Misplaced Pages

#889110

51-470: B4 , B04 , B.IV or B-4 may refer to: Transportation [ edit ] Aviation [ edit ] B4, IATA code of Beond , an airline based in Malé, Maldives B4, IATA code of B.A.C.H. Flugbetrieb , an Austrian charter airline (ICAO code BCF) B4, IATA code of Bankair , an US American charter airline (ICAO code BKA) B4, then-IATA code of Flyglobespan ,

102-665: A 1915 German U-boat 203-mm howitzer M1931 (B-4, "Stalins Hammer") , a World War II Soviet ordnance piece B-4 a US Air Force/USAAF flight bag A level of vehicle armour In science [ edit ] Leukotriene B4 receptor and Leukotriene B4 receptor 2, two human genes Lipoxin B4 , a lipoxin Proanthocyanidin B4 , a B type proanthocyanidin Vitamin B4 , an alternate name for adenine A stellar classification In entertainment [ edit ] B4 (music show) ,

153-517: A defunct British music video show broadcast on Channel 4 B4 (TV channel) , a defunct British music television channel B-4 (Star Trek) , an android in the Star Trek fictional universe Babylon 4 space station, predecessor to Babylon 5 from the Babylon 5 television series The Lost City (B4) , a Dungeons & Dragons adventure module Other uses [ edit ] B4 (classification) ,

204-693: A former British airline Auster B.4 , 1951 British light transport aircraft with rear ramp Bensen B-4 , Bensen Aircraft autogyro Bäumer B IV Sausewind , German 1920s sports aircraft Fokker B.IV , parent company's designation for American branch's F.11 seaplane Hawker B 4 , Swedish designation for Hawker Hart biplane Keystone B-4 , United States biplane bomber Lohner B.IV , an Austro-Hungarian World War 1 reconnaissance biplane Pilatus B-4 , Swiss glider also designated PC-11. Locomotives [ edit ] Alsace-Lorraine B 4 , an Alsace-Lorraine P 1 class steam locomotive Bavarian B IV , an 1852 German steam locomotive GSR Class B4 ,

255-516: A former Cork, Bandon and South Coast Railway steam locomotive of the Great Southern Railways, Ireland LSWR B4 class , an 1891 British dock tank locomotive PRR B4 , an American Pennsylvania Railroad steam locomotive Soo Line B-4 class , an American 0-6-0 steam locomotive LB&SCR B4 class , a British tender locomotive class LNER Class B4 , a British class of locomotives Automotive uses [ edit ] Subaru B4,

306-526: A luminosity class of IIIb, while a luminosity class IIIa indicates a star slightly brighter than a typical giant. A sample of extreme V stars with strong absorption in He II λ4686 spectral lines have been given the Vz designation. An example star is HD 93129 B . Additional nomenclature, in the form of lower-case letters, can follow the spectral type to indicate peculiar features of the spectrum. For example, 59 Cygni

357-665: A nearby observer. The modern classification system is known as the Morgan–Keenan (MK) classification. Each star is assigned a spectral class (from the older Harvard spectral classification, which did not include luminosity ) and a luminosity class using Roman numerals as explained below, forming the star's spectral type. Other modern stellar classification systems , such as the UBV system , are based on color indices —the measured differences in three or more color magnitudes . Those numbers are given labels such as "U−V" or "B−V", which represent

408-459: A new airline by forming a joint venture of two companies, Arabesque and SIMDI Group. beOnd plans to connect the Maldives to multiple European and Asian countries with their cities, as well as to Australia . It announced plans to operate to over 50 destinations in more than 25 countries with a fleet of over 30 aircraft in the next few years. On 10 August 2023, the first aircraft, an A319, joined

459-628: A parasports classification for visually impaired athletes B4 Street Fighter Championships , a 2000 fighting game tournament B4 or B4 II, a Native Instruments virtual synthesizer for Hammond organ (B-3) sound emulation B4-mount , used for professional video cameras such as Betacam An international standard paper size (250×353 mm), defined in ISO 216 B04, Alekhine's Defence chess code 1. b4, Sokolsky Opening in chess See also [ edit ] Before (disambiguation) BIV (disambiguation) [REDACTED] Topics referred to by

