]> Ed Shaya astronomy.owl This ontology covers astronomical classes and properties. It includes terms from the IVOA Thesaurus plus terms from the UMD astronomical ontology 21-cm line 21 cm line 53 Persei star Abell cluster absolute magnitude absorption line system Intergalactic Clouds seen in absorption of light from a more distant source. accretion disk achondrite active galactic nucleus AGN active galaxy eruptive galaxy active prominence active region active star activity index A dwarf aerolite Ae star A giant Algol variable star beta Persei star alpha2 Canum Venaticorum star amateur astronomy AM Canum Venaticorum star AM Herculis star polars Amor group Am star annual parallax heliocentric parallax parallax annular eclipse Anomalous X-ray Pulsars (AXPs) are now widely believed to be magnetars, young, isolated, highly magnetized neutron stars. These energtic X-ray pulsars are characterized by slow rotation periods of ~5 - 12 seconds and large magnetic fields of ~1E13-1E15 gauss. ansa antapex The point on the celestial sphere from which an object is moving away anthropic principle anticenter apastron aperiodic comet apex The celestial point in the direction of motion; usually the Sun's motion wrt to the LSR. aphelion apoapsis apocenter apogee Apollo group apparent intensity apparent magnitude apparent position apparent places apparent superluminal motion superluminal motion apsidal motion apsis apse Ap star peculiar A star archaeoastronomy ancient astronomy astroarchaeology ascending node ashen light First sighted by the astronomer Giovanni Battista Riccioli on January 9, 1643, the Ashen Light is a subtle glow that is seen from the night side of the planet Venus. A star asteroid planetoid minor planet asteroid belt asteroid occultation asteroseismology stellar seismology astrobiology exobiology astrodynamics astrographic catalog astrographic catalogues UK astrometric binary star astrometry positional astronomy astronomer astronomical constant astronomical research astronomical technique astronomy A scientist in the field of astrophysics. This is almost but not quite synonomous with astronomer. astrophysics A subdwarf A subgiant A supergiant asymptotic giant branch AGB ataxite A rare variety of iron meteorite (designated type D) made almost entirely of taenite, a solid solution of iron and 27% to 65% nickel; the Greek name means without structure and refers to the lack of a visible Widmansten pattern (spindles of kamacite being visible only microscopically). atmospheric extinction extinction atmospheric refraction atmospheric scattering atmospheric scintillation twinkling atmospheric window australite Baade-Wesselink method background radiation radiation background Bailey type AB variable star bailys bead barium star Ba II star barred spiral galaxy baryonic Dark Matter B dwarf bediasite Bediasites are part of the 34-million-year-old North American strewnfield coming from the Chesapeake Bay impact crater Two strewnfields and tektite groups are associated with this impact: the black Bediasites in Texas and the green Georgiaites in Georgia. Be star Be dwarf star beta Cephei star beta Canis Majoris star beta Lyrae star B galaxy B giant Bianchi cosmology Big Bang theory binary pulsar binary star double star binaries binary system bipolar galaxy bipolar group bipolar nebula bipolar outflow bipolar flow black dwarf black hole blank field blazar Blazhko effect A secondary variation of the amplitude and period of some RR Lyrae stars and related pulsating variables, named for its discoverer, Sergei Blazko. The effect is displayed, for example, by the RR Lyrae star XZ Cygni, which has a primary pulsation period of about 0.466 days but displays a further modulation with a 57-day cycle. It is thought to involve double-mode pulsation or, in some cases, an oblique rotator. BL Herculis star BL Lac BL Lacertae object BL Lac object blue galaxy blue loop blue object blueshift blue shift blue-shift blue straggler star B magnitude Bodes law Titius-Bode law Bok globule bolide bolometric correction Bp star bright galaxy bright nebula brightness temperature bright star broad band photometry wide-band photometry broad-band photometry brown dwarf B star B subdwarf B supergiant Burkert profile The Burkert profile is an analytic approximation of virialized dark halo density profiles, especially when dark matter particles have a finite cross-section for elastic collisions. burst outburst eruption burster Bw star BY Draconis star canyon carbonaceous chondrite carbon burning carbon flash carbon detonation carbon nitrogen cycle CNO cycle carbon cycle carbon star C star cataclysmic variable star eruptive variable star CV cataclysmic binary star cD galaxy celestial coordinate system celestial mechanics