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(Beta Cygni) Alcyone (Eta Tauri) Aldebaran (Alpha Tauri) Alderamin (Alpha Cephei) Alexandra family (of asteroids) Alfirk (Beta Cephei) Algieba (Gamma Leonis) Algol (Beta Persei) Algol star Algonquin Radio Observatory ALH 84001 Alhena (Gamma Geminorum) Alinda group (of asteroids) Alioth (Epsilon Ursae Majoris) Alkaid (Eta Ursae Majoris) Allegheny Observatory Allen Telescope Array (ATA) Allende meteorite all-sky camera all-sky survey ALMA Almaak (Gamma Andromedae) Almagest almanac Almaz Alnair (Alpha Gruis) Alnath (Beta Tauri) Alnilam (Epsilon Orionis) Alnitak (Zeta Orionis) Alpha Centauri Alpha Cygni star Alpha2 Canum Venaticorum star Alphard (Alpha Hydrae) Alphekka (Alpha Coronae Borealis) Alpheratz (Alpha Andromedae) Alphonsine Tables Altair (Alpha Aquilae) altazimuth mounting Aludra (Eta Canis Majoris) aluminizing AM Canum Venaticorum star AM Herculis star Am star Amalthea Amazonian epoch Ambartsumian’s Knot ambipolar diffusion American Astronomical Society (AAS) amino acids, in space Amor group analemma Ananke anastigmat(ic) andesite Andromeda (constellation) Andromeda Galaxy (M31, NGC 224) anemic spiral galaxy Angelina (minor planet 64) Anglo-Australian Observatory Anglo-Australian Planet Search Anglo-Australian Telescope angrite angular diameter angular separation anisotropy annual variation anomalous X-ray pulsar (AXP) anomaly anorthosite ANRO ansa Ant Nebula (Menzel 3) Antarctic Search for Meteorites (ANSMET) Antares (Alpha Scorpii) antenna antenna array antenna directivity antenna temperature Antennae (NGC 4038 and NGC 4039) antinode Antiope (minor planet 90) antisolar point antitail Antlia (constellation) Antlia Dwarf Galaxy Antoniadi scale AO Cassiopeiae Ap star Apache Point Observatory (APO) apastron aperture aperture synthesis aphelion apoapsis apochromatic apogee apohele Apollo (minor planet 1862) Apollo group apolune Apophis (minor planet 99942) apparent magnitude apparition APRO apsis Apus (constellation) Aquarius (constellation) Aquarius Dwarf 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barred spiral Barringer Crater Barwell meteorite barycenter Barycentric Dynamical Time baryogenesis baryon degenerate matter Bautz and Morgan classification Baxendell’s Nebula (NGC 7088) Bayer constellations Bayer designation B-class asteroid Be star beamwidth beat Cepheid Becklin-Neugebauer Object Belinda Bellatrix (Gamma Orionis) Bennett, Comet (C/1969 Y1) Besselian elements Besselian year Beta Cephei star Beta Lyrae Beta Lyrae star Beta Pictoris Betelgeuse Bianca Biela's Comet Big Bang Big Bear Solar Observatory Big Crunch Big Dipper binary asteroid binary pulsar binary star binoculars bipolar flow bipolar group bipolar nebula BL Herculis star BL Lacertae object Blaauw mechanism black dwarf Black Eye Galaxy (M64, NGC 4826) black hole Black Widow Nebula Black Widow Pulsar blazar Blaze Star Blazkho effect Blinking Nebula (NGC 6826) block universe blue compact dwarf galaxy (BCD) blue giant blue horizontal-branch star blue moon Blue Planetary (NGC 3918) blue shift Blue Snowball Nebula (NGC 7662) blue straggler blue supergiant bolide bolometric magnitude Bol’shoi Teleskop Azimultal’nyi (BTA) Bonner Dürchmusterung (BD) Boomerang Nebula Boötes Borrelly, Comet (19P/Borrelly) Boss General Catalogue (GC) bow shock Box, The (Hickson 61) Bp star brachinite Brackett series Braille (minor planet 9969) Brandon eyepiece bridge, intergalactic bright nebula Bright Star Catalogue brightness brightness temperature bright-rimmed cloud broadband photometry brown dwarf Bubble Nebula (NGC 7635) Bug Nebula (NGC 6302) bump Cepheid Burnham's Nebula burst, solar Butcher-Oemler effect Butterfly Cluster (M6, NGC 6405) butterfly diagram Butterfly Nebula (M 2-9) Bw star BY Draconis star Byurakan Astrophysical Observatory Caelum (constellation) Calabash Nebula (OH231.8+4.2) calcium aluminum inclusions calendar Caliban California Nebula (NGC 1499) Callisto Callisto, ocean and possible life Caltech