In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. Stellar temperatures can be classified by using Wien's displacement law, but this poses difficulties for distant stars. Stellar spectroscopy offers a way to classify stars according to their absorption lines; particular absorption lines can be observed only for a certain range of temperatures because only in that range are the involved atomic energy levels populated. An early scheme (from the 19th century) ranked stars from A to Q, which is the origin of the currently used spectral classes. For other uses, see Astronomy (disambiguation). ... This article is about the astronomical object. ... Solar disk redirects here. ... The noun spectrum (plural: spectra) has a variety of meanings. ... Wiens displacement law is a law of physics that states that there is an inverse relationship between the wavelength of the peak of the emission of a black body and its temperature. ... High resolution spectrum of the Sun showing thousands of elemental absorption lines (fraunhofer lines). ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... A quantum mechanical system can only be in certain states, so that only certain energy levels are possible. ...

Secchi classes

During the 1860s and 1870s, pioneering stellar spectroscopist Father Angelo Secchi created the Secchi classes in order to classify observed spectra. By 1868, he had developed four classes of stars:^[1][2][3] Pietro Angelo Secchi (June 18, 1818 – February 26, 1878) was an Italian astronomer. ...

• Class I: white and blue stars with broad heavy hydrogen lines (modern class A)
• Class II: yellow stars—hydrogen less strong, but evident metallic lines (modern classes G and K)
• Class III: orange to red stars with complex band spectra (modern class M)
• Class IV: red stars with significant carbon bands and lines (carbon stars)

In 1878, he added a fifth class:^[1] This article is about the chemistry of hydrogen. ... For other uses, see Carbon (disambiguation). ... A carbon star is a late type giant star similar to the red giants (or occasionally red dwarf) star whose atmosphere contains more carbon than oxygen; the two elements combine in the upper layers of the star, forming carbon monoxide, which consumes all the oxygen in the atmosphere, leaving carbon...

• Class V: emission lines (e.g., Be, Bf, etc.)

In the late 1890s, this classification was superseded by the Harvard classification, which is discussed in the remainder of this article.^[4][5] A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ...

Harvard spectral classification

Harvard one-dimensional (temperature) classification scheme (based on hydrogen Balmer line strengths) was developed at Harvard College Observatory in about 1912 by Annie Jump Cannon and Edward C. Pickering.^[6] The common classes are normally listed from hottest to coldest (with mass, radius and luminosity compared to the Sun) and are given in the following table. Harvard College Observatory, about 1900. ... Annie Jump Cannon (December 11, 1863 – April 13, 1941) was an American astronomer whose cataloguing work was instrumental in the development of contemporary stellar classification. ... Edward Charles Pickering (July 19, 1846 – February 3, 1919) was an American astronomer and physicist, brother of William Henry Pickering. ...

Hertzsprung-Russell diagram

The mass, radius, and luminosity listed for each class are appropriate only for stars on the main sequence portion of their lives and so are not appropriate for red giants. A popular mnemonic for remembering the order is "Oh Be A Fine Girl/Guy, Kiss Me" (there are many variants of this mnemonic). The Hertzsprung-Russell diagram relates stellar classification with absolute magnitude, luminosity, and surface temperature. In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... In astronomy, the solar radius is a unit of length used to express the size of stars and larger objects such as galaxies. ... The solar luminosity, , is a unit of luminosity (power emitted in the form of photons) conventionally used by astronomers to give the luminosities of stars. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... In astronomy, the solar radius is a unit of length used to express the size of stars and larger objects such as galaxies. ... The solar luminosity, , is a unit of luminosity (power emitted in the form of photons) conventionally used by astronomers to give the luminosities of stars. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... In astronomy, the solar radius is a unit of length used to express the size of stars and larger objects such as galaxies. ... The solar luminosity, , is a unit of luminosity (power emitted in the form of photons) conventionally used by astronomers to give the luminosities of stars. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... In astronomy, the solar radius is a unit of length used to express the size of stars and larger objects such as galaxies. ... The solar luminosity, , is a unit of luminosity (power emitted in the form of photons) conventionally used by astronomers to give the luminosities of stars. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... In astronomy, the solar radius is a unit of length used to express the size of stars and larger objects such as galaxies. ... The solar luminosity, , is a unit of luminosity (power emitted in the form of photons) conventionally used by astronomers to give the luminosities of stars. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... In astronomy, the solar radius is a unit of length used to express the size of stars and larger objects such as galaxies. ... The solar luminosity, , is a unit of luminosity (power emitted in the form of photons) conventionally used by astronomers to give the luminosities of stars. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... In astronomy, the solar radius is a unit of length used to express the size of stars and larger objects such as galaxies. ... The solar luminosity, , is a unit of luminosity (power emitted in the form of photons) conventionally used by astronomers to give the luminosities of stars. ... The Hertzsprung-Russell diagram (usually referred to by the abbreviation H-R diagram or HRD, also known as a Colour-Magnitude diagram, or CMD) shows the relationship between absolute magnitude, luminosity, classification, and effective temperature of stars. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giants. Examples include Aldebaran and Arcturus. ... For other uses, see Mnemonic (disambiguation). ... The Hertzsprung-Russell diagram (usually referred to by the abbreviation H-R diagram or HRD, also known as a Colour-Magnitude diagram, or CMD) shows the relationship between absolute magnitude, luminosity, classification, and effective temperature of stars. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ... This article does not cite any references or sources. ... For other uses, see Temperature (disambiguation). ...

