A marine chronometer is a timepiece, precise and accurate enough to be used as a portable time standard. When first developed in the 18th century, it was a major technical achievement, as accurate knowledge of the time over a long sea voyage is necessary for navigation, lacking electronic or communications aids; the first true chronometer was the life work of one man, John Harrison, spanning 31 years of persistent experimentation and testing that revolutionized naval navigation and enabling the Age of Discovery and Colonialism to accelerate. The term chronometer was coined from the Greek words chronos and meter in 1714 by Jeremy Thacker, an early competitor for the prize set by the Longitude Act in the same year, it has become more used to describe watches tested and certified to meet certain precision standards. Timepieces made in Switzerland may display the word "chronometer" only if certified by the COSC. To determine a position on the Earth's surface, it is necessary and sufficient to know the latitude and altitude.
Altitude considerations can be ignored for vessels operating at sea level. Until the mid-1750s, accurate navigation at sea out of sight of land was an unsolved problem due to the difficulty in calculating longitude. Navigators could determine their latitude by measuring the sun's angle at noon or, in the Northern Hemisphere, to measure the angle of Polaris from the horizon. To find their longitude, they needed a time standard that would work aboard a ship. Observation of regular celestial motions, such as Galileo's method based on observing Jupiter's natural satellites, was not possible at sea due to the ship's motion; the lunar distances method proposed by Johannes Werner in 1514, was developed in parallel with the marine chronometer. The Dutch scientist Gemma Frisius was the first to propose the use of a chronometer to determine longitude in 1530; the purpose of a chronometer is to measure the time of a known fixed location, for example Greenwich Mean Time. This is important for navigation. Knowing GMT at local noon allows a navigator to use the time difference between the ship's position and the Greenwich Meridian to determine the ship's longitude.
As the Earth rotates at a regular rate, the time difference between the chronometer and the ship's local time can be used to calculate the longitude of the ship relative to the Greenwich Meridian using spherical trigonometry. In modern practice, a nautical almanac and trigonometric sight-reduction tables permit navigators to measure the Sun, visible planets, or any of 57 selected stars for navigation at any time that the horizon is visible; the creation of a timepiece which would work reliably at sea was difficult. Until the 20th century, the best timekeepers were pendulum clocks, but both the rolling of a ship at sea and the up to 0.2% variations in the gravity of Earth made a simple gravity-based pendulum useless both in theory and in practice. Christiaan Huygens, following his invention of the pendulum clock in 1656, made the first attempt at a marine chronometer in 1673 in France, under the sponsorship of Jean-Baptiste Colbert. In 1675, receiving a pension from Louis XIV, invented a chronometer that employed a balance wheel and a spiral spring for regulation, instead of a pendulum, opening the way to marine chronometers and modern pocket watches and wristwatches.
He obtained a patent for his invention from Colbert. Huygens' attempt in 1675 to obtain an English patent from Charles II stimulated Robert Hooke, who claimed to have conceived of a spring-driven clock years earlier, to attempt to produce one and patent it. During 1675 Huygens and Hooke each delivered two such devices to Charles, but none worked well and neither Huygens nor Hooke received an English patent, it was during this work. The first published use of the term was in 1684 in Arcanum Navarchicum, a theoretical work by Kiel professor Matthias Wasmuth; this was followed by a further theoretical description of a chronometer in works published by English scientist William Derham in 1713. Derham's principal work, Physico-theology, or a demonstration of the being and attributes of God from his works of creation proposed the use of vacuum sealing to ensure greater accuracy in the operation of clocks. Attempts to construct a working marine chronometer were begun by Jeremy Thacker in England in 1714, by Henry Sully in France two years later.