Submillimeter Observatory Calypso Camelopardalis (constellation) Canada-France-Hawaii Telescope canals, Mars Cancer (constellation) 55 Cancri (Rho1 Cancri) Canes Venatici (constellation) Canes Venatici Cloud Canes Venatici I Group Canes Venatici II Group Canis Major (constellation) Canis Minor (constellation) Canopus (Alpha Carinae) Cape Photographic Dürchmusterung (CPD) Cape York meteorite Capella (Alpha Aurigae) Caph (Beta Cassiopeiae) Capricornus (constellation) Capricornus Dwarf (Palomar 12) capture area captured rotation carbon burning carbon star carbonaceous chondrite Carina (constellation) Carina Dwarf Galaxy Carina OB1 and OB2 Carme Carnegie & California Planet Search Carnegie Observatories Carte du Ciel Cartwheel Galaxy (ESO350-40) Cassegrain telescope Cassiopeia (constellation) Cassiopeia Dwarf (Cas dSph) Cassiopeiae A (3C 461) Castalia (minor planet 4769) Castor (Alpha Geminorum) Castor Moving Group cataclysmic binary cataclysmic variable catadioptric telescope catastrophic hypothesis Cat’s Eye Nebula (NGC 6543) Cauchy horizon CCD C-class asteroid celestial coordinates celestial equator celestial guidance celestial mechanics celestial pole celestial sphere Centaur (minor planet) Centaurus (constellation) Centaurus A (NGC 5128) Centaurus Cluster Centaurus X-3 Center for Astronomical Adaptive Optics (CAAO) central meridian Cepheid variable Cepheus (constellation) Ceres (minor planet 1) Cerro Tololo Inter-American Observatory Cetus (constellation) CH Cygni CH star Chamberlin-Moulton planetesimal hypothesis Chameleon (constellation) Chandler wobble Chandra X-ray Observatory Chandrasekhar Limit chaotic inflationary theory chaotic orbit chaotic terrain Chara (Beta Canum Venaticorum) characteristic length characteristic velocity charge-coupled device (CCD) Charon chassignite Chicxulub Crater Chinese astronomy Chiron chondrite chondrule Christmas Tree Cluster (NGC 2264) chromatic aberration chromosphere chromospheric network chronology horizon chronology-violating spacetime Chryse Planitia Circinus (constellation) Circinus Galaxy Circinus X-1 circular orbit circular velocity circumplanetary space circumpolar star circumstellar disk circumstellar maser circumterrestrial space cislunar classical jovian classical planet close binary Cloverleaf Quasar (H1413+117) cluster of stars cluster of galaxies CN star CNO star Coalsack Coathanger (Collinder 399) COBE (Cosmic Background Explorer) Cocoon Nebula (IC 5146) cocoon star Coddington’s Nebula (IC 2574) coelostat Cold Bokkeveld meteorite color color excess color index color temperature color-magnitude diagram Columba colure coma, cometary coma, optical Coma Berenices (constellation) Coma Cluster Coma Star Cluster (Melotte 111) combined magnitude comet cometary collision hypothesis cometary globule comets, collisions with comets, all entries common-envelope star compact galaxy compact source companion companion, unseen comparator Compton effect Compton Gamma-Ray Observatory Cone Nebula conjunction constellations contact (of an eclipse) contact binary continuous spectrum contrast convection convective envelope convective overshoot convergent point cooling timescale co-orbital Copeland's Septet (Hickson 57) Copernican Revolution Copernican system Cor Caroli (Alpha2 Canum Venaticorum) Coralie Cordelia Córdoba Durchmusterung (CD) core, planetary core, stellar Coriolis effect corona Corona Australis (constellation) Corona Borealis (constellation) coronagraph coronal condensation coronal hole coronal lines coronal loop coronal mass ejection coronal rain coronal streamer co-rotation corrector plate Corvus (constellation) cosmic abundance cosmic background radiation cosmic censorship cosmic coincidences cosmic distance ladder cosmic dust cosmic infrared background cosmic microwave background cosmic rays cosmic string cosmic X-ray background cosmic year cosmic-ray exposure age cosmological constant cosmological model cosmological principle cosmological redshift cosmology cosmology