The reason for the odd arrangement of letters is historical. When people first started taking spectra of stars, they noticed that stars had very different hydrogen spectral lines strengths, and so they classified stars based on the strength of the hydrogen Balmer series lines from A (strongest) to Q (weakest). Other lines of neutral and ionized species then came into play (H and K lines of calcium, sodium D lines, etc). Later it was found that some of the classes were actually duplicates and those classes were removed. It was only much later that it was discovered that the strength of the hydrogen line was connected with the surface temperature of the star. The basic work was done by the "girls" of Harvard College Observatory, primarily Annie Jump Cannon, Henrietta Swan Leavitt and Antonia Maury, based on the work of Williamina Fleming. In the 1920s, the Indian physicist Megh Nad 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 applied to the solar chromosphere, he then applied it to stellar spectra.^[10] The Harvard astronomer Cecilia Helena Payne (later to become Cecilia Payne-Gaposchkin) then demonstrated that the OBAFGKM spectral sequence is actually a sequence in temperature.^[11] The power spectrum is a plot of the portion of a signals power (energy per unit time) falling within given frequency bins. ... This article is about the chemistry of hydrogen. ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... Two of the balmer lines (α and β) are clearly visible in this emission spectrum of a deuterium lamp. ... For other uses, see Calcium (disambiguation). ... For sodium in the diet, see Salt. ... For other uses, see Temperature (disambiguation). ... Harvard College Observatory, about 1900. ... Annie Jump Cannon (December 11, 1863 – April 13, 1941) was an American astronomer whose cataloguing work was instrumental in the development of contemporary stellar classification. ... Henrietta Leavitt Henrietta Swan Leavitt (July 4, 1868 – December 12, 1921) was an American astronomer, and the deaf[1] daughter of a Congregational church minister. ... Antonia Caetana De Paiva Pereira Maury (March 21, 1866 - January 8, 1952) was an American astronomer. ... Williamina Paton Stevens Fleming (May 15, 1857 – May 21, 1911), astronomer, was born in Dundee, Scotland, to Robert Stevens and Mary Walker Stevens. ... Megh Nad Saha (Bangla:মেঘনাদ সাহা) (Devanagari: मेघनाद साहा) (October 6, 1893 – February 16, 1956) was a Bengali Indian astrophysicist. ... Cecilia Payne-Gaposchkin (May 10, 1900 – December 7, 1979) was an English-American astronomer who in 1925 was first to show that the Sun is mainly composed of hydrogen, contradicting accepted wisdom at the time. ...

Spectral classes are further subdivided by Arabic numerals (0–9). For example, A0 denotes the hottest stars in the A class and A9 denotes the coolest ones. Because the classification sequence predates our understanding that it is a temperature sequence, the precise values of these digits depend upon (largely subjective) estimates of the strengths of absorption features in stellar spectra. As a result, the subclasses are not evenly divided into any sort of mathematically representable intervals. The Sun is classified as G2. For other uses, see Arabic numerals (disambiguation). ...

O, B, and A stars are sometimes misleadingly called "early type", while K and M stars are said to be "late type". This stems from an early 20th century theory, now obsolete, that stars start their lives as very hot "early type" stars, and then gradually cool down, thereby evolving into "late type" stars. We now know that this theory is entirely wrong (see: stellar evolution). However, brown dwarfs, whose energy comes from gravitational attraction alone, cool as they age and so progress to later spectral types. The highest mass brown dwarfs start their lives with M-type spectra and will cool through the L, T, and Y spectral classes. Projected timeline of the Suns life In astronomy, stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. ... This article covers the physics of gravitation. ...

Conventional and apparent colors

The Conventional color descriptions are traditional in astronomy, and represent colors relative to Vega, a star that is perceived as white under naked eye observational conditions, but which magnified appears as blue. The Apparent color^[7] descriptions is what the observer would see if trying to describe the stars under a dark sky without aid to the eye, or with binoculars. The table colors used, are D65 standard colors, which are what you would see if the star light would be magnified to be filling non-dazzlingly bright areas. ^[12] Most stars in the sky, except the brightest ones, appear white or bluish white to the unaided eye because they are too dim for color vision to work. For other uses, see Vega (disambiguation). ...

Our Sun itself is white. It is sometimes called a yellow star (spectroscopically, relative to Vega), and may appear yellow or red (viewed through the atmosphere), or appear white (viewed when too bright for the eye to see any color). Astronomy images often use a variety of exaggerated colors (partially founded in faint light conditions observations, partially in conventions). But the Sun's own intrinsic color is white (aside from sunspots), with no trace of color, and closely approximates a black body of 5780 K (see color temperature). This is a natural consequence of the evolution of our optical senses: the response curve that maximizes the overall efficiency against solar illumination will by definition perceive the Sun as white. The sun is known as a G type star. As the temperature decreases, the peak of the black body radiation curve moves to lower intensities and longer wavelengths. ... For other uses, see Kelvin (disambiguation). ... The CIE 1931 x,y chromaticity space, also showing the chromaticities of black-body light sources of various temperatures, and lines of constant correlated color temperature Color temperature is a characteristic of visible light that has important applications in photography, videography, publishing and other fields. ...

Yerkes spectral classification

The Yerkes spectral classification, also called the MKK system from the authors' initials, is a system of stellar spectral classification introduced in 1943 by William Wilson Morgan, Phillip C. Keenan and Edith Kellman from Yerkes Observatory.^[13] William Wilson Morgan (January 3, 1906 – June 21, 1994) was an American astronomer. ... 1897 photo of the 102 cm (40 inch) refractor at the Yerkes Observatory. ...

This classification is based on spectral lines sensitive to stellar surface gravity which is related to luminosity, as opposed to the Harvard classification which is based on surface temperature. A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ...

Later, in 1953, after some revisions of list of standard stars and classification criteria, the scheme was named MK (by William Wilson Morgan and Phillip C. Keenan initials).^[14]

Since the radius of a giant star is much larger than a dwarf star while their masses are roughly comparable, the gravity and thus the gas density and pressure on the surface of a giant star are much lower than for a dwarf. Giant star is a star that has stopped fusing hydrogen in its core. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ...

These differences manifest themselves in the form of luminosity effects which affect both the width and the intensity of spectral lines which can then be measured. Denser stars with higher surface gravity will exhibit greater pressure broadening of spectral lines.