celestial pole celestial sphere central star Cepheid bump Cepheid Cepheid variable star delta Cephei star classical Cepheid Cepheid distance Ceres Chandler wobble polar wandering Chandrasekhar limit Chandrasekhar Mass CH G band G band chondrite chondrules chromosphere chronometer chronograph CH star C I emission C II region circular orbit circumplanetary matter circumstellar disk circumstellar dust circumstellar envelope stellar envelope circumstellar gas circumstellar grain circumstellar matter stellar envelope circumstellar cloud circumstellar shell stellar envelope classical nova nova classical T Tauri star CTTS close binary star closed universe close encounter CNO anomaly CN star cocoon star cold Dark Matter collapsed star collapsing star collapsed object collapsing cloud color color excess color-luminosity relation color luminosity relation color-magnitude relation c m relation c-m relation color-magnitude diagram c-m diagram color magnitude relation c m diagram color-redshift relation color redshift relation comet cometary globule two orbiting objects such as planets, satellites or asteroids are said to be in exhibit commensurability if their orbital periods are in rational proportion compact galaxy compact H II region compact nebula compact nucleus compact object compact source companion galaxy companion star comparison star conjunction constellation contact binary star continuum radiation convective envelope convective shell convective zone cooling flow corona coronas coronal dimming coronal hole coronal line coronal loop coronal mass ejection CME coronal plume coronal transient coronal wave cosmic cosmic abundance cosmic background radiation cosmic electrodynamics cosmic noise cosmic ray primary cosmic ray cosmic radiation cosmic ray astronomy cosmic ray shower air shower auger shower cosmic ray source cosmic string string cosmochemistry astrochemistry cosmic chemistry cosmochronology nucleocosmochronology cosmogony cosmological constant Lambda cosmological distance scale cosmological model cosmology crater CS star curve of growth cusp cusp crossing dark cloud Dark Energy dark energy Dark Matter dark nebula absorption nebula DA star DB star From Van den Bergh 1960. Type, Peculiarity, and Luminosity Class. Type = {E0-9,S,SB,S(B),Sa,sb-,sb,sb+Sc,S-,S+,Ir,Ir+} Peculiar={P,N=Bright nucleus,(n)=mild Nebulous arms, n=normal Nebulous arms, nn=extreme Nebulous arms, (*)=mild Patchy arms, *=Patchy arms, **=extreme patchy arms, (t)=mild distorted arms, t=distorted arms, tt=extreme distorted arms} Luminosity Class: {I, I-II,II,II-III,III,III-IV,IV,IV-V,V} deceleration parameter q-parameter Declination celestial latitude DEC degenerate dwarf degenerate star delta delphini star delta Scuti star AI Velorum star dense cloud density bounded density distribution density fluctuation density perturbation density variation density wave model descending node de Sitter universe detached binary star Defined in the Second Reference Catalogue of DeVaucouleurs, a classification number from -5 to 11. Compared to Hubble Class: -5=E0-E3, -4=E4-E6, -2=S0, -1=S0a, 1=Sa, 2=Sab, 3=Sb, 4=Sbc, 5=Sc, 6=Scd, 7=Sd, 8 = Sd, 9= Sdm, 10=Im, 11=cI D galaxy diffuse nebula dirac cosmology dirty snowball theory discrete radio source disk flaring disk galaxy disk of galaxy galaxy disk disk population disk star distance indicator distance modulus modulus distance scale diurnal parallax DO star double galaxy binary galaxy double-mode Cepheid beat_Cepheid double mode Cepheid double-mode pulsation double mode pulsation double-mode variable star double mode variable star double quasar DQ Herculis star dredge up dust cosmic dust dust cloud dust grain grain dust nebula dust shell dwarf dwarf Cepheid dwarf galaxy dwarf nova DN dwarf planet dynamical evolution dynamical friction dynamical parallax early-type emission star early type emission star earlytype galaxy early type galaxy early-type star hot star early type star blue star early-type supergiant early type supergiant star early-type variable star early type variable star early universe Earth-Moon system Earth Moon system Earth orbit Earth rotation eccentric anomaly eccentricity eclipse eclipsing binary star photometric binary star eclipsing variable star eclipsing star ecliptic ecliptic coordinate system ecliptic latitude ecliptic longitude ecliptic plane ecliptic pole E corona emission-line corona E-corona The component of the light emitted by the corona from the corona itself, as opposed to the scattered light. The Eddington approximation can be used to obtain the intensity in a plane-parallel atmosphere with isotropic frequency-independent scattering. It assumes that the intensity is a linear function of μ = cosθ. i.e. Iν(μ,z) = a(z) + μb(z) where