Misplaced Pages

#868131

35-504: The Pisces–Cetus Supercluster Complex is estimated to be about 1.0 billion light-years (Gly) long and 150 million light years (Mly) wide. It is one of the largest structures known in the observable universe , but is exceeded by the Sloan Great Wall (1.3 Gly), Clowes–Campusano LQG (2.0 Gly), U1.11 LQG (2.5 Gly), Huge-LQG (4.0 Gly), and Hercules–Corona Borealis Great Wall (10 Gly), respectively. Sixty clusters comprise

70-419: A meridian circle from Reichenbach , assisted by some of his qualified students. The most prominent of them was Friedrich Wilhelm Argelander , his successors were Otto August Rosenberger and August Ludwig Busch . Bessel determined the first reliable value for the distance between a star and the solar system with a heliometer from Fraunhofer using the method of stellar parallax . In 1838 he published

105-407: A star system tend to be small fractions of a light-year, and are usually expressed in astronomical units . However, smaller units of length can similarly be formed usefully by multiplying units of time by the speed of light. For example, the light-second , useful in astronomy, telecommunications and relativistic physics, is exactly 299 792 458 metres or ⁠ 1 / 31 557 600 ⁠ of

140-486: A unit of time . The light-year is most often used when expressing distances to stars and other distances on a galactic scale, especially in non-specialist contexts and popular science publications. The unit most commonly used in professional astronomy is the parsec (symbol: pc, about 3.26 light-years). As defined by the International Astronomical Union (IAU), the light-year

175-459: A lasting impact upon the work of Neumann's students and upon the Prussian conception of precision in measurement. Bessel had two sons and three daughters. His elder son became an architect but died suddenly in 1840 aged 26; his younger son died shortly after birth. His eldest daughter, Marie, married the physicist Georg Adolf Erman , member of the scholar family Erman . One of their sons in turn

210-412: A light-year. Units such as the light-minute, light-hour and light-day are sometimes used in popular science publications. The light-month, roughly one-twelfth of a light-year, is also used occasionally for approximate measures. The Hayden Planetarium specifies the light month more precisely as 30 days of light travel time. Light travels approximately one foot in a nanosecond ; the term "light-foot"

245-419: A parallax of 0.314 arcseconds for 61 Cygni , which indicated that the star is 10.3 ly away. Compared with the current measurement of 11.4 ly, Bessel's figure had an error of 9.6%. Thanks to these results astronomers had not only enlarged the vision of the universe well beyond the cosmic magnitude, but after the discovery in 1728 by James Bradley of the aberration of light a second empirical evidence of

280-655: A report on astronomical clocks. Bessel married Johanna Hagen, the daughter of the chemist and pharmacist Karl Gottfried Hagen who was the uncle of the physician and biologist Hermann August Hagen and the hydraulic engineer Gotthilf Hagen , the latter also Bessel's student and assistant from 1816 to 1818. The physicist Franz Ernst Neumann , Bessel's close companion and colleague, was married to Johanna Hagen's sister Florentine. Neumann introduced Bessel's exacting methods of measurement and data reduction into his mathematico-physical seminar, which he co-directed with Carl Gustav Jacob Jacobi at Königsberg. These exacting methods had

315-875: A way of determining longitude . Bessel came to the attention of Heinrich Wilhelm Olbers , a practising physician of Bremen and well-known astronomer, by producing a refinement on the orbital calculations for Halley's Comet in 1804, using old observation data taken from Thomas Harriot and Nathaniel Torporley in 1607. Franz Xaver von Zach edited the results in his journal Monatliche Correspondenz . Having finished his commercial education, Bessel left Kulenkamp in 1806 and became assistant at Johann Hieronymus Schröter 's private observatory in Lilienthal near Bremen as successor of Karl Ludwig Harding . There he worked on James Bradley 's stellar observation data to produce precise positions for some 3,222 stars. Despite lacking any higher education, especially at university, Bessel

350-560: Is "ly", International standards like ISO 80000:2006 (now superseded) have used "l.y." and localized abbreviations are frequent, such as "al" in French, Spanish, and Italian (from année-lumière , año luz and anno luce , respectively), "Lj" in German (from Lichtjahr ), etc. Before 1984, the tropical year (not the Julian year) and a measured (not defined) speed of light were included in

385-402: Is a unit of length used to express astronomical distances and is equal to exactly 9 460 730 472 580 .8 km , which is approximately 5.88 trillion mi. As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in vacuum in one Julian year (365.25 days). Despite its inclusion of the word "year", the term should not be misinterpreted as