510-399: A particular chemical element or molecule , with the line strength indicating the abundance of that element. The strengths of the different spectral lines vary mainly due to the temperature of the photosphere , although in some cases there are true abundance differences. The spectral class of a star is a short code primarily summarizing the ionization state, giving an objective measure of

561-457: A series of twenty-two types numbered from I–XXII. Because the 22 Roman numeral groupings did not account for additional variations in spectra, three additional divisions were made to further specify differences: Lowercase letters were added to differentiate relative line appearance in spectra; the lines were defined as: Antonia Maury published her own stellar classification catalogue in 1897 called "Spectra of Bright Stars Photographed with

SECTION 10

#1732851014890

612-436: A surface temperature around 5,800 K. The conventional colour description takes into account only the peak of the stellar spectrum. In actuality, however, stars radiate in all parts of the spectrum. Because all spectral colours combined appear white, the actual apparent colours the human eye would observe are far lighter than the conventional colour descriptions would suggest. This characteristic of 'lightness' indicates that

663-407: Is a synonym for hotter , while "late" is a synonym for cooler . Depending on the context, "early" and "late" may be absolute or relative terms. "Early" as an absolute term would therefore refer to O or B, and possibly A stars. As a relative reference it relates to stars hotter than others, such as "early K" being perhaps K0, K1, K2 and K3. "Late" is used in the same way, with an unqualified use of

714-554: Is based on spectral lines sensitive to stellar temperature and surface gravity , which is related to luminosity (whilst the Harvard classification is based on just surface temperature). Later, in 1953, after some revisions to the list of standard stars and classification criteria, the scheme was named the Morgan–Keenan classification , or MK , which remains in use today. Denser stars with higher surface gravity exhibit greater pressure broadening of spectral lines. The gravity, and hence

765-594: Is different from Wikidata All article disambiguation pages All disambiguation pages Beond The only way to enter the Maldives from all countries is by air. At present, international airlines dominate operations at Velana International Airport , because the Maldives' flag carrier, Maldivian , has too small a fleet to cater to the growth at the airport and to compete with international airlines, along with connecting more worldwide destinations. Max Nilov, Tero Taskila and Sascha Feuerherd decided to create

816-507: Is listed as spectral type B1.5Vnne, indicating a spectrum with the general classification B1.5V, as well as very broad absorption lines and certain emission lines. The reason for the odd arrangement of letters in the Harvard classification is historical, having evolved from the earlier Secchi classes and been progressively modified as understanding improved. During the 1860s and 1870s, pioneering stellar spectroscopist Angelo Secchi created

867-451: Is used for hypergiants , class  I for supergiants , class  II for bright giants , class  III for regular giants , class  IV for subgiants , class  V for main-sequence stars , class  sd (or VI ) for subdwarfs , and class  D (or VII ) for white dwarfs . The full spectral class for the Sun is then G2V, indicating a main-sequence star with

918-576: The He  II λ4541 disappears. However, with modern equipment, the line is still apparent in the early B-type stars. Today for main-sequence stars, the B class is instead defined by the intensity of the He ;I violet spectrum, with the maximum intensity corresponding to class B2. For supergiants, lines of silicon are used instead; the Si ;IV λ4089 and Si III λ4552 lines are indicative of early B. At mid-B,

969-543: The Kelvin–Helmholtz mechanism , which is now known to not apply to main-sequence stars . If that were true, then stars would start their lives as very hot "early-type" stars and then gradually cool down into "late-type" stars. This mechanism provided ages of the Sun that were much smaller than what is observed in the geologic record , and was rendered obsolete by the discovery that stars are powered by nuclear fusion . The terms "early" and "late" were carried over, beyond

1020-501: The Secchi classes in order to classify observed spectra. By 1866, he had developed three classes of stellar spectra, shown in the table below. In the late 1890s, this classification began to be superseded by the Harvard classification, which is discussed in the remainder of this article. The Roman numerals used for Secchi classes should not be confused with the completely unrelated Roman numerals used for Yerkes luminosity classes and

