Term Index (M)

 M1  M2  M3  M4  M5  M6  M7  M8  M9  MA  MB  MC  MD  ME  MF  MG  MH  MI  MJ  MK  ML  MM  MN  MO  MP  MR  MS  MT  MU  MV  MW  MX  MY  MZ

• M (M-type star): spectral class of star with a temperature in the vicinity of 2500 K
• M (Messier Catalog): catalog of astronomical objects to avoid when looking for comets
• M (absolute magnitude): magnitude as would be seen from 10 parsecs
• M: see NIRSpec
• M: see filter designator
• M: see rare designator prefixes
  • pulsating star: variable star that varies through energy pulses
• m (apparent magnitude): magnitude as seen from Earth adjusted for Earth atmosphere
• m: see electron orbital
• M band: see infrared
• M dwarf: small, cool main-sequence star in stellar class M
  • brown dwarf: star-like object with less mass than a star
  • M-type star: spectral class of star with a temperature in the vicinity of 2500 K
• m sin i (minimum mass): measured bound on the mass of an exoplanet
• M-σ relation (M-sigma relation): relation between galaxy center's velocity dispersion and SMBH mass
• M-class: see M-type star
• M-class star (M-type star): spectral class of star with a temperature in the vicinity of 2500 K
• M-sigma relation: relation between galaxy center's velocity dispersion and SMBH mass
• M-type star: spectral class of star with a temperature in the vicinity of 2500 K
• m.f.u.: see jansky
• M/L (mass-to-light ratio): measure of a population of stars or region
• M/L relation (mass-luminosity relation): model relating stellar mass and luminosity
• M1 (Crab Nebula): supernova remnant in Taurus
• M100 (Messier 100): easily-observed spiral galaxy
• M101 (Pinwheel Galaxy): easily-observed spiral galaxy
• M102 (Spindle Galaxy): disk galaxy for which we have an edge-on view
• M104 (Sombrero Galaxy): striking spiral galaxy with very large bulge
• M106 (Messier 106): spiral galaxy with maser
• M110
• satellite galaxy: galaxy that orbits a larger galaxy
• M15 (Messier 15): globular cluster with collapsed core
• M20
• Gini/M20: an automatable method of detecting whether a galaxy has recently merged
• M31 (Andromeda): spiral galaxy in the Local Group
  • Bologna Catalog of Globular Clusters: catalog of globular clusters in M31
  • Giant Stellar Stream: extensive stellar stream in M31
  • HBK: study of M31 globular clusters
  • Milkomeda: future galaxy resulting from merger of Milky Way and Andromeda
  • PAndAS: survey of M31 and M33
  • PHAT: HST survey of M31 stars
  • POINT-AGAPE: survey of M31 for microlensing
  • shell galaxy: galaxy with one or more surrounding layers of brightness
  • SKHB: survey of globular clusters in M31
  • SPLASH: survey of M31's Giant Stellar Stream
• M31 subgroup
• galaxy subgroup: a major galaxy and its satellites
• M31GC: see rare designator prefixes
• M31N: see rare designator prefixes
• M32
• satellite galaxy: galaxy that orbits a larger galaxy
• M33 (Triangulum Galaxy): small spiral galaxy in the Local Group
• M33 subgroup
• galaxy subgroup: a major galaxy and its satellites
• M42 (Orion Nebula): easily-observed nebula that includes SF regions
• M45 (Pleiades): visible open cluster with seven B-stars
• M51
• Whirlpool Galaxy: easily-observed spiral galaxy
• M51a (Whirlpool Galaxy): easily-observed spiral galaxy
• M64: nearby dusty galaxy
  • Council of Giants: twelve large galaxies surrounding the Local Group
• M67 (Messier 67): old open cluster in Cancer
• M74 (Messier 74): easily-observed spiral galaxy
• M77 (Messier 77): easily-observed spiral galaxy
• M81
• Council of Giants: twelve large galaxies surrounding the Local Group
• M82: nearby starburst galaxy
  • Council of Giants: twelve large galaxies surrounding the Local Group
• M83
• ASTHROS: balloon-borne 2.5-m submillimeter telescope
• Centaurus A: nearby radio galaxy
• Council of Giants: twelve large galaxies surrounding the Local Group
• M84 (Messier 84): elliptical galaxy with jets
• M87: supergiant elliptical galaxy in local universe
  • M87*: SMBH at the center of galaxy M87
• M87*: SMBH at the center of galaxy M87
  • Event Horizon Telescope: growing VLBI network
• M87*: see M87
• M94
• Council of Giants: twelve large galaxies surrounding the Local Group
• M_☉ (solar mass): mass unit representing the mass of the Sun
• M₂₀
• Gini/M20: an automatable method of detecting whether a galaxy has recently merged
• M₅₀₀: see cluster radius
• M_bol (bolometric magnitude): absolute magnitude of all wavelengths
• M_c (chirp mass): a reduced-mass-like quantity that relates to gravitational waves
• M_Earth
• solar mass: mass unit representing the mass of the Sun
• M_Jupiter
• solar mass: mass unit representing the mass of the Sun
• m_s (spin): an angular-momentum quantum number
  • electron orbital: a nucleus's "locations" where an electron can orbit
• M_Sun (solar mass): mass unit representing the mass of the Sun
• m_u (dalton): mass unit used on atomic scale
• MA: see rare designator prefixes
• Ma_MISS: see Rosalind Franklin
• MAC (Multi-instrument Aircraft Campaign): type of aircraft based study of meteor-shower-associated dust
• MAC: see Atacama Submillimeter Telescope Experiment
• MAC-E filter: see KATRIN
• MacC: see rare designator prefixes
• Mach angle
• expansion fan: the "sound" of a supersonic flow flowing around a convex corner
• Mach number: ratio of flow-speed to sound-speed
• Mach's principle: the notion that rotation is relative to all the mass of the universe
• machine learning: use of programs that extract their algorithms from data
  • balanced accuracy: average of true positive and negative rates
  • deep learning: description of machine learning using substantial neural networks
  • mixture density network: machine learning technique
  • neural network: computer program structure inspired by the brain
  • nonparametric model: model developed avoiding assumptions regarding a basic structure
  • random forest: algorithmic method of developing decision trees
  • XGBoost: machine learning software
• MACHO: proposed astronomical objects comprising dark matter
• MACHO (free-floating planet): planet that is not orbiting a star
• MACHO: see MACHO Project
  • dark matter: matter in galaxies and galaxy clusters suggested by their gravity
• MACHO Project: survey searching out microlensing that could indicate a MACHO
• MACHOs
• EROS: search for MACHOs
• GMAN: collaboration to alert on microlensing transients
• Korea Microlensing Telescope Network: survey searching for microlensing transients
• MACHO Project: survey searching out microlensing that could indicate a MACHO
• OGLE: survey searching for microlensing transients
• POINT-AGAPE: survey of M31 for microlensing
• Maclaurin spheroid
• theory of figures: type of model relating a planet's shape to its rotation
• Macquarie/AAO/Strasbourg Hα Planetary Galactic Catalog (MASH Catalog of Planetary Nebulae): 995 possible planetary nebulae
• MacrOmega: see MMX
• macronova (kilonova): transient associated with merging neutron stars
• MACS (Magellanic Catalogue of Stars): 1980s/1990s survey of stars in Magellanic Clouds
• MACS (Massive Cluster Survey): survey of distant clusters evident in ROSAT X-ray data
• MAD (magnetically arrested disk): mechanism for turning accretion into energy
• MAD: see European Southern Observatory Very Large Telescope
  • AGN accretion: an SMBH's accretion, such as powers AGNs/quasars
• MADCASH (Magellanic Analog Dwarf Companions And Stellar Halos): Subaru survey for dwarf glaxies beyond the Local Group
• Madelung equations: quantum hydrodynamic equations
• Madrid Deep Space Communications Complex: see NASA Deep Space Network
• MAE: see Mars Pathfinder
• MAESTRO: see MMT
• Maffei: see rare designator prefixes
• Maffei 1: see IC 342
  • Council of Giants: twelve large galaxies surrounding the Local Group
• Maffei 2
• Council of Giants: twelve large galaxies surrounding the Local Group
• MAG: see Aditya-L1
• MAG: see Advanced Composition Explorer
• MAG: see Cassini
• MAG: see Galileo
• MAG: see Giotto
• MAG: see IMAP
• MAG: see Juno
• MAG: see Lunar Prospector
• MAG: see MAVEN
• MAG: see MESSENGER
• MAG: see NEAR Shoemaker
• MAG: see SWFO-L1
• MAG: see Solar Orbiter
• MAG: see Ulysses
• MAG: see Venus Express
• MAG: see Voyager
• MAG/ER: see Mars Global Surveyor
• MAG/ER: see Mars Observer
• Magakian: see rare designator prefixes
• MagAO: see Magellan Telescopes
• Magdalena Ridge Observatory
• MRO Interferometer: optical interferometer in New Mexico
• Magdalena Ridge Observatory Interferometer (MRO Interferometer): optical interferometer in New Mexico
  • optical interferometer: interferometer of visible light
• MAGE: see Trace Gas Orbiter
• MagE: see Magellan Telescopes
• Magellan: 1980s/1990s Venus probe
• Magellan Planet Search Program: see Magellan Telescopes
• Magellan Telescopes: pair of 6.5 m optical telescopes in Chile
  • Atacama Desert: Chilean high-altitude, dry plateau with numerous observatories
  • CorMASS: near-infrared spectrograph
  • FourStar Galaxy Evolution Survey: infrared deep-survey to detect galaxies
  • Las Campanas Observatory: observatory in southern Atacama Desert
  • Panoramic Imaging Survey of Centaurus and Sculptor: survey of extended halos of two nearby galaxies
  • PRIMUS: spectrographic survey of galaxies out to redshift 1
  • WINERED: near-infrared non-cryogenic spectrograph
• Magellanic Analog Dwarf Companions And Stellar Halos: Subaru survey for dwarf glaxies beyond the Local Group
• Magellanic Bridge: hydrogen clouds joining the Magellanic Clouds
• Magellanic Catalogue of Stars: 1980s/1990s survey of stars in Magellanic Clouds
• Magellanic Clouds: two nearby galaxies
  • DeGaS-MC: APEX survey of potential star formation regions in the Magellanic Clouds
  • EROS: search for MACHOs
  • globular cluster: spherical group of stars orbiting a galaxy
  • irregular galaxy: galaxy that's not a disk or ellipsoid
  • Large Magellanic Cloud: somewhat irregular satellite galaxy of the Milky Way
  • Magellanic Bridge: hydrogen clouds joining the Magellanic Clouds
  • Magellanic Clouds Photometric Survey: UBVI survey of the Magellanic Clouds
  • Magellanic Stream: series of high-velocity clouds associated with the Magellanic Clouds
  • Radcliffe Observatory Magellanic Clouds Catalogue: catalog of stars in
  • SAGE: survey of gas and dust in the Magellanic Clouds
  • Small Magellanic Cloud: dwarf galaxy in the Local Group
• Magellanic Clouds Photometric Survey: UBVI survey of the Magellanic Clouds
• Magellanic Clouds Survey: see Infrared Survey Facility
• Magellanic spiral: see Magellanic Clouds
• Magellanic spiral galaxy: see spiral galaxy
  • Large Magellanic Cloud: somewhat irregular satellite galaxy of the Milky Way
  • Small Magellanic Cloud: dwarf galaxy in the Local Group
• Magellanic Stream: series of high-velocity clouds associated with the Magellanic Clouds
  • high-velocity cloud: fast-moving clouds in galactic halos
• maggie: AB magnitude
• maggies: see AB system
• maggy (maggie): AB magnitude
• maggy (nanomaggie): a billionth of an AB magnitude
• maggy: see AB system
• MAGIC: ground gamma-ray telescope array in the Canary Islands
• MagIC: numerical code to for fluid dynamics including dynamos
• MagIC: see Magellan Telescopes
• MAGIC Florian Goebel Telescopes (MAGIC): ground gamma-ray telescope array in the Canary Islands
• MAGIC Telescopes
• Roque de los Muchachos Observatory: observatory at La Palma in the Canary Islands
• MAGIC-II: see MAGIC
• magma ocean: presumed to occur early in Earth history and potentially on exoplanets
• magnesium: element, Mg, atomic number 12
  • cosmic dust: dust in space such as interstellar dust
  • magnesium lines: spectral lines specific to magnesium
  • neon burning: fusion reaction starting with neon
  • nucleosynthesis: creation of atomic nuclei
  • oxygen burning: fusion reaction starting with oxygen
  • white dwarf: stellar remnant largely of electron degenerate matter
• magnesium lines: spectral lines specific to magnesium
• magnetar: neutron star with a strong magnetic field
  • SGR 1935+2154: Milky Way SGR generating FRBs
  • SGR J1745-2900: magnetar orbiting the Milky Way SMBH
• magnetar flare: see magnetar
• magnetars
• Canadian Institute for Theoretical Astrophysics: national research organization at University of Toronto
• magnetic adiabatic collimation with an electrostatic filter: see KATRIN
• magnetic anomaly: variation in a body's magnetic field
• magnetic arcade: series of arch-like magnetic flux lines on the Sun
  • Sun surface features: features on the Sun's surface
• magnetic braking (magnetic dipole braking): the effect of a reduction in the spinning of a magnetic field
  • gyrochronology: means of estimating stellar age from rotation
• magnetic diffusivity
• Reynolds number: measure reflecting a fluid system's propensity to turbulence
• magnetic dipole braking: the effect of a reduction in the spinning of a magnetic field
• magnetic dipole emission (magnetic dipole radiation): EMR naturally generated by a spinning magnetic dipole
• magnetic dipole radiation: EMR naturally generated by a spinning magnetic dipole
  • magnetic dipole braking: the effect of a reduction in the spinning of a magnetic field
• magnetic dipole spin-down (magnetic dipole braking): the effect of a reduction in the spinning of a magnetic field
• magnetic dynamo: see dynamo
• magnetic energy: see magnetic energy spectrum
• magnetic energy density: see magnetic energy spectrum
• magnetic energy spectrum: spatial spectral density of the energy associated with magnetic fields
• magnetic field: magnetic force as distributed over a space
• magnetic field (magnetic field strength): a field associated with magnetism
• magnetic field (magnetic flux density): vector field describing magnetism in relation to the Lorentz force
  • dipole: field with two poles
  • flux freezing: magnetic field lines becoming attached to plasma they pass through
• magnetic field intensity (magnetic field strength): a field associated with magnetism
• magnetic field lines: see field lines
• magnetic field strength: a field associated with magnetism
• magnetic fields
• spin-down luminosity: pulsar's energy extracted from slowing rotation
• magnetic flux: measure of magnetism passing through a surface
• magnetic flux density: vector field describing magnetism in relation to the Lorentz force
• magnetic induction: voltage across a conductor induced by changing magnetic field
• magnetic induction (magnetic flux density): vector field describing magnetism in relation to the Lorentz force
  • magnetometer: instrument to measure the strength of a magnetic field
• magnetic monopole
• cosmic string: rent in spacetime
• Maxwell's equations: four equations describing electricity and magnetism
• magnetic permeability: see permeability
• magnetic power spectrum: see magnetic field
• magnetic pressure: see magnetic energy spectrum
• magnetic quantum number: see electron orbital
• magnetic reconnection: change in magnetic topology within a fluid
• magnetic Reynolds number: see Reynolds number
• magnetic SPB star: see slowly-pulsating B-star
• magnetic spot: see magnetic field
• magnetic switchback: Z-shaped magnetic field lines
• magnetic tower: length of twisted magnetic field lines produced by rotating field
• magnetic white dwarf: see white dwarf
• magnetically arrested disk: mechanism for turning accretion into energy
• magnetism
• 1947 sunspot: largest sunspot ever recorded
• Alfvén wave: a type of transverse wave along magnetic field lines in plasma
• anomalous X-ray pulsar: X-ray pulsars with no high-mass companion
• BCool: project studying stellar magnetism
• beta: ratio of plasma pressure to magnetic pressure
• Blandford-Payne mechanism: means of by which an accretion disk can power a jet
• Blandford-Znajek mechanism: means of extracting BH rotational energy by magnetized accretion disk
• bow shock: shock wave of a magnetosphere through the surrounding medium
• Carrington event: solar storm September 1-3 1859
• chromospheric activity index: measure of magnetic activity of a star's chromosphere
• coronal loop: visible loop extending out of the Sun's surface and back
• coronal mass ejection: mass of plasma ejected from the Sun
• Coronal Solar Magnetism Observatory: proposed solar observatory
• crustal magnetism: magnetic fields independent of a world's core magnetic field
• current sheet: slender sheet within a magnetic field where current flows
• curvature radiation: synchrotron-like radiation when particles follow curved field lines
• cyclotron radiation: radiation emitted when charged particles are accelerated
• dipole: field with two poles
• dynamo: mechanism for generating magnetic fields around astronomical bodies
• electromagnetism: electricity and magnetism and their interaction
• Faraday rotation: rotation of optical polarization by a medium in a magnetic field
• flux: flow rate per unit area
• flux freezing: magnetic field lines becoming attached to plasma they pass through
• flux rope: rope-shaped structure in magnetic fields associated with coronal mass ejections
• gas flow: dynamics of gas, plasma, i.e., compressible fluids
• gauss: measurement of magnetic field β
• geomagnetic storm: disturbance in Earth's magnetosphere
• Hall effect: voltage generated by interacting current and magnetic field
• Hanle effect: effect of magnetic field on the polarization of emitted photons
• heliosphere: region of space dominated by the Sun
• high-B radio pulsar: pulsar with a strong magnetic field
• IMAGE­: satellite mission to study magnetosphere
• interstellar magnetic field: galactic magnetic field between that of stars
• Lorentz force: force on a point charge due to magnetic fields
• magnetar: neutron star with a strong magnetic field
• magnetic anomaly: variation in a body's magnetic field
• magnetic arcade: series of arch-like magnetic flux lines on the Sun
• magnetic dipole braking: the effect of a reduction in the spinning of a magnetic field
• magnetic dipole radiation: EMR naturally generated by a spinning magnetic dipole
• magnetic energy spectrum: spatial spectral density of the energy associated with magnetic fields
• magnetic field: magnetic force as distributed over a space
• magnetic field strength: a field associated with magnetism
• magnetic flux: measure of magnetism passing through a surface
• magnetic flux density: vector field describing magnetism in relation to the Lorentz force
• magnetic reconnection: change in magnetic topology within a fluid
• magnetic switchback: Z-shaped magnetic field lines
• magnetic tower: length of twisted magnetic field lines produced by rotating field
• magnetically arrested disk: mechanism for turning accretion into energy
• magnetohydrodynamics: dynamics of electrically conducting fluids
• magnetometer: instrument to measure the strength of a magnetic field
• magnetorotational instability: instability in the fluid of a disk from MHD effects
