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78-405: The Bonner Durchmusterung (abbreviated BD), was initiated by Friedrich Argelander and using observations largely carried out by his assistants, which resulted in a catalogue of the positions and apparent magnitudes of 342,198 stars down to approximate apparent magnitude 9.5 and covering the sky from 90°N to 2°S declination. The catalogue, published in three parts, was accompanied by charts plotting

156-456: A protoplanetary disk and powered mainly by the conversion of gravitational energy. The period of gravitational contraction lasts about 10 million years for a star like the sun, up to 100 million years for a red dwarf. Early stars of less than 2  M ☉ are called T Tauri stars , while those with greater mass are Herbig Ae/Be stars . These newly formed stars emit jets of gas along their axis of rotation, which may reduce

234-467: A stellar wind of particles that causes a continual outflow of gas into space. For most stars, the mass lost is negligible. The Sun loses 10   M ☉ every year, or about 0.01% of its total mass over its entire lifespan. However, very massive stars can lose 10 to 10   M ☉ each year, significantly affecting their evolution. Stars that begin with more than 50  M ☉ can lose over half their total mass while on

312-487: A brief period of carbon fusion before the core becomes degenerate. During the AGB phase, stars undergo thermal pulses due to instabilities in the core of the star. In these thermal pulses, the luminosity of the star varies and matter is ejected from the star's atmosphere, ultimately forming a planetary nebula. As much as 50 to 70% of a star's mass can be ejected in this mass loss process. Because energy transport in an AGB star

390-496: A burst of electron capture and inverse beta decay . The shockwave formed by this sudden collapse causes the rest of the star to explode in a supernova. Supernovae become so bright that they may briefly outshine the star's entire home galaxy. When they occur within the Milky Way, supernovae have historically been observed by naked-eye observers as "new stars" where none seemingly existed before. A supernova explosion blows away

468-410: A continuous image due to the effect of refraction from sublunary material, citing his observation of the conjunction of Jupiter and Mars on 500 AH (1106/1107 AD) as evidence. Early European astronomers such as Tycho Brahe identified new stars in the night sky (later termed novae ), suggesting that the heavens were not immutable. In 1584, Giordano Bruno suggested that the stars were like

546-440: A difference between " fixed stars ", whose position on the celestial sphere does not change, and "wandering stars" ( planets ), which move noticeably relative to the fixed stars over days or weeks. Many ancient astronomers believed that the stars were permanently affixed to a heavenly sphere and that they were immutable. By convention, astronomers grouped prominent stars into asterisms and constellations and used them to track

624-655: A manner similar to the BD numbering system. A few decades later, the positional accuracy of the Durchmusterung catalogues began to be insufficient for many projects. To establish a more exact reference system for the Bonner Durchmusterung, astronomers and geodesists began to work on a fundamental celestial coordinate system based on the Earth's rotation axis , the vernal equinox and the ecliptic plane in

702-518: A much larger gravitationally bound structure, such as a star cluster or a galaxy. The word "star" ultimately derives from the Proto-Indo-European root "h₂stḗr" also meaning star, but further analyzable as h₂eh₁s- ("to burn", also the source of the word "ash") + -tēr (agentive suffix). Compare Latin stella , Greek aster , German Stern . Some scholars believe the word is a borrowing from Akkadian " istar " ( Venus ). "Star"

780-546: A net release of energy. Some massive stars, particularly luminous blue variables , are very unstable to the extent that they violently shed their mass into space in events supernova impostors , becoming significantly brighter in the process. Eta Carinae is known for having underwent a supernova impostor event, the Great Eruption, in the 19th century. As a star's core shrinks, the intensity of radiation from that surface increases, creating such radiation pressure on

858-463: A series of star maps and applied Greek letters as designations to the stars in each constellation. Later a numbering system based on the star's right ascension was invented and added to John Flamsteed 's star catalogue in his book "Historia coelestis Britannica" (the 1712 edition), whereby this numbering system came to be called Flamsteed designation or Flamsteed numbering . The internationally recognized authority for naming celestial bodies

