A radio telescope is a specialized antenna and radio receiver used to receive radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the radio frequency portion of the electromagnetic spectrum emitted by astronomical objects, just as optical telescopes are the main observing instrument used in traditional optical astronomy which studies the light wave portion of the spectrum coming from astronomical objects. Radio telescopes are large parabolic antennas similar to those employed in tracking and communicating with satellites and space probes, they may be linked together electronically in an array. Unlike optical telescopes, radio telescopes can be used in the daytime as well as at night. Since astronomical radio sources such as planets, stars and galaxies are far away, the radio waves coming from them are weak, so radio telescopes require large antennas to collect enough radio energy to study them, sensitive receiving equipment.
Radio observatories are preferentially located far from major centers of population to avoid electromagnetic interference from radio, radar, motor vehicles, other man-made electronic devices. Radio waves from space were first detected by engineer Karl Guthe Jansky in 1932 at Bell Telephone Laboratories in Holmdel, New Jersey using an antenna built to study noise in radio receivers; the first purpose-built radio telescope was a 9-meter parabolic dish constructed by radio amateur Grote Reber in his back yard in Wheaton, Illinois in 1937. The sky survey he did with it is considered the beginning of the field of radio astronomy; the first radio antenna used to identify an astronomical radio source was one built by Karl Guthe Jansky, an engineer with Bell Telephone Laboratories, in 1932. Jansky was assigned the job of identifying sources of static that might interfere with radio telephone service. Jansky's antenna was an array of dipoles and reflectors designed to receive short wave radio signals at a frequency of 20.5 MHz.
It was mounted on a turntable that allowed it to rotate in any direction, earning it the name "Jansky's merry-go-round". It had a diameter of 100 ft and stood 20 ft tall. By rotating the antenna, the direction of the received interfering radio source could be pinpointed. A small shed to the side of the antenna housed an analog pen-and-paper recording system. After recording signals from all directions for several months, Jansky categorized them into three types of static: nearby thunderstorms, distant thunderstorms, a faint steady hiss of unknown origin. Jansky determined that the "faint hiss" repeated on a cycle of 23 hours and 56 minutes; this period is the length of an astronomical sidereal day, the time it takes any "fixed" object located on the celestial sphere to come back to the same location in the sky. Thus Jansky suspected that the hiss originated outside of the Solar System, by comparing his observations with optical astronomical maps, Jansky concluded that the radiation was coming from the Milky Way Galaxy and was strongest in the direction of the center of the galaxy, in the constellation of Sagittarius.
An amateur radio operator, Grote Reber, was one of the pioneers of what became known as radio astronomy. He built the first parabolic "dish" radio telescope, 9 metres in diameter, in his back yard in Wheaton, Illinois in 1937, he repeated Jansky's pioneering work, identifying the Milky Way as the first off-world radio source, he went on to conduct the first sky survey at high radio frequencies, discovering other radio sources. The rapid development of radar during World War II created technology, applied to radio astronomy after the war, radio astronomy became a branch of astronomy, with universities and research institutes constructing large radio telescopes; the range of frequencies in the electromagnetic spectrum that makes up the radio spectrum is large. This means that the types of antennas that are used as radio telescopes vary in design and configuration. At wavelengths of 30 meters to 3 meters, they are either directional antenna arrays similar to "TV antennas" or large stationary reflectors with moveable focal points.
Since the wavelengths being observed with these types of antennas are so long, the "reflector" surfaces can be constructed from coarse wire mesh such as chicken wire. At shorter wavelengths parabolic "dish" antennas predominate; the angular resolution of a dish antenna is determined by the ratio of the diameter of the dish to the wavelength of the radio waves being observed. This dictates the dish size. Radio telescopes that operate at wavelengths of 3 meters to 30 cm are well over 100 meters in diameter. Telescopes working at wavelengths shorter than 30 cm range in size from 3 to 90 meters in diameter; the increasing use of radio frequencies for communication makes astronomical observations more and more difficult. Negotiations to defend the frequency allocation for parts of the spectrum most useful for observing the universe are coordinated in the Scientific Committee on Frequency Allocations for Radio Astronomy and Space Science; some of the more notable frequency bands used by radio telescopes include: Every frequency in the United States National Radio Quiet Zone Channel 37: 608 to 614 MHz The "Hydrogen line" known as the "21 centimeter line": 1420.40575177 MHz, used by many radio telescopes including The Big Ear in its discovery of the Wow!