A number of different luminosity classes are distinguished:

• I supergiants
  • Ia-0 (hypergiants or extremely luminous supergiants (later addition), Example: Eta Carinae (spectrum-peculiar)
  • Ia (luminous supergiants), Example: Deneb (spectrum is A2Ia)
  • Iab (intermediate luminous supergiants)
  • Ib (less luminous supergiants), Example: Betelgeuse (spectrum is M2Ib)
• II bright giants
  • IIa, Example: β Scuti (HD 173764) (spectrum is G4 IIa)
  • IIab Example: HR 8752 (spectrum is G0Iab:)
  • IIb, Example: HR 6902 (spectrum is G9 IIb)
• III normal giants
  • IIIa, Example: ρ Persei (spectrum is M4 IIIa)
  • IIIab Example: δ Reticuli (spectrum is M2 IIIab)
  • IIIb, Example: Pollux (spectrum is K2 IIIb)
• IV subgiants
  • IVa, Example: ε Reticuli (spectrum is K1-2 IVa-III)
  • IVb, Example: HR 672 A (spectrum is G0.5 IVb)
• V main sequence stars (dwarfs)
  • Va, Example: AD Leonis (spectrum M4Vae)
  • Vb, Example: 85 Pegasi A (spectrum G5 Vb)
• VI subdwarfs (rarely used)
• VII white dwarfs (rarely used)

Marginal cases are allowed; for instance a star classified as Ia0-Ia would be a very luminous supergiant, verging on hypergiant. Examples are below. The spectral type of the star are not a factor. The Hertzsprung-Russell diagram (usually referred to by the abbreviation H-R diagram or HRD, also known as a Colour-Magnitude diagram, or CMD) shows the relationship between absolute magnitude, luminosity, classification, and effective temperature of stars. ... This brown dwarf (smaller object) orbits the star Gliese 229, which is located in the constellation Lepus about 19 light years from Earth. ... This article or section does not adequately cite its references or sources. ... This article is about the British sitcom. ... A subdwarf star, sometimes denoted by sd, is luminosity class VI under the Yerkes spectral classification system. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... Subgiant are Olly Maw, Dan Hayes and Tushar Joshi, a live dance music band from the UK formed in 2000. ... Giant star is a star that has stopped fusing hydrogen in its core. ... The luminosity class II in the Yerkes spectral classification is given to bright giants. ... Supergiants are the most massive stars. ... This article does not cite its references or sources. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ... Supergiants are the most massive stars. ... This article does not cite its references or sources. ... Supergiants are the most massive stars. ... Eta Carinae (η Carinae or η Car) is a highly luminous hypergiant double star. ... Deneb (α Cyg / α Cygni / Alpha Cygni) is the brightest star in the constellation Cygnus and one of the vertices of the Summer Triangle. ... This article is about the star. ... The luminosity class II in the Yerkes spectral classification is given to bright giants. ... Beta Scuti (β Sct / β Scuti) is a binary star in the constellation Scutum. ... Giant star is a star that has stopped fusing hydrogen in its core. ... Rho Persei (ρ Per / ρ Persei) is a star in the constellation Perseus. ... Subgiant star is a class of stars that are brighter than normal main sequence (dwarf) stars, but not as bright as true giant stars. ... Our inner solar system superimposed behind the orbits of the planets HD 179949 b, HD 164427 b, Epsilon Reticuli ab, and Mu Arae b (each planet has its parent star labeled next to it -- all parent stars are in the center) Epsilon Reticuli (ε Ret / ε Reticuli) is a 4th magnitude star... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... A subdwarf star, sometimes denoted by sd, is luminosity class VI under the Yerkes spectral classification system. ... This article or section does not adequately cite its references or sources. ...

Spectral types

The following illustration represents star classes with the colors very close to those actually perceived by the human eye. The relative sizes are for main sequence or "dwarf" stars. Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ...

The Morgan-Keenan spectral classification

Image File history File links Download high-resolution version (2117x768, 711 KB) Image depicting the Morgan-Keenan spectral classification of stars. ... Image File history File links Download high-resolution version (2117x768, 711 KB) Image depicting the Morgan-Keenan spectral classification of stars. ...

Class O

Class O stars are very hot and very luminous, being bluish in color; in fact, most of their output is in the ultraviolet range. These are the rarest of all main sequence stars, constituting as few as 1 in 3,000,000 in the solar neighborhood (Note: these proportions are fractions of stars brighter than absolute magnitude 16; lowering this limit will render earlier types even rarer while generally adding only to the M class).^[9] O-stars shine with a power over a million times our Sun's output. These 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. Because they are so huge, class O stars burn through their hydrogen fuel very quickly, and are the first stars to leave the main sequence. Recent observations by the Spitzer Space Telescope indicate that planetary formation does not occur around other stars in the vicinity of an O class star due to the photoevaporation effect.^[15] For other uses, see Ultraviolet (disambiguation). ... General Name, symbol, number helium, He, 2 Chemical series noble gases Group, period, block 18, 1, s Appearance colorless Standard atomic weight 4. ... Not to be confused with Silicone. ... This article is about the chemical element and its most stable form, or dioxygen. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... For other uses, see Carbon (disambiguation). ... General Name, symbol, number helium, He, 2 Chemical series noble gases Group, period, block 18, 1, s Appearance colorless Standard atomic weight 4. ... Two of the balmer lines (α and β) are clearly visible in this emission spectrum of a deuterium lamp. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... The Spitzer Space Telescope (formerly the Space Infrared Telescope Facility [SIRTF]) is an infrared space observatory, the fourth and final of NASAs Great Observatories. ...

Examples: Zeta Orionis, Zeta Puppis, Lambda Orionis, Delta Orionis, BD+66°1673^[16]

Zeta Orionis is a star in the constellation Orion. ... Zeta Puppis (ζ Pup / ζ Puppis) is a star in the constellation of Puppis. ... Lambda Orionis (λ Ori / λ Orionis) is a star in the constellation Orion. ... Delta Orionis (δ Ori) is one of the three stars of the belt of the constellation Orion. ...

Class B

The Pleiades open star cluster with many bright B stars

Class B stars are extremely luminous and blue. Their spectra have neutral helium, which are most prominent at the B2 subclass, and moderate hydrogen lines. Ionized metal lines include Mg II and Si II. As O and B stars are so powerful, they only live for a very short time, and thus they do not stray far from the area in which they were formed. These stars tend to cluster together in what are called OB associations, which are associated with giant molecular clouds. The Orion OB1 association occupies a large portion of a spiral arm of our galaxy and contains many of the brighter stars of the constellation Orion. They constitute about 1 in 800 main sequence stars in the solar neighborhood^[9] —rare, but much more common than those of class O. Image File history File links Pleiades_Lanoue. ... Image File history File links Pleiades_Lanoue. ... A shorter exposure shows less nebulosity. ... Galactic cluster redirects here. ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... Not to be confused with Silicone. ... OB stars are hot, massive stars stars which form in loosely organized groups called OB associations. ... A stellar association, or moving group, is a very loose star cluster, looser than both open clusters and globular clusters. ... A molecular cloud is a type of interstellar cloud whose density and size permits the formation of molecules, most commonly molecular hydrogen (H2). ... A spiral galaxy presents a face-on view of its spiral arms. ... For other uses, see Milky Way (disambiguation). ... Orion, a constellation often referred to as The Hunter, is a prominent constellation, perhaps the best-known in the sky. ...