z is the normal direction to the slab atmosphere. Eddington limit Edgeworth-Kuiper belt Kuiper belt Edgeworth-Kuiper belt object EKO KBO Kuiper belt object effective temperature E galaxy Einstein ring Einstein universe ejecta element formation formation of element ellipsoidal variable star ellipsoidal binary star photometric binary star elliptical galaxy e galaxy elliptical orbit eccentric orbit emission line galaxy emission line object emission line star emission nebula envelope Ep galaxy ephemeral active region ephemeris ephemeris time equation of the center equation of the equinox equation of time equator equator correction equator determination equatorial bulge equatorial coordinate system equatorial system equatorial Plane equinox position equivalent width e region eruptive binary star event horizon Evershed-effect Evershed effect evolutionary track evolved star exciting star expanding envelope expanding universe exponential profile extended object extended source extragalactic object extragalactic radio source extrasolar planet extreme carbon star extreme horizontal branch star extreme population I star Faber-Jackson distance Faber-Jackson relation facula faint blue star faint galaxy faint star fast nova F corona Fraunhofer corona F-corona The outer part of the corona where the star's radiation has been scattered from dust. F dwarf Fermi-Dirac statistics Fermi Dirac statistics F giant field galaxy field star filamentary nebula filling factor finding list fireball FK catalog system flare chromospheric eruption flare star flash spectrum flash star F layer F region rate of energy flow across a unit area per unit frequency or unit wavelength. forbush effect A Forbush decrease is a rapid decrease in the observed galactic cosmic ray intensity following a coronal mass ejection (CME). It occurs due to the magnetic field of the plasma solar wind sweeping some of the galactic cosmic rays away from Earth. f region Friedmann universe frozen in element F star F subdwarf F subgiant F supergiant fundamental plane fundamental star fundamental system FU Orionis star galactic Galactic cluster Galactic coordinate system Galactic cosmic ray Galactic latitude Galactic longitude Galactic pole Galactic rotation Galactic spurs Galactic structure Galactic window galaxy Major to Minor Diameter ratio at an isophote. Disk thickness to disk diameter at an isophote. galaxy cluster cluster of galaxies galaxy clustering galaxy content galaxy count galaxy distribution galaxy encounter galaxy evolution galaxy formation formation of galaxies Width of spectral line when most of the galaxy fits inside the aperture gives rotational speed of galaxy. galaxy group galaxy merger galactic nucleus galaxy rotation curve galaxy structure structure of galaxy content of galaxy galaxy theory galaxy void galilean satellite gamma Cassiopeiae star gamma-ray astronomy gamma ray astronomy gamma-ray background gamma ray background gamma-ray burst cosmic gamma ray burst cosmic gamma-ray burst GRB gamma ray burst gamma-ray source gamma ray source gas cloud gaseous nebula gas to dust ratio G dwarf gegenschein counterglow geocentric orbit geocorona the solar far-ultraviolet light that is reflected off the cloud of neutral hydrogen atoms that surrounds the Earth. gf value G giant giant branch RGB red giant branch giant branch star giant elliptical galaxy giant galaxy giant molecular cloud giant planet giant radio galaxy giant star giant globular star cluster globule Goedel universe Goulds belt granule gravitational collapse gravitational deflection gravitational equilibrium gravitational instability gravitational interaction gravitational lens gravitational lensing shear gravitationally lensed source gravitaional microlens gravitational radiation gravity anomaly gravity darkening ground-based astronomy ground based astronomy G star G subdwarf G subgiant G supergiant g value halo star H alpha emission line star Harman-Seaton sequence Harman Seaton sequence The distribution of PNs in the H-R diagram is interpreted as an evolution sequence. 