• magnetosonic wave: a type of sonic wave in a plasma
• magnetosphere: area around an object where its magnetic field dominates
• magnetospheric truncation radius: radius at which the disc ram pressure matches the magnetic field pressure
• Maxwell's equations: four equations describing electricity and magnetism
• paleomagnetism: ancient magnetic fields and their characteristics
• plasma wave: wave incorporating the EM forces within plasma
• quadratic field strength: a measure of a star's varying magnetic field
• radiation belt: regions of energetic charged particles surrounding a planet
• soft gamma repeater: object that produces repeated gamma-ray bursts
• spin-down luminosity: pulsar's energy extracted from slowing rotation
• standard model of a flare: description of how solar flares function
• stellar flare: sudden brightening of a star
• synchrotron radiation: radiation emitted when high-speed charged particles are accelerated
• telegrapher's equations: two equations describing a transmission line
• tesla: unit of magnetic flux density
• THEMIS: set of satellites studying the Earth's magnetic field
• torus coordinates: coordinates for toruses
• TRACE: former solar observing satellite
• Van Allen belts: regions of energetic charged particles surrounding Earth
• Zeeman effect: magnetic field influence on spectral lines
• Zeeman-Doppler imaging: technique for imaging stellar magnetic fields
• magnetized molecular cloud
• molecular cloud: interstellar gas cloud that includes molecules
• magnetizing field (magnetic field strength): a field associated with magnetism
• magneto-brems (synchrotron radiation): radiation emitted when high-speed charged particles are accelerated
• magneto-bremsstrahlung (synchrotron radiation): radiation emitted when high-speed charged particles are accelerated
• magneto-hydrodynamics
• Blandford-Payne mechanism: means of by which an accretion disk can power a jet
• magneto-plasma system: see magnetohydrodynamics
• magnetoacoustic wave (magnetosonic wave): a type of sonic wave in a plasma
• magnetobremsstrahlung (synchrotron radiation): radiation emitted when high-speed charged particles are accelerated
• magnetohydrodynamics: dynamics of electrically conducting fluids
  • hydrodynamics: study of fluids in motion
• magnetometer: instrument to measure the strength of a magnetic field
• magnetopause: see magnetosphere
• magnetorotational instability: instability in the fluid of a disk from MHD effects
• magnetorotational supernova: type of core collapse supernova
• magnetorotational turbulence: see magnetorotational instability
• magnetosonic wave: a type of sonic wave in a plasma
• magnetosphere: area around an object where its magnetic field dominates
  • AMPTE: three spacecraft experimenting on Earth magnetosphere
  • DQ Tau: young binary star system
  • Magnetospheric Multiscale Mission: four spacecraft making Earth magnetosphere measurements
  • space weather: varying conditions in space affecting Earth and humans
• Magnetospheric eternally collapsing object: theoretical state of collapsing object unable to reach BH characteristics
• Magnetospheric Multiscale Mission: four spacecraft making Earth magnetosphere measurements
• magnetospheric truncation radius: radius at which the disc ram pressure matches the magnetic field pressure
• magnetoturbulence: see magnetorotational instability
• magnification: see angular magnification
  • plate scale: relation between angle and distance across an image
• magnitude: a logarithmic measure of brightness
  • AB system: monochromatic magnitude calibration based upon absolute values
  • absolute magnitude: magnitude as would be seen from 10 parsecs
  • apparent magnitude: magnitude as seen from Earth adjusted for Earth atmosphere
  • bolometric correction: difference between an object's bolometric and visual magnitudes
  • bolometric magnitude: absolute magnitude of all wavelengths
  • color index: a number that characterizes the color of an object
  • color-magnitude diagram: graph plotting color index to magnitude
  • distance modulus: apparent magnitude minus absolute magnitude
  • g-r color: difference between SDSS g' and r' magnitudes
  • griz photometric system: photometric system designed for electronic sensors
  • H-R diagram: diagram relating effective temperature to luminosity
  • Hess diagram: diagram relating effective temperature to luminosity
  • Hipparchus: Greek astronomer who developed concept of magnitude
  • infrared excess: more infrared than that of a star's typical spectrum
  • JHK photometric system: system to classify stars according to near-infrared colors
  • K correction: correction to magnitude for redshift
  • limiting magnitude: faintest magnitude that a telescope or instrument can detect
  • maggie: AB magnitude
  • MKO photometric system: 2000s system covering near infrared
  • nanomaggie: a billionth of an AB magnitude
  • passband: range of electromagnetic wavelengths that a filter allows
  • photometric system: specification of a set of filters/passbands
  • sensitivity function: function of wavelength giving the sensitivity of an instrument
  • Strömgren photometric system: four-color photometric system devised in 1950s
  • UBV photometric system: commonly-cited photometric system for describing stars' colors
  • ugriz photometric system: photometric system used for SDSS
  • Vega system: magnitude calibration such that Vega has zero magnitude
  • Wesenheit function: function of magnitudes approximating absolute visual magnitude
• magnitude system: see photometric system
• magnitude-redshift relation (redshift-magnitude relation): how apparent magnitude depends on redshift
• MAIA: see Mercator Telescope
• Mailyan: see rare designator prefixes
• main asteroid belt: see asteroid belt
• main belt: see asteroid belt
• main belt asteroid: see asteroid belt
• main lobe: see beam
• main r-process: see r-process
• main sequence: see main sequence star
• main sequence fitting: cluster star distance determined through fitting with the H-R diagram
• main sequence galaxy: see galaxy main sequence
  • star formation rate: rate at which material such as gas is turned into stars
• main sequence star: star burning hydrogen into helium in its center
  • luminosity class: classification of size/luminosity of stars
• main-sequence lifetime: length of time that a star remains within the main sequence
• main-sequence turn-off point (turn-off point): point in H-R diagram of a cluster where stars turn red
• MAJIS: see JUICE
• Major Atmospheric Gamma Imaging Cherenkov Telescopes (MAGIC): ground gamma-ray telescope array in the Canary Islands
• major circle of latitude: see circle of latitude
• major merger: see galaxy merger
• Majorana equation: see Majorana particle
• Majorana fermion (Majorana particle): theoretical particle that is its own antiparticle
• Majorana particle: theoretical particle that is its own antiparticle
  • CUORE: experiment to sense neutrinoless double beta decay
  • neutrinoless double beta decay: possible type of rare beta decay
• Makemake
• dwarf planet: round like a planet, only smaller
• Kuiper Belt: further part of solar system beyond Neptune
• plutoid: Pluto-like dwarf planet
• solar system object: the Sun, solar system planets, minor planets, comets, and moons
• trans-Neptune object: minor planet beyond Neptune
• MAKO: see Caltech Submillimeter Observatory
• Malin: see rare designator prefixes
• Malmquist bias: selection bias from detecting only the brighter objects
• MALT (Millimeter Astronomy Legacy Team): Australian initiative producing millimeter surveys
• MAMA: see microchannel array
• Mamajek: see rare designator prefixes
• Mamajek's Law: exoplanet discoveries are rising exponentially
• MAMBO: see IRAM 30m Telescope
• MAMBO2: see IRAM 30m Telescope
• MaNGA: see Sloan Digital Sky Survey
  • MaNGA Stellar Library: catalog of SEDs of representative stars
• MaNGA Stellar Library: catalog of SEDs of representative stars
• MANIFEST: see Giant Magellan Telescope
  • TAIPAN: multi-object spectrograph with robot fiber-positioner
• manifold
• anti-de Sitter space: type of curved space
• Lie transform: type of infinitesimal transform
• Manko and Novikov metric
• theoretical modified GR metric: metric devised to define modifications to GR
• mantle
• carbonate-silicate cycle: long-term cycle that sequesters Earth carbon
• many-body problem: see N-body problem
• MAORY: see European Extremely Large Telescope
• MAP (Wilkinson Microwave Anisotropy Probe): spacecraft that measured variations in the cosmic background radiation
• MapMaker: see mlmapper
• mapmaking
• destriping: removing streak-like noise from images
• Mapping Obscuration to Reionization with ALMA (MORA): high resolution 2-mm survey of a portion of the COSMOS field
• Mapping X-Ray Heliometer: see OSO 8
• MAPS: ALMA survey researching planet-formation
• MARA: see Hayabusa2
• March equinox: see equinox
  • J2000.0 equinox: equinox as of the J2000.0 epoch used as a positional reference
• MARCI: see Mars Reconnaissance Orbiter
• MARDI: see Mars Polar Lander
• MARDI: see Mars Science Laboratory
• MARDI: see Phoenix
• Maria
• asteroid family: set of asteroids based on similar orbits
• MARIE: see Mars Odyssey
• Mariner
• Mars: well-explored planet in the solar system
• Mariner 10
• Mercury: inner-most and smallest planet in the solar system
• Mariya: see Kvant 1
• Mark: see Markarian galaxy
• Mark I: see Jodrell Bank Observatory
• Mark II: 38 m radio telescope in England
  • European VLBI Network: consortium of radio telescopes to coordinate VLBI efforts
  • Jodrell Bank Observatory: radio observatory in England
  • MERLIN: VLBI array spread across England
• Markarian: see Markarian galaxy
• Markarian: see rare designator prefixes
• Markarian galaxy: list of galaxies with excess ultraviolet light
• Markov chain: see Markov chain Monte Carlo
• Markov Chain Monte Carlo
• spectral energy distribution: function or plot of brightness at each wavelength in the spectrum
• Markov chain Monte Carlo: model technique to approximate multi-dimensional integrals
  • Monte Carlo method: mathematics and simulation using random samples
• MAROON-X: see Gemini Observatory
• MARS: see Parkes Observatory
• MaRS: see Mars Express
• Mars: well-explored planet in the solar system
  • dust devil: small whirlwind visible from dust it collects
  • ExoMars: program to search for signs of life on Mars
  • Gale Crater: Curiosity rover landing site on Mars
  • Hope Probe: UAE Mars orbiter currently studying Mars
  • InSight: NASA Mars mission to study its interior
  • Jezero Crater: Perseverance rover landing site on Mars
  • Mars 2020: Mars rover mission currently on Mars after 2021 landing
  • Mars Climate Orbiter: failed Mars 1990s probe
  • Mars Exploration Rover: mission to Mars with two rovers
  • Mars Express: Mars probe launched by ESA in 2003
  • Mars Global Surveyor: Mars probe launched by NASA in 1996
  • Mars Observer: failed 1992-1993 Mars orbiter mission
  • Mars Odyssey: Mars orbiter launched by NASA in 2001
  • Mars Pathfinder: 1990s mission to Mars with rover
  • Mars Polar Lander: failed 1999 Mars lander mission
  • Mars Reconnaissance Orbiter: Mars probe launched by NASA in 2005
  • Mars Science Laboratory: mission to Mars with rover
  • MarsWRF: Mars-oriented general circulation model
  • MAVEN: Mars orbiter to study its atmosphere
  • MMX: Japanese probe to bring back a sample of a Martian moon
  • Nili Fossae: region of grabens on Mars
  • Phoenix: Mars polar-region probe launched by NASA in 2007 with lander
  • Rosalind Franklin: Mars rover in development for 2028 launch
  • solar system object: the Sun, solar system planets, minor planets, comets, and moons
  • Tianwen-1: active Chinese Mars rover/orbiter mission
  • Trace Gas Orbiter: ESA and Russian Mars orbiter-probe launched in 2016
• Mars 2020: Mars rover mission currently on Mars after 2021 landing
  • Mars: well-explored planet in the solar system
• Mars 2020 Rover (Mars 2020): Mars rover mission currently on Mars after 2021 landing
• Mars 3
• STEREO: two-satellite system to observe the Sun
• Mars 5
• STEREO: two-satellite system to observe the Sun
• Mars Atmosphere and Volatile Evolution (MAVEN): Mars orbiter to study its atmosphere
• Mars Atmospheric and Gravity Experiment: see Trace Gas Orbiter
• Mars Climate Orbiter: failed Mars 1990s probe
• Mars Climate Orbiter: see Mars Polar Lander
• Mars crosser: asteroid with an orbit that crosses that of Mars
• Mars Exploration Program
• Mars 2020: Mars rover mission currently on Mars after 2021 landing
• Mars Exploration Program Analysis Group: NASA forum to provide input to long-term planning of Mars missions
• Mars Exploration Rover: mission to Mars with two rovers
• Mars Express: Mars probe launched by ESA in 2003
• Mars Geoscience/Climatology Orbiter (Mars Observer): failed 1992-1993 Mars orbiter mission
• Mars Global Surveyor: Mars probe launched by NASA in 1996
• Mars Helicopter Scout: see Mars 2020
• Mars Observer: failed 1992-1993 Mars orbiter mission
  • radio science: radar and other methods of using radio to probe planets and moons
• Mars Odyssey: Mars orbiter launched by NASA in 2001
• Mars Pathfinder: 1990s mission to Mars with rover
• Mars Phoenix (Phoenix): Mars polar-region probe launched by NASA in 2007 with lander
• Mars Polar Lander: failed 1999 Mars lander mission
• Mars Reconnaissance Orbiter: Mars probe launched by NASA in 2005
  • Mars: well-explored planet in the solar system
• Mars Science Laboratory: mission to Mars with rover
  • CSA: includes astronomical research
• Mars Surveyor ' Orbiter: see Mars Polar Lander
• Mars Surveyor '98: see Mars Polar Lander
• Mars Surveyor '98 Lander (Mars Polar Lander): failed 1999 Mars lander mission
• Mars Weather Research and Forecasting Model (MarsWRF): Mars-oriented general circulation model
• Mars-crossing asteroid (Mars crosser): asteroid with an orbit that crosses that of Mars
• Mars-XRD: see Rosalind Franklin
• MarSCoDe: see Tianwen-1
• MARSIS: see Mars Express
• marsquake: see quake
• MarsWRF: Mars-oriented general circulation model
• MART-LIME: see Spektr-RG
• Martian Moons Exploration (MMX): Japanese probe to bring back a sample of a Martian moon
• Martin-Puplett interferometer
• CONCERTO: spectrometer aimed at mapping the [CII] line
• MARVELS: see Sloan Digital Sky Survey
  • Sloan 2.5m Telescope: telescope for SDSS in New Mexico
• MARVELS Spectrograph: see Sloan 2.5m Telescope
• Marvin: see MaNGA Stellar Library
• Maryland
• Goddard Space Flight Center: NASA space research laboratory near Washington D.C.
• mas: see arcsecond
• MASCAM: see Hayabusa2
• MasCam: see Mars Science Laboratory
• MASCARA: distributed array of telescopes to search for exoplanets
  • Roque de los Muchachos Observatory: observatory at La Palma in the Canary Islands
• MASCOT: see Hayabusa2
• MASCS: see MESSENGER
• maser: electromagnetic radiation amplified by stimulated emission
  • stimulated emission: emission triggered by received photons
• maser emission: see maser
• masers
• hydroxyl: one hydrogen atom and one oxygen atom bound together
• OH/IR source: AGB star with strong OH maser
• MASH Catalog of Planetary Nebulae: 995 possible planetary nebulae
• mask: see aperture masking interferometry
  • apodization: improving telescope images by manipulating diffraction
  • point-spread function: function describing an optical system's response to a point of light
• masking (aperture masking interferometry): interferometry by means of a single telescope with a mask
  • apodization: improving telescope images by manipulating diffraction
• MASMAG: see Hayabusa2
• MASPEX: see Europa Clipper
• mass: object's quality that determines the effects of forces and gravity
  • barycenter: center of mass of two orbiting bodies
  • black hole mass function: mass of the distribution of black holes
  • bulk density: total mass divided by total volume
  • Chandrasekhar limit: maximum mass of a white dwarf
  • chirp mass: a reduced-mass-like quantity that relates to gravitational waves
  • Compton wavelength: lower bound on a particle's possible de Broglie wavelength
  • conditional stellar mass function: function characterizing galaxies within a halo of a given mass
  • dalton: mass unit used on atomic scale
  • dense core mass function: function describing range of masses of dense cores
  • electron volt: very small unit of energy
  • energy: physical state needed to do something
  • gas fraction: fraction of a galaxy or cluster consisting of gas
  • gas fraction estimation: methods of estimating various amounts of gas in galaxies
  • halo mass function: mass of distribution of dark matter
  • initial mass function: function describing initial mass of stars
  • isolation mass: mass of an oligarch after accreting all nearby planetesimals
  • Jeans equations: relating the motion of stars to the surrounding gravitational field
  • low mass star: star with less than half a solar mass
  • main-sequence lifetime: length of time that a star remains within the main sequence
  • mass density: mass per unit volume, as opposed to particle density
  • mass loss: a star's reduction in mass
  • mass transport: transfer of mass from one part of a body/disk to another
  • mass-luminosity relation: model relating stellar mass and luminosity
  • mass-radius relation: model relating stellar mass and radius
  • mass-to-light ratio: measure of a population of stars or region
  • mean molecular weight: measurement of a gas usual for approximating in gas models
  • minimum mass: measured bound on the mass of an exoplanet
  • primary: central body of a system such as the Sun within the solar system
  • reduced mass: the reciprocal of the sum of the reciprocals of the masses of two objects
  • relativistic energy: energy of an object including relativistic effects
  • relativistic momentum: momentum of an object including relativistic effects
  • Schönberg-Chandrasekhar limit: maximum stellar isothermal helium core mass
  • solar mass: mass unit representing the mass of the Sun
  • stellar birth rate function: function describing the birth rate of stars by mass
  • stellar mass determination: methods by which the mass of a star is determined
  • supermassive star: star more massive than stars normally form
  • surface density: quantity such as mass per unit area
  • Tolman-Oppenheimer-Volkoff limit: maximum mass of a neutron star
  • very low mass: abbreviation
• mass conservation equation: see stellar structure
• mass continuity equation: see stellar structure
• mass density: mass per unit volume, as opposed to particle density
  • number density: number of objects per volume
• mass extinction: event in which many species went extinct
• mass fraction: measure of a constituent of a star, cloud, etc.