Examples: Rigel, Spica, the brighter Pleiades

Rigel (pronounced ) (β Orionis) is the brightest star in the constellation Orion and the seventh brightest star in the sky, with visual magnitude 0. ... Spica (α Vir / α Virginis / Alpha Virginis) is the brightest star in the constellation Virgo, and one of the brightest stars in the nighttime sky. ... A shorter exposure shows less nebulosity. ...

Class A

Class A stars are amongst the more common naked eye stars, and are white or bluish-white. They have strong hydrogen lines, at a maximum by A0, and also lines of ionized metals (Fe II, Mg II, Si II) at a maximum at A5. The presence of Ca II lines is notably strengthening by this point. They comprise about 1 in 160 of the main sequence stars in the solar neighborhood.^[9] General Name, symbol, number iron, Fe, 26 Chemical series transition metals Group, period, block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... Not to be confused with Silicone. ... For other uses, see Calcium (disambiguation). ...

Examples: Vega, Sirius, Deneb

For other uses, see Vega (disambiguation). ... This article is about the brightest star in the night sky of Earth. ... Deneb (α Cyg / α Cygni / Alpha Cygni) is the brightest star in the constellation Cygnus and one of the vertices of the Summer Triangle. ...

Class F

Class F stars have strengthening H and K lines of Ca II. Neutral metals (Fe I, Cr I) beginning to gain on ionized metal lines by late F. Their spectra are characterized by the weaker hydrogen lines and ionized metals. Their color is white with a slight tinge of yellow. These represent about 1 in 33 of the main sequence stars in the solar neighborhood.^[9] For other uses, see Calcium (disambiguation). ... General Name, symbol, number iron, Fe, 26 Chemical series transition metals Group, period, block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ... REDIRECT [[ Insert text]]EWWWWWWWWWWWWW YO General Name, symbol, number chromium, Cr, 24 Chemical series transition metals Group, period, block 6, 4, d Appearance silvery metallic Standard atomic weight 51. ...

Examples: Canopus, Procyon

This article does not cite any references or sources. ... Procyon (α CMi / α Canis Minoris / Alpha Canis Minoris) is the brightest star in the constellation Canis Minor and the eighth brightest star in the nighttime sky. ...

Class G

The most important class G star to humanity: our Sun. The dark area visible northwest of the South pole is a large sunspot.

Class G stars are probably the best known, if only for the reason that our Sun is of this class. Most notable are the H and K lines of Ca II, which are most prominent at G2. They have even weaker hydrogen lines than F, but along with the ionized metals, they have neutral metals. There is a prominent spike in the G band of CH molecules. G is host to the "Yellow Evolutionary Void".^[17] Supergiant stars often swing between O or B (blue) and K or M (red). While they do this, they do not stay for long in the G classification as this is an extremely unstable place for a supergiant to be. G stars represent about 1 in 13 of the main sequence stars in the solar neighborhood.^[9] Image File history File links Sun920607. ... Image File history File links Sun920607. ... Sol redirects here. ... For other uses, see Sunspot (disambiguation). ... Sol redirects here. ... For other uses, see Calcium (disambiguation). ...

Examples: Sun, Alpha Centauri A, Capella, Tau Ceti

Sol redirects here. ... Alpha Centauri A is a star of the star system Alpha Centauri. ... Capella (α Aur / α Aurigae / Alpha Aurigae) is the brightest star in the constellation Auriga and sixth brightest star in the sky. ... Tau Ceti (τ Cet / τ Ceti) is a star commonly mentioned by science fiction authors since it is similar to the Sun in mass and spectral type in addition to being relatively close to us. ...

Class K

Class K are orangish stars which are slightly cooler than our Sun. Some K stars are giants and supergiants, such as Arcturus, while others, like Alpha Centauri B, are main sequence stars. They have extremely weak hydrogen lines, if they are present at all, and mostly neutral metals (Mn I, Fe I, Si I). By late K, molecular bands of titanium oxide become present. These make up 1 in 8 of the main sequence stars in the solar neighborhood.^[9] According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giants. Examples include Aldebaran and Arcturus. ... Supergiants are the most massive stars. ... For other uses, see Arcturus (disambiguation). ... Alpha Centauri (α Cen / α Centauri, also known as Rigil Kentaurus), is the brightest star system in the southern constellation of Centaurus. ... General Name, symbol, number manganese, Mn, 25 Chemical series transition metals Group, period, block 7, 4, d Appearance silvery metallic Standard atomic weight 54. ... General Name, symbol, number iron, Fe, 26 Chemical series transition metals Group, period, block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ... Not to be confused with Silicone. ... Titanium dioxide, also known as titanium(IV) oxide or titania, is the naturally occurring oxide of titanium, chemical formula TiO2. ...

Examples: Alpha Centauri B, Epsilon Eridani, Arcturus, Aldebaran

Alpha Centauri B (also Rigel Kentaurus B — the foot of the centaur in Arabic) is a star of the Alpha Centauri star system. ... Epsilon Eridani (ε Eri / ε Eridani) is a notable main-sequence K2 class star in the constellation of Eridanus. ... For other uses, see Arcturus (disambiguation). ... Aldebaran from the Arabic (الدبران al-dabarān) meaning the follower, (α Tau / α Tauri / Alpha Tauri) is the brightest star in the constellation Taurus and one of the brightest stars in the nighttime sky. ...

Class M

Betelgeuse is a red supergiant, one of the largest stars known. Image from the Hubble Space Telescope.

