Term Index (M)
- M:
- M band:
- infrared (IR): electromagnetic radiation, wavelength 0.74-300 micrometers
- M dwarf: small, cool main-sequence star in stellar class M
- brown dwarf (BD): star-like object with less mass than a star
- M-type star (M): spectral class of star with a temperature in the vicinity of 2500 K
- m sin i:
- minimum mass (m sin i): 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:
- M-type star (M): spectral class of star with a temperature in the vicinity of 2500 K
- M-class star:
- M-type star (M): 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 (M): spectral class of star with a temperature in the vicinity of 2500 K
- m.f.u.:
- jansky (Jy): unit of measurement of spectral flux density
- M/L:
- M1:
- M100:
- Messier 100 (M100,NGC 4321): easily observed spiral galaxy
- M101:
- M102:
- Spindle Galaxy (NGC 5866): striking spiral galaxy with very large bulge
- M104:
- M106:
- M110:
- M15:
- Messier 15 (M15): globular cluster with collapsed core
- M20:
- Gini/M20: an automatable method of detecting whether a galaxy has recently merged
- M31:
- Andromeda (M31): spiral galaxy in the Local Group
- HBK: study of M31 globular clusters
- Milkomeda: future galaxy resulting from merger of Milky Way and Andromeda
- PAndAS: survey of M31 and M33
- POINT-AGAPE: survey of M31 for microlensing
- SKHB: survey of globular clusters in M31
- M31 subgroup:
- galaxy subgroup: group of fifty or fewer gravitationally bound Milky-Way-sized galaxies
- M32:
- M33:
- M33 subgroup:
- galaxy subgroup: group of fifty or fewer gravitationally bound Milky-Way-sized galaxies
- M42:
- Orion Nebula (M42, NGC 1976): easily observed nebula that includes SF regions
- M45:
- Pleiades (M45): visible open cluster with seven B-stars
- M51:
- M51a:
- M64: nearby dusty galaxy
- M74:
- Messier 74 (M74,NGC 628): easily observed spiral galaxy
- M81:
- M82: nearby starburst galaxy
- M83:
- M84:
- M87: supergiant elliptical galaxy in local universe
- M87*: SMBH at the center of galaxy M87
- M87*: SMBH at the center of galaxy M87
- M87*:
- M87: supergiant elliptical galaxy in local universe
- M94:
- M20:
- Gini/M20: an automatable method of detecting whether a galaxy has recently merged
- M500:
- Mbol:
- Mc:
- chirp mass (Mc,ℳ): a reduced-mass-like quantity that relates to gravitational waves
- ms:
- electron orbital: a nucleus's "locations" where an electron can orbit
- spin (ms): an angular-momentum quantum number
- MSun:
- solar mass (MSun,Msun): mass unit representing the mass of the Sun
- Ma_Miss:
- MAC:
- Mach angle:
- expansion fan: the "sound" of a supersonic flow flowing around a convex corner
- Mach number: ratio of a flow with the speed of sound
- Mach's principle: the notion that rotation is relative to all the mass of the universe
- machine learning:
- MACHO: proposed astronomical objects comprising dark matter
- dark matter: matter suggested by gravity in galaxies and galaxy clusters
- MACHO Project: survey searching out microlensing that could indicate a MACHO
- MACHO Project: survey searching out microlensing that could indicate a MACHO
- MACHOs:
- EROS: search for MACHOs
- GMAN: collaboration to alert on 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
- Macquarie/AAO/Strasbourg Hα Planetary Galactic Catalog:
- MacrOmega:
- MMX: Japanese probe to bring back a sample of a Martian moon
- macronova:
- kilonova (KN): explosive event larger than a nova and smaller than a supernova
- MACS:
- MAD:
- Madelung equations: quantum hydrodynamic equations
- Madrid Deep Space Communications Complex:
- MAESTRO:
- MMT: 6.5 meter telescope at Mt. Hopkins, Arizona
- Maffei:
- Maffei 1:
- Council of Giants: twelve large galaxies surrounding the Local Group
- IC 342: spiral galaxy in the Council of Giants
- Maffei 2:
- MAG:
- Advanced Composition Explorer (ACE): satellite collecting solar wind and cosmic rays
- Cassini: explorer spacecraft sent to Saturn
- Galileo: circa 1990s space mission to Jupiter
- Giotto: 1980s space mission carrying out a Comet Halley flyby
- IMAP: future solar science probe
- Juno: mission to Jupiter
- MAVEN: Mars orbiter to study its atmosphere
- NEAR Shoemaker (NEAR): space mission aiming to return a sample of an asteroid
- Solar Orbiter (SolO): Sun-observing satellite in development
