strong demographic and agricultural development between the 4th and 3rd millennia, metallurgy appeared at the end of the 3rd millennium working gold and bronze, iron. France has numerous megalithic sites from the Neolithic period, including the exceptiona
Observatory of Strasbourg
The Observatory of Strasbourg is an astronomical observatory in Strasbourg, France. Following the Franco-Prussian War of 1870–71, the city of Strasbourg became part of the German Empire; the University of Strasbourg was refounded in 1872 and a new observatory began construction in 1875 in the Neustadt district. The main instrument was a 50 cm Repsold refractor, which saw first light in 1880. At the time this was the largest instrument in the German Empire. In 1881, the ninth General Assembly of the Astronomische Gesellschaft met in Strasbourg to mark the official inauguration; the observatory site was selected for instruction purposes and political symbolism, rather than the observational qualities. It was a low-lying site, prone to mists. During the period up until 1914, the staff was too small to work the instruments and so there was little academic research published prior to World War I; the main observations were of variable stars. After 1909, the instruments were used to observe binary stars and perform photometry of nebulae.
The observatory is the home for the Centre de données astronomiques de Strasbourg, a database for the collection and distribution of astronomical information. This includes SIMBAD, a reference database for astronomical objects, VizieR, an astronomical catalogue service and Aladin, an interactive sky atlas; the modern extension of the building houses Planétarium de Strasbourg. The observatory is surrounded by the Jardin botanique de l'Université de Strasbourg. In the vaulted basement below the observatory, a University-administered museum is located. Called Crypte aux étoiles, it displays old telescopes and other antique astronomical devices such as clocks and theodolites. Julius Bauschinger Adolf Berberich André Danjon William Lewis Elkin Ernest Esclangon Ernst Hartwig Carlos Jaschek Pierre Lacroute Otto Tetens Friedrich Winnecke Carl Wilhelm Wirtz Walter Wislicenus Media related to Strasbourg Observatory at Wikimedia Commons Official website of the Observatory Official website of the Planetarium