1071-630: The 11 inch Draper Telescope as Part of the Henry Draper Memorial", which included 4,800 photographs and Maury's analyses of 681 bright northern stars. This was the first instance in which a woman was credited for an observatory publication. In 1901, Annie Jump Cannon returned to the lettered types, but dropped all letters except O, B, A, F, G, K, M, and N used in that order, as well as P for planetary nebulae and Q for some peculiar spectra. She also used types such as B5A for stars halfway between types B and A, F2G for stars one fifth of

SECTION 20

#1732851014890

1122-450: The B2 subclass, and moderate hydrogen lines. As O- and B-type stars are so energetic, they only live for a relatively short time. Thus, due to the low probability of kinematic interaction during their lifetime, they are unable to stray far from the area in which they formed, apart from runaway stars . The transition from class O to class B was originally defined to be the point at which

1173-515: The alphabet. This classification system was later modified by Annie Jump Cannon and Antonia Maury to produce the Harvard spectral classification scheme. In 1897, another astronomer at Harvard, Antonia Maury , placed the Orion subtype of Secchi class I ahead of the remainder of Secchi class I, thus placing the modern type B ahead of the modern type A. She was the first to do so, although she did not use lettered spectral types, but rather

1224-520: The classes indicate the temperature of the star's atmosphere and are normally listed from hottest to coldest. A common mnemonic for remembering the order of the spectral type letters, from hottest to coolest, is " O h, B e A F ine G uy/ G irl: K iss M e!", or another one is " O ur B right A stronomers F requently G enerate K iller M nemonics!" . The spectral classes O through M, as well as other more specialized classes discussed later, are subdivided by Arabic numerals (0–9), where 0 denotes

1275-511: The classical system: W , S and C . Some non-stellar objects have also been assigned letters: D for white dwarfs and L , T and Y for Brown dwarfs . In the MK system, a luminosity class is added to the spectral class using Roman numerals . This is based on the width of certain absorption lines in the star's spectrum, which vary with the density of the atmosphere and so distinguish giant stars from dwarfs. Luminosity class  0 or Ia+

1326-637: The colors passed by two standard filters (e.g. U ltraviolet, B lue and V isual). The Harvard system is a one-dimensional classification scheme by astronomer Annie Jump Cannon , who re-ordered and simplified the prior alphabetical system by Draper (see History ). Stars are grouped according to their spectral characteristics by single letters of the alphabet, optionally with numeric subdivisions. Main-sequence stars vary in surface temperature from approximately 2,000 to 50,000  K , whereas more-evolved stars – in particular, newly-formed white dwarfs – can have surface temperatures above 100,000 K. Physically,

1377-525: The demise of the model they were based on. O-type stars are very hot and extremely luminous, with most of their radiated output in the ultraviolet range. These are the rarest of all main-sequence stars. About 1 in 3,000,000 (0.00003%) of the main-sequence stars in the solar neighborhood are O-type stars. Some of the most massive stars lie within this spectral class. O-type stars frequently have complicated surroundings that make measurement of their spectra difficult. O-type spectra formerly were defined by

1428-716: The extreme velocity of their stellar wind , which may reach 2,000 km/s. Because they are so massive, O-type stars have very hot cores and burn through their hydrogen fuel very quickly, so they are the first stars to leave the main sequence . When the MKK classification scheme was first described in 1943, the only subtypes of class O used were O5 to O9.5. The MKK scheme was extended to O9.7 in 1971 and O4 in 1978, and new classification schemes that add types O2, O3, and O3.5 have subsequently been introduced. Spectral standards: B-type stars are very luminous and blue. Their spectra have neutral helium lines, which are most prominent at

1479-428: The fleet of beOnd consists of the following aircraft: Stellar classification In astronomy , stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with spectral lines . Each line indicates

1530-478: The fleet with 44 lie-flat seats in a 2-2 configuration. Its Airbus A321 joined the fleet on 2 September 2024 with a seat configuration of 68 lie-flat seats in a 2-2 format. Planned initial destinations were originally disclosed to include Dubai , Delhi , Hong Kong , Milan , Munich , Paris , Riyadh , Singapore , Taipei , Vienna and Zürich and a potential connection to Perth and Melbourne , along with seasonal destinations such as Finland . beOnd