Signal 1406 MHz and 430 MHz The Waterhole: 1,420 to 1,666 MHz The Arecibo Observatory
Square Kilometre Array
The Square Kilometre Array is a radio telescope project proposed to be built in Australia and South Africa. If built, it would have a total collecting area of one square kilometre, it would operate over a wide range of frequencies and its size would make it 50 times more sensitive than any other radio instrument. It would require high performance central computing engines and long-haul links with a capacity greater than the global Internet traffic as of 2013, it should be able to survey the sky more than ten thousand times faster than before. With receiving stations extending out to a distance of at least 3,000 kilometres from a concentrated central core, it would exploit radio astronomy's ability to provide the highest resolution images in all astronomy; the SKA would be built in the southern hemisphere, with cores in South Africa and Australia, where the view of the Milky Way Galaxy is the best and radio interference at its least. The SKA is estimated to cost €1.8 billion, including €650 million for Phase 1, which represents about 10% of the capability of the whole telescope.
The cost of Phase 2 has not yet been established. The headquarters of the project are located at the Jodrell Bank Observatory, in the UK. On 12 March 2019, the Square Kilometre Array Observatory was founded in Rome by seven initial member countries, with several other expected to join in the future; this international organisation is tasked with building and operating the facility, with the first construction contracts scheduled to be awarded in late 2020. The SKA is a global project with eleven member countries that aims to answer fundamental questions about the origin and evolution of the Universe. In the early days of planning, China vied to host the SKA, proposing to build several large dishes in the natural limestone depressions that dimple its southwestern provinces. In April 2011, Jodrell Bank Observatory of the University of Manchester, in Cheshire, England was announced as the location for the project headquarters. In November 2011, the SKA Organisation was formed and the project moved from a collaboration to an independent, not for profit, company.
As of June 2018, the members of the SKA Organisation are: Australia: Department of Industry and Science Canada: National Research Council China: National Astronomical Observatories of the Chinese Academy of Sciences India: National Centre for Radio Astrophysics Italy: National Institute for Astrophysics New Zealand: Ministry of Economic Development South Africa: National Research Foundation Spain: Institute of Astrophysics of Andalusia Sweden: Onsala Space Observatory The Netherlands: Netherlands Organisation for Scientific Research United Kingdom: Science and Technology Facilities Council The SKA will combine the signals received from thousands of small antennas spread over a distance of several thousand kilometres to simulate a single giant radio telescope capable of high sensitivity and angular resolution, using a technique called aperture synthesis. Some of the sub-arrays of the SKA will have a large field-of-view, making it possible to survey large areas of sky at once. One innovative development is the use of focal-plane arrays using phased-array technology to provide multiple FOVs.
This will increase the survey speed of the SKA and enable several users to observe different pieces of the sky, useful for monitoring multiple pulsars. The combination of a large FOV with high sensitivity means that the SKA will be able to compile large surveys of the sky faster than any other telescope; the SKA will provide continuous frequency coverage from 50 MHz to 14 GHz in the first two phases of its construction. A third phase will extend the frequency range up to 30 GHz. Phase 1: Providing ~10% of the total collecting area at low and mid frequencies by 2023. Phase 2: Completion of the full array at low and mid frequencies by 2030; the frequency range from 50 MHz to 14 GHz, spanning more than two decades, cannot be realised using one design of antenna and so the SKA will comprise separate sub-arrays of different types of antenna elements that will make up the SKA-low, SKA-mid and survey arrays: SKA-low array: a phased array of simple dipole antennas to cover the frequency range from 50 to 350 MHz.