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936-614: A set of nominal solar values (defined as SI constants, without uncertainties) which can be used for quoting stellar parameters: The solar mass M ☉ was not explicitly defined by the IAU due to the large relative uncertainty ( 10 ) of the Newtonian constant of gravitation G . Since the product of the Newtonian constant of gravitation and solar mass together ( G M ☉ ) has been determined to much greater precision,

1014-499: A star begins with gravitational instability within a molecular cloud, caused by regions of higher density—often triggered by compression of clouds by radiation from massive stars, expanding bubbles in the interstellar medium, the collision of different molecular clouds, or the collision of galaxies (as in a starburst galaxy ). When a region reaches a sufficient density of matter to satisfy the criteria for Jeans instability , it begins to collapse under its own gravitational force. As

1092-434: A star of more than 9 solar masses expands to form first a blue supergiant and then a red supergiant . Particularly massive stars (exceeding 40 solar masses, like Alnilam , the central blue supergiant of Orion's Belt ) do not become red supergiants due to high mass loss. These may instead evolve to a Wolf–Rayet star , characterised by spectra dominated by emission lines of elements heavier than hydrogen, which have reached

1170-407: A white dwarf is no longer a plasma. Eventually, white dwarfs fade into black dwarfs over a very long period of time. In massive stars, fusion continues until the iron core has grown so large (more than 1.4  M ☉ ) that it can no longer support its own mass. This core will suddenly collapse as its electrons are driven into its protons, forming neutrons, neutrinos , and gamma rays in

1248-420: Is cognate (shares the same root) with the following words: asterisk , asteroid , astral , constellation , Esther . Historically, stars have been important to civilizations throughout the world. They have been part of religious practices, divination rituals, mythology , used for celestial navigation and orientation, to mark the passage of seasons, and to define calendars. Early astronomers recognized

1326-409: Is primarily by convection , this ejected material is enriched with the fusion products dredged up from the core. Therefore, the planetary nebula is enriched with elements like carbon and oxygen. Ultimately, the planetary nebula disperses, enriching the general interstellar medium. Therefore, future generations of stars are made of the "star stuff" from past stars. During their helium-burning phase,

1404-575: Is the International Astronomical Union (IAU). The International Astronomical Union maintains the Working Group on Star Names (WGSN) which catalogs and standardizes proper names for stars. A number of private companies sell names of stars which are not recognized by the IAU, professional astronomers, or the amateur astronomy community. The British Library calls this an unregulated commercial enterprise , and

1482-491: Is the Orion Nebula . Most stars form in groups of dozens to hundreds of thousands of stars. Massive stars in these groups may powerfully illuminate those clouds, ionizing the hydrogen, and creating H II regions . Such feedback effects, from star formation, may ultimately disrupt the cloud and prevent further star formation. All stars spend the majority of their existence as main sequence stars , fueled primarily by

1560-701: The M87 and M100 galaxies of the Virgo Cluster , as well as luminous stars in some other relatively nearby galaxies. With the aid of gravitational lensing , a single star (named Icarus ) has been observed at 9 billion light-years away. The concept of a constellation was known to exist during the Babylonian period. Ancient sky watchers imagined that prominent arrangements of stars formed patterns, and they associated these with particular aspects of nature or their myths. Twelve of these formations lay along

1638-575: The New York City Department of Consumer and Worker Protection issued a violation against one such star-naming company for engaging in a deceptive trade practice. Although stellar parameters can be expressed in SI units or Gaussian units , it is often most convenient to express mass , luminosity , and radii in solar units, based on the characteristics of the Sun. In 2015, the IAU defined

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1716-461: The angular momentum of the collapsing star and result in small patches of nebulosity known as Herbig–Haro objects . These jets, in combination with radiation from nearby massive stars, may help to drive away the surrounding cloud from which the star was formed. Early in their development, T Tauri stars follow the Hayashi track —they contract and decrease in luminosity while remaining at roughly

1794-495: The epoch of B1855.0 . Many astronomical research projects—from studies of celestial mechanics and the Solar System , up to the nascent field of astrophysics —were made possible by the publication of the atlas and data of the Bonner Durchmusterung. However, a deficiency of the BD was that it did not cover the whole sky, because far southern stars are not visible from Germany. This led the scientific community to supplement