  • metallicity: metal fraction of an object
• mass function: measure of binaries that constrains the masses
• mass gap: see stellar-mass black hole
  • intermediate-mass black hole: black hole between stellar mass and supermassive
  • pair-instability supernova: type of large supernova
• mass loading: moving gas gaining mass from clouds or stars
• mass loss: a star's reduction in mass
• mass number: number of nucleons in an atomic nucleus
• mass number: see mass
  • Avogadro's number: number of hydrogen atoms per gram
  • element: class of atom based on its number of protons
  • fusion: formation of an atomic nucleus nuclei from multiple smaller nuclei
  • isotope: subclass of an element with a specific number of nucleons
  • nucleon: proton or neutron
  • radioactive decay: changes in atomic nuclei that happen over time
• mass ratio: ratio of masses of two objects such as a binary star
  • binary star: system of two stars co-orbiting
  • chirp mass: a reduced-mass-like quantity that relates to gravitational waves
• mass shell: conceptual volume of mass shaped like a hollow sphere
• mass spectrograph (mass spectrometer): device to determine the mass of molecules in a mixture
• mass spectrometer: device to determine the mass of molecules in a mixture
  • spectrometer: device to measure light by wavelength across its spectrum
• mass spectrometry: see mass spectrometer
  • spectrometry: measuring the strengths of different electromagnetic wavelengths
• mass transfer: material passing from a star to a binary companion
  • mass: object's quality that determines the effects of forces and gravity
• mass transport: transfer of mass from one part of a body/disk to another
• mass-luminosity relation: model relating stellar mass and luminosity
• mass-metallicity relation
• metallicity: metal fraction of an object
• mass-radius relation: model relating stellar mass and radius
• mass-radius relationship (mass-radius relation): model relating stellar mass and radius
• mass-to-light ratio: measure of a population of stars or region
• mass/age degeneracy: see brown dwarf
• Massachusetts
• Five College Radio Astronomical Observatory: former observatory near Springfield MA
• massive astrophysical compact halo object (MACHO): proposed astronomical objects comprising dark matter
• massive bigravity: see bigravity
• massive black hole: see black hole
• Massive Cluster Survey: survey of distant clusters evident in ROSAT X-ray data
• massive compact halo object (MACHO): proposed astronomical objects comprising dark matter
• massive gravity: see bigravity
• massive X-ray binary: see X-ray binary
• massive young stellar object: see young stellar object
• MAST: archive of data from surveys and missions
• MaStar (MaNGA Stellar Library): catalog of SEDs of representative stars
• MastCam: see Mars Science Laboratory
• Mastcam-Z: see Mars 2020
• MASTER (MASTER Robotic Net): network of automated telescopes to identify transients
• MASTER Global Robotic Telescopes Net (MASTER Robotic Net): network of automated telescopes to identify transients
• MASTER Robotic Net: network of automated telescopes to identify transients
• MAT: see QMAP
• MAT/TOCO: see QMAP
• MATCH: SFH code
• materials
• photoevaporation: dispersal of a gas from UV radiation
• sublimation: single material phase transition from solid to gas
• mathematical analysis
• analytical methods: using solved equations rather than a lot of arithmetic
• mathematical field: function of three variables, potentially representing space
• mathematics
• 2D Fourier transform: type of transformation of 2D functions used for analysis and manipulation
• adaptive mesh refinement: numerical modeling method balancing detail with tractability
• analytical methods: using solved equations rather than a lot of arithmetic
• anti-de Sitter space: type of curved space
• Approximate Bayesian Computation: shortcut-method in Bayesian statistics
• areal coordinate system: coordinate system based upon a known triangle
• axisymmetric: identical in any direction from an axis
• back-of-the-envelope calculation: very short calculation to get a rough idea of a value
• basis function: one of a set of functions used to approximate a function of interest
• Bayesian statistics: statistics method assigning probability to your belief
• Bernstein polynomial: polynomial form capable of producing arbitrary shapes
• Birkhoff's theorem: shows GR qualities of a spherically-symmetric mass
• Boltzmann transport equation: equation for evolving distribution of gas particles
• brane: mathematical object with dimensions
• chaos theory: theory of systems highly sensitive to initial conditions
• complex number: type of number that can be the square root of a negative number
• conformal field theory: a type of quantum field theory
• conic section: orbit shapes, like the intersection of a plane and cone
• convolution: type of product function of two functions
• correction term: term added to a formula to mitigate an imperfection
• correlated: values of two functions having the same sign
• curvature: unflatness of space
• data folding: locating periods in data by trial
• dendrogram: diagram of a "tree", i.e., of a graph without cycles
• dex: a number or ratio's log base 10
• discontinuous Galerkin method: computational method for PDEs handling discontinuities
• displacement: vector quantity showing the position of one point in relation to another
• distance: magnitude of the displacement or length of a curve
• effective field theory: type of useful simplification of a field theory
• eigen-decomposition: useful type of factoring a matrix into the product of three
• eigenmode: vibration mode of an oscillator where all parts move at the same frequency
• eigenvalue: ratio between a vector and a linear transformation of that vector
• ellipticity: degree to which a body's shape is un-spherical
• equation of state: equation relating temperature, pressure, and volume
• Euler's formula: formula relating exponentials to trigonometric functions
• fast folding algorithm: algorithm to find the periods of periodic data
• fast Fourier transform: efficient algorithm for calculating a discrete Fourier transform
• Fastest Fourier Transform in the West: code library implementing efficient FFT
• field lines: lines showing the pattern of a mathematical field
• finite difference method: means of estimating calculus and differential equation solutions
• finite element method: computational method for PDEs suited to physical problems
• finite volume method: computational method for PDEs especially suited to fluid dynamics
• Fisher information: measure of the information provided by experimental data
• flux reconstruction: numerical approach emphasizing joining the subdivisions
• forward model: model producing potential observable values from parameters
• Fourier series: type of series able to approximate a periodic function
• Fourier series expansion: type of series expansion of a function using trigonometric functions
• Fourier space: domain into which the Fourier transform maps a function
• Fourier transform: systematic method of breaking down functions into periodic components
• full width at half maximum: a measure of the width of a hump-shaped curve
• Gaussian function: function producing the bell curve
• geodesic: equivalent to a straight line within curved space
• Godunov scheme: computational fluid dynamics method
• gradient: vector indicating the slope at a point within a field
• Hamiltonian: mathematical transform useful in mechanics
• Hartle-Thorne metric: metric approximating GR effects of slow neutron star rotation
• HEALPix: type of map projection for spheres
• high resolution shock capture: method of modeling shock waves
• instability region: region around an object where orbits cannot persist
• inverse square law: a value's dependency upon reciprocal of the square of the distance from something
• isotropy: uniformity in all directions
• Jacobi integral: method of solving some three-body problems
• Johannsen-Psaltis metric: metric template allowing metrics to be written as a general expansion
• Kerr-NUT spacetime: Kerr spacetime defined in terms of Taub-NUT spacetime
• Klein-Nishina formula: formula for the effects of electrons scattering photons
• Kolmogorov spectrum: energy spectrum of the eddies of different sizes in a turbulent fluid
• Krylov subspace method: efficient method of numerically solving sets of linear equations
• Laplace-Lagrange secular theory: theory of evolution of planetary orbits
• lattice Boltzmann method: computational fluid dynamics method treating the fluid as particles
• Legendre polynomials: useful sequence of polynomials
• Lie transform: type of infinitesimal transform
• Limber approximation: formula approximating the density of galaxies in some direction
• linear theory: theory of operators satisfying the property of superposition
• Lyapunov time: timescale beyond which a dynamical system is chaotic
• Markov chain Monte Carlo: model technique to approximate multi-dimensional integrals
• mathematical field: function of three variables, potentially representing space
• maximum likelihood estimation: statistical method to find likely parameters
• metric: mathematical generalization of the concept of distance
• mixture: type of probability distribution resulting from two others
• Monte Carlo method: mathematics and simulation using random samples
• multipole expansion: series expansion of a function over the surface of a sphere
• N-body problem: calculating the paths of gravitationally-interacting celestial objects
• N-point function: general term for analyses-techniques of spatial data
• non-Gaussian: something requiring adjustment from the Gaussian function
• nondimensionalization: manipulation of an equation to remove units
• nonparametric model: model developed avoiding assumptions regarding a basic structure
• normal mode: resonant surface waves in seismology
• numerical analysis: the study and use of numerical methods of solving equations
• numerical methods: using equations through repetitive arithmetic
• numerical relativity: solving GR-sensitive problems with numerical methods
• paraboloid: circularly-symmetric 3D surface based on parabola
• partial differential equation: equation constructed as if the variables differentiated are independent
• perturbation theory: breaking an equation into a solvable part and approximable part
• phase dispersion minimization: particular method of finding periodic components in signal
• phase space: space of all possible states of a system
• PIC simulation: method used in simulating plasma
• plane wave: simplified wave concept useful for modeling
• Poincaré section: pattern formed by a the locations an orbiting body passes through a plane
• Poisson distribution: statistics on count of events happening within a given interval
• Poisson's equation: relates one function's Laplacian to another function
• positional astronomy: calculation methods for relating sky position to position in space
• power law: relationship between a quantity and a power of another
• pressure integral: integral relating pressure to a gas's characteristics
• probability density function: shows probability of taking a particular value from a continuous range
• probability mass function: shows probability of taking one of a number of discrete values
• quantum Monte Carlo: MC approach to difficult quantum mechanical problems
• radian: angle/arc measurement equivalent to 180/π degrees
• random walk: movement with random turns
• Reynolds decomposition: mathematical separation of average and fluctuating parts of a quantity
• Riemann problem: consequence of discontinuities in numerical methods
• Runge-Kutta method: type of numerical method for integration and differential equations
• scatter plot: plot of points within two dimensions
• series expansion: arithmetic series whose limit is equal to a function
• Sobolev approximation: tractable model used in specific kinds of spectral line analysis
• solid angle: three-dimensional analog of an angle
• spectral method: method of numerically solving differential equations
• spherical harmonics: harmonic functions on the surface of a sphere
• spheroid: sphere-like shape that is flattened or elongated
• stencil: pattern of input to numerical solutions at a point
• Stokes parameters: means of describing a polarization state
• Taub spacetime: early 1950s model for a rotating-black-hole spacetime
• Taub-NUT spacetime: early mathematics for a rotating black hole spacetime
• theoretical modified GR metric: metric devised to define modifications to GR
• theory of figures: type of model relating a planet's shape to its rotation
• time series analysis: analysis of data points collected at uniformly-separated times
• Toomre Q parameter: stability criterion for differentially rotating disks
• umbrella sampling: method usable in MCMC that avoids some problems
• Vlasov-Poisson equation: equation describing plasma ignoring the magnetic field
• window function: function with a zero value outside some specific range
• WKB method: method of numerically solving certain differential equations
• MATISSE: see European Southern Observatory Very Large Telescope
• Matplotlib: Python library for plotting
• matrix
• Krylov subspace method: efficient method of numerically solving sets of linear equations
• matrix mechanics: see Schrödinger equation
• matter density parameter: see Lambda-CDM model
• matter era: see radiation era
• matter power spectrum: see galaxy power spectrum
• matter wave: see de Broglie wavelength
• matter waves
• Compton wavelength: lower bound on a particle's possible de Broglie wavelength
• wave-particle duality: at atomic scale, things act like both particles and waves
• matter-antimatter asymmetry
• antimatter: similar to normal matter but with opposite electrical charge
• matter-dominated era: see radiation era
• Maui Optical Tracking and Identification Facility: USAF optical/infrared telescopes to Earth-orbiting objects
• Maui Space Surveillance Site: USAF observatory to track Earth-orbiting objects
• Mauna Kea: Hawaiian mountain, the site of observatories
  • Caltech Submillimeter Observatory: 10.4 meter submillimeter telescope previously in Hawaii
  • Canada-France-Hawaii Telescope: 3.6 meter optical/infrared telescope in Hawaii
  • Gemini Observatory: pair of telescopes in Hawaii and Chile
  • James Clerk Maxwell Telescope: far-infrared telescope in Hawaii
  • Keck Observatory: observatory in Hawaii with two 10-meter reflectors
  • Mauna Kea Observatories: observatories on Mauna Kea in Hawaii
  • Subaru Telescope: 8.2 meter telescope in Hawaii
  • Submillimeter Array: radio interferometer in Hawaii
  • Thirty Meter Telescope: extremely large telescope planned for Hawaii
  • United Kingdom Infrared Telescope: Mauna Kea 3.8 meter infrared telescope
• Mauna Kea Consortium
• MKO photometric system: 2000s system covering near infrared
• Mauna Kea Consortium photometric system (MKO photometric system): 2000s system covering near infrared
• Mauna Kea Observatories: observatories on Mauna Kea in Hawaii
  • Caltech Submillimeter Observatory: 10.4 meter submillimeter telescope previously in Hawaii
  • Canada-France-Hawaii Telescope: 3.6 meter optical/infrared telescope in Hawaii
  • Gemini Observatory: pair of telescopes in Hawaii and Chile
  • James Clerk Maxwell Telescope: far-infrared telescope in Hawaii
  • Keck Observatory: observatory in Hawaii with two 10-meter reflectors
  • Mauna Kea: Hawaiian mountain, the site of observatories
  • MKO photometric system: 2000s system covering near infrared
  • Subaru Telescope: 8.2 meter telescope in Hawaii
  • Submillimeter Array: radio interferometer in Hawaii
  • Thirty Meter Telescope: extremely large telescope planned for Hawaii
  • United Kingdom Infrared Telescope: Mauna Kea 3.8 meter infrared telescope
• Mauna Loa
• High Altitude Observatory: NCAR unit observing and monitoring the Sun
• Yuan-Tseh Lee Array: microwave interferometer in Hawaii
• Mauna Loa Solar Observatory
• High Altitude Observatory: NCAR unit observing and monitoring the Sun
• Maunakea Spectroscopic Explorer: see Canada-France-Hawaii Telescope
• Maunder Minimum: 1600s-1700s period of fewer sunspots
• MAVEN: Mars orbiter to study its atmosphere
• MAVIS: see European Southern Observatory Very Large Telescope
• Max Planck Gessellschaft (Max Planck Society): association of German research institutions
• Max Planck Institute for Astronomy: Heidelberg research institute
• Max Planck Institute for Radio Astronomy: Bonn research institute
• Max Planck Society: association of German research institutions
  • Max Planck Institute for Astronomy: Heidelberg research institute
  • Max Planck Institute for Radio Astronomy: Bonn research institute
• Max Wolf's catalog of stars with proper motion: early 20th century catalog of 1500 stars
• MAX38: see University of Tokyo Atacama Observatory
• MaxBCG: see rare designator prefixes
• MAXI: Japanese X-ray camera on the International Space Station
• MAXIMA: 1998-1999 balloon-borne 1.3-meter millimeter telescope
• maximum accretion rate: see accretion
• maximum baseline: see baseline
• maximum iron fraction: derived from planet-formation models
• maximum likelihood estimation: statistical method to find likely parameters
  • maximum likelihood mapmaking: method of making maps using varying data
  • mlmapper: software for maximum-likelihood mapmaking
• maximum likelihood mapmaking: method of making maps using varying data
  • mlmapper: software for maximum-likelihood mapmaking
• maxwell: see magnetic flux
  • gauss: measurement of magnetic field β
• Maxwell's demon
• Geroch-Bekenstein engine: hypothetical engine to overcome thermodynamics laws using a black hole
• Maxwell's equations: four equations describing electricity and magnetism
• Maxwell-Boltzmann distribution: distribution of velocities of gas particles
  • Boltzmann equation: equation relating atomic excitation to temperature
  • Gamow peak: relative speed most likely to cause atoms to fuse within a gas
  • Jeans escape: type of ongoing escape of gas particles from atmosphere
  • kappa distribution: one distribution of velocities of particles out of equilibrium
• Maxwell-Boltzmann equation: see Maxwell-Boltzmann distribution
• Maxwell-Boltzmann statistics
• Bose-Einstein statistics: possible distribution of particles not bound by Pauli exclusion
• Maxwell-Faraday equation
• magnetic induction: voltage across a conductor induced by changing magnetic field
• Maxwell's equations: four equations describing electricity and magnetism
• Mayall: see rare designator prefixes
• Mayall 4m
• NOAO Source Catalog: catalog compiled from NOAO public data
• Mayall 4m Telescope: 4 meter reflector telescope at Kitt Peak
  • BigBOSS: BOSS survey follow-on
  • Dark Energy Spectroscopic Instrument: new instrument for measuring red-shift of distant objects
  • Deep Lens Survey: investigating mass distribution of the universe
  • Deep Multicolor Survey: 1990s optical and infrared deep survey
  • Kitt Peak National Observatory: NOIRLab observatory in Arizona with Mayall telescope
  • National Optical Astronomy Observatory: previous name of US optical astronomy organization
  • NOAO Deep Wide-field Survey: survey investigating large scale structure of the universe
  • SKHB: survey of globular clusters in M31
  • SPACEWATCH: survey to study minor planets
  • Víctor M. Blanco Telescope: 4 meter reflector telescope in Chile
• Mayer: see rare designator prefixes
• Mazurek's law: the effect of tweaking parameters is counterbalanced by feedback
• MB: see rare designator prefixes
• MB20: see Parkes Observatory
  • Parkes Multibeam Pulsar Survey: late 1990s radio survey in search of pulsars
• MBA: see asteroid belt
• MBAC: see Atacama Cosmology Telescope
• Mbar: see atm
• mbar: see atm
• MBH: see black hole
• MBJD: see Julian date
• MBM: see rare designator prefixes
• Mbol (bolometric magnitude): absolute magnitude of all wavelengths
• MBR (cosmic microwave background): microwave radiation coming from every direction
• MBR: see Mars Observer
• MBS (synchrotron radiation): radiation emitted when high-speed charged particles are accelerated
• MC (Magellanic Clouds): two nearby galaxies
• MC (Mars crosser): asteroid with an orbit that crosses that of Mars
• MC: see HEAO-1
• MC: see rare designator prefixes
• MCA (Mars crosser): asteroid with an orbit that crosses that of Mars
• MCA: see double star designation
• MCA: see rare designator prefixes
• MCAL: see AGILE
• MCAO: see European Southern Observatory Very Large Telescope
• MCAO: see adaptive optics
• MCAT: see Galaxy Evolution Explorer
• MCC: see rare designator prefixes
• McDonald Observatory
• coudé focus telescope: type of Nasmyth telescope with additional mirrors
• Hobby-Eberly Telescope: 10 meter telescope in Texas
• NEWS: planned near-infrared spectrometer on Discovery Channel Telescope
• MCG (Morphological Catalogue of Galaxies): 1960s catalog from Palomar plates
• MCIN (Ministerio de Ciencia e Innovaciónes): Spanish science ministry
  • Astronet: European astronomy consortium
• MCL (Catalog of Southern Groups of Galaxies): list of southern groups assembled in 1980s
• MCLD: see molecular cloud
• McMath-Pierce Solar Telescope: see Kitt Peak National Observatory
• MCMC (Markov chain Monte Carlo): model technique to approximate multi-dimensional integrals