These will be grouped in 100 m diameter stations each containing about 90 elements. SKA-mid array: an array of several thousand dish antennas to cover the frequency range 350 MHz to 14 GHz, it is expected that the antenna design will follow that of the Allen Telescope Array using an offset Gregorian design having a height of 15 metres and a width of 12 metres. SKA-survey array: a compact array of parabolic dishes of 12–15 meters diameter each for the medium-frequency range, each equipped with a multi-beam, phased array feed with a large field of view and several receiving systems covering about 350 MHz – 4 GHz; the survey sub-array was removed from the SKA1 specification following a "rebaselining" exercise in 2015. The area covered by the SKA – extending out to ~3000 km – will comprise three regions: A central region containing about 5 km diameter cores of SKA-mid antennas and SKA-low dipoles; these central regions will contain half of the total collecting area of the SKA arrays. A mid region extending out to 180 km.
This will contain pairs of SKA-mid and SKA-low stations. In each case they will be randomly placed within the area with the density of dishes and stations falling off towards the outer part of the region. An outer region from 180 km to 3000 km; this will comprise five spiral arms, along which dishes of SKA-mid, grouped into s
Frankfurt is a metropolis and the largest city of the German federal state of Hesse, its 746,878 inhabitants make it the fifth-largest city of Germany after Berlin, Hamburg and Cologne. On the River Main, it forms a continuous conurbation with the neighbouring city of Offenbach am Main, its urban area has a population of 2.3 million. The city is at the centre of the larger Rhine-Main Metropolitan Region, which has a population of 5.5 million and is Germany's second-largest metropolitan region after the Rhine-Ruhr Region. Since the enlargement of the European Union in 2013, the geographic centre of the EU is about 40 km to the east of Frankfurt's central business district. Like France and Franconia, the city is named after the Franks. Frankfurt is the largest city in the Rhine Franconian dialect area. Frankfurt was a city state, the Free City of Frankfurt, for nearly five centuries, was one of the most important cities of the Holy Roman Empire, as a site of imperial coronations, it has been part of the federal state of Hesse since 1945.
A quarter of the population are foreign nationals, including many expatriates. Frankfurt is an alpha world city and a global hub for commerce, education and transportation, it is the site of many European corporate headquarters. Frankfurt Airport is among the world's busiest. Frankfurt is the major financial centre of the European continent, with the headquarters of the European Central Bank, Deutsche Bundesbank, Frankfurt Stock Exchange, Deutsche Bank, DZ Bank, KfW, several cloud and fintech startups and other institutes. Automotive and research, consulting and creative industries complement the economic base. Frankfurt's DE-CIX is the world's largest internet exchange point. Messe Frankfurt is one of the world's largest trade fairs. Major fairs include the Frankfurt Motor Show, the world's largest motor show, the Music Fair, the Frankfurt Book Fair, the world's largest book fair. Frankfurt is home to influential educational institutions, including the Goethe University, the UAS, the FUMPA, graduate schools like the Frankfurt School of Finance & Management.
Its renowned cultural venues include the concert hall Alte Oper, Europe's largest English theatre and many museums. Frankfurt's skyline is shaped by some of Europe's tallest skyscrapers; the city is characterised by various green areas and parks, including the central Wallanlagen, the City Forest and two major botanical gardens, the Palmengarten and the University's Botanical Garden. Important is the Frankfurt Zoo. In electronic music, Frankfurt has been a pioneering city since the 1980s, with renowned DJs including Sven Väth, Marc Trauner, Scot Project, Kai Tracid, the clubs Dorian Gray, U60311, Omen and Cocoon. In sports, the city is known as the home of the top tier football club Eintracht Frankfurt, the Löwen Frankfurt ice hockey team, the basketball club Frankfurt Skyliners, the Frankfurt Marathon and the venue of Ironman Germany. Frankfurt is the largest financial centre in continental Europe, it is home to the European Central Bank, Deutsche Bundesbank, Frankfurt Stock Exchange and several large commercial banks.
The Frankfurt Stock Exchange is one of the world's largest stock exchanges by market capitalization and accounts for more than 90 percent of the turnover in the German market. In 2010, 63 national and 152 international banks had their registered offices in Frankfurt, including Germany's major banks, notably Deutsche Bank, DZ Bank, KfW and Commerzbank, as well as 41 representative offices of international banks. Frankfurt is considered a global city. Among global cities it was ranked 10th by the Global Power City Index 2011 and 11th by the Global City Competitiveness Index 2012. Among financial centres it was ranked 8th by the International Financial Centers Development Index 2013 and 9th by the Global Financial Centres Index 2013, its central location within Germany and Europe makes Frankfurt a major air and road transport hub. Frankfurt Airport is one of the world's busiest international airports by passenger traffic and the main hub for Germany's flag carrier Lufthansa. Frankfurt Central Station is one of the largest rail stations in Europe and the busiest junction operated by Deutsche Bahn, the German national railway company, with 342 trains a day to domestic and European destinations.