Sully published his work in 1726 with Une Horloge inventée et executée par M. Sulli, but neither his nor Thacker's models were able to resist the rolling of the seas and keep precise time while in shipboard conditions. In 1714, the British government offered a longitude prize for a method of determining longitude at sea, with the awards ranging from £10,000 to £20,000 depending on accuracy. John Harrison, a Yorkshire carpenter, submitted a project in 1730, in 1735 completed a clock based on a pair of counter-oscillating weighted beams connected by springs whose motion was not influenced by gravity or the motion of a ship, his first two sea timepieces H1 and H2 used this system, but he realised that they had a fundamental sensitivity to centrifugal force, which meant that they could never be accurate enough at sea. Construction
Umbra, penumbra and antumbra
The umbra and antumbra are three distinct parts of a shadow, created by any light source after impinging on an opaque object. Assuming no diffraction, for a point source only the umbra is cast; these names are most used for the shadows cast by celestial bodies, though they are sometimes used to describe levels of darkness, such as in sunspots. The umbra is the innermost and darkest part of a shadow, where the light source is blocked by the occluding body. An observer in the umbra experiences a total eclipse; the umbra of a round body occluding a round light source forms a right circular cone. The distance from the Moon to the apex of its umbra is equal to that between the Moon and Earth. Since Earth's diameter is 3.70 times the Moon's, its umbra extends correspondingly farther: 1,400,000 km. The penumbra is the region in which only a portion of the light source is obscured by the occluding body. An observer in the penumbra experiences a partial eclipse. An alternative definition is that the penumbra is the region where some or all of the light source is obscured.
For example, NASA's Navigation and Ancillary Information Facility defines that a body in the umbra is within the penumbra. The antumbra is the region from which the occluding body appears within the disc of the light source. An observer in this region experiences an annular eclipse, in which a bright ring is visible around the eclipsing body. If the observer moves closer to the light source, the apparent size of the occluding body increases until it causes a full umbra. Antisolar point Earth's shadow
Alexander Wilson (astronomer)
Alexander Wilson was a Scottish surgeon, type-founder, astronomer and meteorologist. He was the first scientist to record the use of kites in meteorological investigations, his son Patrick Wilson succeeded him as Regius Professor of Practical Astronomy at Glasgow University, in 1784. Wilson was born in St. Andrews, the son of Patrick Wilson, the town clerk. Alexander was educated at the University of St. Andrews from where he graduated MA in 1733, at the age of 18, he was first apprenticed to a physician in St Andrews where he became skilled in constructing mercury thermometers in glass. In 1737 he left for London, to make his fortune and found work as assistant to a French surgeon-apothecary, which included caring for his patients. During this time he was introduced to Lord Isla who like Wilson was interested in astronomy, Wilson constructed instruments for Isla during 1738. After visiting a type foundry with a friend in London, he had an idea for making better typefaces, he and his friend John Baine returned to St Andrews in 1739, where they started a type-founding business in 1742.
The company moved to Camlachie, near Glasgow in 1744. In 1748 he was appointed type-founder to Glasgow University. In the following year the partnership with Baine was dissolved, his sons became partners. He supplied types to the Foulis press making possible their artistic publications. Among modern typefaces, Scotch Roman, Wilson Greek are based on types cut by Alexander Wilson. In 1749 Wilson made the first recorded use of kites in meteorology with his lodger, a 23-year-old Glasgow University student Thomas Melvill, who went on to discover sodium light, they measured air temperature at various levels above the ground with a train of kites. With the help of his friend Lord Isla, now the 3rd Duke of Argyle, he was appointed in 1760 to the new chair of practical astronomy at the University of Glasgow, which had built the Macfarlane Observatory. Wilson made contributions to astronomy and meteorology, posited that "what hinders the fixed stars from falling upon one another", the question that Newton had posed in his Opticks, was that the entire universe rotated around its centre.
This has been found to be true of the stars of the Galaxy, the known universe, which rotates around a central black hole. It is not true for the galaxies of the Universe, expanding. Wilson noted that sunspots viewed near the edge of the Sun's visible disk appear depressed below the solar surface, a phenomenon referred to as the Wilson effect; when the Royal Danish Academy of Sciences and Letters announced a prize to be awarded for the best essay on the nature of solar spots, Wilson submitted an entry. On 18 February 1772 the Academy presented Wilson with a gold medal for his work on sunspots; the crater Wilson on the Moon is named for Ralph Elmer Wilson and CTR Wilson. He, his second son Patrick Wilson, were two of the founding members of the Royal Society of Edinburgh. Peter wrote a biographical article of his father, published both in the Transactions of the RSE and Edinburgh Journal of Science, now available on-line. Royal Society of Edinburgh accessed 10 Mar 2009 Williamson, Peter & Woodby, John,'Scottish Book Trade Index', National Library of Scotland' accessed 19 Dec 2008 Smith, George Fairfull, "Robert & Andrew Foulis, the Foulis Press, Their Legacy", accessed 19 Dec 2008.