  • Monte Carlo method: mathematics and simulation using random samples
  • PyMC: Python package for Bayesian statistical modeling
  • spectral energy distribution: function or plot of brightness at each wavelength in the spectrum
• MCO (Mars Climate Orbiter): failed Mars 1990s probe
• MCPS (Magellanic Clouds Photometric Survey): UBVI survey of the Magellanic Clouds
• MCS: see Mars Reconnaissance Orbiter
• MCS: see Tianwen-1
• MCS: see rare designator prefixes
• MCT: see rare designator prefixes
• MCW: see rare designator prefixes
• MDI: see Solar and Heliospheric Observatory
• MDIS: see MESSENGER
• MDM Observatory: see Hiltner Telescope
• MDN (mixture density network): machine learning technique
• MDR: see MDR/SRR
• MDR/SRR: planning step for a NASA mission
• MDS (Medium Deep Survey): survey to find galaxies in HST WFPC2 images
• MDSCC: see NASA Deep Space Network
• Me: see rare designator prefixes
• mean anomaly: angle describing an object's position within an elliptical orbit
• mean cadence: see cadence
• mean free path: average length that a particle travels before interaction
• mean intensity: see intensity
• mean lifetime: see e-folding time
  • neutron capture: combination of an atomic nucleus and a neutron
• mean molecular weight: measurement of a gas usual for approximating in gas models
• mean specific intensity: see specific intensity
  • intensity: power reaching a surface from a specific source
• mean-field dynamo theory: see dynamo
• mean-field MHD: see dynamo
• mean-motion resonance: see orbital resonance
• MEarth (MEarth Project): automated observatories monitoring nearby red dwarfs for transits
  • Fred Lawrence Whipple Observatory: observatory near Amado, Arizona
  • GJ 1132 b: Earth-like extrasolar planet discovered in 2015
  • GJ 1214 b: super-Earth extrasolar planet discovered in 2009
• MEarth Project: automated observatories monitoring nearby red dwarfs for transits
• MEarth-North
• GJ 1214 b: super-Earth extrasolar planet discovered in 2009
• Mearth-North: see MEarth Project
• MEarth-South: see MEarth Project
  • GJ 1132 b: Earth-like extrasolar planet discovered in 2015
• measure
• AB system: monochromatic magnitude calibration based upon absolute values
• absolute magnitude: magnitude as would be seen from 10 parsecs
• absorption coefficient: measure of how much light a substance absorbs
• accretion rate: rate of addition of mass to an object
• airmass: measure of Earth-atmosphere attenuation for a telescope observation
• alpha-enhanced: metallicity with a high percentage of alpha elements
• amplitude: the height of a wave
• angular diameter: diameter of astronomical object in terms of its angle across the sky
• angular distance: measure of an angle across the sky
• angular resolution: measure of a telescope's ability to distinguish spatial detail
• antenna temperature: a type of measure of the noise introduced by an antenna
• apparent magnitude: magnitude as seen from Earth adjusted for Earth atmosphere
• balanced accuracy: average of true positive and negative rates
• bandwidth: number of hertz between minimum and maximum frequencies
• baroclinicity: measure of misalignment of fluid density and pressure
• baseline: distance between dishes of an interferometer
• beta: ratio of plasma pressure to magnetic pressure
• BJD: barycentric Julian day
• blue shift: shortening of wavelengths due to Doppler effects
• bolometric luminosity: total luminosity of an object at all wavelengths
• bolometric magnitude: absolute magnitude of all wavelengths
• bracket notation: notation for a comparison of an abundance ratio with that of the Sun
• brightness temperature: temperature of an equivalent black body in terms of spectral radiance
• chromospheric activity index: measure of magnetic activity of a star's chromosphere
• circular polarization ratio: ratio of circular polarization handedness in reflected radar signal
• cluster radius: radius of a galaxy cluster
• color index: a number that characterizes the color of an object
• color temperature: temperature-measure of a source based on a color index
• column density: measure of the matter through which EMR is passing
• combined differential photometric precision: calculated relation of photometric variation to SNR
• completeness: measure of how many of a survey's objects of a certain magnitude have been detected
• Compton wavelength: lower bound on a particle's possible de Broglie wavelength
• cosmic time: time since the Big Bang
• cosmological constant: force counteracting the universe's inward gravitational pull
• cosmological redshift: redshift of distant objects due to the Hubble expansion
• critical density: density of the universe which leaves it flat
• de Broglie wavelength: wavelength of a particle's matter wave
• deceleration parameter: measure of the Hubble expansion's deceleration
• declination: direction coordinate above/below celestial equator
• density parameter: ratio of a density with the critical density
• detective quantum efficiency: measure of instrument's ability to create images
• dispersion measure: to what degree an EMR signal's lower frequencies are delayed
• displacement: vector quantity showing the position of one point in relation to another
• distance: magnitude of the displacement or length of a curve
• distance modulus: apparent magnitude minus absolute magnitude
• e-folding time: time to increase by a factor of e
• eccentricity: degree to which an orbit is non-circular
• effective radius: radius of a galaxy within which 1/2 the light is emitted
• effective temperature: temperature of an equivalent black body in terms of total radiation
• elastic thickness: measure of the thickness of a sagging layer of a planet surface
• electromotive force: force that drives an electric current
• elevation range: measure of how high and low a telescope can be pointed
• ellipticity: degree to which a body's shape is un-spherical
• emission coefficient: measure of how much light a substance emits
• emissivity: measure of a material's efficiency at radiating thermal radiation
• energy density: energy per unit volume
• entropy: relative measure of the amount of usable energy available
• equilibrium temperature: temperature a planet would have if it were an externally-heated black body
• escape velocity: minimal velocity that allows something to overcome a body's gravity
• etendue: measure of how wide and deep a telescope observes
• exit pupil: size of the image as presented to the eye
• field of view: angular measure of how much an optical instrument can view
• flux: flow rate per unit area
• flux density: measure of the strength of a radio signal
• free-air anomaly: gravity's local variation after compensating for altitude
• frequency: number of cycles per unit of time, such as waves per second
• Fsky: fraction of the sky, e.g., what a survey covers
• full width at half maximum: a measure of the width of a hump-shaped curve
• g-r color: difference between SDSS g' and r' magnitudes
• galactic electron density: density of electrons in the ISM
• gas fraction: fraction of a galaxy or cluster consisting of gas
• gravitational redshift: redshift due to GR effects of gravity
• gravitational wave strain: a measure of the magnitude of a gravitational wave
• gravity anomaly: difference between measured gravity and that predicted by a model
• HI gas mass: mass of an object's atomic hydrogen
• Holmberg radius: a measure of size of galaxy based on surface brightness
• illumination: measure of light energy producing a telescope's image
• infrared excess: more infrared than that of a star's typical spectrum
• insolation: solar energy received per unit area in given time
• intensity: power reaching a surface from a specific source
• irradiance: EMR power reaching a surface
• J₂: geopotential coefficient regarding a planet's oblateness
• Jeans parameter: ratio measuring a tendency of an atmosphere to escape
• Julian calendar: calendar of 365 days and a leap day once every four years
• Julian date: time in days since noon UT November 24 4714 BC Gregorian
• K correction: correction to magnitude for redshift
• kinematic distance: distance to objects within Milky Way based on radial velocity
• kurtosis: measure of the probability of a distribution's tails
• limiting magnitude: faintest magnitude that a telescope or instrument can detect
• load density: measure of rigidity of the crust of a body
• Love number: measures of rigidity of a body
• luminosity: measure of brightness
• luminosity density: luminosity per unit volume
• luminosity distance: distance to an object based upon the distance's effect on received flux
• Mach number: ratio of flow-speed to sound-speed
• magnetic field strength: a field associated with magnetism
• magnetic flux: measure of magnetism passing through a surface
• magnetic flux density: vector field describing magnetism in relation to the Lorentz force
• magnetospheric truncation radius: radius at which the disc ram pressure matches the magnetic field pressure
• magnitude: a logarithmic measure of brightness
• mass: object's quality that determines the effects of forces and gravity
• mass density: mass per unit volume, as opposed to particle density
• mass fraction: measure of a constituent of a star, cloud, etc.
• mass-to-light ratio: measure of a population of stars or region
• mean anomaly: angle describing an object's position within an elliptical orbit
• mean molecular weight: measurement of a gas usual for approximating in gas models
• metallicity: metal fraction of an object
• metallicity gradient: the degree to which metallicity changes across a galaxy
• minimum mass: measured bound on the mass of an exoplanet
• moment of inertia factor: characterization of mass distribution within a planet
• monochromatic luminosity: luminosity at a specific wavelength
• neutron rich: more than usual neutrons
• noise temperature: a measure of noise in electronic devices
• noise-equivalent power: signal power that equals the noise
• number density: number of objects per volume
• opacity: a measure of opaqueness of a material
• optical depth: a measure of opaqueness of a path of light
• orbital inclination: angle between plane of an orbit and a reference plane
• orbital speed: speed of an orbiting body around the barycenter of a system
• parallax: angle due to different lines of sight
• particle number: number of particles
• peculiar velocity: velocity with respect to local rest
• permeability: ability of a material to allow fluids to pass through it
• photographic magnitude: magnitude derived from photographic plate
• photometric redshift: method of estimating redshift without spectroscopy
• photon energy: the energy carried by a single photon
• plate scale: relation between angle and distance across an image
• point source sensitivity: determination of how readily an instrument detects a point source
• pointing error: discrepancy in telescope's aim
• Population I: stars with substantial metallicity
• Population II: stars with lower metallicity
• Population III: stars with no metallicity
• porosity: fraction of the volume of solid material that is open or void
• position angle: indication of a direction across the celestial sphere
• Poynting vector: measures directional energy flux density
• precipitable water vapor: depth of liquid water equivalent to the atmosphere's water vapor
• projected semi-major axis: semi-major axis projected onto line-of-sight or plane of the sky
• projected separation: lower limit on distance between two objects in same part of the sky
• proper motion: apparent motion in relation to the position of the Sun
• quadratic field strength: a measure of a star's varying magnetic field
• quantum efficiency: measure of instrument's ability to sense EMR
• radiance: measure of EMR to/from a solid angle through an area
• radiant flux: measure of brightness
• radiative flux: power passing through a unit area
• radiative forcing: difference between a planet's incoming and outgoing radiation
• Rayleigh number: measure reflecting a fluid system's propensity to convection
• redshift: change to longer wavelengths due to Doppler effects
• redshift-angular size relation: how observed size of an object depends on its redshift
• redshift-magnitude relation: how apparent magnitude depends on redshift
• refractive index: measure of how much a material slows down light
• relaxation time: time associated with exponential falloff
• Reynolds number: measure reflecting a fluid system's propensity to turbulence
• right ascension: direction coordinate along celestial equator
• Rossby number: ratio of inertial to Coriolis force
• scan speed: the speed at which the telescope changes angle on the sky while observing
• semi-major axis: maximum radius of an ellipse
• sensitivity function: function of wavelength giving the sensitivity of an instrument
• sigma: indication of the confidence level of an experiment
• signal-to-noise ratio: ratio of the power of a signal to the power of the background noise
• solar day: length of a solar system planet or Moon's day
• sound speed: speed at which compression waves traverse a gas
• source function: measure indicating the effect of a material on EMR passing through
• specific angular momentum: absolute angular momentum divided by mass
• specific heat: ratio of added temperature to added heat for a material
• specific intensity: intensity per unit wavelength or frequency
• specific volume: ratio of volume to mass
• spectral flux density: flux or power of radiation per unit area per unit wavelength
• spectral index: power by which an object's flux depends on frequency
• spectral resolution: measure of a spectrograph's ability to resolve features of the spectrum
• spectral temperature: temperature-measure of a source based on a spectrum
• spectroscopic parallax: stellar distance determined through spectroscopy
• standard gravitational parameter: a body's mass times the universal gravitational constant
• star formation rate: rate at which material such as gas is turned into stars
• stellar population: grouping of stars according to metallicity
• Stokes number: measure of a particle's tendency to follow the flow of a fluid
• Stokes parameters: means of describing a polarization state
• Strehl ratio: measure of optical aberration
• surface abundance: quantity such as mass per surface area
• surface brightness: brightness per unit area of a surface
• surface gravity: measure of gravity at the surface of a body
• synodic period: period until a planet returns to the same position relative to the Sun
• systemic velocity: average velocity of grouped objects, such as a galaxy
• temperature: measure of hotness/coldness of matter
• thermal inertia: a measure of a material's ability to absorb heat through conduction
• Thomson optical depth: a measure of effects of Thomson scattering
• tidal Q: measure of orbital energy dissipated per orbit due to tidal forces
• Toomre Q parameter: stability criterion for differentially rotating disks
• tortuosity: describes something curved with many twists and turns
• torus coordinates: coordinates for toruses
• Vega system: magnitude calibration such that Vega has zero magnitude
• velocity dispersion: statistical dispersion of velocities of a group of objects
• virial parameter: calculated quantity showing whether a cloud is gravitationally bound
• water activity: measure of partial vapor pressure of water
• wavefront error: measure of a class of telescope distortion
• wavelength: distance over which a repeating wave repeats
• wavenumber: reciprocal of wavelength
• measurement
• aperture synthesis: interferometry to simulate a larger aperture telescope
• astrometry: precise measurement of the position and movement of stars
• CGS: metric system variant
• cosmic distance ladder: sequence of methods of measuring distance to astronomical objects
• Earth-sized VLBI: ground-based VLBI with near-maximal baseline
• electronic very-long-baseline interferometry: real-time VLBI using electronic links
• European VLBI Network: consortium of radio telescopes to coordinate VLBI efforts
• interferometer: device detecting EMR properties using interference between waves
• interferometry: analysis of superimposed EMR waves
• Lick indices: defined set of spectral line indexes for stars
• mass ratio: ratio of masses of two objects such as a binary star
• moving-cluster method: method of measuring distance to a nearby star cluster
• photon counting: sensing EMR down to the photon level
• Planck units: a set of units based on Planck constant and other fundamental constants
• polarimetry: measurement of polarization of EMR
• SI: standardized metric system
• sigma: indication of the confidence level of an experiment
• solar neutrino unit: unit for the detection rate of neutrino detectors
• solid angle: three-dimensional analog of an angle
• spectrography: charting the strengths of different electromagnetic wavelengths
• spectrometry: measuring the strengths of different electromagnetic wavelengths
• spectropolarimetry: measurement of light's polarization by wavelength
• spectroscopy: measurement of light with various electromagnetic wavelengths
• standard candle: astronomical object whose brightness can be determined
• standard ruler: astronomical phenomenon whose size can be determined
• standard siren: transient whose gravitational waves indicate a specific distance
• timescale: general length of time something takes
• very-long-baseline interferometry: interferometry based upon storing timing data at each telescope
• Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanet host Stars (MUSCLES): HST UV survey of some M Dwarfs that host exoplanets
• Measuring Oscillations in Nearby Stars: past plan for asteroseismology mission
• MEC: see Subaru Telescope
• MECA: see Phoenix
• mechanical equilibrium
• thermal equilibrium: state of a system with no net heat flows
• mechanics: the science of forces and motions
  • celestial mechanics: study of forces and motion of celestial objects
  • centripetal force: whatever force keeps an object moving in circles
  • de Broglie wavelength: wavelength of a particle's matter wave
  • frame of reference: region, possibly in motion, from which something is observed/considered
  • gravitational potential: conceptual field indicating the strength of gravity at each point
  • gravitational potential well: a dip in the gravitational-potential field
  • Hamiltonian: mathematical transform useful in mechanics
  • Jacobi integral: method of solving some three-body problems
  • quantum field theory: reworking of quantum mechanics incorporating fields
  • quantum mechanics: modern mechanical theory of small things, on the scale of atoms
  • reduced mass: the reciprocal of the sum of the reciprocals of the masses of two objects
  • standard gravitational parameter: a body's mass times the universal gravitational constant
  • statistical mechanics: mechanical behavior based upon probability
  • traditional approximation of rotation: approximation of waves on a rotating body
• mechanisms
• actuator: telescope control motor
• MECO (Magnetospheric eternally collapsing object): theoretical state of collapsing object unable to reach BH characteristics
• MECS: see BeppoSAX
• MEDA: see Mars 2020
• Medicina Radio Observatory
• Bologna Survey of Radio Sources: 1970s-1980s radio survey
• Mediterranean Sea
• KM3NeT: neutrino detector under construction in the Mediterranean Sea
• medium
• cosmic dust: dust in space such as interstellar dust
• intergalactic dust: dust not within galaxies
• Medium Deep Survey: survey to find galaxies in HST WFPC2 images
• Medium Explorers
• NASA: includes space-based astronomy research
• medium frequency
• high frequency: electromagnetic radiation, frequency 3-30 MHz
• medium-band photometric system
• Strömgren photometric system: four-color photometric system devised in 1950s
• Medium-class Explorer Program: NASA program for small science spacecraft
  • Advanced Composition Explorer: satellite collecting solar wind and cosmic rays
  • Far Ultraviolet Spectroscopic Explorer: early 2000s space telescope for short-wavelength ultraviolet
  • IMAGE­: satellite mission to study magnetosphere
  • RXTE: space mission to time X-ray variations
  • SPHEREx: all-sky spectral survey space-mission plan
  • THEMIS: set of satellites studying the Earth's magnetic field
  • Transiting Exoplanet Survey Satellite: observatory-satellite searching for transiting exoplanets
  • Wide-field Infrared Survey Explorer: infrared space telescope aimed at an all-sky survey
  • Wilkinson Microwave Anisotropy Probe: spacecraft that measured variations in the cosmic background radiation
• Medium-class explorer program
• Swift: satellite for studying gamma-ray bursts
• Medium-class Explorers Program
• FINESSE: planned space mission for exoplanet spectrography
• NASA: includes space-based astronomy research
• STAR-X: plan for a future X-ray space telescope
• Medium-Sized Telescope: see Cherenkov Telescope Array
• Medusae Fossae Formation: see Mars
• MeerKAT: new radio telescope in South Africa
• MeerKAT International GigaHertz Tiered Extragalactic Exploration Survey (MIGHTEE): radio survey of four established deep fields
• MeerKAT Large Area Synoptic Survey (MeerKLASS): 21-cm-line survey using MeerKAT
• MeerKAT Precursor Array