Class M is by far the most common class. About 76% of the main sequence stars in the solar neighborhood are red dwarfs (78.6% if we include all stars: see the note under Class O),^[9] such as Proxima Centauri. M is also host to most giants and some supergiants such as Antares and Betelgeuse, as well as Mira variables. The late-M group holds hotter brown dwarfs that are above the L spectrum. This is usually in the range of M6.5 to M9.5. The spectrum of an M star shows lines belonging to molecules and all neutral metals but hydrogen lines are usually absent. Titanium oxide can be strong in M stars, usually dominating by about M5. Vanadium oxide bands become present by late M. Image File history File links Download high-resolution version (950x950, 35 KB) This is the first direct image of a star other than the Sun. ... Image File history File links Download high-resolution version (950x950, 35 KB) This is the first direct image of a star other than the Sun. ... This article is about the star. ... Betelgeuse, viewed from a distance of 8 AU. By comparison, this is our own Sun, and how it would appear when viewed from the same distance. ... Below is a list of the largest known stars, by solar diameter. ... The Hubble Space Telescope (HST) is a telescope in orbit around the Earth, named after astronomer Edwin Hubble. ... This article is about the British sitcom. ... Proxima Centauri (Latin proximus, -a, -um: meaning next to or nearest to)[4] is a red dwarf star that is likely a part of the Alpha Centauri star system and is the nearest star to the Sun at a distance of 4. ... This article or section does not cite its references or sources. ... This article is about the star. ... For other uses, see Mira (disambiguation). ... This article or section contains a plot summary that is overly long or excessively detailed. ... This brown dwarf (smaller object) orbits the star Gliese 229, which is located in the constellation Lepus about 19 light years from Earth. ... 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ... Titanium dioxide, also known as titanium(IV) oxide or titania, is the naturally occurring oxide of titanium, chemical formula TiO2. ... Vanadium oxide is a compund molecule of two Vanadium atoms and five Oxygen molecules(V2O5) Category: ...

Example: Betelgeuse (supergiant)

Examples: Proxima Centauri, Barnard's star, Gliese 581 (red dwarf)

Example: LEHPM 2-59 ^[18] (subdwarf)

Examples: Teide 1 (field brown dwarf), GSC 08047-00232 B ^[19] (companion brown dwarf)

This article is about the star. ... Supergiants are the most massive stars. ... Proxima Centauri (Latin proximus, -a, -um: meaning next to or nearest to)[4] is a red dwarf star that is likely a part of the Alpha Centauri star system and is the nearest star to the Sun at a distance of 4. ... Barnards Star is a very low-mass star in the constellation Ophiuchus which was discovered by the astronomer E. E. Barnard in 1916. ... Gliese 581 (IPA: ) is an M2. ...

Extended spectral types

A number of new spectral types have been taken into use from newly discovered types of stars.

Hot blue emission star classes

Spectra of some very hot and bluish stars exhibit marked emission lines from carbon or nitrogen, or sometimes oxygen.

Class W: Wolf-Rayet

Main article: Wolf-Rayet stars

Artist's impression of a Wolf-Rayet star

Class W or WR represents the superluminous Wolf-Rayet stars, notably unusual since they have mostly helium in their atmospheres instead of hydrogen. They are thought to be dying supergiants with their hydrogen layer blown away by hot stellar winds caused by their high temperatures, thereby directly exposing their hot helium shell. Class W is subdivided into subclasses WC (WCE early-type, WCL late-type), WN (WNE early-type, WNL late-type), and WO according to the dominance of carbon, nitrogen, or oxygen emission in their spectra (and outer layers). Wolf-Rayet stars are evolved, hot, massive stars, that exhibit high mass-loss caused by strong stellar winds. ... Image File history File links Wolf-rayet. ... Image File history File links Wolf-rayet. ... A solar wind is a stream of particles (mostly high-energy protons ~ 500 keV) which are ejected from the upper atmosphere of a star (in the case of a star other than the Earths Sun, it may be called a stellar wind instead). ...

• W: Up to 70,000 K

Example: Gamma Velorum A (WC)

Example: WR124 (WN)

Example: WR93B (WO)

Gamma Velorum (γ Vel / γ Velorum) is a star system in the constellation Vela. ...

Classes OC, ON, BC, BN: Wolf-Rayet related O and B stars

Intermediary between the genuine Wolf-Rayet's and ordinary hot stars of classes O and early B, there are OC, ON, BC and BN stars. They seem to constitute a short continuum from the Wolf-Rayet's into the ordinary OB:s.

Example: HD 152249 (OC)

Example: HD 105056 (ON)

Example: HD 2905 (BC)

Example: HD 163181 (BN)

The "class" OB

Main article: OB star

In lists of spectra, the "spectrum OB" may occur. This is in fact not a spectrum, but a marker which means that "the spectrum of this star is unknown, but it belongs to an OB association, so probably either a class O or class B star, or perhaps a fairly hot class A star." OB stars are hot, massive stars stars which form in loosely organized groups called OB associations. ... A stellar association is a very loose star cluster, looser than both open clusters and globular clusters. ...

Cool red and brown dwarf classes

The novel spectral types L and T were created to classify infrared spectra of cool stars and brown dwarfs which were very faint in the visual spectrum. The hypothetical spectral type Y has been reserved for objects cooler than T dwarfs having spectra which are qualitatively distinct from T dwarfs.^[20] Brown dwarfs are sub-stellar objects (~13 to 75 Jupiter masses) that never fuse hydrogen into helium in their cores, as do stars on the main sequence. ... The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ...

Class L

Artists vision of an L-dwarf

Class L dwarfs get their designation because they are cooler than M stars and L is the remaining letter alphabetically closest to M. L does not mean lithium dwarf; a large fraction of these stars do not have lithium in their spectra. Some of these objects have mass large enough to support hydrogen fusion, but some are of substellar mass and do not, so collectively these objects should be referred to as L dwarfs, not L stars. They are a very dark red in color and brightest in infrared. Their atmosphere is cool enough to allow metal hydrides and alkali metals to be prominent in their spectra.^[21][22] Due to low gravities in giant stars, TiO- and VO-bearing condensates never form. Thus, larger L-type stars can never form in an isolated environment. It may be possible for these L-type supergiants to form through stellar collisions, however, an example of which is V838 Monocerotis. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... This article is about the chemical element. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... For other uses, see Infrared (disambiguation). ... Atmospheres redirects here. ... A Hydride is a chemical compound or form of a bond between hydrogen with a metal usually found in group 1 of the Periodic table, usually with a more electropositive element or group. ... The alkali metals are a series of elements comprising Group 1 (IUPAC style) of the periodic table: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). ... V838 Monocerotis (V838 Mon) is an enigmatic variable star in the constellation Monoceros about 20,000 light years (6 kpc)[1] from the Sun. ...

• L: 1,300–2,000 K, dwarfs (some stellar, some substellar) with metal hydrides and alkali metals prominent in their spectra.