- Voyager: space probes to observe planets and the edge of the solar system
- MAG/ER:
- MagAO:
- Magdalena Ridge Observatory:
- Magdalena Ridge Observatory Interferometer:
- MAGE:
- Magellan: 1980s/1990s Venus probe
- Magellan Planet Search Program:
- Magellan Telescopes: pair of 6.5 m optical telescopes in Chile
- Magellanic Bridge: hydrogen cloud joining the Magellanic Clouds
- Magellanic Catalogue of Stars (MACS): 1980s/1990s survey of stars in Magellanic Clouds
- Magellanic Clouds:
- Magellanic Clouds Photometric Survey (MCPS): UBVI survey of the Magellanic Clouds
- Magellanic Clouds Survey:
- Magellanic spiral:
- Magellanic spiral galaxy:
- Magellanic Stream: series of high-velocity clouds associated with the Magellanic Clouds
- MagIC: numerical code to for fluid dynamics including dynamos
- magma ocean: presumed to occur early in Earth history and potentially on exoplanets
- magnesium (Mg): element, Mg, atomic number 12
- magnesium lines (Mg lines): spectral lines specific to magnesium
- magnetar: neutron star with a strong magnetic field
- magnetar flare:
- magnetar: neutron star with a strong magnetic field
- magnetars:
- magnetic:
- magnetic anomaly: variation in a body's magnetic field
- magnetic arcade: series of arch-like magnetic flux lines on the Sun
- magnetic breaking:
- magnetic diffusivity:
- Reynolds number (Re): 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 spin-down:
- magnetic dynamo:
- dynamo: mechanism for generating magnetic fields around astronomical bodies
- magnetic energy:
- magnetic energy density:
- magnetic energy spectrum: spatial spectral density of the energy associated with magnetic fields
- magnetic field: magnetic force as distributed over a space
- magnetic field intensity:
- magnetic field lines:
- field lines: lines showing the pattern of a mathematical field
- magnetic field strength (H,H field): a field associated with magnetism
- magnetic fields:
- magnetic flux (Φ): total magnetism passing through a surface
- magnetic flux density (B): vector field describing magnetism in relation to the Lorentz force
- magnetic induction: voltage across a conductor induced by changing magnetic field
- magnetic monopole:
- magnetic permeability:
- permeability (κ,k): ability of a material to allow fluids to pass through it
- magnetic power spectrum:
- magnetic pressure:
- magnetic quantum number:
- magnetic reconnection: change in magnetic topology within a fluid
- magnetic Reynolds number:
- Reynolds number (Re): measure reflecting a fluid system's propensity to turbulence
- magnetic spots:
- magnetic white dwarf:
- white dwarf (WD): stellar remnant of mostly electron degenerate matter
- magnetism:
- magnetized molecular cloud:
- magnetizing field:
- magneto-brems:
- magneto-bremsstrahlung:
- magneto-hydrodynamics:
- magneto-plasma system:
- magnetoacoustic wave:
- magnetobremsstrahlung:
- magnetohydrodynamics (MHD): dynamics of electrically conducting fluids
- magnetometer: instrument to measure the strength of a magnetic field
- magnetopause:
- magnetosphere: area around an object where its magnetic field dominates
- magnetorotational instability (MRI): instability in the fluid of a disk from MHD effects
- magnetorotational turbulence:
- magnetosonic wave: a type of sonic wave in a plasma
- magnetosphere: area around an object where its magnetic field dominates
- Magnetospheric Multiscale Mission (MMS): four spacecraft making Earth magnetosphere measurements
- magnetospheric truncation radius: radius at which the disc ram pressure matches the magnetic field pressure
- magnetoturbulence:
- magnification:
- magnitude: a logarithmic measure of brightness
- Magnitude-redshift relation:
- MAIA:
- main asteroid belt:
- main belt:
- main belt asteroid:
- main lobe:
- beam: portion of a sky that a radio telescope is viewing
- main sequence:
- main sequence fitting: cluster star distance determined through fitting with the H-R diagram
- main sequence galaxy:
- main sequence star (MS,V): star burning hydrogen into helium in its center
- main-sequence lifetime (MS lifetime): length of time that a star remains within the main sequence
- main-sequence turn-off point:
- turn-off point (TO): point in H-R diagram of a cluster where stars turn red