1/HarmonicRadius = Sum 1/R Haro galaxy Hayashi track head tail galaxy heavy element heavy metal star He II ionization zone He+ ionisation zone UK He+ ionization zone heliocentric correction heliocentric orbit heliocentric velocity heliopause helioseismology solar seismology heliosphere helium burning helium flash helium detonation helium-poor star helium poor star helium-rich star helium rich star helium shell flash Helmholtz-Kelvin contraction Helmholtz Kelvin contraction Kelvin-Helmholtz contraction Henry Draper system HD system Harvard classification Henyey track Herbig AeBe star Herbig Ae-Be star Herbig star Herbig-Haro object HH-object Hertzsprung gap Hertzsprung-Russell diagram Hertzsprung Russell diagram HR diagram Hess diagram H I absorption Hickson compact group HCG H I cloud H I content H I emission hierarchical cosmology high-energy astrophysics high-energy process high energy process high energy astrophysics high-luminosity star high luminosity star luminous star high-mass star high-mass X-ray binary star high-velocity cloud HVC high velocity cloud high-velocity star high velocity star H II region HII region Hirayama family H I region neutral hydrogen region H I Region neutral hydrogen Region atomic hydrogen Region history of astronomy H magnitude Holmberg radius holmium star Holtsmark approximation horizon coordinate system horizontal branch star horizontal parallax hour angle HA From Hubble Tuning Fork diagram, E0-E6, S0, S0a, Sa,Sab,Sb,Sbc,Sc,Scd,Sd,Im Hubble classification Hubble sequence Hubble constant Hubble diagram Hubble law Hubble radius Hubble Sandage variable star H S variable star H-S variable star Hubble time hydrogen burning hydrogen deficient star hyperbolic orbit hypergalaxy A system consisting of a dominant spiral galaxy surrounded by a cloud of dwarf satellite galaxies, often ellipticals. hypergiant hypernova HZ Herculis star I galaxy I magnitude impact crater inclination indochinite inflationary universe infrared astronomy infrared galaxy infrared photometry infrared source infrared transmission window initial mass function IMF An observed IMF as an array with a mass axis inner core inner planet terrestrial planet instability strip integrated magnitude total magnitude interacting binary star interacting galaxy intercloud gas intercloud matter interferometry intergalactic absorption intergalactic cloud intergalactic gas intergalactic matter intergalactic space intermediate population star intermediate type star interplanetary dust interplanetary gas interplanetary grain interplanetary magnetic field interplanetary matter interplanetary medium interplanetary scintillation interstellar absorption interstellar extinction interstellar bubble interstellar cloud interstellar communication interstellar dust interstellar gas interstellar magnetic field interstellar matter interstellar medium interstellar molecule interstellar reddening interstellar scintillation interstellar wind intracluster matter intrinsic color intrinsic variable star unstable star The plane through the center of mass of the solar system and perpendicular to the angular momentum vector of the solar system. ion density ionospheric scintillation IRAS galaxy iron meteorite irregular galaxy irregular variable star isophotal diameter isophotal radius Julian Date Time jet astrophysical jet J magnitude Jovian planet kappa mechanism The process that drives the pulsations of many types of variable star, including Cepheid variables and RR Lyrae stars. It is named from the Greek letter kappa, the symbol for the coefficient of absorption (or opacity ) of stellar material. Kapteyn selected area K corona K-corona The inner region of the corona, where the star's light is scattered by electron scattering. k correction k-term K dwarf Kelvin timescale Keplerian orbit Kerr black hole K giant kinematic parallax Kirkwood gap K line K magnitude Kramers opacity Kreutz sungrazer sungrazer Kruskal diagram K star K subdwarf K subgiant K supergiant Lagrangian point libration point lambda eridani star large scale structure late-type dwarf late type dwarf star cool dwarf star late-type galaxy late type galaxy late-type giant late type giant star cool giant star late-type star cool star late type star late-type subdwarf cool subdwarf star late-type supergiant cool supergiant star late-type variable star Lb variable star Lc variable star L dwarf Lemaitre universe lenticular galaxy S0 galaxy L galaxy libration physical libration light curve limb brightening limb darkening limiting magnitude line blanketing line blending line blocking line profile liner galaxy lithium-poor star lithium poor star lithium star Li star lithium rich star lithium-rich star L magnitude lobe Local Standard of Rest L.S.R. LSR log g value long period comet long period variable star low-luminosity star low luminosity star low-mass star low mass star low-mass X-ray binary star LMXB L subdwarf Energy per Second emitted by an object. Can be within a wavelength band or total. luminosity class luminosity classification luminosity-dispersion relation luminosity distribution luminosity function luminous arc luminous blue variable star lunar lunar dome A lunar dome is a type of shield volcano that is found on the surface of the Earth's moon. They are typically formed by highly viscous, possibly silica-rich lava, erupting from localized vents followed by relatively slow cooling. lunar eclipse lunar occultation lunar