Example: VW Hyi

Example: 2MASSW J0746425+2000321 binary^[23]

Component A is an L dwarf star

Component B is an L brown dwarf

Example: V838 Monocerotis (supergiants)

A Hydride is a chemical compound or form of a bond between hydrogen with a metal usually found in group 1 of the Periodic table, usually with a more electropositive element or group. ... The alkali metals are a series of elements comprising Group 1 (IUPAC style) of the periodic table: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). ... V838 Monocerotis (V838 Mon) is an enigmatic variable star in the constellation Monoceros about 20,000 light years (6 kpc)[1] from the Sun. ...

Class T: methane dwarfs

Artists vision of a T-dwarf

Class T dwarfs are cool brown dwarfs with surface temperatures of between ~1500 and 700K. Their emission peaks in the infrared. Methane is prominent in their spectra.^[21][22] Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Brown dwarfs are sub-stellar objects (~13 to 75 Jupiter masses) that never fuse hydrogen into helium in their cores, as do stars on the main sequence. ... For other uses, see Infrared (disambiguation). ... Methane is a chemical compound with the molecular formula . ...

• T: ~700-1,000 K, cooler brown dwarfs with methane in the spectrum

Examples: SIMP 0136 (the brightest T dwarf discovered in northern hemisphere)^[24]

Examples: Epsilon Indi Ba & Epsilon Indi Bb

Class T and L could be more common than all the other classes combined, if recent research is accurate. From studying the number of proplyds (protoplanetary discs, clumps of gas in nebulae from which stars and solar systems are formed) then the number of stars in the galaxy should be several orders of magnitude higher than what we know about. It is theorized that these proplyds are in a race with each other. The first one to form will become a proto-star, which are very violent objects and will disrupt other proplyds in the vicinity, stripping them of their gas. The victim proplyds will then probably go on to become main sequence stars or brown dwarf stars of the L and T classes, but quite invisible to us. Since they live so long, these smaller stars will accumulate over time. This brown dwarf (smaller object) orbits the star Gliese 229, which is located in the constellation Lepus about 19 light years from Earth. ... Methane is a chemical compound with the molecular formula . ... Epsilon Indi (ε Ind / ε Indi) is a star approximately 11. ... A protoplanetary disc (also protoplanetary disk, proplyd) is an accretion disc surrounding a T Tauri star. ... The Triangulum Emission Nebula NGC 604 The Pillars of Creation from the Eagle Nebula For other uses, see Nebula (disambiguation). ... For other uses, see Galaxy (disambiguation). ... An order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. ... The protostar period is the period in the evolution of a star after the cloud of hydrogen, helium and dust has started contraction and before the star has reached the main sequence on the Hertzsprung-Russell diagram. ...

Class Y

Class Y dwarfs are expected to be much cooler than T-dwarfs. They have been modelled^[25], though there is no well-defined spectral sequence yet with prototypes. In March 2008, a 620 kelvin brown dwarf named CFBDS J005910.90-011401.3 was discovered, displaying wide ammonia absorption in the near-infrared. It is believed to be the first prototype of a Y0 dwarf. ^[26] 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ...

• Y: < 700 K, ultra-cool brown dwarfs (theoretical)

This brown dwarf (smaller object) orbits the star Gliese 229, which is located in the constellation Lepus about 19 light years from Earth. ...

Carbon related late giant star classes

Carbon related stars are stars whose spectra indicate production of carbon by helium triple-alpha fusion. With increased carbon abundance, and some parallel s-process heavy element production, the spectra of these stars are becoming increasingly deviant from the usual late spectral classes G, K and M. The giants among those stars are presumed to produce this carbon themselves, but not too few of this class of stars are believed to be double stars whose odd atmosphere once was transferred from a former carbon star companion that is now a white dwarf. Overview of the Triple-alpha process. ... This article or section does not cite its references or sources. ...

Class C: carbon stars

Main article: Carbon star

Originally classified as R and N stars, these are also known as 'carbon stars'. These are red giants, near the end of their lives, in which there is an excess of carbon in the atmosphere. The old R and N classes ran parallel to the normal classification system from roughly mid G to late M. These have more recently been remapped into a unified carbon classifier C, with N0 starting at roughly C6. Another subset of cool carbon stars are the J-type stars, which are characterized by the strong presence of molecules of ¹³CN in addition to those of ¹²CN.^[27] A few dwarf (that is, main sequence) carbon stars are known, but the overwhelming majority of known carbon stars are giants or supergiants. A carbon star is a late type giant star similar to the red giants (or occasionally red dwarf) star whose atmosphere contains more carbon than oxygen; the two elements combine in the upper layers of the star, forming carbon monoxide, which consumes all the oxygen in the atmosphere, leaving carbon...

• C: Carbon stars, e.g. R CMi
  • C-R: Formerly a class on its own representing the carbon star equivalent of late G to early K stars. Example: S Camelopardalis
  • C-N: Formerly a class on its own representing the carbon star equivalent of late K to M stars. Example: R Leporis
  • C-J: A subtype of cool C stars with a high content of ¹³C. Example: Y Canum Venaticorum
  • C-H: Population II analogues of the C-R stars. Examples: V Ari, TT CVn^[28]
  • C-Hd: Hydrogen-Deficient Carbon Stars, similar to late G supergiants with CH and C₂ bands added. Example: HD 137613

R Leporis, sometimes called Hinds Crimson Star, is a well-known variable star, in the constellation Lepus, near the border with Eridanus. ... This article needs to be cleaned up to conform to a higher standard of quality. ...

