Term Index (M)
Astrophysical terms and names of things beginning with the letter 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
- 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
- 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
- M31 subgroup
- M31GC: see rare designator prefixes
- M31N: see rare designator prefixes
- M32
- M33 (Triangulum Galaxy): small spiral galaxy in the Local Group
- M33 subgroup
- M42 (Orion Nebula): easily-observed nebula that includes SF regions
- M45 (Pleiades): visible open cluster with seven B-stars
- M51
- M51a (Whirlpool Galaxy): easily-observed spiral galaxy
- M64: nearby dusty galaxy
- M67 (Messier 67): old open cluster in Cancer
- M74 (Messier 74): easily-observed spiral galaxy
- M77 (Messier 77): easily-observed spiral galaxy
- M81
- M82: nearby starburst galaxy
- M83
- 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
- M87*: see M87
- M94
- 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
- Mbol (bolometric magnitude): absolute magnitude of all wavelengths
- Mc (chirp mass): a reduced-mass-like quantity that relates to gravitational waves
- MEarth
- solar mass: mass unit representing the mass of the Sun
- MJupiter
- solar mass: mass unit representing the mass of the Sun
- ms (spin): an angular-momentum quantum number
- MSun (solar mass): mass unit representing the mass of the Sun
- mu (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
- 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
- Maclaurin spheroid
- 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
- 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
- Maffei 2
- 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
- Magdalena Ridge Observatory Interferometer (MRO Interferometer): optical interferometer in New Mexico
- 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
- 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
- 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
- Magellanic Stream: series of high-velocity clouds associated with the Magellanic Clouds
- 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
- MAGIC-II: see MAGIC
- magma ocean: presumed to occur early in Earth history and potentially on exoplanets
- magnesium: element, Mg, atomic number 12
- magnesium lines: spectral lines specific to magnesium
- magnetar: neutron star with a strong magnetic field
- magnetar flare: see magnetar
- magnetars
- 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
- magnetic braking (magnetic dipole braking): the effect of a reduction in the spinning of a magnetic field
- 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 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
- 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
- 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
- magnetized molecular cloud
- 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
- 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
- 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
- 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
- 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
- main sequence star: star burning hydrogen into helium in its center
- 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
- Makemake
- 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
- MANIFEST: see Giant Magellan Telescope
- TAIPAN: multi-object spectrograph with robot fiber-positioner
- manifold
- Manko and Novikov metric
- mantle
- 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
- 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
- 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
- Markov chain Monte Carlo: model technique to approximate multi-dimensional integrals
- MAROON-X: see Gemini Observatory
- MARS: see Parkes Observatory
- MaRS: see Mars Express
- Mars: well-explored planet in the solar system
- 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
- MARVELS Spectrograph: see Sloan 2.5m Telescope
- Marvin: see MaNGA Stellar Library
- Maryland
- mas: see arcsecond
- MASCAM: see Hayabusa2
- MasCam: see Mars Science Laboratory
- MASCARA: distributed array of telescopes to search for exoplanets
- MASCOT: see Hayabusa2
- MASCS: see MESSENGER
- maser: electromagnetic radiation amplified by stimulated emission
- 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
- 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
- mass conservation equation: see stellar structure
- mass continuity equation: see stellar structure
- mass density: mass per unit volume, as opposed to particle density
- mass extinction: event in which many species went extinct
- mass fraction: measure of a constituent of a star, cloud, etc.