entries cosmos coudé focus Crab Nebula (M1, NGC 1952) crater Crater (constellation) crater chain Crescent Nebula (NGC 6888) Cressida Crimean Astrophysical Observatory critical density cross-cutting crown glass Cruithne (minor planet 3753) crust Crux (constellation) cryovolcanism cryptovolcano CTIO cubewano culmination curvature of field CW Leonis cyanogen bands Cybele group cyclotron radiation 16 Cygni 61 Cygni Cygnus (constellation) Cygnus A Cygnus Loop Cygnus X-1 (3U 1956+35) D galaxy D lines Dactyl Damocloid family dark adaptation dark energy dark galaxy dark halo dark halo crater dark matter dark nebula Davida (minor planet 511) Dawes' limit dawn day Daylight Comet of 1910 daylight stream db galaxy D-class asteroid De Sitter model decaying orbit declination deep sky object deep space degenerate electron pressure degenerate matter degenerate neutron pressure degenerate star Deimos Delphinus (constellation) Delta Cephei Delta Cephei star Delta Scuti star Dembowska (minor planet 349) Deneb (Alpha Cygni) Deneb Kaitos (Beta Ceti) Denebola (Beta Leonis) density parameter density wave descending node Desdemona Despina deuterium diagonal diamond ring effect differential rotation diffraction-limited diffuse galactic light diffuse interstellar bands (DIBs) diffuse nebula Digital Sky Survey (DSS) diogenite Dione direct (rotation) discordant redshift discrete radio source disk disk, galactic disk galaxy disk star dispersion distortion Dobsonian telescope Dominian Astrophysical Observatory (DAO) Donati's Comet (C/1858 L1) Doppler boosting Doppler broadening Doppler effect Doppler shift Dorado (constellation) Double Cluster (h and Chi Persei; NGC 869 and NGC 884) double planet Double Quasar (Q0957+561A/B) double radio source double star double-mode variable doublet DQ Herculis star Draco Draco Dwarf DRAGN (double radio source associated with a galactic nucleus) Dschubba (Delta Scorpii) Dubhe (Alpha Ursae Majoris) Dumbbell Nebula (M27, NGC 6853) dust dust disk dust lane dwarf Cepheid dwarf elliptical galaxy dwarf galaxy dwarf irregular galaxy dwarf molecular cloud dwarf spheroidal galaxy dwarf star Dwingeloo 1 dynamical method dynamical time dynamical timescale Eagle Nebula (IC 4703) early-type galaxy early-type star Earth Earth, atmosphere Earth, early history Earth impact craters Earth-class planet Earth-crossing asteroid Earth-grazer earthshine eccentric jovians eccentric orbit eccentricity echelle grating echelle spectrograph E-class asteroid eclipse eclipse season eclipsing binary ecliptic ecliptic coordinates Eddington (space telescope) Eddington limit effective radius Effelsberg Radio Observatory Egg Nebula (CRL 2688) Egyptian astronomy Eight-burst Nebula (NGC 3132) Einstein Cross (G2237+030) Einstein ring Einstein-Rosen bridge ejecta ejecta blanket Elara electromagnetic field electromagnetic radiation electromagnetic spectrum electromagnetism electron electron degenerate matter electron temperature elements, cosmic abundance Elephant's Trunk Nebula Ellerman bomb elliptical galaxy ellipticity elongation Eltanin (Gamma Draconis) Elysium Planitia Emilie emission emission line emission nebula emission spectrum Enceladus Encke’s Comet encounter hypothesis Enif (Epsilon Pegasi) Ensisheim meteorite enstatite entrainment entrance pupil entropy envelope Eos family Ep galaxy ephemeral region (EFR) ephemeris Epimetheus epistellar jovians Epsilon Aurigae Epsilon Eridani Epsilon Indi Epsilon Lyrae equation of light equation of the center equation of time equator equatorial bulge equatorial coordinates equatorial mounting equinox equipotential surface equivalent width Equuleus (constellation) ER Ursae Majoris star ergosphere Eridanus (constellation) Eris (minor planet 136199) Eros (minor planet 433) eruptive variable escape velocity Eskimo Nebula (NGC 2392) ESO Coudé Échelle Spectrometer Eta Aquilae Eta Carinae Eta Carinae Nebula (NGC 3372) eucrite Eugenia (minor planet 45) Eunomia Family (of asteroids) Europa Europa (minor planet 52) Europa, ocean