Class S

Class S stars have zirconium oxide lines in addition to (or, rarely, instead of) those of titanium oxide, and are in between the Class M stars and the carbon stars.^[29] S stars have excess amounts of zirconium and other elements produced by the s-process, and have their carbon and oxygen abundances closer to equal than is the case for M stars. The latter condition results in both carbon and oxygen being locked up almost entirely in carbon monoxide molecules. For stars cool enough for carbon monoxide to form that molecule tends to "eat up" all of whichever element is less abundant, resulting in "leftover oxygen" (which becomes available to form titanium oxide) in stars of normal composition, "leftover carbon" (which becomes available to form the diatomic carbon molecules) in carbon stars, and "leftover nothing" in the S stars. The relation between these stars and the ordinary M stars indicates a continuum of carbon abundance. Like carbon stars, nearly all known S stars are giants or supergiants. Zirconia (ZrO2) is a white crystalline oxide of zirconium that is used as a refractory, in insulation, abrasives, enamels and glazes. ... Titanium dioxide, also known as titanium(IV) oxide or titania, is the naturally occurring oxide of titanium, chemical formula TiO2. ... General Name, Symbol, Number zirconium, Zr, 40 Chemical series transition metals Group, Period, Block 4, 5, d Appearance silvery white Standard atomic weight 91. ... This article or section does not cite its references or sources. ... For other uses, see Carbon (disambiguation). ... This article is about the chemical element and its most stable form, or dioxygen. ... Carbon monoxide, with the chemical formula CO, is a colorless, odorless, and tasteless gas. ... A diatomic molecule of Carbon (C2), which occurs when you strike an arc (along with some buckyballs), in comets, and in the blue light we see in flames. ...

Examples: S Ursae Majoris, HR 1105

Classes MS and SC: intermediary carbon related classes

In between the M class and the S class, border cases are named MS stars. In a similar way border cases between the S class and the C-N class are named SC or CS. The sequence M → MS → S → SC → C-N is believed to be a sequence of increased carbon abundance with age for carbon stars in the asymptotic giant branch. A carbon star is a red giant (or occasionally red dwarf) star whose atmosphere contains more carbon than oxygen; the two elements combine in the upper layers of the star, forming carbon monoxide and other carbon compounds. ... A period of Stellar evolution undertaken by all low to intermediate mass stars (0. ...

Examples: R Serpentis, ST Monocerotis (MS)

Examples: CY Cygni, BH Crucis (SC)

White dwarf classifications

Main article: White dwarf spectroscopy

Sirius A and B (a white dwarf of type DA2) resolved by HST

The class D is the modern classification used for white dwarfs, low-mass stars that are no longer undergoing nuclear fusion and have shrunk to planetary size, slowly cooling down. Class D is further divided into spectral types DA, DB, DC, DO, DQ, DX, and DZ. The letters are not related to the letters used in the classification of other stars, but instead indicate the composition of the white dwarf's visible outer layer or atmosphere. Image File history File linksMetadata Sirius_A_and_B_Hubble_photo. ... Image File history File linksMetadata Sirius_A_and_B_Hubble_photo. ... This article is about the brightest star in the night sky of Earth. ... This article or section does not adequately cite its references or sources. ... The Hubble Space Telescope (HST) is a telescope in orbit around the Earth, named after astronomer Edwin Hubble. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing sustainable fusion power. ...

Examples: Sirius B (DA2), Procyon B (DA4), Van Maanen's star (DZ7)^{[30], Table 1}

The white dwarf types are as follows:^[31] This article is about the star. ... This article is about the star. ... Van Maanens Star is a white dwarf, the second such star discovered and the third closest one to the Sun after Sirius B and Procyon B. It is located 14. ...

• DA: a hydrogen-rich atmosphere or outer layer, indicated by strong Balmer hydrogen spectral lines.
• DB: a helium-rich atmosphere, indicated by neutral helium, He I, spectral lines.
• DO: a helium-rich atmosphere, indicated by ionized helium, He II, spectral lines.
• DQ: a carbon-rich atmosphere, indicated by atomic or molecular carbon lines.
• DZ: a metal-rich atmosphere, indicated by metal spectral lines.
• DC: no strong spectral lines indicating one of the above categories.
• DX: spectral lines are insufficiently clear to classify into one of the above categories.

The type is followed by a number giving the white dwarf's surface temperature. This number is a rounded form of 50400/T_eff, where T_eff is the effective surface temperature, measured in kelvins. Originally, this number was rounded to one of the digits 1 through 9, but more recently fractional values have started to be used, as well as values below 1 and above 9.^[31][32] This article is about the chemistry of hydrogen. ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... General Name, symbol, number helium, He, 2 Chemical series noble gases Group, period, block 18, 1, s Appearance colorless Standard atomic weight 4. ... Before the atom electron states were known, spectroscopists saw distinctive series in atom spectra, and so they assigned letters to characteristic spectra. ... Before the atom electron states were known, spectroscopists saw distinctive series in atom spectra, and so they assigned letters to characteristic spectra. ... For other uses, see Carbon (disambiguation). ... In astronomy, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium. ... The effective temperature of a star is the temperature of a black body with the same luminosity (L) as the star and is defined according to the Stefan-Boltzman law L = sigma T_{eff}^{4}. The effective temperature of our Sun is around 5,800 kelvins (K) and correspond to... The kelvin (symbol: K) is the SI unit of temperature, and is one of the seven SI base units. ...

Two or more of the type letters may be used to indicate a white dwarf which displays more than one of the spectral features above. Also, the letter V is used to indicate a variable white dwarf.^[31] A pulsating white dwarf is a white dwarf star whose luminosity varies due to non-radial gravity wave pulsations within itself. ...

Extended white dwarf spectral types:^[31]

• DAB: a hydrogen- and helium-rich white dwarf displaying neutral helium lines.
• DAO: a hydrogen- and helium-rich white dwarf displaying ionized helium lines.
• DAZ: a hydrogen-rich metallic white dwarf.
• DBZ: a helium-rich metallic white dwarf.

Variable star designations:

• DAV or ZZ Ceti: a hydrogen-rich pulsating white dwarf.^{[33], pp. 891, 895}
• DBV or V777 Her: a helium-rich pulsating white dwarf.^{[34], p. 3525}
• GW Vir, DOV or PNNV: a hot helium-rich pulsating white dwarf (or pre-white dwarf.)^{[35], §1.1, 1.2;[36][37]}

A pulsating white dwarf is a white dwarf star whose luminosity varies due to non-radial gravity wave pulsations within itself. ... // A pulsating white dwarf is a white dwarf star whose luminosity varies due to non-radial gravity wave pulsations within itself. ...

Non-stellar spectral types: Class P & Q

Finally, the classes P and Q are occasionally used for certain non-stellar objects. Type P objects are planetary nebulae and type Q objects are novae. NGC 6543, The Cats Eye Nebula NGC 6853, The Dumbbell Nebula A planetary nebula is an astronomical object consisting of a glowing shell of gas and plasma formed by certain types of stars at the end of their lives. ... Artists conception of a white dwarf star accreting hydrogen from a larger companion A nova (pl. ...