Stronach, rev. Hutchins, Roger, "Wilson, Alexander", Oxford Dictionary of National Biography, Oxford University Press, 2004, accessed 19 Dec 2008 Wilson, Alexander "Observations on Solar Spots", Philosophical Transactions of the Royal Society of London 64, part I. Wilson, Patrick. "Biographical account of Alexander Wilson, MD, late professor of practical astronomy in Glasgow". Transactions of the Royal Society of Edinburgh. 10: 279–97. Published in Edinburgh Journal of Science 10:1–17 from the Biodiversity Heritage Library. "Alexander Wilson". MacTutor archive. Retrieved 4 December 2005
A prime meridian is a meridian in a geographic coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its anti-meridian form a great circle; this great circle divides e.g. Earth, into two hemispheres. If one uses directions of East and West from a defined prime meridian they can be called the Eastern Hemisphere and the Western Hemisphere. A prime meridian is arbitrary, unlike an equator, determined by the axis of rotation—and various conventions have been used or advocated in different regions and throughout history; the most used modern meridian is the IERS Reference Meridian. It is derived but deviates from the Greenwich Meridian, selected as an international standard in 1884; the notion of longitude was developed by the Greek Eratosthenes in Alexandria, Hipparchus in Rhodes, applied to a large number of cities by the geographer Strabo. But it was Ptolemy. Ptolemy used as his basis the "Fortunate Isles", a group of islands in the Atlantic which are associated with the Canary Islands, although his maps correspond more to the Cape Verde islands.
The main point is to be comfortably west of the western tip of Africa as negative numbers were not yet in use. His prime meridian corresponds to 18° 40' west of Winchester today. At that time the chief method of determining longitude was by using the reported times of lunar eclipses in different countries. Ptolemy's Geographia was first printed with maps at Bologna in 1477, many early globes in the 16th century followed his lead, but there was still a hope. Christopher Columbus reported that the compass pointed due north somewhere in mid-Atlantic, this fact was used in the important Treaty of Tordesillas of 1494 which settled the territorial dispute between Spain and Portugal over newly discovered lands; the Tordesillas line was settled at 370 leagues west of Cape Verde. This is shown in Diogo Ribeiro's 1529 map. São Miguel Island in the Azores was still used for the same reason as late as 1594 by Christopher Saxton, although by it had been shown that the zero magnetic deviation line did not follow a line of longitude.
In 1541, Mercator produced his famous 41 cm terrestrial globe and drew his prime meridian through Fuerteventura in the Canaries. His maps used the Azores, following the magnetic hypothesis, but by the time that Ortelius produced the first modern atlas in 1570, other islands such as Cape Verde were coming into use. In his atlas longitudes were counted from 0° to 360°, not 180°W to 180°E as is usual today; this practice was followed by navigators well into the 18th century. In 1634, Cardinal Richelieu used the westernmost island of the Canaries, Ferro, 19° 55' west of Paris, as the choice of meridian; the geographer Delisle decided to round this off to 20°, so that it became the meridian of Paris disguised. In the early 18th century the battle was on to improve the determination of longitude at sea, leading to the development of the marine chronometer by John Harrison, but it was the development of accurate star charts, principally by the first British Astronomer Royal, John Flamsteed between 1680 and 1719 and disseminated by his successor Edmund Halley, that enabled navigators to use the lunar method of determining longitude more using the octant developed by Thomas Godfrey and John Hadley.