1872-632: The interstellar medium . These elements are then recycled into new stars. Astronomers can determine stellar properties—including mass, age, metallicity (chemical composition), variability , distance , and motion through space —by carrying out observations of a star's apparent brightness , spectrum , and changes in its position in the sky over time. Stars can form orbital systems with other astronomical objects, as in planetary systems and star systems with two or more stars. When two such stars orbit closely, their gravitational interaction can significantly impact their evolution. Stars can form part of

1950-453: The photographic magnitude . The development of the photoelectric photometer allowed precise measurements of magnitude at multiple wavelength intervals. In 1921 Albert A. Michelson made the first measurements of a stellar diameter using an interferometer on the Hooker telescope at Mount Wilson Observatory . Important theoretical work on the physical structure of stars occurred during

2028-555: The thermonuclear fusion of hydrogen into helium in its core. This process releases energy that traverses the star's interior and radiates into outer space . At the end of a star's lifetime as a fusor , its core becomes a stellar remnant : a white dwarf , a neutron star , or—if it is sufficiently massive—a black hole . Stellar nucleosynthesis in stars or their remnants creates almost all naturally occurring chemical elements heavier than lithium . Stellar mass loss or supernova explosions return chemically enriched material to

2106-591: The 11th century, the Persian polymath scholar Abu Rayhan Biruni described the Milky Way galaxy as a multitude of fragments having the properties of nebulous stars, and gave the latitudes of various stars during a lunar eclipse in 1019. According to Josep Puig, the Andalusian astronomer Ibn Bajjah proposed that the Milky Way was made up of many stars that almost touched one another and appeared to be

2184-476: The 2015 IAU nominal constants will remain the same SI values as they remain useful measures for quoting stellar parameters. Large lengths, such as the radius of a giant star or the semi-major axis of a binary star system, are often expressed in terms of the astronomical unit —approximately equal to the mean distance between the Earth and the Sun (150 million km or approximately 93 million miles). In 2012,

2262-709: The BD with two additional astrometric surveys carried out by observatories located in the Southern Hemisphere: Córdoba, Argentina , and Cape Town , South Africa. The Cordoba Durchmusterung (abbreviated CD, or, less commonly, CoD) was made visually (as was the BD), but the Cape Photographic Durchmusterung (CP or CPD) was conducted by the then-new photographic technique, which had just been shown to have sufficient accuracy. The southern stars are identified by CD and CPD numbers in

2340-694: The Finnish observatory , first in Turku and then in Helsinki . He then moved to Bonn , Germany . There he designed and built a new observatory at the University of Bonn with funding approved directly by King Frederick William IV whom Argelander had become friends with in his childhood. This lifelong friendship had started when the then crown prince temporarily lived in Argelander's parents house after

2418-413: The IAU defined the astronomical constant to be an exact length in meters: 149,597,870,700 m. Stars condense from regions of space of higher matter density, yet those regions are less dense than within a vacuum chamber . These regions—known as molecular clouds —consist mostly of hydrogen, with about 23 to 28 percent helium and a few percent heavier elements. One example of such a star-forming region

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2496-413: The IAU defined the nominal solar mass parameter to be: The nominal solar mass parameter can be combined with the most recent (2014) CODATA estimate of the Newtonian constant of gravitation G to derive the solar mass to be approximately 1.9885 × 10  kg . Although the exact values for the luminosity, radius, mass parameter, and mass may vary slightly in the future due to observational uncertainties,

2574-620: The Prussian royal family fled to Memel after the Battle of Jena–Auerstedt during the Napoleonic Wars . Argelander excelled in developing effective, simple and fast methods for measuring star positions and magnitudes, thereby making a pioneering work for modern astronomy. He also measured star distances with heliometers . His, and his collaborators', great practical works of star cataloging and variable star research were made possible by

2652-497: The Solar System, Isaac Newton suggested that the stars were equally distributed in every direction, an idea prompted by the theologian Richard Bentley . The Italian astronomer Geminiano Montanari recorded observing variations in luminosity of the star Algol in 1667. Edmond Halley published the first measurements of the proper motion of a pair of nearby "fixed" stars, demonstrating that they had changed positions since