Spectral peculiarities

Additional nomenclature, in the form of lower-case letters, can follow the spectral type to indicate peculiar features of the spectrum.^[38]

For example, Epsilon Ursae Majoris is listed as spectral type A0pCr, indicating general classification A0 with a strong emission lines of the element chromium. There are several common classes of chemically peculiar stars, where the spectral lines of a number of elements appear abnormally strong. P Cygni is itself slowly a star variable in the brightness in the constellation swan. ... Delta Scuti (δ Sct / δ Scuti) is a triple star system in the constellation Scutum. ... For other uses, see Barium (disambiguation). ... For other uses, see Calcium (disambiguation). ... REDIRECT [[ Insert text]]EWWWWWWWWWWWWW YO General Name, symbol, number chromium, Cr, 24 Chemical series transition metals Group, period, block 6, 4, d Appearance silvery metallic Standard atomic weight 51. ... General Name, Symbol, Number europium, Eu, 63 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Atomic mass 151. ... General Name, symbol, number helium, He, 2 Chemical series noble gases Group, period, block 18, 1, s Appearance colorless Standard atomic weight 4. ... This article is about the element. ... General Name, symbol, number manganese, Mn, 25 Chemical series transition metals Group, period, block 7, 4, d Appearance silvery metallic Standard atomic weight 54. ... Not to be confused with Silicone. ... General Name, Symbol, Number strontium, Sr, 38 Chemical series alkaline earth metals Group, Period, Block 2, 5, s Appearance silvery white metallic Standard atomic weight 87. ... Ursa Major Epsilon Ursae Majoris (ε UMa / ε Ursae Majoris) is the brightest star in the constellation Ursa Major (despite its Bayer designation being merely epsilon), and at magnitude 1. ... REDIRECT [[ Insert text]]EWWWWWWWWWWWWW YO General Name, symbol, number chromium, Cr, 24 Chemical series transition metals Group, period, block 6, 4, d Appearance silvery metallic Standard atomic weight 51. ... This article or section does not cite any references or sources. ...

Photometric classification

Stars can also be classified using photometric data from any photometric system. For example, we can calibrate color index diagrams of U−B and B−V in the UBV system according to spectral and luminosity classes. Nevertheless, this calibration is not straightforward, because many effects are superimposed in such diagrams: interstellar reddening, color changes due to metallicity, and the blending of light from binary and multiple stars. In astronomy, a Photometric system is a set of discrete passbands (of filters), with a known sensitivity to incident radiation. ... In astronomy, the color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. ... UBV photometric system, also called the Johnson system (or Johnson-Morgan system), is a wide band photometric system for classifying stars according to their colors. ... In astronomy one method of classifying stars is through the analysis of their absorption spectra, by this method stars are assigned a spectral class. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. ... In astronomy, interstellar reddening is a phenomenon associated with interstellar extinction where the spectrum of electromagnetic radiation from a radiation source changes characteristics from that which was emitted. ... The globular cluster M80. ... For the band of the same name, see: Binary Star (band) Hubble image of the Sirius binary system, in which Sirius B can be clearly distinguished (lower left). ... Artists impression of the orbits of HD 188753, a triple star system A multiple star consists of three or more stars which appear from the Earth to be close to one another. ...

Photometric systems with more colors and narrower passbands allow a star's class, and hence physical parameters, to be determined more precisely. The most accurate determination comes of course from spectral measurements, but there is not always enough time to get qualitative spectra with high signal-to-noise ratio. Signal-to-noise ratio (often abbreviated SNR or S/N) is an electrical engineering concept defined as the ratio of a signal power to the noise power corrupting the signal. ...

See also

• Stellar evolution
• Stellar associations
• Metallicity
• Astrograph
• H-R diagram

Projected timeline of the Suns life In astronomy, stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. ... A stellar association is a very loose star cluster, looser than both open clusters and globular clusters. ... The globular cluster M80. ... A 13-inch, f/5. ... In stellar astronomy, the Hertzsprung-Russell diagram (usually referred to by the abbreviation H-R diagram or HRD) shows the relationship between absolute magnitude, luminosity, stellar classification, and surface temperature. ...

References

A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 269th day of the year (270th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 133rd day of the year (134th in leap years) in the Gregorian calendar. ... This is the article on the publisher Annual Reviews whose titles are invariably called Annual review of . ... This is the article on the publisher Annual Reviews whose titles are invariably called Annual review of . ... is the 261st day of the year (262nd in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 191st day of the year (192nd in leap years) in the Gregorian calendar. ... Events of 2008: (EMILY) Me Lesley and MIley are going to China! This article is about the year. ... The Astrophysical Journal is one of the foremost research journals devoted to recent developments, discoveries, and theories in astronomy and astrophysics. ... The University of Chicago Press is the largest university press in the U.S. It is operated by the University of Chicago and publishes a wide variety of academic titles, including The Chicago Manual of Style, dozens of academic journals including Critical Inquiry, and a wide array of texts covering... This is the article on the publisher Annual Reviews whose titles are invariably called Annual review of . ... This is the article on the publisher Annual Reviews whose titles are invariably called Annual review of . ... is the 152nd day of the year (153rd in leap years) in the Gregorian calendar. ... For the Jimi Hendrix song, see 1983. ...

External links

• Libraries of stellar spectra, D. Montes, UCM
• Webfooted Astronomer
• The rate of period change in pulsating DB white dwarf stars, A. H. Corsico, L. G. Althaus, has the DAV, DBV, & DOV explanation.
• The Close DAO+dM Binary RE J0720-318: A Stratified White Dwarf with a Thin H Layer and a Possible Circumbinary Disk DAO type White Dwarf.
• The Spatial Distribution and Kinematics of Cool Metallic Line White Dwarfs, has DAZ and DBZ spectrums
• A K-Band Spectral Atlas of Wolf-Rayet Stars, has WC, WN, and WO spectrums
• Properties of the WO Wolf-Rayet stars, has WO spectrum ranging from WO1 to WO5
• Spectral Types for Hipparcos Catalogue Entries
• [1], has the luminous subclasses.
• Discovery of a Very Young Field L Dwarf, 2MASS J01415823-4633574, J. Davy Kirkpatrick et al.