SECTION 10

#1732786705869

420-533: Is an odd name. In 1868 an English journal labelled the light-year as a unit used by the Germans. Eddington called the light-year an inconvenient and irrelevant unit, which had sometimes crept from popular use into technical investigations. Although modern astronomers often prefer to use the parsec , light-years are also popularly used to gauge the expanses of interstellar and intergalactic space. Distances expressed in light-years include those between stars in

455-583: Is sometimes used as an informal measure of time. Friedrich Bessel Friedrich Wilhelm Bessel ( German: [ˈbɛsl̩] ; 22 July 1784 – 17 March 1846) was a German astronomer , mathematician , physicist , and geodesist . He was the first astronomer who determined reliable values for the distance from the sun to another star by the method of parallax . Certain important mathematical functions were named Bessel functions after Bessel's death, though they had originally been discovered by Daniel Bernoulli before being generalised by Bessel. Bessel

490-570: Is the product of the Julian year (365.25 days, as opposed to the 365.2425-day Gregorian year or the 365.24219-day Tropical year that both approximate) and the speed of light ( 299 792 458  m/s ). Both of these values are included in the IAU (1976) System of Astronomical Constants , used since 1984. From this, the following conversions can be derived: The abbreviation used by the IAU for light-year

525-598: Is the product of the J1900.0 mean tropical year and the defined speed of light. Abbreviations used for light-years and multiples of light-years are: The light-year unit appeared a few years after the first successful measurement of the distance to a star other than the Sun, by Friedrich Bessel in 1838. The star was 61 Cygni , and he used a 160-millimetre (6.2 in) heliometre designed by Joseph von Fraunhofer . The largest unit for expressing distances across space at that time

560-716: The University of Göttingen in March 1811. Both scientists were in correspondence from 1804 to 1843. In 1837 they got in quarrel about Gauss's habit of very slow publication. In 1842 Bessel took part in the annual meeting of the British Association for the Advancement of Science in Manchester, accompanied by the geophysicist Georg Adolf Erman and the mathematician Carl Gustav Jacob Jacobi , where he gave

595-507: The Earth's relative movement was produced. A short time later Friedrich Georg Wilhelm Struve and Thomas Henderson reported the parallaxes of Vega and Alpha Centauri . Precise measurements with a new meridian circle from Adolf Repsold allowed Bessel to notice deviations in the motions of Sirius and Procyon , which must be caused by the gravitational attraction of unseen companions. His announcement of Sirius's "dark companion" in 1844

630-496: The IAU (1964) System of Astronomical Constants, used from 1968 to 1983. The product of Simon Newcomb 's J1900.0 mean tropical year of 31 556 925 .9747 ephemeris seconds and a speed of light of 299 792 .5 km/s produced a light-year of 9.460 530 × 10  m (rounded to the seven significant digits in the speed of light) found in several modern sources was probably derived from an old source such as C. W. Allen 's 1973 Astrophysical Quantities reference work, which

665-665: The Moon's Mare Serenitatis . The main-belt asteroid 1552 Bessel was named at the centenary of the parallaxe determination in 1938. Geographical commemorations are two fjords in Greenland, Bessel Fjord, NE Greenland and Bessel Fjord, NW Greenland . Xyletinus besseli a fossil beetle from the Eocene belonging to the family Ptinidae , found in the Baltic amber in Sambia ,

700-567: The Prussian army; the final report was published in 1838. He also obtained an estimate of increased accuracy for the Earth's ellipsoid , nowadays called the Bessel ellipsoid , based on several arc measurements . Bessel was one of the first members of the Order Pour le Merite (Civil class) when it was established in 1842. The first cosmic object named after Bessel is the largest crater in

735-539: The complex, which is estimated to have a total mass of 10 M ☉ . According to the discoverer, the complex is composed of 5 parts: With its mass of 10 M ☉ , our Virgo Supercluster accounts only for 0.1 percent of the total mass of the complex. The complex was named after the Pisces–Cetus Superclusters, which are its richest superclusters. Light-year A light-year , alternatively spelled light year ( ly or lyr ),

SECTION 20

#1732786705869

770-413: The formula for the sample variance estimator is named in his honour. This is the use of the factor n  − 1 in the denominator of the formula, rather than just n . This occurs when the sample mean rather than the population mean is used to centre the data and since the sample mean is a linear combination of the data the residual to the sample mean overcounts the number of degrees of freedom by

805-438: The mental picture of the approximate transit time for light, but he refrained from using the light-year as a unit. He may have resisted expressing distances in light-years because it would reduce the accuracy of his parallax data due to multiplying with the uncertain parameter of the speed of light. The speed of light was not yet precisely known in 1838; the estimate of its value changed in 1849 ( Fizeau ) and 1862 ( Foucault ). It