- MAJIS:
- JUICE: mission to Jupiter in development
- major circle of latitude:
- circle of latitude: circle around the Earth of points equidistant from a pole or the equator
- major merger:
- Makemake:
- MAKO:
- Malin:
- Malmquist bias: selection bias from detecting only the brighter objects
- Mamajek:
- MaNGA:
- MANIFEST:
- manifold:
- mantle:
- many-body problem:
- N-body problem: calculating the paths of gravitationally-interacting celestial objects
- MAORY:
- MAP:
- mapmaking:
- destriping: removing streak-like noise from images
- March equinox:
- J2000.0 equinox: equinox as of the J2000.0 epoch used as a positional reference
- MARCI:
- MARDI:
- Maria:
- Mariner:
- Mars: well-explored planet in the solar system
- Mariner 10:
- Mercury: inner-most and smallest planet in the solar system
- Mark:
- Mark I:
- Mark II (MKII): 38 m radio telescope in England
- Markarian:
- Markarian galaxy (Mkn): list of galaxies with excess ultraviolet light
- Markov chain:
- Markov Chain Monte Carlo:
- 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 Atmosphere and Volatile Evolution:
- MAVEN: Mars orbiter to study its atmosphere
- Mars Atmospheric and Gravity Experiment:
- Mars crosser (MC,MCA): 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 Rover (MER): mission to Mars with two rovers
- Mars Express: Mars probe launched by ESA in 2003
- Mars Geoscience/Climatology Orbiter:
- Mars Global Surveyor (MGS): Mars probe launched by NASA in 1996
- Mars Observer (MO): failed 1992-1993 Mars orbiter mission
- radio science: radar and other methods of using radio to probe planets and moons
- Mars Pathfinder (MPF): 1990s mission to Mars with rover
- Mars Phoenix:
- Phoenix: Mars polar-region probe launched by NASA in 2007 with lander
- Mars Polar Lander (MPL): failed 1999 Mars lander mission
- Mars Reconnaissance Orbiter (MRO): Mars probe launched by NASA in 2005
- Mars: well-explored planet in the solar system
- Mars Science Laboratory (MSL): mission to Mars with rover
- Mars Weather Research and Forecasting Model:
- MarsWRF: Mars-oriented general circulation model
- Mars-crossing asteroid:
- Mars crosser (MC,MCA): asteroid with an orbit that crosses that of Mars
- Mars-XRD:
- MARSIS:
- MarsWRF: Mars-oriented general circulation model
- MART-LIME:
- Spektr-RG (SRG, SXG): Russian-German X-ray observatory launched in 2019
- 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:
- MARVELS Spectrograph:
- mas:
- arcsecond (arcsec,sec,second of arc): a 3600th of an angular degree
- MasCam:
- MASCARA: distributed array of telescopes to search for exoplanets
- maser: electromagnetic radiation amplified by stimulated emission
- maser emission:
- maser: electromagnetic radiation amplified by stimulated emission
- masers:
- hydroxyl (OH): neutral compound of hydrogen and oxygen, one atom each
- OH/IR source: AGB star with strong OH maser
- MASH Catalog of Planetary Nebulae: 995 possible planetary nebulae
- mask:
- masking:
- MASPEX:
- mass: object's quality that determines the effects of forces and gravity
- mass conservation equation:
- mass continuity equation:
- mass density: density of a volume of space
- 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:
- mass loading: moving gas gaining mass from clouds or stars
- mass loss: a star's reduction in mass
- mass number:
- Avogadro's number (NA): roughly number of hydrogen atoms in a 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
- mass: object's quality that determines the effects of forces and gravity
- radioactive decay: changes in atomic nuclei that happen over time
- mass ratio (μ,q): ratio of masses of two objects such as a binary star
- binary star: system of two stars co-orbiting
- chirp mass (Mc,ℳ): 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
- spectrometer: device to measure light by wavelength across its spectrum
- mass spectrometry:
- mass spectrometer: device to determine the mass of molecules in a mixture
- 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-to-light ratio (M/L,ϒ): measure of a population of stars or region
- mass/age degeneracy:
- brown dwarf (BD): star-like object with less mass than a star
- massive astrophysical compact halo object:
- MACHO: proposed astronomical objects comprising dark matter