phase phase Moon lunar theory Intergalactic Clouds seen in absorption by Hydrogen, but not having metal lines. Lyman alpha forest macro spicule Magellanic cloud Clouds of Magellan Magellanic stream magnetar A magnetar is a neutron star with an extremely powerful magnetic field, the decay of which powers the emission of copious amounts of high-energy electromagnetic radiation, particularly X-rays and gamma-rays. magnetic star cobalt star magnetic variable star magnetosphere magnitude main sequence main sequence star manganese star maria Markarian galaxy mass function massive galaxy massive object massive star mass-loss mass loss mass-ejection mass-luminosity relation mass luminosity relation mass-radius relation mass radius relation mass to light ratio mass-transfer mass transfer M dwarf mean anomaly Average of SpecificIntensity integrated over all 4*pi solid angles. medium band photometry megalithic astronomy megamaser mercury manganese star meridian observation Me star metagalaxy metal-deficient star metal-poor star metal poor star metal-rich star metallic line star meteor meteorite meteorite crater meteorite impact meteoroid meteorids meteoroid dust cloud meteor shower meteor stream meteor trail Me variable star M giant micrometeorite micrometeoroid microwave background millimeter astronomy A millisecond pulsar (MSP), often referred to as "recycled pulsar", is a pulsar with a rotational period in the range of about 1-10 milliseconds. Milne Eddington approximation minor planet family Mira variable star zeta Aurigae star omicron Ceti star Miras missing mass Modified Julian Day Time. JDTime-2400,000.5 days MK classification M magnitude moldavite molecular astrophysics molecular cloud moonquake moving cluster parallax cluster parallax m region M star M subdwarf M subgiant M supergiant multi-color photometry multicolor photometry multi-periodic pulsation multiperiodic pulsation multi-periodic variable star multiperiodic variable star multiple galaxy multiple star narrow band photometry natural satellite moon Navarro-Frenk-White profile NFW NFW profile NFW-profile N-body problem many body problem N body problem many-body problem N-body simulation nearby dwarf nearby galaxy nearby star near-Earth asteroid NEO near Earth asteroid near-Earth object nebula nebular filament Neumann line any of the fine, straight, scratchlike marks that appear when some iron meteorites are cut open and the exposed surface polished and etched. The lines reveal an internal structure. thought to result from some violent strain, such as a collision between astronomical bodies, that the meteorite was subjected to before its fall. They are named for their discoverer, German mineralogist Franz Ernst Neumann (1798 - 1895). Encyclopedia Britannica. 2008. neutron star N galaxy night sky brightness night sky background N magnitude node line of node non-LTE transfer nonLTE transfer non-main sequence star nonmain_sequence star non-thermal source nonthermal source nova nova-like variable N star nuclear astrophysics nucleosynthesis nucleus celestial object number density per unit mass O association O-association OB association obliquity of ecliptic obliquity observational cosmology observing technique method of observation OB star OB supergiant occultation O dwarf Oef star Oe star Of star O giant OH absorption OH cloud OH emission OH IR star OH-IR star OH maser OH source old star O magnitude Omega baryon Omega(baryon) Omega Lambda Omega(Lambda) Omega mass Omega(mass) Omega parameter Oort cloud Oort comet cloud Oort formulae Oort formulas Oosterhoff group Pieter Oosterhoff noticed that there appear to be two populations of globular clusters, which became known as Oosterhoff groups. The second group has a slightly longer period of RR Lyrae variable stars.[16] Both groups have weak lines of metallic elements. But the lines in the stars of Oosterhoff type I (OoI) cluster are not quite as weak as those in type II (OoII).[16] Hence type I are referred to as "metal-rich" while type II are "metal-poor". open star cluster open universe opposition optical burst optical depth optical thickness optical double star optical flare optical identification optical counterparts optical outburst optical position optical pulsar orbit orbital anomaly apparent anomaly orbital element orbital evolution orbital hump Peaks in time series plots of mass exchanging binary stars, orbital humps are believed to arise from the hot spot where the accretion stream from the secondary collides with the accretion disk orbital motion orbital period orbital theory orbital velocity orbit determination oscillating universe osculating orbit osculatory element O star O subdwarf O supergiant outer planet B band Telluric lines due to O2 absorption