Frankfurter Kreuz, the Autobahn interchange close to the airport, is the most used interchange in the EU, used by 320,000 cars daily. In 2011 human-resource-consulting firm Mercer ranked Frankfurt as seventh in its annual'Quality of Living' survey of cities around the world. According to The Economist cost-of-living survey, Frankfurt is Germany's most expensive city and the world's 10th most expensive. Frankfurt has many high-rise buildings in the city centre, forming the Frankfurt skyline, it is one of the few cities in the European Union to have such a skyline and because of it Germans sometimes refer to Frankfurt as Mainhattan, a portmanteau of the local Main River and Manhattan. The other well known and obvious nickname is Bankfurt. Before World War II the city was globally noted for its unique old town with timber-framed buildings, the largest timber-framed old town in Europe; the Römer area was rebuilt and is popular with visitors and for eve
Brussels the Brussels-Capital Region, is a region of Belgium comprising 19 municipalities, including the City of Brussels, the capital of Belgium. The Brussels-Capital Region is located in the central portion of the country and is a part of both the French Community of Belgium and the Flemish Community, but is separate from the Flemish Region and the Walloon Region. Brussels is the most densely populated and the richest region in Belgium in terms of GDP per capita, it covers 161 km2, a small area compared to the two other regions, has a population of 1.2 million. The metropolitan area of Brussels counts over 2.1 million people, which makes it the largest in Belgium. It is part of a large conurbation extending towards Ghent, Antwerp and Walloon Brabant, home to over 5 million people. Brussels grew from a small rural settlement on the river Senne to become an important city-region in Europe. Since the end of the Second World War, it has been a major centre for international politics and the home of numerous international organisations, politicians and civil servants.
Brussels is the de facto capital of the European Union, as it hosts a number of principal EU institutions, including its administrative-legislative, executive-political, legislative branches and its name is sometimes used metonymically to describe the EU and its institutions. The secretariat of the Benelux and headquarters of NATO are located in Brussels; as the economic capital of Belgium and one of the top financial centres of Western Europe with Euronext Brussels, it is classified as an Alpha global city. Brussels is a hub for rail and air traffic, sometimes earning the moniker "Crossroads of Europe"; the Brussels Metro is the only rapid transit system in Belgium. In addition, both its airport and railway stations are the busiest in the country. Dutch-speaking, Brussels saw a language shift to French from the late 19th century; the Brussels-Capital Region is bilingual in French and Dutch though French is now the de facto main language with over 90% of the population speaking it. Brussels is increasingly becoming multilingual.
English is spoken as a second language by nearly a third of the population and a large number of migrants and expatriates speak other languages. Brussels is known for its cuisine and gastronomy, as well as its historical and architectural landmarks. Main attractions include its historic Grand Place, Manneken Pis and cultural institutions such as La Monnaie and the Museums of Art and History; because of its long tradition of Belgian comics, Brussels is hailed as a capital of the comic strip. The most common theory of the origin of the name Brussels is that it derives from the Old Dutch Bruocsella, Broekzele or Broeksel, meaning "marsh" and "home" or "home in the marsh". Saint Vindicianus, the bishop of Cambrai, made the first recorded reference to the place Brosella in 695, when it was still a hamlet; the names of all the municipalities in the Brussels-Capital Region are of Dutch origin, except for Evere, Celtic. In French, Bruxelles is pronounced and in Dutch, Brussel is pronounced. Inhabitants of Brussels are known in French in Dutch as Brusselaars.