- massive black hole:
- black hole (BH): region of such high mass that light cannot escape
- Massive Cluster Survey (MACS): survey of distant clusters evident in ROSAT X-ray data
- massive compact halo object:
- MACHO: proposed astronomical objects comprising dark matter
- massive X-ray binary:
- massive young stellar object:
- MAST: archive of data from surveys and missions
- Mastcam-Z:
- Mars 2020: Mars rover mission currently on Mars after 2021 landing
- MASTER:
- MASTER Global Robotic Telescopes Net:
- MASTER Robotic Net: network of automated telescopes to identify transients
- MAT:
- QMAP: mid 1990s balloon-based CMB survey
- MAT/TOCO:
- QMAP: mid 1990s balloon-based CMB survey
- materials:
- mathematical field: function of three variables, potentially representing space
- mathematics:
- MATISSE:
- matrix:
- matrix mechanics:
- matter density:
- Lambda-CDM model (ΛCDM,LCDM): Big-Bang cosmological model with a cosmological constant and cold dark matter
- matter era:
- radiation era: early universe era when radiation pressure dominated
- matter power spectrum:
- matter wave:
- matter waves:
- matter-antimatter asymmetry:
- antimatter: similar to normal matter but with opposite electrical charge
- matter-dominated era:
- radiation era: early universe era when radiation pressure dominated
- Mauna Kea: Hawaiian mountain, the site of observatories
- Mauna Kea Consortium:
- Mauna Kea Consortium photometric system:
- Mauna Kea Observatories (MKO): observatories on Mauna Kea in Hawaii
- Mauna Loa:
- Mauna Loa Solar Observatory:
- MAVEN: Mars orbiter to study its atmosphere
- Max Planck Institute for Astronomy (MPIA): Heidelberg research institute
- Max Planck Institute for Radio Astronomy (MPIR): Bonn research institute
- Max Planck Society:
- Max Wolf's catalog of stars with proper motion: early 20th century catalog of 1500 stars
- MAX38:
- MAXI: Japanese X-ray camera on the International Space Station
- MAXIMA: 1998-1999 balloon-borne 1.3-meter millimeter telescope
- maximum accretion rate:
- accretion: enlargement of an astronomical body by gravitationally attracting additional mass
- maximum baseline:
- baseline: distance between dishes of an interferometer
- maximum iron fraction: derived from planet-formation models
- maximum likelihood estimation:
- maximum likelihood mapmaking: method of making maps using varying data
- maxwell:
- gauss (G,Gs): measurement of magnetic field β
- magnetic flux (Φ): total magnetism passing through a surface
- 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
- Maxwell-Boltzmann equation:
- Maxwell-Boltzmann statistics:
- Maxwell-Faraday equation:
- Mayall:
- Mayall 4m Telescope: 4 meter reflector telescope at Kitt Peak
- Mayer:
- Mazurek's law: the effect of tweaking parameters is counterbalanced by feedback
- MB:
- MB20:
- MBA:
- MBAC:
- mbar:
- MBH:
- black hole (BH): region of such high mass that light cannot escape
- MBJD:
- Julian date (JD): time in days since noon UT November 24 4714 BC Gregorian
- Mbol:
- MBR:
- MBS:
- MC:
- MCA:
- Mars crosser (MC,MCA): asteroid with an orbit that crosses that of Mars
- MCAL:
- AGILE: Italian space gamma-ray observatory
- MCAO:
- adaptive optics (AO): optical instruments that dynamically adapt to atmospheric distortion
- MCAT:
- MCC:
- McDonald Observatory:
- MCG:
- MCINN:
- McMath-Pierce Solar Telescope:
- MCMC:
- MCPS:
- MCS:
- MCW:
- MDI:
- MDR:
- MDR/SRR: planning step for a NASA mission
- MDR/SRR: planning step for a NASA mission
- MDS:
- MDSCC:
- Me:
- mean anomaly: angle describing an object's position within an elliptical orbit
- mean cadence:
- cadence: period between observations
- mean free path: average length that a particle travels before interaction
- mean intensity:
- intensity: power reaching a surface from a specific source
- mean molecular weight (μ): measurement of a gas usual for approximating in gas models
- mean motion resonance:
- orbital resonance: tendency of orbits of multiple bodies to remain in a simple pattern
- mean-field dynamo theory:
- dynamo: mechanism for generating magnetic fields around astronomical bodies
- mean-field MHD:
- dynamo: mechanism for generating magnetic fields around astronomical bodies
- MEarth:
- MEarth Project (MEarth): automated observatories monitoring nearby red dwarfs for transits