2730-439: The Sun enters the helium burning phase, it will expand to a maximum radius of roughly 1 astronomical unit (150 million kilometres), 250 times its present size, and lose 30% of its current mass. As the hydrogen-burning shell produces more helium, the core increases in mass and temperature. In a red giant of up to 2.25  M ☉ , the mass of the helium core becomes degenerate prior to helium fusion . Finally, when

2808-449: The Sun, and may have other planets , possibly even Earth-like, in orbit around them, an idea that had been suggested earlier by the ancient Greek philosophers , Democritus and Epicurus , and by medieval Islamic cosmologists such as Fakhr al-Din al-Razi . By the following century, the idea of the stars being the same as the Sun was reaching a consensus among astronomers. To explain why these stars exerted no net gravitational pull on

2886-502: The band of the ecliptic and these became the basis of astrology . Many of the more prominent individual stars were given names, particularly with Arabic or Latin designations. As well as certain constellations and the Sun itself, individual stars have their own myths . To the Ancient Greeks , some "stars", known as planets (Greek πλανήτης (planētēs), meaning "wanderer"), represented various important deities, from which

2964-616: The brightest stars have proper names . Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations . The observable universe contains an estimated 10 to 10 stars. Only about 4,000 of these stars are visible to the naked eye—all within the Milky Way galaxy . A star's life begins with the gravitational collapse of a gaseous nebula of material largely comprising hydrogen , helium, and trace heavier elements. Its total mass mainly determines its evolution and eventual fate. A star shines for most of its active life due to

3042-502: The chemical composition of the stellar atmosphere to be determined. With the exception of rare events such as supernovae and supernova impostors , individual stars have primarily been observed in the Local Group , and especially in the visible part of the Milky Way (as demonstrated by the detailed star catalogues available for the Milky Way galaxy) and its satellites. Individual stars such as Cepheid variables have been observed in

3120-408: The cloud collapses, individual conglomerations of dense dust and gas form " Bok globules ". As a globule collapses and the density increases, the gravitational energy converts into heat and the temperature rises. When the protostellar cloud has approximately reached the stable condition of hydrostatic equilibrium , a protostar forms at the core. These pre-main-sequence stars are often surrounded by

3198-612: The cloud into multiple stars distributes some of that angular momentum. The primordial binaries transfer some angular momentum by gravitational interactions during close encounters with other stars in young stellar clusters. These interactions tend to split apart more widely separated (soft) binaries while causing hard binaries to become more tightly bound. This produces the separation of binaries into their two observed populations distributions. Stars spend about 90% of their lifetimes fusing hydrogen into helium in high-temperature-and-pressure reactions in their cores. Such stars are said to be on

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3276-400: The core. The blown-off outer layers of dying stars include heavy elements, which may be recycled during the formation of new stars. These heavy elements allow the formation of rocky planets. The outflow from supernovae and the stellar wind of large stars play an important part in shaping the interstellar medium. Binary stars ' evolution may significantly differ from that of single stars of

3354-417: The direction of the Milky Way core . His son John Herschel repeated this study in the southern hemisphere and found a corresponding increase in the same direction. In addition to his other accomplishments, William Herschel is noted for his discovery that some stars do not merely lie along the same line of sight, but are physical companions that form binary star systems. The science of stellar spectroscopy

3432-405: The end of the star's life, fusion continues along a series of onion-layer shells within a massive star. Each shell fuses a different element, with the outermost shell fusing hydrogen; the next shell fusing helium, and so forth. The final stage occurs when a massive star begins producing iron. Since iron nuclei are more tightly bound than any heavier nuclei, any fusion beyond iron does not produce

3510-526: The first decades of the twentieth century. In 1913, the Hertzsprung-Russell diagram was developed, propelling the astrophysical study of stars. Successful models were developed to explain the interiors of stars and stellar evolution. Cecilia Payne-Gaposchkin first proposed that stars were made primarily of hydrogen and helium in her 1925 PhD thesis. The spectra of stars were further understood through advances in quantum physics . This allowed