• MeerKAT: new radio telescope in South Africa
• MeerKAT Pulsar Timing Array: group of pulsars timed by MeerKAT
• MeerKLASS: 21-cm-line survey using MeerKAT
• MeerKLASS Pilot: see MeerKLASS
• MeerLICHT: South African telescope coordinated with MeerKAT
  • South African Astronomical Observatory: South African observatory with SALT telescope
• MeerTime: see MeerKAT Pulsar Timing Array
• MeerTime Pulsar Timing Array: see MeerKAT Pulsar Timing Array
• meeting
• American Workshop on Cometary Astronomy: renamed to be international, i.e., IWCA
• AMOS: Advanced Maui Optical and Space Surveillance Technologies Conference
• Asteroids, Comets, and Meteors: special-interest meeting
• IAU symposium: IAU-sponsored science symposiums
• International Astronomical Youth Camp: summer camp
• International Cosmic Ray Conference: bi-annual cosmic ray conference since 1947
• International Monitoring Programs for Asteroid and Comet Threat: 1999 IAU-sponsored conference in Italy
• International Workshop on Cometary Astronomy: occasional meeting
• Meeting of European Planetary & Cometary Observers: 1990s planet/comet observer meetings
• Toward Other Planetary Systems: workshops on developing techniques and observing programs
• Meeting of European Planetary & Cometary Observers: 1990s planet/comet observer meetings
• Mega-Carrington: 10³⁴ ergs, a million times that of the Carrington Event
• mega-Earth: rocky planet ten times the size of Earth
• megabar: see atm
• MEGACAM: see Magellan Telescopes
  • Panoramic Imaging Survey of Centaurus and Sculptor: survey of extended halos of two nearby galaxies
• MegaCam: see Canada-France-Hawaii Telescope
  • Canadian Cluster Comparison Project: multi-wavelength survey of fifty X-ray-selected galaxy clusters
  • CFHTLS: surveys of transients and stars
  • Dynamical Analysis of Nearby Clusters: survey of stars in stellar clusters
  • Multi-Epoch Nearby Cluster Survey: Type Ia supernova survey in clusters at z = 0.1
  • Supernova Legacy Survey: detect and monitor supernovae to measure the effects of dark energy
• Megacam: see MMT
• megaflare
• stellar flare: sudden brightening of a star
• megajansky: see jansky
• megamaser: see maser
• megamaser galaxy: see Messier 106
• MEGANE: see MMX
• megaparsec: see parsec
• MegaPrime: see Canada-France-Hawaii Telescope
  • Outer Solar System Origins Survey: 2013-2017 survey that searched for trans-Neptune objects
• MEGARA: see Gran Telescopio Canarias
• Meier paradox: mysterious decline in number of radio galaxy jets
• Mel: see Melotte Catalog
• MELACOM: see Mars Express
• Melb: see double star designation
• melilite
• CAI: calcium/aluminum specs in chondrites
• Melipal Telescope: see European Southern Observatory Very Large Telescope
• Melnick: see rare designator prefixes
• Melotte: see Melotte Catalog
• Melotte 25 (Hyades Cluster): nearest open cluster
• Melotte Catalog: 1915 catalog of open and globular clusters
• membrane paradigm: simplified black-hole model enabling calculation of some effects
• memorandum of understanding: agreement between NSF and other research entities
• memory burst (gravitational-wave memory): a gravitational wave that does not return
• MEMS: see gravimetry
• MEMS accelerometer: see gravimetry
• MEMS gravimeter: see gravimetry
• MENA: see IMAGE­
• MENeaCS (Multi-Epoch Nearby Cluster Survey): Type Ia supernova survey in clusters at z = 0.1
• MEPA: see Tianwen-1
• MEPAG (Mars Exploration Program Analysis Group): NASA forum to provide input to long-term planning of Mars missions
• MEPCO (Meeting of European Planetary & Cometary Observers): 1990s planet/comet observer meetings
• MER (Mars Exploration Rover): mission to Mars with two rovers
• MER-A: see Mars Exploration Rover
• MER-B: see Mars Exploration Rover
• Mercator Telescope: 1.2 m telescope in the Canary Islands
  • HERMES: four-channel spectrograph on the Anglo-Australian Telescope
  • Roque de los Muchachos Observatory: observatory at La Palma in the Canary Islands
• Mercer: see rare designator prefixes
• MERCURY: code to carry out N-body simulations
• Mercury: inner-most and smallest planet in the solar system
  • BepiColombo: mission to Mercury
  • MESSENGER: Mercury probe launched by NASA in 2004
  • solar system object: the Sun, solar system planets, minor planets, comets, and moons
• mercury barometer
• torr: unit of pressure approximating a millimeter of mercury on Earth
• Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER): Mercury probe launched by NASA in 2004
• mercury-manganese star: see chemically peculiar star
• merger (galaxy merger): combination of galaxies upon collision
• mergers
• black hole merger: two black holes meeting and forming one
• COMPAS: SPS code for compact object binaries
• final parsec problem: lack of a convincing theory on how SMBHs can reach each other
• galaxy merger: combination of galaxies upon collision
• Gini/M20: an automatable method of detecting whether a galaxy has recently merged
• kilonova: transient associated with merging neutron stars
• neutron star merger: two neutron stars meeting and forming one
• neutron-star black-hole merger: a neutron star falling into a black hole
• PCA analysis: an automatable method of determining galaxy morphology
• tidal arm: arm of gas and potentially stars leading from a galaxy
• tidal tail: string of mass ejected by a tidal forces in a neutron star merger
• Toomre sequence: model relating galaxy mergers to observation
• meridian: circle around the Earth passing through both poles
• meridian (celestial meridian): celestial sphere's meridian passing overhead
• meridian circle: instrument for timing the passage of stars over a meridian
  • Tokyo Photoelectric Meridian Circle: Japanese telescope to determine the position of stars and planets
• meridian telescope: see meridian circle
• meridian transit: see transit
• meridional current (meridional flow): north-south air circulation
• meridional flow: north-south air circulation
• MERLIN: VLBI array spread across England
• MEROPE: see Mercator Telescope
• MESA: collection of stellar astrophysics code
• meson: see particle
  • baryon: protons, neutrons, and other three-quark particles
  • pion: first type of meson discovered
  • quark: type of elementary particle incorporated in protons and neutrons
• mesopause: see atmospheric temperature profile
• mesosphere: see atmospheric temperature profile
• Message Passing Interface: mechanism for passing data between processors of a multiprocessor
• MESSENGER: Mercury probe launched by NASA in 2004
  • Mercury: inner-most and smallest planet in the solar system
• Messier: see Messier Catalog
• Messier 1 (Crab Nebula): supernova remnant in Taurus
• Messier 100: easily-observed spiral galaxy
• Messier 101 (Pinwheel Galaxy): easily-observed spiral galaxy
• Messier 104 (Sombrero Galaxy): striking spiral galaxy with very large bulge
• Messier 106: spiral galaxy with maser
• Messier 15: globular cluster with collapsed core
• Messier 31 (Andromeda): spiral galaxy in the Local Group
• Messier 33 (Triangulum Galaxy): small spiral galaxy in the Local Group
• Messier 45 (Pleiades): visible open cluster with seven B-stars
• Messier 64 (M64): nearby dusty galaxy
• Messier 67: old open cluster in Cancer
• Messier 74: easily-observed spiral galaxy
• Messier 77: easily-observed spiral galaxy
• Messier 82 (M82): nearby starburst galaxy
• Messier 84: elliptical galaxy with jets
• Messier 87 (M87): supergiant elliptical galaxy in local universe
• Messier Catalog: catalog of astronomical objects to avoid when looking for comets
• Messier Catalog (Messier Catalog): catalog of astronomical objects to avoid when looking for comets
• Messier Objects (Messier Catalog): catalog of astronomical objects to avoid when looking for comets
• MESUR Pathfinder (Mars Pathfinder): 1990s mission to Mars with rover
• MET: see Mars Polar Lander
• metal: in astrophysics, any element more massive than helium
  • aluminum: element, Al, atomic number 13
  • calcium: element, Ca, atomic number 20
  • carbon: element, C, atomic number 6
  • iron: metal, Fe, atomic number 26
  • lithium: metal, Li, atomic number 3
  • magnesium: element, Mg, atomic number 12
  • neon: element, Ne, atomic number 10
  • nickel: metal, Ni, atomic number 28
  • nitrogen: metal, N, atomic number 7
  • oxygen: element, O, atomic number 8
  • phosphorus: metal, P, atomic number 15
  • silicon: metal, Si, atomic number 14
  • sodium: metal, Na, atomic number 11
  • sulfur: metal, S, atomic number 16
  • titanium: metal, Ti, atomic number 22
• metal abundance
• metallicity: metal fraction of an object
• metal weak star (weak-line star): star with faint spectral lines compared to its spectral class
• metal-free stars
• metallicity: metal fraction of an object
• stellar population: grouping of stars according to metallicity
• metal-poor
• globular cluster: spherical group of stars orbiting a galaxy
• metal-poor carbon-enhance: see carbon star
• metal-poor cluster
• metallicity: metal fraction of an object
• metal-poor population
• metallicity: metal fraction of an object
• metal-poor star: see Population II
• metal-poor stars
• metallicity: metal fraction of an object
• stellar population: grouping of stars according to metallicity
• metal-rich
• globular cluster: spherical group of stars orbiting a galaxy
• metal-rich cluster
• metallicity: metal fraction of an object
• metal-rich population
• metallicity: metal fraction of an object
• metal-rich star: see Population I
• metal-rich stars
• metallicity: metal fraction of an object
• stellar population: grouping of stars according to metallicity
• metal-silicate equilibrium: see chemical equilibrium
• metallic helium: see metallic hydrogen
  • metal: in astrophysics, any element more massive than helium
• metallic hydrogen: a high-pressure state of hydrogen that is conductive
  • Jupiter: largest planet in the solar system
  • metal: in astrophysics, any element more massive than helium
• metallic-line star (Am star): A-type star with metallic lines
• metallicity: metal fraction of an object
  • age-metallicity relation: older stars generally have lower metallicity
  • chemically peculiar star: star with SED showing presence metals unusual for stars
  • extremely metal poor galaxy: galaxy of interest for its very low metallicity
  • G-dwarf problem: lack of metal-poor G dwarfs in the Milky Way
  • HK Survey: 1985 search for metal poor-stars using calcium lines
  • Honda-like star: very-low-metallicity star with r-process elements
  • Lambda Boötis star: peculiar star with metallicity only with lighter elements
  • mass fraction: measure of a constituent of a star, cloud, etc.
  • Milky Way chemical evolution: process of the development of metals in the Milky Way
  • Population I: stars with substantial metallicity
  • Population II: stars with lower metallicity
  • Population III: stars with no metallicity
  • SMSS J2003-1142: unusual giant star in Milky Way halo
  • stellar population: grouping of stars according to metallicity
• metallicity gradient: the degree to which metallicity changes across a galaxy
• metals
• alpha capture: combination of a nucleus and an incoming alpha particle
• alpha element: element created by alpha capture
• alpha process: synthesis of elements through alpha capture
• alpha-enhanced: metallicity with a high percentage of alpha elements
• iron peak: peak in the distribution of abundances surrounding iron
• iron peak element: element near the iron peak
• metallicity: metal fraction of an object
• metallicity gradient: the degree to which metallicity changes across a galaxy
• neutron rich: more than usual neutrons
• neutrons from carbon-13: process by which neutrons are freed in the s process
• p-process: synthesis of elements through proton capture
• photodisintegration: breakdown of a nucleus by a gamma ray
• r-process: synthesis of elements through neutron capture faster than beta decay
• rp-process: synthesis of elements through repeated proton capture
• s-process: synthesis of elements through neutron capture and beta decay
• trans-iron element: elements with atomic number greater than that of iron
• [α/Fe] versus [Fe/H] diagram: diagram indicating stars' degree of alpha enhancement
• metastable: characteristic of an excited state that lasts longer than typical
• metastable energy level: see metastable
• metastable helium line (helium 1083 nm line): line useful in probing exoplanet atmospheres
• meteor: see meteoroid
  • meteorite: rock found on Earth that is the remnant of a meteor
• meteor shower: see meteoroid
  • celestial event: something astronomical occurring visibly in the sky
• meteor stream: see meteoroid
• meteorite: rock found on Earth that is the remnant of a meteor
  • meteoroid: rocky object in solar system, smaller than an asteroid
• meteorite fall
• strewn field: region with fragments of a meteor impact
• meteorite type
• carbonaceous chondrite: stony meteorites with carbon compounds showing no melting
• chondrite: stony class of meteorites not modified by melting
• meteorites
• CAI: calcium/aluminum specs in chondrites
• presolar grain: grains of dust within meteorites predating the solar system
• meteoroid: rocky object in solar system, smaller than an asteroid
  • meteorite: rock found on Earth that is the remnant of a meteor
• meteors
• American Meteor Society: meteor-science promotion organization
• Automated Lunar and Meteor Observatory: ground observatory in Alabama to record Moon-meteoroid impacts
• International Meteor Organization: amateur/professional meteor organization
• North American Meteor Network: former group of amateurs with an interest in meteors
• strewn field: region with fragments of a meteor impact
• Virtual Meteor Observatory: online database of meteors
• zenith hourly rate: a meteor shower's maximum meteors/per/hour rate
• meter size barrier: a barrier to planet formation on the order of a meter diameter
  • barrier: challenging issue regarding planet formation
• meter-wave astronomy: see radio astronomy
• METH6: see Parkes Observatory
• methane: compound of one carbon and 4 hydrogen atoms
  • hydrocarbon: any compound of just carbon and hydrogen
• methane clathrate: see clathrate
• methane ice: see ice
• method
• angular differential imaging: using telescope rotation to suppress speckles
• CLEAN: algorithm to extract usable images from interferometry-produced images
• data folding: locating periods in data by trial
• fast folding algorithm: algorithm to find the periods of periodic data
• gyrochronology: means of estimating stellar age from rotation
• isochronal fitting: method of estimating stellar age from retrievable parameters
• kinemetry: method of determining galaxy kinematics through photometry
• lucky imaging: method of combining short-term images to yield better resolution
• Monte Carlo method: mathematics and simulation using random samples
• parameterized post-Newtonian formalism: method of approximating GR-based gravity from Newtonian gravity
• perturbation theory: breaking an equation into a solvable part and approximable part
• phase dispersion minimization: particular method of finding periodic components in signal
• post-Newtonian formalism: method of approximating GR-based mechanics from Newtonian mechanics
• reference star differential imaging: identifying speckles by comparing star-images
• shift-and-add: common speckle-suppression technique
• speckle imaging: method of combining short-term images to yield better resolution
• stacking: combining images of the same object
• synthetic field method: method of testing galaxy opacity
• Sys-Rem: algorithm to remove systematics from light curve data
• time series analysis: analysis of data points collected at uniformly-separated times
• traditional approximation of rotation: approximation of waves on a rotating body
• methyladyne (methylidyne): compound of one carbon and one hydrogen atom
• methylidyne: compound of one carbon and one hydrogen atom
• METIS: see European Extremely Large Telescope
• Metis: see Solar Orbiter
• Metis: see shepherd moon
• metric: mathematical generalization of the concept of distance
  • bigravity: modifications to GR defining two metrics
• Metropolis
• PyMC: Python package for Bayesian statistical modeling
• Metropolis algorithm
• umbrella sampling: method usable in MCMC that avoids some problems
• MeWe: see rare designator prefixes
• Mexico
• Chicxulub crater: ancient giant impact crater under Mexico and the Gulf of Mexico
• High-altitude Water Cherenkov Observatory: New Mexico gamma ray telescope using Cherenkov radiation
• Large Millimeter Telescope: large microwave telescope in Mexico
• Tonantzintla Surveys: surveys providing early images of quasars and Seyfert galaxies
• MF
• high frequency: electromagnetic radiation, frequency 3-30 MHz
• MFAA: see Square Kilometre Array
• MFF: see Mars
• MFFE: see Westerbork Synthesis Radio Telescope
• MFI: see QUIJOTE
• MG: see rare designator prefixes
• Mg (magnesium): element, Mg, atomic number 12
  • magnesium lines: spectral lines specific to magnesium
• Mg I: see magnesium lines
• Mg II: see magnesium lines
• Mg lines (magnesium lines): spectral lines specific to magnesium
• mGal: see Gal
  • admittance: effect of atmospheric pressure on gravity
• MGBK metric
• theoretical modified GR metric: metric devised to define modifications to GR
• MGC (Millennium Galaxy Catalogue): 2000s catalog of 10,000 galaxies
• MGC: see rare designator prefixes
• MGE
• Jeans anisotropic modeling: method of determining stellar kinematics of early type galaxies
• MGG: see rare designator prefixes
• MGRO: see Milagro
• MGS (Mars Global Surveyor): Mars probe launched by NASA in 1996
• MHA: see rare designator prefixes
• MHD (magnetohydrodynamics): dynamics of electrically conducting fluids
  • Alfvén wave: a type of transverse wave along magnetic field lines in plasma
  • AstroBEAR: MHD simulation system
  • Blandford-Payne mechanism: means of by which an accretion disk can power a jet
  • current sheet: slender sheet within a magnetic field where current flows
  • dynamo: mechanism for generating magnetic fields around astronomical bodies
  • Faraday rotation: rotation of optical polarization by a medium in a magnetic field
  • flux rope: rope-shaped structure in magnetic fields associated with coronal mass ejections
  • gas flow: dynamics of gas, plasma, i.e., compressible fluids
  • hydrodynamics: study of fluids in motion
  • LA-COMPASS: MHD-capable hydrodynamic code
  • MagIC: numerical code to for fluid dynamics including dynamos
  • magnetic arcade: series of arch-like magnetic flux lines on the Sun
  • magnetic tower: length of twisted magnetic field lines produced by rotating field
  • magnetorotational instability: instability in the fluid of a disk from MHD effects
  • magnetosonic wave: a type of sonic wave in a plasma
  • magnetospheric truncation radius: radius at which the disc ram pressure matches the magnetic field pressure
  • plasma astrophysics: includes cosmology, IGM, ISM, HI regions
  • plasma wave: wave incorporating the EM forces within plasma
  • shearing box: method of simulating 3D MHD in disks
  • SWMF: software package of tools for modeling space weather
• MHD drag
• Lorentz force: force on a point charge due to magnetic fields
• MHD dynamo (dynamo): mechanism for generating magnetic fields around astronomical bodies
• MHD wave (plasma wave): wave incorporating the EM forces within plasma
• MHO: see Fred Lawrence Whipple Observatory
• MHO: see rare designator prefixes
• mho (siemens): SI unit of electrical conductance
• MHS: see Mars 2020
• MI: see Mars Exploration Rover
• MI: see SELENE
• MIA: see CASA-MIA
• MICA (Multiyear Interactive Computer Almanac 1800-2050): ephemerides app created by USNO
• MICADO: camera planned for E-ELT
• MICADO: see European Extremely Large Telescope
• MICAS: see Deep Space 1
• Michelle: see Gemini Observatory
• Michelle: see United Kingdom Infrared Telescope
• Michelson interferometer: device to measure small changes in distance or light speed
  • imaging Fourier transform spectroscopy: Michelson-interferometer-based imaging spectroscopy
• Michelson-Morley experiment: see relativity
• Michigan Muon Array: see CASA-MIA
• Michigan Sun-to-Earth Model with Quantified Uncertainty and Data Assimilation: see SWMF
• micro black hole: see black hole
  • primordial black hole: black holes forming at the most dense volumes when inflation ceased
• micro-arcsecond: see arcsecond
• micro-bolometer: see bolometer
• microarcseconds: see arcsecond
• microcalorimeter: instrument to measure small amounts of heat
• microchannel: see microchannel array
• microchannel array: electronic device to EMR
• microchannel plate: see microchannel array
• microchannel plate detector (microchannel array): electronic device to EMR
• microelectromechanical systems: see gravimetry
• MicroFUN: observers following up on microlensing events in the galactic bulge
  • Probing Lensing Anomalies Network: survey that recorded microlensing event lightcurves
• microgal: see Gal
• microkelvin: see kelvin
• microlensing (gravitational microlensing): gravitational lensing by "small" objects such as individual stars and planets
  • EROS: search for MACHOs
  • GERLUMPH: hardware/software simulator of lensing light curves
  • GMAN: collaboration to alert on microlensing transients
  • gravitational lensing: focusing electromagnetic radiation by gravitational force