in Earth's atmosphere, but originally thought to originate in the Sun by Fraunhofer. oxygen burning parabolic orbit parabolic velocity parallax The apparent change in the position of a nearby star when observed from Earth due to our planet's yearly orbit around the Sun. parsec parallax second partial eclipse P Cygni line profile peculiar galaxy peculiar giant peculiar motion peculiar object peculiar star peculiar variable star peculiar velocity pencil beam penumbra penumbras penumbral filament periapsis pericenter periastron perigee perihelion period-age relation period age relation period-color relation period color relation period-density relation period density relation periodic comet periodic orbit periodic variable star period-luminosity-color relation period luminosity color relation PLC relation period-luminosity relation period luminosity relation PL relation period-mass relation period mass relation period-radius relation period radius relation period-spectrum relation period spectrum relation PG1159 star PG1159-35 star GW Virginis star photoelectric magnitude photographic magnitude photometric parallax photometric period light curve period photometric standard star photometry filter photometry photosphere reversing layer photovisual magnitude plage planet planetar planetary planetary alignment planetary nebula planetary ring planetary system planetary theory equator of planet planet's equator planetesimal planetology planet satellite plasma cloud plasma jet P magnitude Pogson scale polarimetry population II Cepheid population III star PopIII population II star Pop II star PopII population I star PopI position angle post-asymptotic giant branch post-AGB post-main sequence star post main sequence star pre-Galactic star pregalactic star pre-main sequence star early stage star premainsequence star pre-nova prenova pre-solar nebula presolar nebula pre-supernova presupernova primary star primordial fireball primordial galaxy prominence chromospheric eruption prominence prominence chromospheric eruption proper motion protocluster protogalaxy proton-proton reaction proton proton cycle proton proton reaction proton-proton cycle protoplanet protoplanetary nebula proplyds protostar pulsar pulsating variable star pulsation pulsation theory Q magnitude quantum cosmology quasar quasi-stellar object QSO quasi-stellar galaxy quasi-stellar radio_source quasar galaxy pair quiescent prominence quiet Sun radar astronomy radiant meteor radiant moving cluster radiation belt radiative braking radio astrometry radio astronomy radio background radio frequency interference radio noise radio burst radio core radio flare radio galaxy radio interferometry radio jet radio occultation radio pulsar radio quiet quasar radio source radio source catalog radio source count radio star radio structure radius-luminosity relation radius luminosity relation rapid burst R association R-association R Canis Majoris star R CMa star R Coronae Borealis star R Cor Bor star RCB star real anomaly receiver recurrent nova reddened star reddening reddening law red dwarf red dwarf flare star red giant red giant bump red bump red giant clump red clump red giant tip redshift red shift redshift distance relation Hubble relation redshift magnitude relation red star red supergiant reflection nebula relativistic astrophysics relativistic cosmology relativistic disk relativistic star resonance gap RGB tip distance rho Cassiopeiae star rho Cas star Right Ascension celestial longitude rill ring division ring galaxy ring nebula R magnitude Roche limit Roche lobe Rosseland opacity rotating star r-process r process RRab star RRa star RRb star RRc star RR Lyrae star cluster type variable star RR Telescopii star RS Canum Venaticorum star R star runaway star RV Tauri star RW Aurigae star Saha equation IMF Fit in which there is a single slope as in that by Ed Salpeter, usually expressed as N ~ M^{-2.35}. Saros cycle SBF distance SBF Schonberg-Chandrasekhar limit S Doradus star P Cygni star secondary cosmic ray secondary star secular parallax semi-barium star semibarium star semi-detached binary star semidetached binary star semi-regular variable star semiregular variable star Seyfert galaxy Seyfert nucleus S galaxy supergalactic X-value supergalactic-Y-value supergalactic X-value shadow band shell burning shell star shepherd satellite short period variable star sigma8 sigma_8 silicon burning silicon star SiO maser sky brightness sky noise sky survey slow nova novoid a type of magnetar, which emits large bursts of gamma rays and X-rays at irregular intervals. solar solar activity solar atmosphere solar constant solar corona solar cycle solar day solar eclipse solar filament solar interior solar motion solar nebula solar neutrino