Between 1765 and 1811, Nevil Maskelyne published 49 issues of the Nautical Almanac based on the meridian of the Royal Observatory, Greenwich. "Maskelyne's tables not only made the lunar method practicable, they made the Greenwich meridian the universal reference point. The French translations of the Nautical Almanac retained Maskelyne's calculations from Greenwich—in spite of the fact that every other table in the Connaissance des Temps considered the Paris meridian as the prime." In 1884, at the International Meridian Conference in Washington, D. C. 22 countries voted to adopt the Greenwich meridian as the prime meridian of the world. The French argued for a neutral line, mentioning the Azores and the Bering Strait, but abstained and continued to use the Paris meridian until 1911. In October 1884 the Greenwich Meridian was selected by delegates to the International Meridian Conference held in Washington, D. C. United States to be the common zero of longitude and standard of time reckoning throughout the world.
The modern prime meridian, the IERS Reference Meridian, is placed near this meridian and is the prime meridian that has the widest use. The modern prime meridian, based at the Royal Observatory, was established by Sir George Airy in 1851; the position of the Greenwich Meridian has been defined by the location of the Airy Transit Circle since the first observation was taken with it by Sir George Airy in 1851. Prior to that, it was defined by a succession of earlier transit instruments, the first of, acquired by the second Astronomer Royal, Edmond Halley in 1721, it was set up in the extreme north-west corner of the Observatory between Flamsteed House and the Western Summer House. This spot, now subsumed into Flamsteed House, is 43 metres to the west of the Airy Transit Circle, a distance equivalent to 0.15 seconds of time. It was Airy's transit circle, adopted in principle as the Prime Meridian of th
University of Rochester
The University of Rochester is a private research university in Rochester, New York. The university grants undergraduate and graduate degrees, including doctoral and professional degrees; the University of Rochester enrolls 5,600 undergraduates and 4,600 graduate students. Its 158 buildings house over 200 academic majors. Additionally, the university is the largest employer in the Greater Rochester area and the 6th largest employer in New York. According to the National Science Foundation ranking of total research and development expenditures, the University of Rochester spent $346 million on R&D in 2016, the 66th highest figure, nationally; the College of Arts and Engineering is home to departments and divisions of note. The Institute of Optics was founded in 1929 through a grant from Eastman Kodak and Bausch and Lomb as the first educational program in the US devoted to optics, awards half of all optics degrees nationwide, is regarded as the premier optics program in the nation; the Departments of Political Science and Economics have made a significant and consistent impact on positivist social science since the 1960s, rank in the top 5 in their fields.
The Department of Chemistry is noted for its contributions to synthetic organic chemistry, including the first lab based synthesis of morphine. The Rossell Hope Robbins Library serves as the university's resource for Old and Middle English texts and expertise; the university is home to Rochester's Laboratory for Laser Energetics, a US Department of Energy supported national laboratory. The University of Rochester's Eastman School of Music, ranks first among music schools in the U. S; the Sibley Music Library at Eastman is the largest academic music library in North America and holds the third largest collection in the United States. In its history, 7 university alumni, 4 faculty, 1 senior research associate at Strong Memorial Hospital have been awarded Nobel Prizes; the University of Rochester traces its origins to The First Baptist Church of Hamilton, founded in 1796. The church established the Baptist Education Society of the State of New York renamed the Hamilton Literary and Theological Institution, in 1817.
This institution gave birth to The University of Rochester. Its function was to train clergy in the Baptist tradition; when it aspired to grant higher degrees, it created a collegiate division separate from the theological division. The collegiate division was granted a charter by the State of New York in 1846, after which its name was changed to Madison University. John Wilder and the Baptist Education Society urged that the new university be moved to Rochester, New York. However, legal action prevented the move. In response, dissenting faculty and trustees defected and departed for Rochester, where they sought a new charter for a new university. Madison University was renamed as Colgate University. Asahel C. Kendrick, professor of Greek, was among the faculty. Kendrick served as acting president, he reprised this role until 1853, when Martin Brewer Anderson of the Newton Theological Seminary in Massachusetts was selected to fill the inaugural posting. The University of Rochester's new charter was awarded by the Regents of the State of New York on January 31, 1850.