  • Korea Microlensing Telescope Network: survey searching for microlensing transients
  • MACHO Project: survey searching out microlensing that could indicate a MACHO
  • MicroFUN: observers following up on microlensing events in the galactic bulge
  • MOA: search for microlensing events
  • OGLE: survey searching for microlensing transients
  • OGLE-2005-BLG-390Lb: probable rocky planet orbiting red dwarf
  • POINT-AGAPE: survey of M31 for microlensing
  • Probing Lensing Anomalies Network: survey that recorded microlensing event lightcurves
• microlensing event: see gravitational microlensing
• Microlensing Follow-up Network (MicroFUN): observers following up on microlensing events in the galactic bulge
• Microlensing Observations in Astrophysics (MOA): search for microlensing events
• Microlensing Planet Search: program to follow up on microlensing detections
• MicrOmega: see Hayabusa2
• MicrOmega-IR: see Rosalind Franklin
• micrometeorite: see meteorite
• micrometeorite: see meteoroid
• micrometeoroid: see meteoroid
• micrometer
• heliometer: instrument to precisely measure angles across the sky
• microquasar: stellar-sized black hole with quasar-like activity
  • GRO J1655-40: microquasar
  • GRS 1915+105: stellar-mass black hole microquasar
• Microrover Flight Experiment: see Mars Pathfinder
• microsat (microsatellite): NASA term for a 10-100 kg small satellite
• microsatellite: NASA term for a 10-100 kg small satellite
  • CHIPS: small satellite to investigate ISM plasma
• microturbulence: see line broadening
• Microvariability and Oscillations of Stars (MOST): 2000s observatory-satellite looking for stellar oscillations
  • CSA: includes astronomical research
• microvariable: see variable star
• microwave: electromagnetic radiation, frequency 300 MHz to 300 GHz
  • 1.3-mm observation: observation frequency useful for detecting dust
  • ACBAR: instrument used in a CMB survey
  • Allen Telescope Array: array of radio telescopes in northern California for SETI
  • anomalous microwave emission: component of microwave background discovered in the 1990s
  • ARCADE: balloon-borne centimeter-wavelength surveyor
  • Arcminute Microkelvin Imager: pair of microwave arrays
  • Atacama Cosmology Telescope: 6-meter microwave survey telescope in Chile
  • Atacama Pathfinder Experiment: 12-meter submillimeter telescope in Chile
  • BOOMERanG: 1990s-2000s balloon-borne 1.3-meter millimeter telescope
  • C-BASS: 6 cm survey of the entire sky
  • CAPMAP: early 2000s array that surveyed CMB polarization
  • CMB Stage-4: planned 2020s-generation of ground CMB observations
  • Combined Array for Research in Millimeter-wave Astronomy: former array of radio telescopes in eastern California
  • confusion limit: limit on telescope imaging due to too many sources in the same region
  • Cosmic Background Explorer: 1989 satellite for surveying the CMB
  • Cosmic Background Imager: radio telescope in Chile observing the CMB
  • cosmic microwave background: microwave radiation coming from every direction
  • COSMOSOMAS: 1990s-2000s microwave survey
  • DASI: 2000-2003 South Pole CMB telescope
  • High Resolution Microwave Survey: 1990s microwave SETI search
  • LAMBDA: NASA archive center re CMB data
  • Large Millimeter Telescope: large microwave telescope in Mexico
  • maser: electromagnetic radiation amplified by stimulated emission
  • MAXIMA: 1998-1999 balloon-borne 1.3-meter millimeter telescope
  • NRAO VLA Sky Survey: 1990s microwave survey of 82% of the sky
  • Planck: microwave telescope in space
  • Plateau de Bure Interferometer: 6-dish interferometer in French Alps
  • Q band: name for EMR frequency-range on the order of 45 GHz
  • QUIJOTE: survey to measure the polarization of the CMB
  • Saskatoon: 1990s survey to measure CMB anisotropy
  • South Pole Telescope: a millimeter/microwave telescope at South Pole
  • SPIDER: 2015 balloon-borne observatory to observe CMB polarization
  • spinning dust emission: source of microwave signal
  • Sunyaev-Zel'dovich Array: array of eight 3.5 meter microwave telescopes
  • Taurus­: balloon-borne polarimeter to study the CMB
  • TolTEC: sensitive infrared camera under construction for the LMT
  • Wilkinson Microwave Anisotropy Probe: spacecraft that measured variations in the cosmic background radiation
• microwave amplification by stimulated emission of radiation (maser): electromagnetic radiation amplified by stimulated emission
• Microwave Anisotropy Probe (Wilkinson Microwave Anisotropy Probe): spacecraft that measured variations in the cosmic background radiation
• microwave astronomy: see microwave
• microwave astronomy: see millimeter astronomy
• microwave KID: see KID
• microwave radio (microwave): electromagnetic radiation, frequency 300 MHz to 300 GHz
• microwave radio astronomy: see microwave
• microwave radiometer: see radiometer
• microwave source: see microwave
• microwave source: see source
  • radio source: astronomical object producing observable radio
• mid infrared: infrared radiation with wavelengths in the 7.5-25 μm range
• mid-IR (mid infrared): infrared radiation with wavelengths in the 7.5-25 μm range
• Mid-scale Dark Energy Spectroscopic Instrument (Dark Energy Spectroscopic Instrument): new instrument for measuring red-shift of distant objects
• Mid-scale Innovations Program: see NSF AST
• MIDAS: see Rosetta
• Midcourse Space Experiment: 1990s space telescope
• middle ultraviolet: see ultraviolet
• MIDEX (Medium-class Explorer Program): NASA program for small science spacecraft
  • Advanced Composition Explorer: satellite collecting solar wind and cosmic rays
  • Far Ultraviolet Spectroscopic Explorer: early 2000s space telescope for short-wavelength ultraviolet
  • FINESSE: planned space mission for exoplanet spectrography
  • IMAGE­: satellite mission to study magnetosphere
  • NASA: includes space-based astronomy research
  • RXTE: space mission to time X-ray variations
  • SPHEREx: all-sky spectral survey space-mission plan
  • STAR-X: plan for a future X-ray space telescope
  • Swift: satellite for studying gamma-ray bursts
  • THEMIS: set of satellites studying the Earth's magnetic field
  • Transiting Exoplanet Survey Satellite: observatory-satellite searching for transiting exoplanets
  • Wide-field Infrared Survey Explorer: infrared space telescope aimed at an all-sky survey
  • Wilkinson Microwave Anisotropy Probe: spacecraft that measured variations in the cosmic background radiation
• MIDI: see European Southern Observatory Very Large Telescope
• Mie scattering: scattering of light by large particles
• Mie theory: see Mie scattering
• MIGHTEE: radio survey of four established deep fields
• migration
• baroclinicity: measure of misalignment of fluid density and pressure
• bouncing barrier: the problem that the seeds of planets would rebound rather than merge
• corotation resonance: orbit resonant with a nearby high-density portion of a disk
• corotation torque: a torque on a planet from co-orbiting planetary disk material
• dead zone: area within a disk where normal things don't happen
• electrostatic barrier: the problem that dust grains will repel and not join to form planet seeds
• fragmentation barrier: the problem that the seeds of planets would break apart rather than merge
• grand tack hypothesis: solar system formation model with Jupiter and Saturn migrating
• Lindblad torque: torque due to Lindblad resonances
• magnetorotational instability: instability in the fluid of a disk from MHD effects
• meter size barrier: a barrier to planet formation on the order of a meter diameter
• planetary migration: change in planet's orbit
• Poynting-Robertson effect: force that slows dust grains orbiting a star
• radial-drift barrier: the problem that forming planets would drift inward into the star
• radiation pressure: the pressure exerted by electromagnetic radiation
• tidal migration: interaction between tide and orbiting body that changes the orbit
• Yarkovsky effect: force on spinning, orbiting objects from asymmetric radiation
• Yarkovsky-O'Keefe-Radzievskii-Paddack effect: rotational effect on asymmetric asteroids
• MIKE: see Magellan Telescopes
• Mikheyev-Smirnov-Wolfenstein effect: effect of matter on neutrino oscillation
• Mikulski Archive for Space Telescopes (MAST): archive of data from surveys and missions
• MIL: see double star designation
• Milagro: gamma ray telescope using Cherenkov radiation
  • Fenton Hill Observatory: New Mexico GRB-oriented astronomical observatory
• Milkdromeda (Milkomeda): future galaxy resulting from merger of Milky Way and Andromeda
• Milkomeda: future galaxy resulting from merger of Milky Way and Andromeda
• Milky Way: our galaxy
  • age-metallicity relation: older stars generally have lower metallicity
  • age-velocity-dispersion relation: relation between stellar age and peculiar velocity
  • anomalous microwave emission: component of microwave background discovered in the 1990s
  • Atlas of Galactic Nebulae: 1980s catalog of Milky-Way nebulae
  • Baade's Window: region of sky allowing observation into the galactic center
  • BATC: photometric survey of Milky Way stars
  • Fermi bubbles: gamma-ray features associated with Milky Way center
  • Field of Streams: region of sky crossed by a number of stellar streams
  • Gaia Enceladus: galaxy that merged with the Milky Way
  • Galactic All-sky Survey: HI survey of the Milky Way
  • galactic anticenter: direction opposite the galactic center
  • galactic astronomy: astronomy confined to the Milky Way
  • galactic bulge: bulge of many stars in the center of the Milky Way
  • galactic center: region at the middle of the Milky Way
  • galactic coordinate system: celestial coordinate system system based upon the galactic plane
  • galactic north: determination of the more northern direction of the Milky Way's axis
  • galactic plane: plane in which the stars of the Milky Way reside
  • GALAH: survey of Milky Way with an emphasis on old structures
  • HI 4-Pi Survey: HI map based upon EBHIS and GASS
  • Kapteyn universe: early 20th century model of the universe centered on the Milky Way
  • kinematic distance: distance to objects within Milky Way based on radial velocity
  • Koposov I: low-luminosity globular cluster in the constellation Virgo
  • Koposov II: low-luminosity globular cluster in the constellation Gemini
  • Lockman hole: region of sky with little Milky-Way neutral hydrogen
  • Magellanic Clouds: two nearby galaxies
  • Magellanic Stream: series of high-velocity clouds associated with the Magellanic Clouds
  • Milkomeda: future galaxy resulting from merger of Milky Way and Andromeda
  • Milky Way chemical evolution: process of the development of metals in the Milky Way
  • Milky Way subgroup: the Milky Way and its satellites
  • Oort constants: two constants characterizing local Milky-Way motion
  • S-Star Cluster: stellar cluster at the center of the Milky Way
  • Sag A*: SMBH at the center of Milky Way
  • Scutum-Centaurus Arm: one of two spiral galaxy arms from the Milky-Way bar
  • Segue 3: faint star cluster i the constellation Pegasus
  • Smith Cloud: high-velocity cloud on collision course with Milky Way
  • solar circle: Sun's orbit around the Milky Way
  • solar neighborhood: Milky Way in the vicinity of the Sun
  • thick disk: disk-shaped set of older stars within the Milky Way
  • thin disk: disk-shaped set of younger stars within the Milky Way
  • velocity-metallicity relation: higher stellar velocity correlates with lower metallicity
  • VERA: VLBI project to map the Milky Way
  • zone of avoidance: region of sky obscured by Milky Way
• Milky Way chemical evolution: process of the development of metals in the Milky Way
• Milky Way Mapper: SDSS spectrographic survey of Milky Way stars
• Milky Way Mapper: see Sloan Digital Sky Survey
• Milky Way subgroup: the Milky Way and its satellites
• Milky Way subgroup: see galaxy group
  • galaxy subgroup: a major galaxy and its satellites
  • Magellanic Clouds: two nearby galaxies
  • satellite galaxy: galaxy that orbits a larger galaxy
• Milky-Way demographics: see demographics
• Millennium Galaxy Catalogue: 2000s catalog of 10,000 galaxies
• milli flux unit: see jansky
• milli-arcsecond: see arcsecond
• millibar: see atm
• milligal: see Gal
• millijansky: see jansky
• millikelvin: see kelvin
• millimeter
• Atacama Large Millimeter Array: large millimeter telescope array in Chile
• BIMA telescope: millimeter interferometer in operation 1985 to 2005
• DSHARP: ALMA survey of imageable protoplanetary disks
• IRAM 30m Telescope: millimeter-range radio telescope in Sierra Nevada, Spain
• millimeter astronomy: observation and analysis at wavelengths on the order of a millimeter
• multichroic feedhorn array: radio array with sensors for two or more bands
• NANTEN2: millimeter telescope in Chile
• RMS astronomy: collective term for radio, millimeter, and submillimeter
• Millimeter Anisotropy Experiment Imaging Array (MAXIMA): 1998-1999 balloon-borne 1.3-meter millimeter telescope
• Millimeter Array: see Owens Valley Radio Observatory
• Millimeter Astronomer's Legacy Team (Millimeter Astronomy Legacy Team): Australian initiative producing millimeter surveys
• millimeter astronomy: observation and analysis at wavelengths on the order of a millimeter
  • microwave: electromagnetic radiation, frequency 300 MHz to 300 GHz
  • submillimeter astronomy: astronomy observation and analysis of borderline infrared EMR
• Millimeter Astronomy Legacy Team: Australian initiative producing millimeter surveys
• millimeter wave: see microwave
• millimeter wave: see millimeter astronomy
• millimeter wave astronomy (millimeter astronomy): observation and analysis at wavelengths on the order of a millimeter
• Millimeter-wave Intensity Mapping Experiment: project to map CO and [CII]
• millimeter/submillimeter astronomy: see millimeter astronomy
  • radio astronomy: astronomy observation and analysis of radio EMR
  • submillimeter astronomy: astronomy observation and analysis of borderline infrared EMR
• million-body problem: see N-body problem
• millisecond magnetar: see magnetar
• millisecond pulsar: pulsar spinning with a period in the range of milliseconds
• millitorr: see torr
• Mills (Badgerys Creek Interferometer 101-MHz Survey): early 1950s survey of southern-hemisphere radio sources
• Mills Cross Array: see MSH Catalog
• Mills Cross Radio Telescope: see MSH Catalog
• Milne-Eddington model: see Schuster-Schwarzschild model
• MIMA: see Rosalind Franklin
• Mimas: see Saturn
  • moon: a planet's natural satellite, such as Earth's
• MIMI: see Cassini
• Mimir: multi-function near-infrared instrument on Perkins Telescope
• MIMIZUKU: see University of Tokyo Atacama Observatory
• MIMOS II: see Mars Exploration Rover
• MIMOS-II: see Rosalind Franklin
• min: see arcsecond
• MINERVA-II Rover 2: see Hayabusa2
• MINERVA-II Rover-1B: see Hayabusa2
• MINERVA-II-2: see Hayabusa2
• MINEVA-II Rover-1A: see Hayabusa2
• mini black hole: see black hole
• mini gas giant (mini-Neptune): planet with characteristics a bit like Earth but more like Neptune
• mini gas giant: see super-Earth
• mini-Neptune: planet with characteristics a bit like Earth but more like Neptune
  • super-Earth: exoplanet more massive than Earth but substantially less than Neptune
• mini-Neptunes: see extra-solar planet
• Mini-RF: see Lunar Reconnaissance Orbiter
• Mini-TES: see Mars Exploration Rover
• miniature black hole: see black hole
  • primordial black hole: black holes forming at the most dense volumes when inflation ceased
• Miniature X-ray Solar Spectrometer
• CubIXSS: solar spectrometer satellite concept
• minihalo: see dark matter halo
• minimal supersymmetric standard model: see supersymmetry
• minimum mass: measured bound on the mass of an exoplanet
• minimum mass solar nebula: see solar nebula
• minimum orbit intersection distance: smallest distance between paths of two orbiting bodies
• Ministerio de Ciencia e Innovaciónes: Spanish science ministry
• miniTAO: see University of Tokyo Atacama Observatory
• minkasi: code for processing MUSTANG-2 data
• Minkowski diagram (spacetime diagram): graph of simplified spacetime, with fewer space dimensions
• Minkowski metric: see metric
• Minkowski space: see spacetime
• minor merger: see galaxy merger
• minor planet: lesser solar system body without comet characteristics
  • 101955 Bennu: near-Earth asteroid that is the target of a sample-return mission
  • 10199 Chariklo: largest minor planet in the outer solar system
  • Ceres: dwarf planet and largest asteroid
  • Haumea: dwarf planet discovered in 2004
  • Pluto: dwarf planet formerly listed as one of the nine planets
  • Psyche: asteroid discovered in 1852
  • Sedna: distant solar system planetoid discovered in 2003
• Minor Planet Center: organization collecting and organizing minor planet data
• Minor Planet Circular: monthly IAU publication of observations of minor planets and comets
• Minor Planet Circulars Supplement: monthly detailed IAU publication of observations of minor planets
• Minor Planet Electronic Circular: daily news publication of IAU Minor Planet Center
• minor planet moon: see moon
• minor planets
• asteroid: minor planet without comet characteristics
• asteroid belt: ring of orbiting planetoids/asteroids
• asteroid family: set of asteroids based on similar orbits
• centaur: asteroid-like body orbiting among the outer planets
• damocloid: minor planet with a comet-like orbit
• Deep Ecliptic Survey: late 1990s/early 2000s survey for KBOs
• dwarf planet: round like a planet, only smaller
• Ephemerides of Minor Planets: annual catalog on minor planet positions
• Hills Cloud: cloud of comets and minor planets around the solar system
• Kuiper Belt: further part of solar system beyond Neptune
• LaSilla-QUEST Variability Survey: survey for transients
• Minor Planet Center: organization collecting and organizing minor planet data
• Oort Cloud: cloud of distant comets surrounding the solar system
• Oort Cloud Object: object in Oort Cloud such as a comet
• Outer Solar System Origins Survey: 2013-2017 survey that searched for trans-Neptune objects
• planetoid: an asteroid or physically similar body
• solar system object: the Sun, solar system planets, minor planets, comets, and moons
• SPACEWATCH: survey to study minor planets
• vulcanoid: theoretical asteroid orbiting within Mercury's orbit
• Minor Planets And Comets (Minor Planet Circular): monthly IAU publication of observations of minor planets and comets
• MINPA: see Tianwen-1
• Mintaka
• Orion: well-known constellation in the northern hemisphere
• minute: see arcsecond
• minute: see right ascension
• minute of arc: see arcsecond
• minute of right ascension: see arcsecond
• MinXSS
• CubIXSS: solar spectrometer satellite concept
• MIPS: see Spitzer Space Telescope
• MIPSGAL: see Spitzer Space Telescope
• MIR (mid infrared): infrared radiation with wavelengths in the 7.5-25 μm range
• Mir
• Glazar: 1980s UV space telescope on MIR space station
• International Space Station: long-term manned space station operated by numerous nations
• Kvant 1: scientific module on Mir space station
• Mira variable
• asymptotic giant branch: a second stage of helium burning in some stars
• pulsating star: variable star that varies through energy pulses
• MIRAC-BLINC: see MMT
• MIRADAS: see Gran Telescopio Canarias
• Miranda: see Uranus
  • moon: a planet's natural satellite, such as Earth's
• MIRI: see James Webb Space Telescope
• MIRI MRS: see James Webb Space Telescope
• MIRIM: see James Webb Space Telescope
• MIRO: see Rosetta
• mirror
• aspheric mirror: mirror with other than a spherical curvature
• deformable mirror: mirror that can be flexed for fine control
• fold mirror: flat mirror in a telescope to redirect the light
• liquid mirror telescope: reflector telescope with primary mirror formed of spinning liquid
• monolithic mirror: telescope mirror made of one piece of material
• null corrector: instrument for testing mirrors
• primary mirror: main mirror in a reflector telescope
• segmented mirror: a telescope mirror formed of an array of smaller mirrors
• mirror cell (mirror support cell): units in a telescope that support the mirror
• mirror support cell: units in a telescope that support the mirror
• MIRS: see MMX
• MIRSI: see IRTF
• MIS: see Galaxy Evolution Explorer
• Mis: see MISAO project
• misaligned gas
• quenched galaxy: galaxy currently producing minimal stars
• MISAO project: search for variable stars and transients
• MISC-T: see Origins Space Telescope
• miscibility
• supercritical fluid: state of matter at sufficient pressure and temperature
• miscible: see supercritical fluid
• MISE: see Europa Clipper
• missing baryon problem: standard theory suggests more baryonic matter than observed
• missing satellite problem (dwarf galaxy problem): theories have more dwarf galaxies than are observed
• mission
• Deep Impact: mission to create and observe an impact with a comet
• EPOXI: mission using Deep Impact for further exploration
• K2: second Kepler mission that worked around failed equipment
• Mission Definition Review: see MDR/SRR
• Mission Definition Review/System Requirements Review (MDR/SRR): planning step for a NASA mission
• Mission of Opportunity
• NASA: includes space-based astronomy research
• Mission Shakti: Indian antisatellite test.