3588-665: The late 19th century. This astrometric project led to the Catalogues of Fundamental Stars of the Berlin observatory, and was used as an exact coordinate frame for the BD and AGK. It was modernized in the 1920s ( FK3 , mean accuracy ±1″), and in 2000 ( FK6 , accuracy 0.1″) as successive steps of cosmic geodesy . Together with radioastronomical measurements, the FK6 accuracy was better than ±0.1″. The Hipparcos satellite operated between 1989 and 1993 and observed around 118,000 stars over

3666-437: The main sequence and are called dwarf stars. Starting at zero-age main sequence, the proportion of helium in a star's core will steadily increase, the rate of nuclear fusion at the core will slowly increase, as will the star's temperature and luminosity. The Sun, for example, is estimated to have increased in luminosity by about 40% since it reached the main sequence 4.6 billion ( 4.6 × 10 ) years ago. Every star generates

3744-677: The main sequence. The time a star spends on the main sequence depends primarily on the amount of fuel it has and the rate at which it fuses it. The Sun is expected to live 10 billion ( 10 ) years. Massive stars consume their fuel very rapidly and are short-lived. Low mass stars consume their fuel very slowly. Stars less massive than 0.25  M ☉ , called red dwarfs , are able to fuse nearly all of their mass while stars of about 1  M ☉ can only fuse about 10% of their mass. The combination of their slow fuel-consumption and relatively large usable fuel supply allows low mass stars to last about one trillion ( 10 × 10 ) years;

3822-412: The main sequence. Besides mass, the elements heavier than helium can play a significant role in the evolution of stars. Astronomers label all elements heavier than helium "metals", and call the chemical concentration of these elements in a star, its metallicity . A star's metallicity can influence the time the star takes to burn its fuel, and controls the formation of its magnetic fields, which affects

3900-456: The most extreme of 0.08  M ☉ will last for about 12 trillion years. Red dwarfs become hotter and more luminous as they accumulate helium. When they eventually run out of hydrogen, they contract into a white dwarf and decline in temperature. Since the lifespan of such stars is greater than the current age of the universe (13.8 billion years), no stars under about 0.85  M ☉ are expected to have moved off

3978-445: The motions of the planets and the inferred position of the Sun. The motion of the Sun against the background stars (and the horizon) was used to create calendars , which could be used to regulate agricultural practices. The Gregorian calendar , currently used nearly everywhere in the world, is a solar calendar based on the angle of the Earth's rotational axis relative to its local star, the Sun. The oldest accurately dated star chart

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4056-484: The names of the planets Mercury , Venus , Mars , Jupiter and Saturn were taken. ( Uranus and Neptune were Greek and Roman gods , but neither planet was known in Antiquity because of their low brightness. Their names were assigned by later astronomers.) Circa 1600, the names of the constellations were used to name the stars in the corresponding regions of the sky. The German astronomer Johann Bayer created

4134-403: The nuclear fusion of hydrogen into helium within their cores. However, stars of different masses have markedly different properties at various stages of their development. The ultimate fate of more massive stars differs from that of less massive stars, as do their luminosities and the impact they have on their environment. Accordingly, astronomers often group stars by their mass: The formation of

4212-417: The outer convective envelope collapses and the star then moves to the horizontal branch. After a star has fused the helium of its core, it begins fusing helium along a shell surrounding the hot carbon core. The star then follows an evolutionary path called the asymptotic giant branch (AGB) that parallels the other described red-giant phase, but with a higher luminosity. The more massive AGB stars may undergo

4290-404: The outer shell of gas that it will push those layers away, forming a planetary nebula. If what remains after the outer atmosphere has been shed is less than roughly 1.4  M ☉ , it shrinks to a relatively tiny object about the size of Earth, known as a white dwarf . White dwarfs lack the mass for further gravitational compression to take place. The electron-degenerate matter inside

4368-624: The positions of the stars, and was the basis for the Astronomische Gesellschaft Katalog (AGK) and Smithsonian Astrophysical Observatory Star Catalog (SAO) catalogues of the 20th century. In 1886 Eduard Schönfeld , also in Bonn, published an extension from 2°S to 23°S declination. (A further extension from an observatory in Cordoba Argentina was published in five parts between 1892 and 1932 to cover

