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32-500: 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

64-419: 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

96-404: 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 highly ambitious people who own science-grade telescopes and instruments with which they are able to make their own discoveries, create astrophotographs , and assist professional astronomers in research. Georg Adolf Erman Erman

128-438: 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 also have outreach programs, including public telescope time and sometimes planetariums , as a public service to encourage interest in

160-459: 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

192-416: 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

224-653: 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

256-738: 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, evolve, and die. They use this 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 , astrobiology , stellar astronomy , astrometry , galactic astronomy , extragalactic astronomy , or physical cosmology . Astronomers can also specialize in certain specialties of observational astronomy, such as infrared astronomy , neutrino astronomy , x-ray astronomy , and gravitational-wave astronomy . Historically , astronomy

288-873: 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

320-552: The Bar and Spiral Structure Legacy Survey , is named after him. Astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth . Astronomers observe astronomical objects , such as stars , planets , moons , comets and galaxies – in either observational (by analyzing the data) or theoretical astronomy . Examples of topics or fields astronomers study include planetary science , solar astronomy ,

352-715: 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

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384-568: The origin or evolution of stars , or the formation of galaxies . A related but distinct subject is physical cosmology , which studies the Universe as a whole. Astronomers usually fall under either of two main types: observational and theoretical . Observational astronomers make direct observations of celestial objects and 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

416-504: 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

448-697: 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 , was named in his honour. BeSSel,

480-545: The PhD level and beyond (as of 2024). 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 (CCD) 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 relatively little time at telescopes, usually just

512-563: 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

544-421: The core sciences, a competency examination, experience with teaching undergraduates and participating in outreach programs, work on research projects under the student's supervising professor, completion of a PhD thesis , and passing a final oral exam . Throughout the PhD training, a successful student is financially supported with a stipend . While there is a relatively low number of professional astronomers,

576-474: The field is popular among amateurs . Most cities have amateur astronomy clubs that meet on a regular basis and often 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. As with any hobby , most people who practice amateur astronomy may devote

608-489: The field. Those who become astronomers usually have a broad background in physics, mathematics , sciences, and computing in high school. Taking courses that teach how to research, write, and present papers are part of the higher education of an astronomer, while most astronomers attain both a Master's degree and eventually a PhD degree in astronomy, physics or astrophysics . PhD training typically involves 5-6 years of study, including completion of upper-level courses in

640-413: 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

672-694: The majority of their time working on research, although they quite often have other duties such as teaching, building instruments, or aiding in the operation of an observatory. The American Astronomical Society , which is the major organization of professional astronomers in North America , has approximately 8,200 members (as of 2024). This number includes scientists from other fields such as physics, geology , and engineering , whose research interests are closely related to astronomy. The International Astronomical Union comprises about 12,700 members from 92 countries who are involved in astronomical research at

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704-467: 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

736-600: 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

768-539: 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

800-817: 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

832-562: 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

864-511: Was appointed professor of physics at Berlin in 1839, and died there in 1877. From 1841 to 1865 he edited the Archiv für wissenschaftliche Kunde von Russland , and in 1874 he published, with H. J. R. Petersen, Die Grundlagen der Gauss'schen Theorie und die Erscheinungen des Erdmagnetismus im Jahre 1829. Erman married, Marie Bessel, daughter of Friedrich Bessel , and they were the parents of Johann Peter Adolf Erman . This article about

896-587: 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

928-526: Was born in Berlin as the son of Paul Erman . He studied natural science at the universities of Berlin and Königsberg , spent from 1828 to 1830 in a journey round the world, an account of which he published in Reise um die Erde durch Nordasien und die beiden Ozeane (1833-1848). The magnetic observations he made during his travels were utilized by Carl Friedrich Gauss in his theory of terrestrial magnetism . He

960-498: 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 mostly disappeared and the terms "astronomer" and "astrophysicist" are interchangeable. Professional astronomers are highly educated individuals who typically have a PhD in physics or astronomy and are employed by research institutions or universities. They spend

992-525: 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

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1024-457: 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

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