• mission-based designator (survey-based designator): astronomical object designators based on name of survey
• missions
• MDR/SRR: planning step for a NASA mission
• PDR: review checking initial design with requirements
• RIX: enquiry/answer about some issue regarding a project review
• MIT
• Kavli Institute: any of a number of science institutes supported by Kavli Foundation
• MIT Cosmic X-ray Experiment: see OSO 7
• MIT General Circulation Model (MITgcm): well-known general circulation model
• MIT X-ray Burst Source Catalog: 1970s catalog of X-ray bursters
• MIT/OSO 7 Catalog of X-ray Sources: see OSO 7
• MITgcm: well-known general circulation model
• mixing length: see mixing length theory
  • convection: a heated fluid's flow due to its low density and buoyancy
• mixing length model (mixing length theory): tractable simplified model of convection
• mixing length theory: tractable simplified model of convection
• mixing ratio: ratio of two components of a gas
• mixture: type of probability distribution resulting from two others
• mixture: see mixture density network
• mixture density network: machine learning technique
• mixture distribution (mixture): type of probability distribution resulting from two others
• mixture model: see mixture
• Mizuguchi-Dragone design: see Dragone telescope
• MJD: see Julian date
• MJy: see jansky
• mJy: see jansky
• mK: see kelvin
• MK class (luminosity class): classification of size/luminosity of stars
• MK luminosity class (luminosity class): classification of size/luminosity of stars
• Mk1: see High Altitude Observatory
• Mk2: see High Altitude Observatory
• Mk3: see High Altitude Observatory
• Mk4: see High Altitude Observatory
• MKI: see Kavli Institute
• MKID: see KID
  • DESHIMA: submillimeter spectrometer
• MKII (Mark II): 38 m radio telescope in England
  • MERLIN: VLBI array spread across England
• Mkn (Markarian galaxy): list of galaxies with excess ultraviolet light
• MKO (Mauna Kea Observatories): observatories on Mauna Kea in Hawaii
  • Caltech Submillimeter Observatory: 10.4 meter submillimeter telescope previously in Hawaii
  • Canada-France-Hawaii Telescope: 3.6 meter optical/infrared telescope in Hawaii
  • Gemini Observatory: pair of telescopes in Hawaii and Chile
  • James Clerk Maxwell Telescope: far-infrared telescope in Hawaii
  • Keck Observatory: observatory in Hawaii with two 10-meter reflectors
  • Mauna Kea: Hawaiian mountain, the site of observatories
  • MKO photometric system: 2000s system covering near infrared
  • Subaru Telescope: 8.2 meter telescope in Hawaii
  • Submillimeter Array: radio interferometer in Hawaii
  • Thirty Meter Telescope: extremely large telescope planned for Hawaii
  • United Kingdom Infrared Telescope: Mauna Kea 3.8 meter infrared telescope
• MKO photometric system: 2000s system covering near infrared
• MKS
• SI: standardized metric system
• MKW: see rare designator prefixes
• ML (machine learning): use of programs that extract their algorithms from data
  • deep learning: description of machine learning using substantial neural networks
  • neural network: computer program structure inspired by the brain
  • nonparametric model: model developed avoiding assumptions regarding a basic structure
  • XGBoost: machine learning software
• ML mapmaking (maximum likelihood mapmaking): method of making maps using varying data
• ML Mapper (mlmapper): software for maximum-likelihood mapmaking
• ML technique: see machine learning
• MLA: see MESSENGER
• MLB: see double star designation
• MlbO: see double star designation
• MLE (maximum likelihood estimation): statistical method to find likely parameters
  • maximum likelihood mapmaking: method of making maps using varying data
• MLF: see double star designation
• mlmapper: software for maximum-likelihood mapmaking
• MLO: see double star designation
• MLR: see double star designation
• MLS: see Upper Atmosphere Research Satellite
• MLSO
• High Altitude Observatory: NCAR unit observing and monitoring the Sun
• Mly: see light-year
• MMA (multi-messenger astronomy): astronomy using more than one type of observation
• MMA: see Owens Valley Radio Observatory
• mmIME (Millimeter-wave Intensity Mapping Experiment): project to map CO and [CII]
• MMIRS: see MMT
• MMIRS: see Magellan Telescopes
• MMO: see BepiColombo
• MMR: see orbital resonance
• MMRTG: power source for space probes
• MMS (Magnetospheric Multiscale Mission): four spacecraft making Earth magnetosphere measurements
• MMS: see Tianwen-1
• MMSN: see solar nebula
• MMT: 6.5 meter telescope at Mt. Hopkins, Arizona
  • CfA Redshift Survey: 1970s-1990s surveys of galaxy redshifts
  • ELM Survey: survey of extremely-low-mass white dwarfs
  • Fred Lawrence Whipple Observatory: observatory near Amado, Arizona
  • H3 Survey: spectroscopic survey of Milky Way halo stars
  • HBK: study of M31 globular clusters
  • Multi-Epoch Nearby Cluster Survey: Type Ia supernova survey in clusters at z = 0.1
• MMT Observatory
• MMT: 6.5 meter telescope at Mt. Hopkins, Arizona
• MMT Spectrograph: see MMT
• MMT-pol: see MMT
• MMTCam: see MMT
• MMTO
• MMT: 6.5 meter telescope at Mt. Hopkins, Arizona
• MMX: Japanese probe to bring back a sample of a Martian moon
• MN metric
• theoretical modified GR metric: metric devised to define modifications to GR
• MNRAS (Monthly Notices of the Royal Astronomical Society): UK peer-reviewed astronomy research journal
• MO (Mars Observer): failed 1992-1993 Mars orbiter mission
  • NASA: includes space-based astronomy research
• MOA: search for microlensing events
• MOA-I: see MOA
• MOA-II: see MOA
• Mobile Anisotropy Telescope: see QMAP
• Mobile Astronomical System of Telescope Robot (MASTER Robotic Net): network of automated telescopes to identify transients
• MOC: see Mars Global Surveyor
• MOC: see Mars Observer
• MOCCA: code to model the evolution of stellar clusters
• mock catalog: catalog of simulated astronomical bodies
• mode: see CMB anisotropies
• mode: see spherical harmonics
• model
• ADAM: procedure to retrieve the shape of an asteroid
• alpha disk: well-known model of an accretion disk
• AREPO: cosmology simulation using moving mesh technique
• ARTEMIS: simulations of Milky-Way-like galaxy halos
• ATLAS Stellar Model: computer model of a stellar photosphere
• axion: proposed light, electrically neutral elementary particle
• Boltzmann equation: equation relating atomic excitation to temperature
• Bondi radius: radius within which a body moving through a medium will draw it in
• BT-Settl: model atmosphere of small stars and brown dwarfs
• Castro: hydrodynamics simulation software
• ChaNGa: cosmological-simulation project active since circa 2015
• CMBFAST: software to calculate CMB anisotropies
• COMPAS: SPS code for compact object binaries
• conditional luminosity function: function characterizing luminosity of galaxies with a given halo mass
• conditional stellar mass function: function characterizing galaxies within a halo of a given mass
• cosmological model: model of the workings and history of the universe
• Dartmouth Stellar Evolution Database: database relating isochrones to stellar parameters
• dense core mass function: function describing range of masses of dense cores
• DISORT: simulation of radiative transfer in an atmosphere
• Einstein-de Sitter model: universe tuned to the smallest expansion that continues forever
• flux-weighted gravity-luminosity relationship: method of determining luminosity of distant stars
• FORNAX: hydrodynamics simulation software
• Friedmann model: type of model of universe incorporating general relativity
• GADGET-2: an n-body/SPH simulation computer program
• GALFORM: semi-analytic galaxy formation model
• Gasoline: an SPH code
• HITEMP: spectroscopic parameters for modeling gas optics
• HITRAN: spectroscopic parameters for modeling atmospheric optics
• initial mass function: function describing initial mass of stars
• J₂: geopotential coefficient regarding a planet's oblateness
• Lambda-CDM model: Big-Bang cosmological model with a cosmological constant and cold dark matter
• luminosity function: function giving number of stars or galaxies at different luminosities
• magnetically arrested disk: mechanism for turning accretion into energy
• mass-luminosity relation: model relating stellar mass and luminosity
• mass-radius relation: model relating stellar mass and radius
• MITgcm: well-known general circulation model
• Navarro-Frenk-White profile: a dark matter spatial mass distribution function
• Nice model: model of the evolution of the solar system
• orrery: mechanical device to simulate the solar system
• PHOENIX stellar model: computer model of a stellar photosphere
• Press-Schechter formalism: cosmological model of how structures form from fluctuations
• PROMETHEUS/VERTEX: hydrodynamic simulation system
• RAMSES: hydrodynamic simulation system
• RHAPSODY: simulation of galaxy cluster dark-matter halos
• ROCKE-3D: rocky-planet-oriented general circulation model
• Romulus simulations: cosmological-simulation project active since circa 2015
• Saha equation: equation relating ionization to temperature
• smoothed-particle hydrodynamics: computational method for simulating fluid flows
• Sobolev approximation: tractable model used in specific kinds of spectral line analysis
• standard model: model of elementary particles including quarks
• STARBURST99: software to simulate star-forming galaxies
• StarTrack: stellar population synthesis code
• stellar birth rate function: function describing the birth rate of stars by mass
• supergravity: combination of general relativity and supersymmetry
• TAM: non-gray-RT 3D model of Titan's atmosphere
• Tolman VII object: theoretical object adhering to exact GR solution
• traditional approximation of rotation: approximation of waves on a rotating body
• UCLCHEM: code to simulate the chemical reactions due to heat
• wCDM: Big-Bang cosmological model with constant cosmological equation of state
• wind-momentum luminosity relationship: method of determining luminosity of distant stars
• WSA-Enlil: computer model of heliosphere for space weather prediction
• X-ray luminosity function: maps X-ray luminosities to count of such sources
• model BH (black hole model): description of a BH using math or computation
• model black hole (black hole model): description of a BH using math or computation
• models
• 2.5 dimensional model: model such as computer simulation between 2D and 3D
• adaptive mesh refinement: numerical modeling method balancing detail with tractability
• autoconversion rate: rate at which water changes from cloud droplets to new raindrops
• black hole model: description of a BH using math or computation
• correction term: term added to a formula to mitigate an imperfection
• dynesty: code for comparing the applicability of multiple models
• fiducial: taken as a standard
• gray atmosphere: a model atmosphere whose opacity does not depend upon wavelength
• Jeans anisotropic modeling: method of determining stellar kinematics of early type galaxies
• Kerr black hole: spinning black hole with no charge
• Markov chain Monte Carlo: model technique to approximate multi-dimensional integrals
• Mazurek's law: the effect of tweaking parameters is counterbalanced by feedback
• mock catalog: catalog of simulated astronomical bodies
• N-body simulation: simulation of many objects gravitationally-bound to each other
• nonparametric model: model developed avoiding assumptions regarding a basic structure
• one dimensional climate model: atmospheric model ignoring all horizontal motion
• passive dust: dust in a model that is influenced but does not influence
• plane wave: simplified wave concept useful for modeling
• planet structure: internal structure of planets
• quantum Monte Carlo: MC approach to difficult quantum mechanical problems
• radiative transfer code: computer model of a gas's radiative transfer
• radiative transfer model: models of radiative transfer, often computerized
• stellar evolution: the pattern of a star's changing structure over its life
• stellar model atmosphere: simulation of the star's production of emitted EMR
• stellar population synthesis: using spectral characteristics of galaxies to characterize their stellar populations
• stellar population synthesis code: software to perform stellar population synthesis
• stellar structure: the presumed internal structure of stars
• subgrid-scale physics: shortcuts handling physics on a smaller scale than a simulation's grid
• SWMF: software package of tools for modeling space weather
• synthetic spectrum: simulated spectrum, e.g., of a type of star
• three dimensional model: computer simulation handling variation in all three dimensions
• umbrella sampling: method usable in MCMC that avoids some problems
• modern constellation: see constellation
  • asterism: easily recognizable star pattern
• modified GR
• metric: mathematical generalization of the concept of distance
• modified GR bumpy Kerr metric
• theoretical modified GR metric: metric devised to define modifications to GR
• modified Julian day: see Julian date
• modified Newtonian dynamics: alternative theory to "dark matter"
• modified Urca process: see Urca process
• MODS: see Large Binocular Telescope
• MODS1: see Large Binocular Telescope
• MODS2: see Large Binocular Telescope
• Modular Open Source Fitter for Transients: see Astrocats
• Modular Open-Source Fitter for Transients (MOSFiT): code to match light-curves with light-curve models
• modulation
• frequency modulation: changing the frequency of a signal's carrier
• Modules for Experiments in Stellar Astrophysics (MESA): collection of stellar astrophysics code
• MOID (minimum orbit intersection distance): smallest distance between paths of two orbiting bodies
• MOIRCS: see Subaru Telescope
• moist greenhouse effect: see greenhouse effect
• MOJAVE: program to monitor AGN jet radio brightness and polarization
• mol (mole): unit roughly the count of hydrogen atoms in a gram
  • Avogadro's number: number of hydrogen atoms per gram
• MOLA: see Mars Global Surveyor
• MOLA: see Mars Observer
• mole: unit roughly the count of hydrogen atoms in a gram
• mole: see InSight
  • Avogadro's number: number of hydrogen atoms per gram
  • diffusion: the spreading of particles toward an even distribution
  • ideal gas law: relates pressure, temperature, and volume
• molecular cloud: interstellar gas cloud that includes molecules
  • CO to H₂ factor: assumed ratio between observed CO emission lines and H₂ mass
  • filament: linear volume of high molecular gas density within a galaxy
  • Nessie: star-forming filament found in the Orion star-forming region
  • Radcliffe wave: wave-shaped string of molecular clouds
• molecular cloud complex: see molecular cloud
• molecular cloud filament (filament): linear volume of high molecular gas density within a galaxy
• molecular cloud turbulence: observed turbulence in molecular clouds
• Molecular Deep Field: survey of molecular lines in Hubble Deep Field
• molecular gas
• CARMA EDGE: survey CO-mapping galaxies
• cold gas: gas cool enough to form galaxies and stars
• DeGaS-MC: APEX survey of potential star formation regions in the Magellanic Clouds
• EMPIRE Survey: survey of gas in M51a to follow up PAWS
• filament: linear volume of high molecular gas density within a galaxy
• PAH emissions: infrared emission from polycyclic aromatic hydrocarbons in gas clouds
• star formation rate: rate at which material such as gas is turned into stars
• molecular gas depletion time
• galaxy: gravitationally-bound group of stars
• molecular gas fraction: see gas fraction
• molecular handedness: mirror-imaged variants of some molecules
• molecular hydrogen: see hydrogen
  • alpha CO: ratio of CO emissions to H₂
  • Bok globule: dense molecular cloud
  • CO to H₂ factor: assumed ratio between observed CO emission lines and H₂ mass
  • dense core: dense molecular cloud
  • giant molecular cloud: interstellar gas cloud with molecules, thousands of solar masses
  • infrared dark cloud: molecular cloud not emitting nor transmitting infrared
  • Lyman-Werner photon: ultraviolet photon with proper energy to excite molecular hydrogen
  • molecular cloud: interstellar gas cloud that includes molecules
  • star-forming region: area forming stars and/or ready for star formation
• molecular hydrogen dissociation front: point in a gas cloud where it is hot enough to dissociate hydrogen
• molecular ISM: see interstellar medium
• molecular orbital: see electron orbital
• molecular star formation law: see star formation rate
• molecules
• RASCALL: efficient code to locate suspected molecular lines
• Molecules with ALMA at Planet-forming Scales (MAPS): ALMA survey researching planet-formation
• Mollweide projection: see HEALPix
• Molonglo Cross Telescope: see MOST­
• Molonglo Cross Telescope: see UTMOST
  • Molonglo Reference Catalog: 1981 catalog of mostly southern hemisphere radio sources
• Molonglo Observatory Synthesis Telescope (MOST­): radio telescope in New South Wales
• Molonglo Observatory Synthesis Telescope: see UTMOST
• Molonglo Radio Telescope
• Molonglo Reference Catalog: 1981 catalog of mostly southern hemisphere radio sources
• Molonglo Reference Catalog: 1981 catalog of mostly southern hemisphere radio sources
  • 1 Jansky Empty Field Survey: 1980s survey to find optical identifications for weak radio sources
  • USS Sources: catalog of sources with steep spectral index
• Molonglo Reference Catalog of Radio Sources (Molonglo Reference Catalog): 1981 catalog of mostly southern hemisphere radio sources
• molten core
• dynamo: mechanism for generating magnetic fields around astronomical bodies
• MOMA: see Rosalind Franklin
• MOMAG: see Tianwen-1
• moment of inertia: see moment of inertia factor
  • precession: periodic change in a body's rotation or orbit
• moment of inertia factor: characterization of mass distribution within a planet
• monatomic
• fluorescence: emission from a molecule excited by absorption
• MOND (modified Newtonian dynamics): alternative theory to "dark matter"
• Monitor of All-sky X-ray Image (MAXI): Japanese X-ray camera on the International Space Station
• Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments (MOJAVE): program to monitor AGN jet radio brightness and polarization
• Monoceros Ring: stellar stream wrapping around the Milky Way
  • Field of Streams: region of sky crossed by a number of stellar streams
• Monoceros Tidal Stream (Monoceros Ring): stellar stream wrapping around the Milky Way
• monochromatic luminosity: luminosity at a specific wavelength
• monochromator: see spectroscopy
• monolithic
• segmented mirror: a telescope mirror formed of an array of smaller mirrors
• monolithic collapse: see galaxy formation
• monolithic collapse model: see galaxy formation
• monolithic mirror: telescope mirror made of one piece of material
• monopole: see multipole expansion
• monopole: see topological defect
• MONS (Measuring Oscillations in Nearby Stars): past plan for asteroseismology mission
• monsoon
• intertropical convergence zone: circulation pattern near equator where north and south Hadley cells meet
• monsoon trough
• intertropical convergence zone: circulation pattern near equator where north and south Hadley cells meet
• Monte Agliate Supernova and Asteroid Survey: see supernova survey
• Monte Carlo
• Hyperion: Monte Carlo radiative transfer code
• Monte Carlo Cluster Simulator (MOCCA): code to model the evolution of stellar clusters
• Monte Carlo method: mathematics and simulation using random samples
• Monte Carlo method: see Markov chain Monte Carlo
  • MOCCA: code to model the evolution of stellar clusters
• Monthly Notices of the Royal Astronomical Society: UK peer-reviewed astronomy research journal
• Moon
• Artemis program: NASA's program in development to send people to the moon
• Automated Lunar and Meteor Observatory: ground observatory in Alabama to record Moon-meteoroid impacts
• complex crater: crater with central high-point
• Earth: third solar system planet from the Sun
• GRAIL: 2011 NASA lunar orbiters to collect gravity data
• In-situ Lunar Orientation Measurement: planned experiment to monitor lunar rotation via astrometry from the Moon
• LCROSS: space probe observing the lunar poles
• Lunar and Planetary Institute: scientific research arm of USRA
• Lunar Prospector: NASA 1998 lunar orbiter
• Lunar Reconnaissance Orbiter: space probe orbiting the Moon
• lunar swirl: swirly spot on the surface of the Moon
• lunar transient phenomenon: observed transient on the Moon such as a flash of light
• lunar water: water on the moon
• Lunary and Planetary Laboratory: U Arizona lab
• Moon formation: process by which the Moon and other moons formed
• phase angle: view angle of reflected light implied by the phase of the Moon
• SELENE: 2007-2008 Japanese lunar probe
• moon: a planet's natural satellite, such as Earth's
  • Callisto: well-known Jupiter moon
  • Enceladus: Saturn moon considered possible carrier of life
  • Europa: well-known Jupiter moon
  • Ganymede: well-known Jupiter moon
  • Io: well-known Jupiter moon
  • Titan: well-known Saturn moon
  • Triton: Neptune's one significant moon
• Moon formation: process by which the Moon and other moons formed
• Moon mass: see mass
• MoonKAM: see GRAIL
• moonmoon (subsatellite): object orbiting a moon
• moonquake: see quake
• MOONS (Multi-object Optical and Near-IR Spectrograph): advanced spectrograph under development for VLT
• MOONS: see European Southern Observatory Very Large Telescope
  • fiber positioner: machine to set up fibers in multi-object spectrograph
• moons
• cryovolcano: eruption of substances that are liquid or gas at cold temperatures
• host planet: the planet associated with a moon or ring, etc.