4446-664: The positions of the stars. They built the first large observatory research institutes, mainly to produce Zij star catalogues. Among these, the Book of Fixed Stars (964) was written by the Persian astronomer Abd al-Rahman al-Sufi , who observed a number of stars, star clusters (including the Omicron Velorum and Brocchi's Clusters ) and galaxies (including the Andromeda Galaxy ). According to A. Zahoor, in

4524-403: The problem of deriving an orbit of binary stars from telescope observations was made by Felix Savary in 1827. The twentieth century saw increasingly rapid advances in the scientific study of stars. The photograph became a valuable astronomical tool. Karl Schwarzschild discovered that the color of a star and, hence, its temperature, could be determined by comparing the visual magnitude against

4602-497: The proper motion of the star Sirius and inferred a hidden companion. Edward Pickering discovered the first spectroscopic binary in 1899 when he observed the periodic splitting of the spectral lines of the star Mizar in a 104-day period. Detailed observations of many binary star systems were collected by astronomers such as Friedrich Georg Wilhelm von Struve and S. W. Burnham , allowing the masses of stars to be determined from computation of orbital elements . The first solution to

4680-461: The same mass. For example, when any star expands to become a red giant, it may overflow its Roche lobe , the surrounding region where material is gravitationally bound to it; if stars in a binary system are close enough, some of that material may overflow to the other star, yielding phenomena including contact binaries , common-envelope binaries, cataclysmic variables , blue stragglers , and type Ia supernovae . Mass transfer leads to cases such as

4758-455: The same temperature. Less massive T Tauri stars follow this track to the main sequence, while more massive stars turn onto the Henyey track . Most stars are observed to be members of binary star systems, and the properties of those binaries are the result of the conditions in which they formed. A gas cloud must lose its angular momentum in order to collapse and form a star. The fragmentation of

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4836-726: The sky. This was the last star map to be published without the use of photography. In 1863, Argelander helped lead in the founding of an international organization of astronomers named the Astronomische Gesellschaft . Star A star is a luminous spheroid of plasma held together by self-gravity . The nearest star to Earth is the Sun . Many other stars are visible to the naked eye at night ; their immense distances from Earth make them appear as fixed points of light. The most prominent stars have been categorised into constellations and asterisms , and many of

4914-472: The southern sky from 22°S to 90°S declination.) BD star numbers are still used and allow the correlation of the work with modern projects. The format of a BD number is exemplified by "BD−16 1591", which is the BD number of Sirius . This number signifies that in the catalog, Sirius is the 1591st star listed in the declination zone between −16 and −17 degrees, counting from 0 hours right ascension . Stellar positions and zone boundaries use an equinox for

4992-506: The star's outer layers, leaving a remnant such as the Crab Nebula. The core is compressed into a neutron star , which sometimes manifests itself as a pulsar or X-ray burster . In the case of the largest stars, the remnant is a black hole greater than 4  M ☉ . In a neutron star the matter is in a state known as neutron-degenerate matter , with a more exotic form of degenerate matter, QCD matter , possibly present in

5070-400: The strength of its stellar wind. Older, population II stars have substantially less metallicity than the younger, population I stars due to the composition of the molecular clouds from which they formed. Over time, such clouds become increasingly enriched in heavier elements as older stars die and shed portions of their atmospheres . As stars of at least 0.4  M ☉ exhaust

5148-485: The supply of hydrogen at their core, they start to fuse hydrogen in a shell surrounding the helium core. The outer layers of the star expand and cool greatly as they transition into a red giant . In some cases, they will fuse heavier elements at the core or in shells around the core. As the stars expand, they throw part of their mass, enriched with those heavier elements, into the interstellar environment, to be recycled later as new stars. In about 5 billion years, when

5226-468: The surface due to strong convection and intense mass loss, or from stripping of the outer layers. When helium is exhausted at the core of a massive star, the core contracts and the temperature and pressure rises enough to fuse carbon (see Carbon-burning process ). This process continues, with the successive stages being fueled by neon (see neon-burning process ), oxygen (see oxygen-burning process ), and silicon (see silicon-burning process ). Near