- Mearth-North:
- GJ 1214 b: super-Earth extrasolar planet discovered in 2009
- MEarth Project (MEarth): automated observatories monitoring nearby red dwarfs for transits
- MEarth-South:
- GJ 1132 b: Earth-like extrasolar planet discovered in 2015
- MEarth Project (MEarth): automated observatories monitoring nearby red dwarfs for transits
- measure:
- AB system: monochromatic magnitude calibration based upon absolute values
- absolute magnitude (M): 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
- amplitude: the height of a wave
- angular resolution: measure of a telescope's ability to distinguish spatial detail
- antenna temperature: parameter in determining noise introduced by an antenna
- apparent magnitude (m): magnitude as seen from Earth adjusted for Earth atmosphere
- 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 (β): ratio of plasma pressure to magnetic pressure
- bolometric luminosity (LBol): total luminosity of an object at all wavelengths
- bolometric magnitude (Mbol,Mbol): absolute magnitude of all wavelengths
- brightness temperature (TB): temperature of an equivalent black body in terms of intensity
- chromospheric activity index: measure of magnetic activity of a star's chromosphere
- circular polarization ratio (CPR): 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 (TC): 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 (CDPP): 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 (Λ): force counteracting the universe's inward gravitational pull
- critical density (ρc): density of the universe which leaves it flat
- de Broglie wavelength: wavelength of a particle's matter wave
- declination (dec): direction coordinate above/below celestial equator
- detective quantum efficiency (DQE): measure of instrument's ability to create images
- dispersion measure (DM): to what degree an EMR signal's lower frequencies are delayed
- distance modulus (μ): apparent magnitude minus absolute magnitude
- eccentricity (e): degree to which an orbit is non-circular
- effective radius (Re): radius of a galaxy within which 1/2 the light is emitted
- effective temperature (Teff,Teff): temperature of an equivalent black body in terms of total radiation
- elastic thickness (Te): measure of the thickness of a sagging layer of a planet surface
- electromotive force (EMF): force that drives an electric current
- elevation range: measure of how high and low a telescope can be pointed
- emission coefficient (j): 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 (S): relative measure of the amount of usable energy available
- equilibrium temperature (Teq,Teq): temperature a planet would have if it were an externally-heated black body
- escape velocity (Ve): minimal velocity that allows something to overcome a body's gravity
- etendue (AΩ): measure of how wide and deep a telescope observes
- exit pupil: size of the image as presented to the eye
- field of view (FOV): 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 (fsky): fraction of the sky, e.g., what a survey covers
- full width at half maximum (FWHM): a measure of the width of a hump-shaped curve
- 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 (h): a measure of the magnitude of a gravitational wave
- gravity anomaly: difference between measured gravity and that predicted by a model
- Holmberg radius (RH,RHO): a measure of size of galaxy based on surface brightness
- illumination: measure of light energy producing a telescope's image
- infrared excess (IRX): 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 (λ): 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 (JD): 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 (L): measure of brightness
- luminosity density: luminosity per unit volume
- luminosity distance (dL, DL): distance to an object based upon the distance's effect on received flux
- Mach number: ratio of a flow with the speed of sound
- magnetic field strength (H,H field): a field associated with magnetism
- magnetic flux (Φ): total magnetism passing through a surface
- magnetic flux density (B): 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: density of a volume of space
- mass fraction: measure of a constituent of a star, cloud, etc.