• irregular moon: moon with an atypical orbit, such as retrograde
• Moon formation: process by which the Moon and other moons formed
• planetary differentiation: stratification of the materials making up a planet
• retrograde orbit: orbit opposite the usual direction
• shepherd moon: small moon affecting outer edge of a planet's ring
• solar system object: the Sun, solar system planets, minor planets, comets, and moons
• subsatellite: object orbiting a moon
• tidal migration: interaction between tide and orbiting body that changes the orbit
• Mopra Spectrometer: see Mopra Telescope
  • The H2O Southern Galactic Plane Survey: survey of molecular clouds in the galactic plane
• Mopra Telescope: Australian 22 m radio telescope
  • Long Baseline Array: radio interferometer using Australian telescopes
  • The H2O Southern Galactic Plane Survey: survey of molecular clouds in the galactic plane
• MOPS: see Mopra Telescope
  • The H2O Southern Galactic Plane Survey: survey of molecular clouds in the galactic plane
• MOPTOP: see Liverpool Telescope
• MORA: high resolution 2-mm survey of a portion of the COSMOS field
• Moreton wave: type of wave moving across the chromosphere
  • Sun surface features: features on the Sun's surface
• Moreton-Ramsey wave (Moreton wave): type of wave moving across the chromosphere
• MORFEO: see European Extremely Large Telescope
• Morgan classification: classification of galaxies by stellar spectrum and morphology
  • N galaxy: galaxy with bright nucleus and faint surroundings
• Morgan galaxy classification (Morgan classification): classification of galaxies by stellar spectrum and morphology
• Morgan's classification (Morgan classification): classification of galaxies by stellar spectrum and morphology
• Morgan-Keenan classification system: see luminosity class
• Morgan-Keenan luminosity class (luminosity class): classification of size/luminosity of stars
• MoRIC: see Tianwen-1
• MORIS: see IRTF
• Morita Array: see Atacama Large Millimeter Array
• morning width: see horizontal coordinate system
• Morocco
• TRAPPIST: a ground-based automated transiting-planet finding telescope
• Morphological Catalog of Galaxies (Morphological Catalogue of Galaxies): 1960s catalog from Palomar plates
• Morphological Catalogue of Galaxies: 1960s catalog from Palomar plates
• morphological classification: see morphology
• morphological peculiarity: see peculiar galaxy
• morphology: form and structure
• morphology: see galaxy classification
  • galaxy: gravitationally-bound group of stars
• morphology-density relation: a galaxy is more likely to be elliptical if surrounded by galaxies
• MOSAIC: see European Extremely Large Telescope
• MOSAIC II: see Víctor M. Blanco Telescope
  • Multiwavelength Survey by Yale-Chile: optical/NIR survey of four deep fields
  • Supernova Cosmology Project: used supernova data to determine a history of the universe's expansion
• Mosaic3
• NOAO Source Catalog: catalog compiled from NOAO public data
• MOSES: see ESIS
• MOSFIRE: see Keck Observatory
• MOSFiT: code to match light-curves with light-curve models
• MOSFiT: see Astrocats
• MOSIR: see Tianwen-1
• MOST: 2000s observatory-satellite looking for stellar oscillations
  • CSA: includes astronomical research
• MOST­: radio telescope in New South Wales
• MOST­: see UTMOST
• MOTIF (Maui Optical Tracking and Identification Facility): USAF optical/infrared telescopes to Earth-orbiting objects
• MOU (memorandum of understanding): agreement between NSF and other research entities
• mount
• altazimuth mount: simple two-axis telescope mount
• equatorial mount: telescope mount with axis parallel to Earth's
• Mount Graham
• Submillimeter Telescope: 10-meter far-infrared telescope
• Mount Hopkins Observatory: see Fred Lawrence Whipple Observatory
• Mount Laguna Observatory
• Evryscope: automated array of telescopes to uncover transients
• Mount Palomar Observatory (Palomar Observatory): California observatory with Hale telescope
• Mount Sharp: see Mars Science Laboratory
• Mount Stromlo Observatory
• MACHO Project: survey searching out microlensing that could indicate a MACHO
• Mount Teide
• Teide Observatory: observatory on Mount Teide in the Canary Islands
• Mount Wilson Observatory: Los Angeles observatory with Hooker telescope
  • coudé focus telescope: type of Nasmyth telescope with additional mirrors
• Mount Wilson S-index (chromospheric activity index): measure of magnetic activity of a star's chromosphere
• moving cluster (moving group): observed group of stars with similar motion
• moving group: observed group of stars with similar motion
• moving group: see stellar association
  • stellar cluster: group of stars apparently formed by a single cloud
• moving mesh
• AREPO: cosmology simulation using moving mesh technique
• moving-cluster method: method of measuring distance to a nearby star cluster
• MOXE: see Spektr-RG
• MOXIE: see Mars 2020
• MOXSI: see CubIXSS
• MP: see USS Sources
• MP-Gadget
• Astrid simulation: cosmological simulation over z = 99 to 3
• MPA
• MeerKAT: new radio telescope in South Africa
• MPC (Minor Planet Center): organization collecting and organizing minor planet data
• MPC (Minor Planet Circular): monthly IAU publication of observations of minor planets and comets
• MPC: see HEAO-2
  • metallicity: metal fraction of an object
• Mpc: see parsec
• MPCS (Minor Planet Circulars Supplement): monthly detailed IAU publication of observations of minor planets
• MPEC (Minor Planet Electronic Circular): daily news publication of IAU Minor Planet Center
• MPF (Mars Pathfinder): 1990s mission to Mars with rover
• MPG (Max Planck Society): association of German research institutions
• MPG/ESO Telescope: see La Silla Observatory
  • Pre-OmegaTranS: transit search using MPG/ESO Telescope
• MPI (Message Passing Interface): mechanism for passing data between processors of a multiprocessor
• MPI PAF: see Parkes Observatory
• MPIA (Max Planck Institute for Astronomy): Heidelberg research institute
• MPIR (Max Planck Institute for Radio Astronomy): Bonn research institute
• MPL (Mars Polar Lander): failed 1999 Mars lander mission
• MPO: see BepiColombo
• MPP (Multi-Pinned-Phase): type of CCD with reduced signal noise
  • metallicity: metal fraction of an object
• MPPP: see Large Altazimuth Telescope
• MPS (Microlensing Planet Search): program to follow up on microlensing detections
• MPTA (MeerKAT Pulsar Timing Array): group of pulsars timed by MeerKAT
• MR: see Mars Global Surveyor
• MR: see rare designator prefixes
• MR-sn (magnetorotational supernova): type of core collapse supernova
• MRAO (Mullard Radio Astronomy Observatory): radio observatory near Cambridge, UK
  • Arcminute Microkelvin Imager: pair of microwave arrays
  • COAST: optical interferometer in England
  • Cosmic Anisotropy Telescope: 1990s interferometer to measure CMB variations
  • Interplanetary Scintillation Array: UK radio telescope that first detected pulsars
• MRC (Molonglo Reference Catalog): 1981 catalog of mostly southern hemisphere radio sources
  • 1 Jansky Empty Field Survey: 1980s survey to find optical identifications for weak radio sources
  • USS Sources: catalog of sources with steep spectral index
• Mre: see Reynolds number
• MRFE: see Mars Pathfinder
• MRI (magnetorotational instability): instability in the fluid of a disk from MHD effects
• Mrk: see Markarian galaxy
• Mrk 209 (Haro 29): a blue compact galaxy
• MRO (Mars Reconnaissance Orbiter): Mars probe launched by NASA in 2005
• MRO: see Murchison Widefield Array
  • Australian Square Kilometre Array Pathfinder: radio telescope array of 36 12-meter dishes
  • Mars: well-explored planet in the solar system
  • MRO Interferometer: optical interferometer in New Mexico
• MRO Interferometer: optical interferometer in New Mexico
  • optical interferometer: interferometer of visible light
• MROI (MRO Interferometer): optical interferometer in New Mexico
• MRP
• metallicity: metal fraction of an object
• MRS: see Hobby-Eberly Telescope
• MRS: see James Webb Space Telescope
• MS (main sequence star): star burning hydrogen into helium in its center
• MS: see HEAO-2
• MS galaxy: see galaxy main sequence
• MS lifetime (main-sequence lifetime): length of time that a star remains within the main sequence
• MS-DESI (Dark Energy Spectroscopic Instrument): new instrument for measuring red-shift of distant objects
• MSA: see MMX
• MSCam: see Tianwen-1
• MSDESI (Dark Energy Spectroscopic Instrument): new instrument for measuring red-shift of distant objects
• MSE: see BepiColombo
• MSE: see Canada-France-Hawaii Telescope
• MSH (MSH Catalog): 1950s catalog of radio sources from a Mills Cross survey
• MSH Catalog: 1950s catalog of radio sources from a Mills Cross survey
• MSI: see NEAR Shoemaker
• MSIP: see NSF AST
• MSIP1mm: see Large Millimeter Telescope
• MSL (Mars Science Laboratory): mission to Mars with rover
  • CSA: includes astronomical research
• MSM: see MMX
• MSM: see magnetar
• MSP (millisecond pulsar): pulsar spinning with a period in the range of milliseconds
• MSP: see rare designator prefixes
• MSS: see Galaxy Evolution Explorer
• MSS: see Hubble Space Telescope
• MSS: see Large Altazimuth Telescope
• MSSM: see supersymmetry
• MSSS (Maui Space Surveillance Site): USAF observatory to track Earth-orbiting objects
• MSSSO: Mount Stromlo and Siding Spring Observatories
• MST: see Cherenkov Telescope Array
• MSTEM-QUDA: see SWMF
• Msun (solar mass): mass unit representing the mass of the Sun
  • Sun: star at center of solar system
• MSW effect (Mikheyev-Smirnov-Wolfenstein effect): effect of matter on neutrino oscillation
  • tau neutrino: neutrino flavor that becomes a tau particle during interactions
• MSX (Midcourse Space Experiment): 1990s space telescope
• Mt. Bigelow
• Catalina Sky Survey: survey of near-Earth objects
• Mt. John University Observatory
• MOA: search for microlensing events
• Mt. Lemon
• Catalina Sky Survey: survey of near-Earth objects
• Mt. Stromlo 1.9 m telescope
• Microlensing Planet Search: program to follow up on microlensing detections
• MTL: see double star designation
• mTorr: see torr
• MTRLI: see MERLIN
• Mu Columbae
• O-type star: star with spectral characteristics of above 30000 K
• Mu Normae
• O-type star: star with spectral characteristics of above 30000 K
• Mu Space Engineering Spacecraft: series of Japanese astronomy space missions
• MUFASA: see SIMBA
• Mullard Observatory (Mullard Radio Astronomy Observatory): radio observatory near Cambridge, UK
• Mullard Radio Astronomy Observatory: radio observatory near Cambridge, UK
  • Arcminute Microkelvin Imager: pair of microwave arrays
  • COAST: optical interferometer in England
  • Cosmic Anisotropy Telescope: 1990s interferometer to measure CMB variations
  • Interplanetary Scintillation Array: UK radio telescope that first detected pulsars
• Multi Element Radio Linked Interferometer (MERLIN): VLBI array spread across England
• Multi-Adaptive Optics Imaging Camera for Deep Observations (MICADO): camera planned for E-ELT
• multi-anode microchannel array: see microchannel array
• multi-conjugate AO: see adaptive optics
• Multi-Epoch Nearby Cluster Survey: Type Ia supernova survey in clusters at z = 0.1
• multi-Gaussian expansion
• Jeans anisotropic modeling: method of determining stellar kinematics of early type galaxies
• Multi-instrument Aircraft Campaign: type of aircraft based study of meteor-shower-associated dust
• multi-messenger astronomy: astronomy using more than one type of observation
• multi-messenger astrophysics (multi-messenger astronomy): astronomy using more than one type of observation
• Multi-mission Radioisotope Thermoelectric Generator (MMRTG): power source for space probes
• Multi-object Optical and Near-IR Spectrograph: advanced spectrograph under development for VLT
• multi-object spectrograph: device to record the spectrum of multiple targets simultaneously
• multi-object spectrography: see multi-object spectrograph
• multi-object spectrometer (multi-object spectrograph): device to record the spectrum of multiple targets simultaneously
• Multi-Order Solar EUV Spectrograph: see ESIS
• Multi-Pinned-Phase: type of CCD with reduced signal noise
• Multi-site All-sky Camera (MASCARA): distributed array of telescopes to search for exoplanets
  • Roque de los Muchachos Observatory: observatory at La Palma in the Canary Islands
• multi-star system: see star system
• Multi-Telescope Radio Linked Interferometer: see MERLIN
• multi-wavelength data: see multi-messenger astronomy
• multichroic array (multichroic feedhorn array): radio array with sensors for two or more bands
• multichroic feedhorn array: radio array with sensors for two or more bands
• multilevel relaxation
• adaptive refinement tree: algorithm-type for solving n-body problem
• Multimission Archive for Space Telescopes (MAST): archive of data from surveys and missions
• multiple expansion
• CMB anisotropies: variations in the spectrum of the CMB
• Multiple Mirror Telescope
• MMT: 6.5 meter telescope at Mt. Hopkins, Arizona
• multiple star (multiple star system): system of two or more stars co-orbiting
• multiple star: see star system
  • binary star: system of two stars co-orbiting
• multiple star system: system of two or more stars co-orbiting
  • binary star: system of two stars co-orbiting
  • solar system: the Sun and what's gravitationally bound to it
• multiple-impact model: see Moon formation
• Multiplexed SQUID TES Array at Ninety GHz (MUSTANG): bolometer array on the Green Bank Telescope
• multiplicity fraction: fraction of star systems that are multiple-star systems
• multipole: see dipole
• multipole expansion: series expansion of a function over the surface of a sphere
  • angular power spectrum: method of characterizing the CMB
  • dipole: field with two poles
• multipole magnetic field: see magnetic field
• multipole moment: see spherical harmonics
  • CMB anisotropies: variations in the spectrum of the CMB
• multipole number: see spherical harmonics
  • CMB anisotropies: variations in the spectrum of the CMB
• Multitudinous Image-based Sky-survey and Accumulative Observations (MISAO project): search for variable stars and transients
• Multiwavelength Survey by Yale-Chile: optical/NIR survey of four deep fields
• Multiyear Interactive Computer Almanac 1800-2050: ephemerides app created by USNO
• Munich
• semi-analytic model: cosmological model combining analytic and other methods
• Munich Near-Infrared Cluster Survey: 1990s-2000s galaxy cluster survey
• MUNICS (Munich Near-Infrared Cluster Survey): 1990s-2000s galaxy cluster survey
• muon: see lepton
• muon: see particle
  • GRAPES-3: Cherenkov telescope at Ooty, India
  • standard model: model of elementary particles including quarks
  • supersymmetry: extension to standard model of particle physics
  • tau neutrino: neutrino flavor that becomes a tau particle during interactions
• muon neutrino: see tau neutrino
  • flavor: subtype of some type of particle
  • lepton: elementary particle with 1/2 integer spin such as electron
  • Mikheyev-Smirnov-Wolfenstein effect: effect of matter on neutrino oscillation
  • neutrino oscillation: neutrinos regularly morph into another flavor
  • standard model: model of elementary particles including quarks
• MUPUS: see Rosetta
• mUrca: see Urca process
• Murchison Radio-astronomy Observatory
• Australian Square Kilometre Array Pathfinder: radio telescope array of 36 12-meter dishes
• EDGES: survey aiming at highly-redshifted 21-cm detection
• Murchison Widefield Array: low frequency radio telescope
• Murchison Widefield Array: low frequency radio telescope
• Murriyang (Parkes Observatory): Australian observatory with large single-dish radio telescope
• MuSCAT3: see Las Cumbres Observatory
• MUSCLES: HST UV survey of some M Dwarfs that host exoplanets
• MUSE: see European Southern Observatory Very Large Telescope
• MUSES (Mu Space Engineering Spacecraft): series of Japanese astronomy space missions
• MUSES-C: see Hayabusa2
• MUSIC: see Caltech Submillimeter Observatory
• MUSTANG: bolometer array on the Green Bank Telescope
• MUSTANG: see Green Bank Telescope
• MUSTANG-2: see Green Bank Telescope
• MUSTANG-2: see MUSTANG
• MUSYC (Multiwavelength Survey by Yale-Chile): optical/NIR survey of four deep fields
• MUV: see ultraviolet
• MVIC: see Lucy
• MW (Milky Way): our galaxy
• MWA (Murchison Widefield Array): low frequency radio telescope
• MWA-128: see Murchison Widefield Array
• MWC: see rare designator prefixes
• MWC 480
• MAPS: ALMA survey researching planet-formation
• MWC 758: protostar with spiral disk
• MWD: see white dwarf
• MWM (Milky Way Mapper): SDSS spectrographic survey of Milky Way stars
• MWM: see Sloan Digital Sky Survey
• MWO (Mount Wilson Observatory): Los Angeles observatory with Hooker telescope
• MWR: see Juno
• MX: see OSO 7
• Mx: see magnetic flux
• MXB (MIT X-ray Burst Source Catalog): 1970s catalog of X-ray bursters
• MXRB: see X-ray binary
• MyCn: see rare designator prefixes
• MYSO: see young stellar object
• Mz: see rare designator prefixes