5304-461: The systematic usage of then newly developed techniques. Argelander was the first astronomer to begin a careful study of variable stars . Only a handful were known when he began, and he was responsible for introducing the modern system of identifying them. He also made a rough determination of the direction in which the Sun was moving. In 1842, he discovered that Groombridge 1830 had a very high proper motion . For many decades its proper motion

5382-458: The temperature increases sufficiently, core helium fusion begins explosively in what is called a helium flash , and the star rapidly shrinks in radius, increases its surface temperature, and moves to the horizontal branch of the HR diagram. For more massive stars, helium core fusion starts before the core becomes degenerate, and the star spends some time in the red clump , slowly burning helium, before

5460-400: The time of the ancient Greek astronomers Ptolemy and Hipparchus. William Herschel was the first astronomer to attempt to determine the distribution of stars in the sky. During the 1780s, he established a series of gauges in 600 directions and counted the stars observed along each line of sight. From this, he deduced that the number of stars steadily increased toward one side of the sky, in

5538-518: The whole sky. Three star catalogues were published from its data: The Gaia space observatory , launched in December 2013, has catalogued a billion stars with an accuracy down to 20 microarcseconds (0.00002″). Friedrich Wilhelm Argelander Friedrich Wilhelm August Argelander (22 March 1799 – 17 February 1875) was a German astronomer . He is known for his determinations of stellar brightnesses, positions, and distances. Argelander

5616-562: Was born in Memel in the Kingdom of Prussia (now Klaipėda in Lithuania ), the son of a father of Finnish descent, Johann Gottlieb Argelander, and German ( Prussian ) mother, Dorothea Wilhelmina Grünhagen. He studied with Friedrich Bessel , whose assistant he became in 1820, and obtained his Ph.D. in 1822 at University of Königsberg . From 1823 until 1837, Argelander was the head of

5694-435: Was developed by Annie J. Cannon during the early 1900s. The first direct measurement of the distance to a star ( 61 Cygni at 11.4 light-years ) was made in 1838 by Friedrich Bessel using the parallax technique. Parallax measurements demonstrated the vast separation of the stars in the heavens. Observation of double stars gained increasing importance during the 19th century. In 1834, Friedrich Bessel observed changes in

5772-419: Was pioneered by Joseph von Fraunhofer and Angelo Secchi . By comparing the spectra of stars such as Sirius to the Sun, they found differences in the strength and number of their absorption lines —the dark lines in stellar spectra caused by the atmosphere's absorption of specific frequencies. In 1865, Secchi began classifying stars into spectral types . The modern version of the stellar classification scheme

5850-600: Was the SN 1006 supernova, which was observed in 1006 and written about by the Egyptian astronomer Ali ibn Ridwan and several Chinese astronomers. The SN 1054 supernova, which gave birth to the Crab Nebula , was also observed by Chinese and Islamic astronomers. Medieval Islamic astronomers gave Arabic names to many stars that are still used today and they invented numerous astronomical instruments that could compute

5928-486: Was the highest known; today it still occupies third place. For a time, it was known as Argelander's Star . Together with Adalbert Krüger and Eduard Schönfeld , Argelander was responsible for the star catalogue known as the Bonner Durchmusterung , published between 1859 and 1862, which gave the positions and brightness of more than 324,000 stars, although it did not cover much of the southern half of

6006-614: Was the result of ancient Egyptian astronomy in 1534 BC. The earliest known star catalogues were compiled by the ancient Babylonian astronomers of Mesopotamia in the late 2nd millennium BC, during the Kassite Period ( c.  1531 BC  – c.  1155 BC ). The first star catalogue in Greek astronomy was created by Aristillus in approximately 300 BC, with the help of Timocharis . The star catalog of Hipparchus (2nd century BC) included 1,020 stars, and

6084-480: Was used to assemble Ptolemy 's star catalogue. Hipparchus is known for the discovery of the first recorded nova (new star). Many of the constellations and star names in use today derive from Greek astronomy. Despite the apparent immutability of the heavens, Chinese astronomers were aware that new stars could appear. In 185 AD, they were the first to observe and write about a supernova , now known as SN 185 . The brightest stellar event in recorded history

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