840-469: The number of constraint equations — in this case one. Like numerous astronomers of his time Bessel dealt on the field of geodesy , too, first theoretically, when he published a method for solving the main geodetic problem . In 1830 he got the royal order for the survey of East Prussia with the purpose to connect the yet existing Prussian and Russian triangulation networks . This work was carried out in cooperation with Johann Jacob Baeyer , then major of

875-600: The observatory was still in construction Bessel elaborated the Fundamenta Astronomiae based on Bradley's observations. As a preliminary result he produced tables of atmospheric refraction that won him the Lalande Prize from the French Academy of Sciences in 1811. The Königsberg Observatory began operation in 1813. Starting in 1819, Bessel determined the position of over 50,000 stars with

910-539: The position calculated by Le Verrier in September 1846 at Berlin Observatory . In the second decade of the 19th century, while studying the dynamics gravitational systems as multi-body problem , Bessel developed what are now known as Bessel functions . Critical for the solution of certain differential equations , these functions are used throughout both classical and quantum physics . A correction term in

945-427: The same general area, such as those belonging to the same spiral arm or globular cluster . Galaxies themselves span from a few thousand to a few hundred thousand light-years in diameter, and are separated from neighbouring galaxies and galaxy clusters by millions of light-years. Distances to objects such as quasars and the Sloan Great Wall run up into the billions of light-years. Distances between objects within

980-819: The transit time of stars. In 1824, Bessel developed a new method for calculating the circumstances of eclipses using the so-called Besselian elements . His method simplified the calculation to such an extent, without sacrificing accuracy, that it is still in use today. On Bessel's proposal the Prussian Academy of Sciences started the edition of the Berliner Akademische Sternkarten ( Berlin Academic Star Charts ) in 1825 as an international project with Johann Franz Encke as executive editor. One unpublished new chart enabled Johann Gottfried Galle to find Neptune near

1015-562: Was appointed director of the newly founded Königsberg Observatory by King Frederick William III of Prussia in January 1810, at the age of 25, and remained in that position until his death. Some elder professors of the Philosophical Faculty disputed Bessel's right to teach mathematics without any academic degree. Therefore, he turned to his fellow Carl Friedrich Gauss , who provided the award of an honorary doctor degree from

1050-587: Was born in Minden , Westphalia , then capital of the Prussian administrative region Minden-Ravensberg , as second son of a civil servant into a large family. At the age of 14 he left the school, because he did not like the education in Latin language, and apprenticed in the import-export concern Kulenkamp at Bremen . The business's reliance on cargo ships led him to turn his mathematical skills to problems in navigation . This in turn led to an interest in astronomy as

1085-432: Was not yet considered to be a fundamental constant of nature, and the propagation of light through the aether or space was still enigmatic. The light-year unit appeared in 1851 in a German popular astronomical article by Otto Ule . Ule explained the oddity of a distance unit name ending in "year" by comparing it to a walking hour ( Wegstunde ). A contemporary German popular astronomical book also noticed that light-year

Pisces–Cetus Supercluster Complex - Misplaced Pages Continue

1120-440: Was the astronomical unit , equal to the radius of the Earth's orbit at 150 million kilometres (93 million miles). In those terms, trigonometric calculations based on 61 Cygni's parallax of 0.314 arcseconds, showed the distance to the star to be 660 000 astronomical units (9.9 × 10  km; 6.1 × 10  mi). Bessel added that light takes 10.3 years to traverse this distance. He recognized that his readers would enjoy

1155-525: Was the first correct claim of a previously unobserved companion by positional measurement, and eventually led to the discovery of Sirius B by Alvan Graham Clark in 1862, the first discovery of a white dwarf . John Martin Schaeberle discovered Procyon B in 1896. Bessel was the first scientist who realized the effect later called personal equation , that several simultaneously observing persons determine slightly different values, especially recording

1190-459: Was the renowned Egyptologist Adolf Erman . His third daughter Johanna married the politician Adolf Hermann Hagen ; one of their sons was the physicist Ernst Bessel Hagen , and the mathematician Erich Bessel-Hagen was a grandson of them. Bessel was godfather of Adolf von Baeyer , son of his collaborator Johann Jacob Baeyer . After several months of illness Bessel died in March 1846 at his observatory from retroperitoneal fibrosis . While

1225-438: Was updated in 2000, including the IAU (1976) value cited above (truncated to 10 significant digits). Other high-precision values are not derived from a coherent IAU system. A value of 9.460 536 207 × 10  m found in some modern sources is the product of a mean Gregorian year (365.2425 days or 31 556 952  s ) and the defined speed of light ( 299 792 458  m/s ). Another value, 9.460 528 405 × 10  m ,

#868131