The charter stipulated that the university have $100,000 in endowment within five years, upon which the charter would be reaffirmed. An initial gift of $10,000 was pledged by John Wilder, which helped catalyze significant gifts from individuals and institutions. Classes began that November, with 60 students enrolled, including 28 transfers from Madison. From 1850 to 1862, the university was housed in the old United States Hotel in downtown Rochester on Buffalo Street near Elizabeth Street, West Main Street near the I-490 overpass. On a February 1851 visit, Ralph Waldo Emerson said of the university:'They had bought a hotel, once a railroad terminus depot, for $8,500, turned the dining room into a chapel by putting up a pulpit on one side, made the barroom into a Pythologian Society's Hall, & the chambers into Recitation rooms, Libraries, & professors' apartments, all for $700 a year, they had brought an omnibus load of professors down from Madison bag and baggage... called in a painter and sent him up the ladder to paint the title "University of Rochester" on the wall, they had runners on the road to catch students.
And they are confident of graduating a class of ten by the time green peas are ripe."For the next 10 years, the college expanded its scope and secured its future through an expanding endowment, student body, faculty. In parallel, a gift of 8 acres of farmland from local businessman and Congressman Azariah Boody secured the first campus of the university, upon which Anderson Hall was constructed and dedicated in 1862. Over the next sixty years, this Prince Street Campus grew by a further 17 acres and was developed to include fraternities houses and academic buildings including Anderson Hall, Sibley Library and Carnegie Laboratories, the Memorial Art Gallery, Cutler Union; the first female students were admitted in 1900, the result of an effort led by Susan B. Anthony and Helen Barrett Montgomery. During the 1890s, a number of women took classes and labs at the university as "visitors" but were not enrolled nor were their records included in the college register. President David Jayne Hill allowed the first woman, Hele
Royal Observatory, Greenwich
The Royal Observatory, Greenwich is an observatory situated on a hill in Greenwich Park, overlooking the River Thames. It played a major role in the history of astronomy and navigation, is best known for the fact that the prime meridian passes through it, thereby gave its name to Greenwich Mean Time; the ROG has the IAU observatory code of the first in the list. ROG, the National Maritime Museum, the Queen's House and Cutty Sark are collectively designated Royal Museums Greenwich; the observatory was commissioned in 1675 by King Charles II, with the foundation stone being laid on 10 August. The site was chosen by Sir Christopher Wren. At that time the king created the position of Astronomer Royal, to serve as the director of the observatory and to "apply himself with the most exact care and diligence to the rectifying of the tables of the motions of the heavens, the places of the fixed stars, so as to find out the so much desired longitude of places for the perfecting of the art of navigation."
He appointed John Flamsteed as the first Astronomer Royal. The building was completed in the summer of 1676; the building was called "Flamsteed House", in reference to its first occupant. The scientific work of the observatory was relocated elsewhere in stages in the first half of the 20th century, the Greenwich site is now maintained exclusively as a museum, although the AMAT telescope became operational for astronomical research in 2018. 1675 – 22 June, Royal Observatory founded. 1675 – 10 August, construction began. 1714 Longitude Act established the Board of Longitude rewards. The Astronomer Royal was, until the Board was dissolved in 1828, always an ex officio Commissioner of Longitude. 1767 Astronomer Royal Nevil Maskelyne began publication of the Nautical Almanac, based on observations made at the Observatory. 1818 Oversight of the Royal Observatory was transferred from the Board of Ordnance to the Board of Admiralty. 1833 Daily time signals began. 1899 The New Physical Observatory was completed.
1924 Hourly time signals from the Royal Observatory were first broadcast on 5 February. 1948 Office of the Astronomer Royal was moved to Herstmonceux. 1957 Royal Observatory completed its move to Herstmonceux. The Greenwich site is renamed the Old Royal Observatory. 1990 RGO moved to Cambridge. 1998 RGO closed. Greenwich site is returned to its original name, the Royal Observatory, is made part of the National Maritime Museum. 2011 The Greenwich museums, including the ROG, become collectively the Royal Museums Greenwich. There had been significant buildings on this land since the reign of William I. Greenwich Palace, on the site of the present-day Maritime Museum, was the birthplace of both Henry VIII and his daughters Mary I and Elizabeth I. Greenwich Castle was a favourite place for Henry VIII to house his mistresses, so that he could travel from the Palace to see them; the establishment of a Royal Observatory was proposed in 1674 by Sir Jonas Moore who, in his role as Surveyor General at the Ordnance Office, persuaded King Charles II to create the observatory, with John Flamsteed installed as its director.