1581-614: The help of the Harvard computers , especially Williamina Fleming , the first iteration of the Henry Draper catalogue was devised to replace the Roman-numeral scheme established by Angelo Secchi. The catalogue used a scheme in which the previously used Secchi classes (I to V) were subdivided into more specific classes, given letters from A to P. Also, the letter Q was used for stars not fitting into any other class. Fleming worked with Pickering to differentiate 17 different classes based on

B4 - Misplaced Pages Continue

1632-404: The hottest stars of a given class. For example, A0 denotes the hottest stars in class A and A9 denotes the coolest ones. Fractional numbers are allowed; for example, the star Mu Normae is classified as O9.7. The Sun is classified as G2. The fact that the Harvard classification of a star indicated its surface or photospheric temperature (or more precisely, its effective temperature )

1683-408: The intensity of hydrogen spectral lines, which causes variation in the wavelengths emanated from stars and results in variation in color appearance. The spectra in class A tended to produce the strongest hydrogen absorption lines while spectra in class O produced virtually no visible lines. The lettering system displayed the gradual decrease in hydrogen absorption in the spectral classes when moving down

1734-479: The intensity of the latter relative to that of Si II λλ4128-30 is the defining characteristic, while for late B, it is the intensity of Mg II λ4481 relative to that of He I λ4471. These stars tend to be found in their originating OB associations , which are associated with giant molecular clouds . The Orion OB1 association occupies a large portion of a spiral arm of the Milky Way and contains many of

1785-419: The main sequence). Nominal luminosity class VII (and sometimes higher numerals) is now rarely used for white dwarf or "hot sub-dwarf" classes, since the temperature-letters of the main sequence and giant stars no longer apply to white dwarfs. Occasionally, letters a and b are applied to luminosity classes other than supergiants; for example, a giant star slightly less luminous than typical may be given

1836-485: The modern definition uses the ratio of the nitrogen line N IV λ4058 to N III λλ4634-40-42. O-type stars have dominant lines of absorption and sometimes emission for He  II lines, prominent ionized ( Si  IV, O  III, N  III, and C  III) and neutral helium lines, strengthening from O5 to O9, and prominent hydrogen Balmer lines , although not as strong as in later types. Higher-mass O-type stars do not retain extensive atmospheres due to

1887-679: The name under which the Subaru Legacy is marketed in Israel B4 (New York City bus) , serving Brooklyn B4 road (Namibia) Bundesstraße 4 , federal highway in Germany Alpina B4 , a German sports executive car In the military [ edit ] [REDACTED] A painted B-4 bag HMS B4 , a British B-class submarine of the Royal Navy Keystone B-4 , a United States Army Air Corps biplane bomber SM UB-4 ,

1938-538: The photosphere's temperature. Most stars are currently classified under the Morgan–Keenan (MK) system using the letters O , B , A , F , G , K , and M , a sequence from the hottest ( O type) to the coolest ( M type). Each letter class is then subdivided using a numeric digit with 0 being hottest and 9 being coolest (e.g., A8, A9, F0, and F1 form a sequence from hotter to cooler). The sequence has been expanded with three classes for other stars that do not fit in

1989-401: The pressure, on the surface of a giant star is much lower than for a dwarf star because the radius of the giant is much greater than a dwarf of similar mass. Therefore, differences in the spectrum can be interpreted as luminosity effects and a luminosity class can be assigned purely from examination of the spectrum. A number of different luminosity classes are distinguished, as listed in

2040-619: The proposed neutron star classes. In the 1880s, the astronomer Edward C. Pickering began to make a survey of stellar spectra at the Harvard College Observatory , using the objective-prism method. A first result of this work was the Draper Catalogue of Stellar Spectra , published in 1890. Williamina Fleming classified most of the spectra in this catalogue and was credited with classifying over 10,000 featured stars and discovering 10 novae and more than 200 variable stars. With