on European Northern Observatory (ENO) European Southern Observatory (ESO) EUV event horizon Evershed effect excitation excited state exit pupil exoplanets exosphere exposure age extended source extinction, interstellar extragalactic background light (EBL) extragalactic reference frame Extrasolar Planet Observational Research Team (EXPORT) extrasolar planets extrasolar planets, detection extrasolar planets, searches extreme horizontal branch star (EHB star) extreme Population I star extremely large telescope extrinsic variable eye relief eyepiece Eyes, The (NGC 4435 and 4438) F star Faber-Jackson relation Fabry lens Fabry-Pérot interferometer facula FAME Fanaroff-Riley classification Faraday rotation Faye's Comet F-class asteroid Fermi acceleration fermion FG Sagittae FGK stars fibril field field galaxy field lens field of view field rotation field star figuring filament filigree filter filtergram find fine structure fireball first contact "first light" first lunar meridian fixed star FK Comae Berenices star Flame Nebula (NGC 2024) Flaming Star Nebula (IC 405) Flamsteed number flare flare star flash spectrum flat flat field FLIERs (fast, low ionization emission regions) flint glass Flora family (of asteroids) flux flux collector flux density flux tube focal length focal ratio focal reducer focus, orbital Fokker-Planck equation following Fomalhaut (Alpha Piscis Austrini) forbidden line Forbush decrease formation age formation interval Fornax (constellation) Fornax A Fornax Cluster Fornax Dwarf forsterite forward scattering Foucault knife-edge test Foucault pendulum Fp star frame-dragging Franklin-Adams charts Fraunhofer lines Fred Lawrence Whipple Observatory free-bound transition free-free transition frequency frequency bands fringing FU Orionis star fundamental catalogue Fundamental Katalog (FK) fundamental star fusion, nuclear fusion crust G star Gacrux (Gamma Crucis) galactic anticenter galactic bulge galactic center galactic coordinates galactic disk galactic equator galactic halo galactic magnetic field galactic noise galactic nucleus galactic plane galactic rotation galactic window galactic year galactocentric distance Galatea galaxies, all entries galaxy galaxy cannibalism galaxy classification galaxy formation galaxy interaction galaxy merger Galaxy, The Galilean satellites Galilean telescope Gamma Cassiopeiae Gamma Cassiopeiae star gamma rays Gamma Velorum gamma-ray burst Ganymede gardening Garnet Star (Mu Cephei) Garnet Star Nebula (IC 1396) gas giant gas-bounded nebula gaseous nebula Gaspra (minor planet 951) G-class asteroid gegenschein Gemini (constellation) Gemini Observatory General Catalogue of Variable Stars (GCVS) general precession general theory of relativity Geneva Extrasolar Planet Search Program geocentric geocorona geodetic precession Geographos (minor planet 1620) geoid geology and planetary science geomagnetic field geomagnetic storm geospace ghost crater Ghost Head Nebula (NGC 2080) Ghost of Jupiter (NGC 3242) Giacobini-Zinner, Comet (Comet 21P/) giant branch giant molecular cloud giant planet giant star Gliese 229B Gliese 67 (HD 10307, HIP 7918) Gliese 86 Gliese 876 Gliese Catalogue glitch Global Microlensing Alert Network (GMAN) Global Oscillation Network Group (GONG) globular cluster globule GMAN GMT (Greenwich Mean Time) Gödel universe Gould Belt graben Gran Telescopio Canarias (GTC) grand unified theory (GUT) granulation granule gravipause gravisphere gravitational collapse gravitational constant (G) gravitational energy gravitational equilibrium gravitational field gravitational instability gravitational lens gravitational lock gravitational microlensing gravitational slingshot effect gravitational waves gravity grazing-incidence telescope Great Annihilator Great Attractor great circle Great Comets Great Hercules Cluster (M13, NGC 6205) Great Observatories Great Red Spot Great Rift (in Milky Way) Great Square of Pegasus Great Wall greatest elongation Green Bank Green Bank Telescope