In the Brabantian dialect of Brussels, they are called Brusseleirs. The written x noted the group. In the Belgian French pronunciation as well as in Dutch, the k disappeared and z became s, as reflected in the current Dutch spelling, whereas in the more conservative French form, the spelling remained; the pronunciation in French only dates from the 18th century, but this modification did not affect the traditional Brussels' usage. In France, the pronunciations and are heard, but are rather rare in Belgium. See also: History of Brussels The history of Brussels is linked to that of Western Europe. Traces of human settlement go back to the Stone Age, with vestiges and place-names related to the civilisation of megaliths and standing stones. During late antiquity, the region was home to Roman occupation, as attested by archaeological evidence discovered near the centre. Following the decline of the Western Roman Empire, it was incorporated into the Frankish Empire; the origin of the settlement, to become Brussels lies in Saint Gaugericus' construction of a chapel on an island in the river Senne around 580.
The official founding of Brussels is situated around 979, when Duke Charles of Lower Lotharingia transferred the relics of Saint Gudula from Moorsel to the Saint Gaugericus chapel. Charles would construct the first permanent fortification in the city, doing so on that same island. Lambert I of Leuven, Count of Leuven, gained the County of Brussels around 1000, by marrying Charles' daughter; because of its location on the shores of the Senne, on an important trade route between Bruges and Ghent, Cologne, Brussels became a commercial centre specialised in the textile trade. The town grew quite and extended towards the upper town, where there was a smaller risk of floods; as it grew to a population of around 30,000, the surrounding marshes were drained to allow for further expansion. Around
International Bureau of Weights and Measures
The International Bureau of Weights and Measures is an intergovernmental organization, established by the Metre Convention, through which member states act together on matters related to measurement science and measurement standards. The organisation is referred to by its French initialism, BIPM; the BIPM's headquarters is based at France. It has custody of the International Prototype of the Kilogram and houses the secretariat for this organization as well as hosting its formal meetings; the BIPM reports to the International Committee for Weights and Measures, a directorate of eighteen members that meet biannually, in turn overseen by the General Conference on Weights and Measures that meets in Paris once every four years, consisting of delegates of the governments of the Member States and observers from the Associates of the CGPM. These organizations are commonly referred to by their French initialisms; the BIPM was created on 20 May 1875, following the signing of the Metre Convention, a treaty among 59 Member States.
It is based at the Pavillon de Breteuil in Sèvres, France, a 4.35 ha site granted to the Bureau by the French Government in 1876. Since 1969 the site of the Pavillon de Breteuil is considered international territory and the BIPM has all the rights and privileges accorded to an intergovernmental organization; the status was further clarified by the French decree No 70-820 of 9 September 1970. The BIPM has the mandate to provide the basis for a single, coherent system of measurements throughout the world, traceable to the International System of Units; this task takes many forms, from direct dissemination of units to coordination through international comparisons of national measurement standards. Following consultation, a draft version of the BIPM Work Programme is presented at each meeting of the General Conference for consideration with the BIPM dotation; the final programme of work is determined by the CIPM in accordance with the dotation agreed by the CGPM. Main work of the BIPM include: scientific and technical activities carried out in its four departments: chemistry, ionizing radiation, physical metrology, time.
The BIPM has an important role in maintaining accurate worldwide time of day. It combines and averages the official atomic time standards of member nations around the world to create a single, official Coordinated Universal Time. Since its establishment, the directors of the BIPM have been: The BIPM centralises diverse international projects involving public & independent institutes of metrology. For example: BIPM: International Key Comparison of Liquid Hydrocarbon Flow Facilities CCM-FF-K2. Metrologia History of the metre Institute for Reference Materials and Measurements International Organization for Standardization National Institute of Standards and Technology Seconds pendulum World Metrology Day The BIPM YouTube channel BIPM BIPM
The Watergate is in Chester, Cheshire and spans the A548 road between Watergate Street and New Crane Street. It carries a footpath over the road, it is recorded in the National Heritage List for England as a designated Grade I listed building. Watergate was replaced a medieval gate; the architect was Joseph Turner. It consists of a basket arch of short rusticated voussoirs; the parapet consists of stone balusters interspersed with panels. A drinking fountain, now dry, is fixed to the north abutment and is dated 1857. Grade I listed buildings in Cheshire West and Chester Bridgegate, Chester Northgate, Chester The Watergate on'Chester: a Virtual Stroll Around the Walls'
Chester is a walled city in Cheshire, England, on the River Dee, close to the border with Wales. With a population of 118,200 in 2011, it is the most populous settlement of Cheshire West and Chester, which had a population of 332,200 in 2014. Chester was granted city status in 1541. Chester was founded as a "castrum" or Roman fort with the name Deva Victrix in the reign of the Emperor Vespasian in 79 AD. One of the main army camps in Roman Britain, Deva became a major civilian settlement. In 689, King Æthelred of Mercia founded the Minster Church of West Mercia, which became Chester's first cathedral, the Saxons extended and strengthened the walls to protect the city against the Danes. Chester was one of the last cities in England to fall to the Normans. William the Conqueror ordered the construction of a castle, to dominate the town and the nearby Welsh border. Chester is one of the best preserved walled cities in Britain, it has a number of medieval buildings, but some of the black-and-white buildings within the city centre are Victorian restorations.