2091-428: The ratio of the strength of the He  II λ4541 relative to that of He I λ4471, where λ is the radiation wavelength . Spectral type O7 was defined to be the point at which the two intensities are equal, with the He I line weakening towards earlier types. Type O3 was, by definition, the point at which said line disappears altogether, although it can be seen very faintly with modern technology. Due to this,

B4 - Misplaced Pages Continue

2142-447: The same term This disambiguation page lists articles associated with the same title formed as a letter–number combination. If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=B4&oldid=1187838276 " Category : Letter–number combination disambiguation pages Hidden categories: Short description

2193-410: The simplified assignment of colours within the spectrum can be misleading. Excluding colour-contrast effects in dim light, in typical viewing conditions there are no green, cyan, indigo, or violet stars. "Yellow" dwarfs such as the Sun are white, "red" dwarfs are a deep shade of yellow/orange, and "brown" dwarfs do not literally appear brown, but hypothetically would appear dim red or grey/black to

2244-455: The solar chromosphere, then to stellar spectra. Harvard astronomer Cecilia Payne then demonstrated that the O-B-A-F-G-K-M spectral sequence is actually a sequence in temperature. Because the classification sequence predates our understanding that it is a temperature sequence, the placement of a spectrum into a given subtype, such as B3 or A7, depends upon (largely subjective) estimates of

2295-627: The strengths of absorption features in stellar spectra. As a result, these subtypes are not evenly divided into any sort of mathematically representable intervals. The Yerkes spectral classification , also called the MK, or Morgan-Keenan (alternatively referred to as the MKK, or Morgan-Keenan-Kellman) system from the authors' initials, is a system of stellar spectral classification introduced in 1943 by William Wilson Morgan , Philip C. Keenan , and Edith Kellman from Yerkes Observatory . This two-dimensional ( temperature and luminosity ) classification scheme

2346-463: The table below. Marginal cases are allowed; for example, a star may be either a supergiant or a bright giant, or may be in between the subgiant and main-sequence classifications. In these cases, two special symbols are used: For example, a star classified as A3-4III/IV would be in between spectral types A3 and A4, while being either a giant star or a subgiant. Sub-dwarf classes have also been used: VI for sub-dwarfs (stars slightly less luminous than

2397-483: The term indicating stars with spectral types such as K and M, but it can also be used for stars that are cool relative to other stars, as in using "late G" to refer to G7, G8, and G9. In the relative sense, "early" means a lower Arabic numeral following the class letter, and "late" means a higher number. This obscure terminology is a hold-over from a late nineteenth century model of stellar evolution , which supposed that stars were powered by gravitational contraction via

2448-476: The way from F to G, and so on. Finally, by 1912, Cannon had changed the types B, A, B5A, F2G, etc. to B0, A0, B5, F2, etc. This is essentially the modern form of the Harvard classification system. This system was developed through the analysis of spectra on photographic plates, which could convert light emanated from stars into a readable spectrum. A luminosity classification known as the Mount Wilson system

2499-457: Was not fully understood until after its development, though by the time the first Hertzsprung–Russell diagram was formulated (by 1914), this was generally suspected to be true. In the 1920s, the Indian physicist Meghnad Saha derived a theory of ionization by extending well-known ideas in physical chemistry pertaining to the dissociation of molecules to the ionization of atoms. First he applied it to

2550-559: Was originally slated to begin commercial operations by September 2023. The actual start was in November 2023. In February 2024, the airline announced it would downgrade its services to Munich to a seasonal route, citing economic reasons. At the same time, the new route to Bangkok originally announced for a start in July 2024 had also been cancelled. As of October 2024, beOnd serves the following scheduled destinations. As of November 2024,

2601-488: Was used to distinguish between stars of different luminosities. This notation system is still sometimes seen on modern spectra. The stellar classification system is taxonomic , based on type specimens , similar to classification of species in biology : The categories are defined by one or more standard stars for each category and sub-category, with an associated description of the distinguishing features. Stars are often referred to as early or late types. "Early"

SECTION 50

#1732851014890
#889110