Gregorian calendar Groombridge Catalogue grooved terrain ground-level event (GLE) Grus (constellation) Grus Quartet (NGC 7552, NGC 7582, NGC 7590, and NGC 7599) Guide Star Catalog (GSC) Gum Nebula Gusev Crater gyrofrequency Gyulbudagian's Nebula (HH215) H I region H II region H and K lines habitable zone (HZ) Hadar (Beta Centauri) Hadley circulation Hale cycle Hale Observatories Hale Telescope Hale-Bopp, Comet (C/1995 O1) Hale's polarity law Halley's Comet Halley-type comet halo, atmospheric halo, galactic halo population H-alpha Hamal (Alpha Arietis) Haro galaxy HARPS (High Accuracy Radial Velocity Planetary Search) Hartmann test Harvard College Observatory Harvard Revised Photometry (HR Photometry) Catalogue Harvard-Smithsonian Center for Astrophysics (CfA) Harvard-Smithsonian radio telescope harvest moon Hat Creek Observatory Hawking radiation Hayashi track HD HD 10697 HD 37124 HD 75289 HD 98618 HD 114762 HD 130322 HD 134987 HD 168443 HD 177830 HD 187123 HD 189773 A HD 192263 HD 195019 HD 209458 HD 210277 HD 217107 HD 222582 head-tail_galaxy heavy element concentration, related to occurrence of planets heavy elements HED group Hektor (minor planet 624) Helene helical rising heliocentric heliocentric coordinates heliograph heliographic coordinates heliopause helioseismology heliosphere heliostat helium burning helium star Helix Galaxy (NGC 2685) Helix Nebula (NGC 7293) Hellas Planitia helmet streamer Henry Draper Catalogue Henyey track Herbig Ae/Be star Herbig-Haro object Hercules (constellation) Hercules Cluster (Abell 2151) Hercules Globular Cluster (M13, NGC 6205) Hercules X-1 14 Herculis Herschelian telescope Hertzsprung Gap Hertzsprung-Russell diagram Hesperian epoch HET hexahedrite Hidalgo (minor planet 944) High Accuracy Radial velocity Planetary Search (HARPS) high mass fraction High Resolution Échelle Spectrometer (HIRES) high-gain antenna (HGA) high-velocity cloud (HVC) high-velocity star Hilda group Himalia Hind's Crimson Star Hind's Variable Nebula Hipparcos Catalogue Hirayama family HIRES history of astronomy Hoag’s Object (PGC 54559) Hoba meteorite Hobby-Eberly Telescope (HET) Hockey Stick Galaxy (NGC 4656) Holmberg II Dwarf Irregular Galaxy Holmberg radius horizon horizontal branch Horologium (constellation) Horsehead Nebula (Barnard 33) host star "hot Jupiter" hot spot hot subdwarf hour hour angle hour circle Hourglass Nebula (MyCn 18) howardite HR 4796A HR 810 Hubble constant Hubble flow Hubble law Hubble radius Hubble Space Telescope (HST) Hubble’s Variable Nebula (NGC 2261) Hulse-Taylor Pulsar (PSR 1913+16) Humason, Comet (1961e) Hungaria group hunter’s moon Hyades Hyakutake, Comet (C/1996 B2) Hydra (constellation) hydrogen burning hydrogen spectrum Hydrus (constellation) Hygiea (minor planet 10) hyperbolic orbit hypergiant Hyperion hypernova hypersensitization hypersthene hypervelocity impact hypervelocity star HZ Herculis star Iapetus IAU IC 349 (Barnard's Merope Nebula) IC 434 (emission nebula) Icarus (minor planet 1566) ice dwarf ice volcanism Ida (minor planet 243) igneous age IGY (International Geophysical Year) Ikeya-Seki, Comet (C/1965 S1) ilmenite image tube imaging, of extrasolar planets impact basin impact crater impact feature impact melt impactor inclination Index Catalogue (IC) Indian astronomy Indus (constellation) infall velocity inferior planet inflationary model infrared astronomy infrared cirrus infrared excess infrared galaxy infrared star Innisfree meteorite instability strip instantaneous bandwidth Integral Sign Galaxy (UGC 3697) interacting binary Interamnia (minor planet 704) interferometer intergalactic absorption intergalactic magnetic field intergalactic medium (IGM) Intergalactic Wanderer (NGC 2419) intergranular lane intermediate population star International Astronomical Union (IAU) International Atomic Time (TAI) International Celestial Reference Frame (ICFR) International Dark-Sky Association (IDA) International Geophysical Year (IGY) International Quiet Sun Years (IQSY) interplanetary magnetic field (IMF) interplanetary medium interplanetary space interstellar absorption interstellar and interplanetary matter interstellar cloud interstellar dust interstellar extinction interstellar maser interstellar medium (ISM) interstellar molecules interstellar polarization interstellar reddening interstellar scintillation interstellar space interstellar wind intra-cluster medium intrinsic color index intrinsic variable invariant plane inverse P Cygni profile inward orbital migration Io ionization equilibrium ionization front ionization temperature ionosphere Iota Horologii Iota Orionis IP Pegasi IRAS-Araki-Alcock, Comet (C/1983 H1) Iris (minor planet 7) iron meteorite irradiation irregular galaxy irregular moon irregular variable Isidis Planitia ISM Itokawa (minor planet 25143) Ivuna meteorite Izar (Epsilon Bootis) jansky (Jy) Janus Jeans length Jeans mass Jeans-Jeffreys tidal hypothesis jet Jewel Box (NGC 4755) Jilin meteorite jovian Julian calendar Julian date (JD) Julian epoch Juliet Juno (minor planet 3) Jupiter Jupiter, moons Jupiter, rings Jupiter-crosser Jupiter-type comet K star K40506A Kaba meteorite kakangariite Kakkab (Alpha Lupi) kamacite Kapteyn's Star (HD 33793) Karin Cluster Kaus Australis (Epsilon Sagittarii) Keck Interferometer Keck Observatory Keck Telescopes Keenan’s System (NGC 5216 and NGC 5218) Kelvin-Helmholtz contraction Kemplerer Rosette Keplerian orbit Keplerian rotation curve Keplerian telescope Kepler's equation Kepler's laws of planetary motion Kepler’s Star (SN Oph 1604) Kerr black hole kinetic temperature Kirkwood gaps Kitt Peak National Observatory (KPNO) Kitt Peak 12-Meter Telescope Kleopatra (minor planet 216) Kochab (Beta Ursae Minoris) Kohoutek, Comet (C/1973 E1) Kordylewski Clouds Koronis family (of asteroids) Kramers' law KREEP Krüger 60 Kuiper Belt Kuiper Belt object Kuiper Belt objects, largest L1551 (IR5) La Silla Observatory La Superba (Y Canum Venaticorum) Lacerta (constellation) Lagoon Nebula (M8, NGC 6523) Lagrangian orbit Lagrangian points L'Aigle meteorite shower Laing-Garrington effect Lalande 21185 Lambda Bootis star Lambda Eridani star Large Binocular Telescope (LBT) Large Magellanic Cloud (LMC) Large Millimeter Telescope (LMT) Large Southern Array (LSA) large-scale structure Larissa late heavy bombardment late-type galaxy late-type star latitude latitude variation LBT leading hemisphere leap second leap year Leda lens Lense-Thiring effect lenticular galaxy Leo (constellation) Leo I Leo II Leo III Leo Minor (constellation) Leonard Euler Telescope Leonids Lepus (constellation) Leuschner Observatory Lexell, Comet (D/1770 L1) Libra (constellation) libration Lick Observatory light curve light echo light element light pollution light-year (ly) limb limb correction limb darkening limiting magnitude Lindsay-Shapley Ring (AM0644-741) line line blanketing line broadening line displacement line of nodes line spectrum line width LINEAR, Comet (C/1999 S4) LINER (low-ionization nuclear emission-line region) LISA (Laser Interferometer Space Antenna) lithium depletion boundary lithium-rich star Little Dipper Little Dumbbell Nebula (M76, NGC 650 and 651) Little Gem Annular Nebula (NGC 6818) lobe Local Bubble Local Group local horizon local hour angle (LHA) Local Interstellar Cloud (LIC) local standard of rest Local Supercluster local time local vertical Lockman Hole lodranite longitude longitude at the epoch longitude of perihelion longitude of the ascending node long-period comet long-period variable loop prominence Lost City meteorite Lovell Telescope low surface brightness galaxy Lowell Observatory lower transit low-velocity star Lucky 13 luminosity luminosity class luminosity function luminous mass Lump Star (NGC 2023) lunar eclipse lunar parallax lunar phases lunar polarization lunation lunisolar Lupus (constellation) Luyten 726-8 (UV Ceti) Lyman series Lyman-alpha Lyman-alpha forest Lynx (constellation) Lyra (constellation) Lysithea M star M1 (NGC 1952, Crab Nebula) M4 (NGC 6121, globular cluster) M6 (NGC 6405, Butterfly Cluster) M7 (NGC 6475, Ptolemy's Cluster) M8 (NGC 6523, Lagoon Nebula) M11 (NGC 6705, Wild Duck Cluster) M13 (NGC 6205, Great Cluster in Hercules) M16 (NGC 6611) M17 (NGC 6618, Omega Nebula) M20 (NGC 6514, Trifid Nebula) M27 (NGC 6853, Dumbbell Nebula) M31 (NGC 224, Andromeda Galaxy) M32 (NGC 221, companion to M31) M33 (NGC 598, Triangulum Galaxy) M42 (NGC 1976, Orion Nebula) M44 (NGC 2632, Praesepe) M45 (Pleiades) M50 (NGC 2323) M51 (NGC 5194, Whirlpool Galaxy) M57 (NGC 6720, Ring Nebula) M63 (NGC 5055, Sunflower Galaxy) M64 (NGC 4826, Black Eye Galaxy) M74 (NGC 628, spiral galaxy) M76 (NGC 650, Little Dumbbell Nebula) M80 (NGC 6093, globular cluster) M81 (NGC 3031, spiral galaxy) M82 (NGC 3034, companion to M81) M87 (NGC 4486, elliptical galaxy) M97 (NGC 3587, Owl Nebula) M101 (NGC 5457, spiral galaxy) M104 (NGC 4594, Sombrero Galaxy) M110 (NGC 205, companion to M31) Mach's principle MACHO Project MACHOs macroturbulence Maffei 1 Group Magellan Telescopes Magellanic Clouds Magellanic Stream magnetar magnetic cataclysmic variable magnetic star magnetogram magnetograph magnetopause magnetosheath magnetosphere magnetotail magnitude magnitude, of the tenth brightest member magnitude scale Maia (20 Tauri) main asteroid belt main sequence main-sequence fitting major axis major planet Maksutov telescope Malmquist effect manganese star manned spaceflight maria Maria family (of asteroids) Markarian Chain Mars Mars, all topics Mars, ammonia on Mars, atmosphere Mars, canals Mars, changes on Mars, dust devils Mars, meteorites from Mars, methane on Mars, moons Mars, oppositions Mars, past conditions Mars, polar caps Mars, water Mars Trojan Mars-crosser Martian meteorites mascon mass discrepancy mass function mass loss mass transfer mass-luminosity ratio mass-luminosity relation mass-luminosity-radius relation mass-radius relation Mauna Kea observatories Mayall Telescope McDonald Observatory McIntosh (sunspot) scheme M-class asteroid McMath-Pierce Solar Telescope Me star mean motion mean motion resonance mean orbital elements mean parallax mean place mean sun megamaser Meissa (Lambda Orionis) Mekbuda (Zeta Geminorum) Menkalinan (Beta Aurigae) Menkent (Theta Centauri) Menkib (Xi Persei) Mensa (constellation) Merak (Beta Ursae Majoris) Mercury (planet) Mercury, rotation mercury-manganese star meridian Meridiani Planum Merope (23 Tauri) Merope Nebula (NGC 1435) mesopause mesosiderite mesosphere Messier Catalogue metallicity metal-poor star metal-rich star meteor meteor, sporadic meteor shower meteor storm meteor train meteorite meteorite shower meteorites, famous meteorites, from Mars meteoroid meteoroid stream meteoroid swarm meteors and meteorites Metis Metonic cycle Meudon Observatory Miaplacidus (Beta Carinae) Mice, The (NGC 4676 A and B) microlensing Microlensing Observations in Astrophysics (MOA) Microlensing Planet Search (MPS) Project micrometeorites microquasar Microscopium microturbulence microwave window Milky Way Milky Way Galaxy millisecond pulsar Mimas Mimosa (Beta Crucis) Minkowski space Minkowski’s Object (Arp 133) minor axis minor planet Minor Planet Center (MPC) Mintaka Mira Mira variable Mirach (Beta Andromedae) Mirach's Ghost (NGC 404) Miranda Mirfak (Alpha Persei) MIRLIN mirror Mirzam (Beta Canis Majoris) missing mass Mizar (Zeta Ursae Majoris) MMT MOA molecular cloud molecule molecules, in space Monoceros (constellation) Monogem Ring month Moon Moon, water moonquake moons, atmospheres of Mopra Telescope Moreton wave Morgan-Keenan classification Mount Hopkins Observatory Mount Palomar Observatory Mount Stromlo and Siding Spring Observatory Mount Wilson magnetic classification (of sunspots) Mount Wilson Observatory mounting moving cluster MS star Mu Arae Multichannel Astrometric Photometer (MAP) Multichannel Astrometric Photometer and Spectrometer (MAPS) Multiple Mirror Telescope (MMT) multiple star multiringed basin Murchison meteorite Murray meteorite Musca (constellation) N galaxy N star N44 superbubble nadir Naiad naked-eye star Nakhla meteorite nakhlite Naos (Zeta Puppis) Nasmyth focus National Astronomy and Ionosphere Center National Optical Astronomy Observatories (NOAO) National Radio Astronomy Observatory (NRAO) National Solar Observatory (NSO) near-Earth asteroid near-Earth object (NEO) nearest stars nebula nebula filter nebulae and star clusters nebular hypothesis Neptune Neptune, moons Neptune Trojan Mars trojan Nereid Nereus (minor planet 4660) Neumann line neutral point neutron star neutronium New General Catalogue of Nebulae and Star Clusters (NGC) New Style date (NS) Newtonian telescope Newtonian-Cassegrain telescope Ney-Allen Nebula NGC 2261 (Hubble's Variable Nebula) NGC 2346 NGC 253 NGC 4622 NGC 5128 Group night-sky light Noachian epoch Nobeyama Radio Observatory (NRO) noctilucent clouds nodal line node non-radial pulsation non-thermal radiation noon norite Norma (constellation) North America Nebula (NGC 7000) North Galactic Spur Northern Cross nova Nova Cygni 1975 (V1500 Cygni) Nova Persei 1901 (GK Persei) Nova Herculis 1934 nuclear fusion nuclear timescale nucleus (cometary) nucleus, galactic Nuffield Radio Astronomy Laboratory nulling interferometry nutation Nysa-Polana family O star Oak Ridge Observatory OB association OB stars Oberon objective oblique rotator obliquity Observatoire de Haut-Provence observatories and telescopes occultation occulting disk octahedrite Octans (constellation) OGLE OGLE-2005-BLG-390Lb Ohio State University Radio Observatory Olber's Paradox old Olympus Mons Omega Centauri Omega Nebula (M17, NGC 6618) One Hectare Telescope (1HT) Oort Cloud Oort Limit opacity open cluster Ophelia Ophiuchus (constellation) Oppenheimer-Volkoff limit opposition optical depth Optical Gravitational Lensing Experiment (OGLE) optical interferometer optically violent variable (OVV) optics and optical phenomena orbit orbital element orbital energy orbital migration orbital node orbital period orbital plane orbital resonance orbital rotation orbital velocity Orcus (minor planet 90482) ordinary chondrite Orgueil meteorite Orion (constellation) Orion Arm Orion Complex Orion Nebula (M42, NGC 1976) Orion variable Orion's Belt Orion's Sword Orion-type star orrery orthopyroxenite osculating orbit overcontact binary Overwhelmingly Large Telescope (OWL) Owens Valley Radio Observatory (OVRO) Owl Nebula (M97, NGC 3587) P Cygni profile palimpsest Pallas (minor planet 2) pallasite Palomar Observatory Palomar Observatory Sky Survey (POSS) Palomar Testbed Interferometer Pan Pandora parallactic angle parallactic displacement parallax Paranal Observatory parent star Paris Observatory (Observatoire de Paris) Parkes Observatory Parkes Radio Telescope parsec (pc) partial eclipse particle physics entries Pasiphaë Patroclus (minor planet 617) Paul Wild Observatory P-class asteroid peculiar galaxy peculiar motion peculiar star Peekskill meteorite 51 Pegasi 51 Pegasi-type planets Pegasus Dwarf Spheroidal (Peg dSph, DDO 216) Pelican Nebula (IC 5070) Pennsylvania State Pulsar Group penumbra periapsis periastron peridotite perigalacticon perigee perihelion perilune period period-age relation period-luminosity relation period-mass relation period-spectra relation Perseus Arm Perseus Cluster (Abell 426) Perseus-Pisces Supercluster persistent train perturbation Petit-Prince PG 1159 star Phaethon (minor planet 3200) phase phase angle Phobos Phocaea group Phoebe Phoenix Dwarf Pholus photographic magnitude photoionization photometry photopolarimeter photosphere Pic-du-Midi Observatory Pinwheel Galaxy Pioneer anomaly Pipe Nebula Pisces Cloud (NGC 379, 380, 382-5) Pisces Dwarf (LGS-3) Pistol Star plage Planck time planet PLANET (Probing Lensing Anomalies Network) planet migration planet swallowing Planet X planetary features planetary nebula planetary system planetary systems, formation planetesimals planetocentric coordinates planisphere Plaskett’s Star (V640 Mon) plasma (physics) plasma sheet