- mass-to-light ratio (M/L,ϒ): measure of a population of stars or region
- mean anomaly: angle describing an object's position within an elliptical orbit
- mean molecular weight (μ): measurement of a gas usual for approximating in gas models
- metallicity (Z): metal fraction of an object
- minimum mass (m sin i): 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
- noise temperature: a measure of noise in electronic devices
- noise-equivalent power (NEP): signal power that equals the noise
- number density (n): number of objects per volume
- opacity (κ): a measure of opaqueness of a material
- optical depth (τ): 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 (N): number of particles
- peculiar velocity: velocity with respect to local rest
- permeability (κ,k): ability of a material to allow fluids to pass through it
- photometric redshift (photo-z): 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 (PE): discrepancy in telescope's aim
- porosity: fraction of the volume of solid material that is open or void
- position angle (PA): indication of a direction across the celestial sphere
- Poynting vector (S): measures directional energy flux density
- 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 (PM): apparent motion in relation to the position of the Sun
- quadratic field strength: a measure of a star's varying magnetic field
- quantum efficiency (QE): measure of instrument's ability to sense EMR
- radiance: measure of EMR to/from a solid angle through and area
- radiant flux: measure of brightness
- radiative flux: power passing through a unit area
- radiative forcing (RF): difference between a planet's incoming and outgoing radiation
- Rayleigh number (Ra): measure reflecting a fluid system's propensity to turbulence
- redshift (z): change to longer wavelengths due to Doppler effects
- redshift-angular size relation: how observed size depends on redshift
- redshift-magnitude relation: how apparent magnitude depends on redshift
- Reynolds number (Re): measure reflecting a fluid system's propensity to turbulence
- right ascension (RA): direction coordinate along celestial equator
- Rossby number (Ro): ratio of inertial to Coriolis force
- scan speed: the speed at which the telescope changes angle on the sky while observing
- semi-major axis (a): maximum radius of an ellipse
- sensitivity function (S): function of wavelength giving the sensitivity of an instrument
- sigma (σ): indication of the confidence level of an experiment
- signal-to-noise ratio (SNR,S/N): 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 (S): measure indicating the effect of a material on EMR passing through
- specific angular momentum (J): absolute angular momentum divided by mass
- specific intensity: intensity per unit wavelength or frequency
- specific volume: ratio of volume to mass
- spectral flux density (S): flux or power of radiation per unit area per unit wavelength
- spectral index (α): power by which an object's flux depends on frequency
- spectral resolution: measure of a spectrograph's ability to resolve features of the spectrum
- spectroscopic parallax: stellar distance determined through spectroscopy
- standard gravitational parameter (μ): a body's mass times the universal gravitational constant
- star formation rate (SFR): rate at which material such as gas is turned into stars
- stellar population: grouping of stars according to metallicity
- Stokes number (Stk,St): measure of a particle's tendency to flow 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 (SB): brightness per unit area of a surface
- 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 (τT,τ): a measure of effects of Thomson scattering
- tidal Q: measure of orbital energy dissipated per orbit due to tidal forces
- Toomre Q parameter (Q): 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 (σ): statistical dispersion of velocities of a group of objects
- virial parameter: calculated quantity showing whether a cloud is gravitationally bound