Apart from a 100-metre section, the listed Grade I walls are complete. The Industrial Revolution brought railways and new roads to the city, which saw substantial expansion and development – Chester Town Hall and the Grosvenor Museum are examples of Victorian architecture from this period; the Roman Legio II Adiutrix during the reign of the Emperor Vespasian founded Chester in AD 79, as a "castrum" or Roman fort with the name Deva Victrix. It was established in the land of the Celtic Cornovii, according to ancient cartographer Ptolemy, as a fortress during the Roman expansion northward, was named Deva either after the goddess of the Dee, or directly from the British name for the river. The'victrix' part of the name was taken from the title of the Legio XX Valeria Victrix, based at Deva. Central Chester's four main roads, Northgate and Bridgegate, follow routes laid out at this time. A civilian settlement grew around the military base originating from trade with the fortress; the fortress was 20% larger than other fortresses in the Roman province of Britannia built around the same time at York and Caerleon.
The civilian amphitheatre, built in the 1st century, could seat between 8,000 and 10,000 people. It is the largest known military amphitheatre in Britain, is a Scheduled Monument; the Minerva Shrine in the Roman quarry is the only rock cut. The fortress was garrisoned by the legion until at least the late 4th century. Although the army had abandoned the fortress by 410 when the Romans retreated from Britannia, the Romano-British civilian settlement continued and its occupants continued to use the fortress and its defences as protection from raiders from the Irish Sea. After the Roman troops withdrew, the Romano-British established a number of petty kingdoms. Chester is thought to have become part of Powys. Deverdoeu was a Welsh name for Chester as late as the 12th century. Another, attested in the 9th-century History of the Britons traditionally attributed to Nennius, is Cair Legion. King Arthur is said to have fought his ninth battle at the "city of the legions" and St Augustine came to the city to try to unite the church, held his synod with the Welsh Bishops.
In 616, Æthelfrith of Northumbria defeated a Welsh army at the brutal and decisive Battle of Chester, established the Anglo-Saxon position in the area from on. The Northumbrian Anglo-Saxons used an Old English equivalent of the British name, Legacæstir, current until the 11th century, when, in a further parallel with Welsh usage, the first element fell out of use and the simple name Chester emerged. In 689, King Æthelred of Mercia founded the Minster Church of West Mercia on what is considered to be an early Christian site: it is known as the Minster of St John the Baptist, Chester which became the first cathedral. Much the body of Æthelred's niece, St Werburgh, was removed from Hanbury in Staffordshire in the 9th century and, to save it from desecration by Danish marauders, was reburied in the Church of SS Peter & Paul - to become the Abbey Church, her name is still remembered in St Werburgh's Street which passes alongside the cathedral, near the city walls. The Saxons extended and strengthened the walls of Chester to protect the city against the Danes, who occupied it for a short time until Alfred seized all the cattle and laid waste the surrounding land to drive them out.
It was Lady of the Mercians, that built the new Saxon burh. A new Church dedicated to St Peter alone was founded in AD 907 by the Lady Æthelfleda at what was to become the Cross. In 973, the Anglo-Saxon Chronicle records that, two years after his coronation at Bath, King Edgar of England came to Chester where he held his court in a palace in a place now known as Edgar's Field near the old Dee bridge in Handbridge. Taking the helm of a barge, he was rowed the short distance up the River Dee from Edgar's Field to the great Minster Church of St John the Baptist by six (the monk Henry Bradshaw records he