problem solar oscillation five minute oscillation solar parallax solar physics solar-planetary relation solar planetary relation solar storm solar surface solar-terrestrial relation solar terrestiral relation solar wind source space space astronomy space biology Amount of energy, per unit frequency interval, passing through a unit area oriented normal to a direction n, into a unit solid angle, in a unit time. I(nu,r,n,t) where nu is a frequency, r is position of measurement, n is direction from r. For a surface A with normal an angle theta from n the energy passing dA in the dw solid angle is dE = I*dA*cos(theta)*dnu*dw*dt spectral classification spectral type spectrophotometry spectroscopic binary star spectrum binary star spectroscopy spectrometry spectrum variable star spicule spiral arm arm S star Se star standard star star association star atlas starburst galaxy star cluster cluster of star star count star distribution star formation formation of star starspot star system catalog statistical parallax steady-state theory steady state theory stellar stellar atmosphere stellar black hole A stellar black hole is a black hole formed by the gravitational collapse of a massive star (3 or more solar masses) at the end of its lifetime. The process is observed as a supernova explosion or as a gamma ray burst. Such a black hole will have a mass of at least 1.44 solar masses (Chandrasekhar limit). stellar dynamics stellar evolution stellar evolution phase stellar phase stellar interior stellar motion stellar object stellar oscillation stellar population stellar ring stellar structure stellar surface feature stellar systems catalog stellar theory stellar wind streamer Stromgren sphere strontium star subdwarf subgiant subluminous star submillimeter astronomy sunspot sun spot sunspot cycle sunspot group sunspot number Wolf number relative sunspot number Sunyaev-Zeldovich effect Sunyaev Zeldovich effect supercluster supergalactic coordinate system supergalactic latitude supergalactic longitude supergiant supergranulation superhump Superoutburst in SU UMa-type dwarf novae are characterized by the existence of superhumps. Superhumps resemble, in their shape in time series plots, orbital humps observed during quiescence (which are believed to arise from the hot spot where the accretion stream from the secondary collides with the accretion disk), but have a much larger (~100 times) luminosity, which amounts to an amplitude of a few tenths of magnitude during superoutbursts. supermassive star supernova SN supernova envelope supernova remnant SNR surface brightness surface gravity acceleration of gravity surface of celestial body surface celestial body surface photometry area photometry SU Ursae Majoris star S Vulpeculae star Swan band SX Arietis star helium variable star SX Phoenicis star symbiotic nova symbiotic star synchronous rotation synodic period T association T-association T dwarf teaching in astronomy education technetium star tektite telluric line terminator line tertiary star theoretical astrophysics tidal disruption tidal distortion tidal friction tidal interaction tidal radius Radius at which material is pulled off an object by external tides. total eclipse transit transit time trans-Neptunian object TNO transplutonian planet transverse velocity trigonometric parallax triple star Trojan group true anomaly true position T subdwarf T Tauri star YY Orionis star TTS Tully-Fisher relation turnoff point two-body problem two body problem two-color photometry two color photometry two-spectrum binary star spectrum binary star two spectrum binary star Type Ia supernova Type Ib supernova Type Ic supernova Type II supernova U Geminorum star SS Cygni star ultraviolet astronomy UV astronomy ultraviolet background ultraviolet color ultraviolet continuum ultraviolet excess star UV excess star ultraviolet extinction ultraviolet luminosity ultraviolet photometry ultraviolet source ultraviolet object ultraviolet survey U magnitude umbra universe cosmos upsilon Sagittarii star urca process UU Herculis star UV Ceti star UV Persei star UX Ursae Majoris star van Allen radiation belt variable source variable star velocity curve visual binary star visual magnitude visual observation V magnitude Voigt profile von Zeipel theorem VY Sculpturis star 21 centimeter linewidth at 20% of maximum brightness for galaxy that fits in fov of aperture. water maser WCN star WC star weak G band star weak-line T Tauri star WTTS white dwarf white hole wide binary star Wilson-Bappu effect Wilson Bappu effect Wilson effect WN star Wolf diagram Dependency of the cumulative star count N(m) as function of apparent magnitude for a dark cloud and a comparison field (Wolf 1923). Wolf-Rayet star WR star evolved, massive