The Ordnance Office was given responsibility for building the Observatory, with Moore providing the key instruments and equipment for the observatory at his own personal cost. Flamsteed House, the original part of the Observatory, was designed by Sir Christopher Wren assisted by Robert Hooke, was the first purpose-built scientific research facility in Britain, it was built for a cost of £520 out of recycled materials on the foundations of Duke Humphrey's Tower, the forerunner of Greenwich Castle, which resulted in the alignment being 13 degrees away from true North, somewhat to Flamsteed's chagrin. The original observatory at first housed the scientific instruments to be used by Flamsteed in his work on stellar tables, over time incorporated additional responsibilities such as marking the official time of day, housing Her Majesty's Nautical Almanac Office. Moore donated two clocks, built by Thomas Tompion, which were installed in the 20 foot high Octagon Room, the principal room of the building.
They were of unusual design, each with a pendulum 13 feet in length mounted above the clock face, giving a period of four seconds and an accuracy unparalleled, of seven seconds per day. British astronomers have long used the Royal Observatory as a basis for measurement. Four separate meridians have passed through the buildings, defined by successive instruments; the basis of longitude, the meridian that passes through the Airy transit circle, first used in 1851, was adopted as the world's Prime Meridian at the International Meridian Conference on 22 October 1884. Subsequently, nations across the world used it as their standard for timekeeping; the Prime Meridian was marked by a brass strip in the Observatory's courtyard once the buildings became a museum in 1960, since 16 December 1999, has been marked by a powerful green laser shining north across the London night sky. Since the first triangulation of Great Britain in the period 1783–1853, Ordnance Survey maps have been based on an earlier version of the Greenwich meridian, defined by the transit instrument of James
Dava Sobel is an American writer of popular expositions of scientific topics. Her books include Longitude, about English clockmaker John Harrison, Galileo's Daughter, about Galileo's daughter Maria Celeste, The Glass Universe: How the Ladies of the Harvard Observatory Took the Measure of the Stars. Sobel was born in The New York City, she graduated from the Bronx High School of Binghamton University. She wrote Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time in 1995; the story was made into a television movie, of the same name by Charles Sturridge and Granada Film in 1999, was shown in the United States by A&E. Her book Galileo's Daughter: A Historical Memoir of Science and Love was a finalist for the 2000 Pulitzer Prize for Biography or Autobiography, she holds honorary doctor of letters degrees from the University of Bath and Middlebury College, both awarded in 2002. Sobel made her first foray into teaching at the University of Chicago as the Vare Writer-in-Residence in the winter of 2006.
She taught a one-quarter seminar on writing about science. She served as a judge for the PEN/E. O. Wilson Literary Science Writing Award in 2012. Sobel is the cousin of epidemiologist David Michaels; the asteroid 30935 Davasobel is named after her. Sobel states she is a chaser of solar eclipses and that "it's the closest thing to witnessing a miracle"; as of August 2012 she had seen eight, planned to see the November 2012 total solar eclipse in Australia. Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time ISBN 1-85702-571-7. OCLC 909490210 – the genius in question was John Harrison, who spent decades trying to convince the British Admiralty of the accuracy of his naval timepieces and their use in determining longitude when at sea in order to win the longitude prize; the book itself won the 1997 British Book of the Year award. Galileo's Daughter: A Historical Memoir of Science and Love ISBN 0-14-028055-3 The Best American Science Writing 2004 ISBN 9780060726409, OCLC 916515131 The Planets: A discourse on the discovery, science and mythology, of the planets in our solar system, with one chapter devoted to each of the celestial spheres.
ISBN 1-85702-850-3, OCLC 77646686 A More Perfect Heaven: How Copernicus Revolutionized the Cosmos. Bloomsbury Publishing. 4 October 2011. ISBN 978-0-8027-7893-2. OCLC 819387028 The Glass Universe: How the Ladies of the Harvard Observatory Took the Measure of the Stars ISBN 9780143111344, OCLC 972263666 Official website Dava Sobel on IMDb Podcast of Dava Sobel discussing The Origins of Longitude at the Shanghai International Literary Festival Appearances on C-SPAN