- mass function: measure of binaries that constrains the masses
- mass gap: see stellar-mass black hole
- 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
- 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
- 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
- mathematical analysis
- mathematical field: function of three variables, potentially representing space
- mathematics
- MATISSE: see European Southern Observatory Very Large Telescope
- Matplotlib: Python library for plotting
- matrix
- 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
- 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
- Mauna Kea Consortium
- Mauna Kea Consortium photometric system (MKO photometric system): 2000s system covering near infrared
- Mauna Kea Observatories: observatories on Mauna Kea in Hawaii
- Mauna Loa
- Mauna Loa Solar Observatory: solar observatory on Mauna Loa
- 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 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
- maxwell: see magnetic flux
- gauss: measurement of magnetic field β
- Maxwell's demon
- 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
- Maxwell-Faraday equation
- Mayall: see rare designator prefixes
- Mayall 4m
- Mayall 4m Telescope: 4 meter reflector telescope at Kitt Peak
- 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
- 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
- MCG (Morphological Catalogue of Galaxies): 1960s catalog from Palomar plates
- MCIN (Ministerio de Ciencia e Innovaciónes): Spanish science ministry
- 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
- 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
- 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
- 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
- measurement
- 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
- mechanics: the science of forces and motions
- mechanisms
- 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
- Mediterranean Sea
- KM3NeT: neutrino detector under construction in the Mediterranean Sea
- medium
- Medium Deep Survey: survey to find galaxies in HST WFPC2 images
- Medium Explorers
- NASA: includes space-based astronomy research
- medium frequency
- medium-band photometric system
- Medium-class Explorer Program: NASA program for small science spacecraft
- 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
- MeerTime: see MeerKAT Pulsar Timing Array
- MeerTime Pulsar Timing Array: see MeerKAT Pulsar Timing Array
- meeting
- 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
- MegaCam: see Canada-France-Hawaii Telescope
- Megacam: see MMT
- megaflare
- megajansky: see jansky
- megamaser: see maser
- megamaser galaxy: see Messier 106
- MEGANE: see MMX
- megaparsec: see parsec
- MegaPrime: see Canada-France-Hawaii Telescope
- 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
- Mercer: see rare designator prefixes
- MERCURY: code to carry out N-body simulations
- Mercury: inner-most and smallest planet in the solar system
- 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
- 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
- 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
- metal weak star (weak-line star): star with faint spectral lines compared to its spectral class
- metal-free stars
- metal-poor
- metal-poor carbon-enhance: see carbon star
- metal-poor cluster
- metal-poor population
- metal-poor star: see Population II
- metal-poor stars
- metal-rich
- metal-rich cluster
- metal-rich population
- metal-rich star: see Population I
- metal-rich stars
- 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
- metallicity gradient: the degree to which metallicity changes across a galaxy
- metals
- 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
- 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
- meteorite type
- 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
- 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
- methane clathrate: see clathrate
- methane ice: see ice
- method
- 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
- MeWe: see rare designator prefixes
- Mexico
- MF
- 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
- 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
- MGC (Millennium Galaxy Catalogue): 2000s catalog of 10,000 galaxies
- MGC: see rare designator prefixes
- MGE
- 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
- MHD drag
- 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
- 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
- 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
- microgal: see Gal
- microkelvin: see kelvin
- microlensing (gravitational microlensing): gravitational lensing by "small" objects such as individual stars and planets
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- Mira variable
- 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
- 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
- MISAO project: search for variable stars and transients
- MISC-T: see Origins Space Telescope
- miscibility
- 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 Mauna Loa Solar Observatory
- Mk2: see Mauna Loa Solar Observatory
- Mk3: see Mauna Loa Solar Observatory
- Mk4: see Mauna Loa Solar 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
- 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
- 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 (Mauna Loa Solar Observatory): solar observatory on Mauna Loa
- 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
- 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
- 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
- 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
- modern constellation: see constellation
- asterism: easily recognizable star pattern
- modified GR
- metric: mathematical generalization of the concept of distance
- modified GR bumpy Kerr metric
- 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
- 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
- MOLA: see Mars Global Surveyor
- MOLA: see Mars Observer
- mole: unit roughly the count of hydrogen atoms in a gram
- mole: see InSight
- 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
- 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 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 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
- Monoceros Tidal Stream (Monoceros Ring): stellar stream wrapping around the Milky Way
- monochromatic luminosity: luminosity at a specific wavelength
- monochromator: see spectroscopy
- monolithic
- 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
- monsoon trough
- 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
- 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
- moons
- Mopra Spectrometer: see Mopra Telescope
- Mopra Telescope: Australian 22 m radio telescope
- MOPS: see Mopra Telescope
- 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
- 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
- Mosaic3
- 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
- Mount Graham
- 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
- Mount Wilson Observatory: Los Angeles observatory with Hooker telescope
- 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
- 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
- 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
- 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
- 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
- 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
- MRC (Molonglo Reference Catalog): 1981 catalog of mostly southern hemisphere radio sources
- 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
- MRO Interferometer: optical interferometer in New Mexico
- MROI (MRO Interferometer): optical interferometer in New Mexico
- MRP
- 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
- Mt. John University Observatory
- MOA: search for microlensing events
- Mt. Lemon
- Mt. Stromlo 1.9 m telescope
- 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
- 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
- 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
- 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
- Multimission Archive for Space Telescopes (MAST): archive of data from surveys and missions
- multiple expansion
- 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
- multiple star system: system of two or more stars co-orbiting
- 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
- multipole magnetic field: see magnetic field
- multipole moment: see spherical harmonics
- multipole number: see spherical harmonics
- 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
- 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
- MUPUS: see Rosetta
- mUrca: see Urca process
- Murchison Radio-astronomy Observatory
- 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
Index