stars (over 20 solar masses) losing their mass rapidly by means of a very strong stellar wind. These stars are also very hot: their temperature are in the range of 25,000 K to 50,000 K. W Ursae Majoris star W Virginis star WZ Sagittae star X-ray astronomy X-ray background X-ray binary star X-ray bright point X-ray burst X-ray continuum X-ray flare X-ray identification X-ray luminosity X-ray map X-ray nova X-ray pulsar X-ray quasar X-ray source X-ray star X-ray structure X-ray survey X-ray transient Galaxy classification scheme developed by Morgan (1958) motivated by a correlation between concentration index and integrated spectral class. Possible values are "a, af, f, fg, g, gk, k". Yerkes classification young disk Cepheid young star young star cluster Z Andromedae star Z Camelopardalis star zero-age horizontal branch zero-age main sequence ZAMS zirconium star zodiac zodiacal dust zodiacal dust cloud zodiacal light zone of totality ZZ Ceti star Fanaroff-Riley class Class I, the brightest regions in the radio lobes are separated by less than half of the overall extent of the radio-emitting lobes. Class II have larger separations. Class II are generally more powerful. II I Denote whether object is cause of weak or strong graviational lensed. gravitational lensed Weak Strong gravitational microlensed microlensed Denote number of subcomponents detected. As in, a star that is detectedt to be composed of several stars. Code Spectral peculiarities for stars : bleeding and/or uncertain spectral value _ undescribed spectral peculiarities exist ! special peculiarity comp composite spectrum e emission lines present [e] "forbidden" emission lines present er "reversed" center of emission lines weaker than edges ep emission lines with peculiarity eq emission lines with P-Cygni//gr 304.446667, 38.032944 profile ev spectral emission that exhibits variability f NIII and HeII emission (f) weak emission lines of He ((f)) no emission of He He wk weak He lines k spectra with interstellar absorption features m enhanced metal features n broad ("nebulous") absorption due to spinning nn very broad absorption features due to spinning very fast neb a nebula's spectrum mixed in p peculiar spectrum, strong spectral lines due to metal pq peculiar spectrum, similar to the spectra of novae q red and blue shifts line present s narrowly "sharp" absorption lines ss very narrow lines sh shell star v variable spectral feature (also "var") w weak lines (also "wl" and "wk") d Del type A and F giants with weak calcium H and K lines, as in prototype delta Delphini//gr 310.8647916, 15.074694 d Sct type A and F stars with spectra similar to that of short-period variable delta Scuti//gr 280.568417, -9.0525556 Code If spectrum shows enhanced metal features Ba abnormally strong Barium Ca abnormally strong Calcium Cr abnormally strong Chromium Eu abnormally strong Europium He abnormally strong Helium Hg abnormally strong Mercury Mn abnormally strong Manganese Si abnormally strong Silicon Sr abnormally strong Strontium Code Spectral peculiarities for white dwarfs P polarized light H magnetic field from Zeeman splitting V variable PEC spetral peculiarities exist Ib IIb IIIb IVa IVb Vb Va IIIab IIIa IIab IIa Ia-0 Iab Ia VII VI V IV III II I A number of different luminosity classes are distinguished: * I supergiants Ia-0 (hypergiants or extremely luminous supergiants (later addition)), Example: HD 183143 (spectrum is B6-8 Ia-0) 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: 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: Persei (spectrum is M4 IIIa) IIIab Example: Reticuli (spectrum is M2 IIIab) IIIb, Example: Pollux (spectrum is K2 IIIb) * IV subgiants IVa, Example: 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) The point on the celestial sphere which the Sun is moving toward in the Local Standard of Rest solar apex The point on the celestial sphere from which the Sun is moving away in the Local Standard of Rest solar antapex Direction defined by going from GalacticCenter to Earth (and beyond) Galactic center solar apex The point on the celestial sphere, in the constellation Hercules, toward which the Sun is moving with respect to the local standard of rest North Celestial Pole NCP N.C.P. S.C.P. SCP South Celestial Pole North Galactic Pole NGP N.G.P. SGP S.G.P. South Galactic Pole NEP N.E.P. North Ecliptic Pole SEP S.E.P. South Ecliptic Pole Galactic bulge Galactic halo the great circle of the celestial sphere whose plane is an extension of the Earth's equator Celestial Equator LMC Large Magellanic Cloud SMC Small Magellanic Cloud Moon Galactic Plane solar system Milky Way galaxy the Galaxy Local Supercluster Great Attractor Sun celestial equator Oort constant Astronomical Unit A.U. AU