- water activity (aw): measure of partial vapor pressure of water
- wavefront error (WFE): measure of a class of telescope distortion
- wavelength: an alternative description of an electromagnetic wave's frequency or photon energy
- wavenumber (ν): reciprocal of wavelength
- measurement:
- Measurements and Bibliography for Astronomical Data:
- Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanet host Stars:
- MUSCLES: HST UV survey of some M Dwarfs that host exoplanets
- MECA:
- Phoenix: Mars polar-region probe launched by NASA in 2007 with lander
- mechanics:
- mechanisms:
- MECS:
- BeppoSAX: Italian-Dutch space X-ray telescope
- MEDA:
- Mars 2020: Mars rover mission currently on Mars after 2021 landing
- Medicina Radio Observatory:
- medium:
- Medium Deep Survey (MDS): survey to find galaxies in HST WFPC2 images
- Medium Explorers:
- NASA: includes space-based astronomy research
- medium-band photometric system:
- Medium-class Explorers Program:
- FINESSE: planned space mission for exoplanet spectrography
- NASA: includes space-based astronomy research
- SPHEREx: all-sky spectral survey space-mission plan
- STAR-X: concept for a future X-ray space telescope
- Medusae Fossae Formation:
- Mars: well-explored planet in the solar system
- MeerKAT: new radio telescope in South Africa
- MeerKAT International GigaHertz Tiered Extragalactic Exploration Survey:
- MIGHTEE: radio survey of four established deep fields
- MeerKAT Precursor Array:
- MeerKAT: new radio telescope in South Africa
- MeerLICHT: South African telescope coordinated with MeerKAT
- mega-Earth: rocky planet ten times the size of Earth
- megabar:
- MegaCam:
- megaflare:
- megajansky:
- jansky (Jy): unit of measurement of spectral flux density
- megamaser:
- maser: electromagnetic radiation amplified by stimulated emission
- megamaser galaxy:
- MEGANE:
- MMX: Japanese probe to bring back a sample of a Martian moon
- MegaPrime:
- MEGARA:
- Meier paradox: mysterious decline in number of radio galaxy jets
- Mel:
- MELACOM:
- melilite:
- CAI: calcium/aluminum specs in chondrites
- Melipal Telescope:
- Melnick:
- Melotte:
- Melotte 25:
- Melotte Catalog: 1915 catalog of open and globular clusters
- memory burst:
- MEMS:
- MEMS accelerometer:
- MEMS gravimeter:
- MENA:
- IMAGE: satellite mission to study magnetosphere
- MENeaCS:
- MER:
- MER-A:
- MER-B:
- Mercator Telescope: 1.2 m telescope in the Canary Islands
- Mercer:
- Mercury: inner-most and smallest planet in the solar system
- mercury barometer:
- torr: unit of pressure approximating a millimeter of mercury on Earth
- mercury-manganese star:
- merger:
- 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 (KN): explosive event larger than a nova and smaller than a supernova
- neutron star merger: two neutron stars meeting and forming one
- 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 circle: instrument for timing the passage of stars over a meridian
- meridian telescope:
- meridian circle: instrument for timing the passage of stars over a meridian
- meridian transit:
- transit: a celestial body passing between another and an observer
- meridional current:
- meridional flow: north-south air circulation
- MERLIN: VLBI array spread across England
- MEROPE:
- meson:
- baryon: protons, neutrons, and other three-quark particles
- particle: very small thing
- pion (π): first type of meson discovered
- quark: type of elementary particle incorporated in protons and neutrons
- mesopause:
- mesosphere:
- Message Passing Interface (MPI): mechanism for passing data between processors of a multiprocessor
- MESSENGER:
- Mercury: inner-most and smallest planet in the solar system
- Messier 1:
- Messier 100 (M100,NGC 4321): easily observed spiral galaxy
- Messier 101:
- Messier 104:
- Messier 106 (M106,NGC 4258): spiral galaxy with maser
- Messier 15 (M15): globular cluster with collapsed core
- Messier 31:
- Andromeda (M31): spiral galaxy in the Local Group
- Messier 33:
- Messier 45:
- Pleiades (M45): visible open cluster with seven B-stars
- Messier 64:
- Messier 74 (M74,NGC 628): easily observed spiral galaxy
- Messier 82:
- M82: nearby starburst galaxy
- Messier 84 (M84): elliptical galaxy with jets
- Messier 87:
- M87: supergiant elliptical galaxy in local universe
- Messier Catalog (M): catalog of astronomical objects to avoid when looking for comets
- Messier Objects:
- Messier Catalog (M): catalog of astronomical objects to avoid when looking for comets
- MESUR Pathfinder:
- metal: in astrophysics, any element more massive than helium
- calcium (Ca): element, Ca, atomic number 20
- carbon (C): element, C, atomic number 6
- iron (Fe): metal, Fe, atomic number 26
- lithium (Li): metal, Li, atomic number 3
- magnesium (Mg): element, Mg, atomic number 12
- neon (Ne): element, Ne, atomic number 10
- nickel (Ni): metal, Ni, atomic number 28
- nitrogen (N): metal, N, atomic number 7
- oxygen (O): element, O, atomic number 8
- silicon (Si): metal, Si, atomic number 14
- sodium (Na): metal, Na, atomic number 11
- sulfur (S): metal, S, atomic number 16
- 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 cluster:
- metal-poor population:
- metal-poor stars:
- metal-rich:
- metal-rich cluster:
- metal-rich population:
- metal-rich stars:
- metal-silicate equilibrium:
- metallic:
- metallic helium:
- metal: in astrophysics, any element more massive than helium
- metallic hydrogen: a high-pressure state of hydrogen that is conductive
- 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 (Z): metal fraction of an object
- metals:
- alpha capture: combination of a nucleus and an incoming alpha particle
- alpha element: element created by alpha capture
- alpha process: synthesization of elements through alpha capture
- iron peak: relatively high abundance of iron and nearby elements
- metallicity (Z): metal fraction of an object
- neutrons from carbon-13: process by which neutrons are freed in the s process
- p-process: synthesization of elements through proton capture
- photodisintegration: breakdown of a nucleus by a gamma ray
- r-process: synthesization of elements through neutron capture faster than beta decay
- rp-process: synthesization of elements through repeated proton capture
- s-process: synthesization of elements through neutron capture and beta decay
- trans-iron element: elements with atomic number greater than that of iron
- metastable: characteristic of an excited state that lasts longer than typical
- metastable energy level:
- metastable: characteristic of an excited state that lasts longer than typical
- meteor:
- meteoroid: rocky object in solar system, smaller than an asteroid
- meteor shower:
- celestial event: generally something happening visible in the sky
- meteoroid: rocky object in solar system, smaller than an asteroid
- meteor stream:
- meteoroid: rocky object in solar system, smaller than an asteroid
- meteorite:
- meteoroid: rocky object in solar system, smaller than an asteroid
- 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
- 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:
- METH6:
- methane (CH4): compound of one carbon and 4 hydrogen atoms
- hydrocarbon (HC): any compound of just carbon and hydrogen
- methane clathrate:
- clathrate: crystal lattice with voids that can trap molecules
- methane ice:
- ice: solid state of water
- method:
- methyladyne:
- methylidyne (CH): compound of one carbon and one hydrogen atom
- methylidyne (CH): compound of one carbon and one hydrogen atom
- Metis:
- metric: mathematical generalization of the concept of distance
- Mexico:
- MFF:
- Mars: well-explored planet in the solar system
- MFFE:
- MFI:
- QUIJOTE: survey to measure the polarization of the CMB
- Mg:
- Mg I:
- Mg II:
- Mg lines:
- mGal:
- admittance: effect of atmospheric pressure on gravity
- Gal: gravimetry unit of the effect of a planet's gravity
- MGC:
- MGRO:
- Milagro: gamma ray telescope using Cherenkov radiation
- MGS:
- MHD:
- MHD drag:
- MHD dynamo:
- dynamo: mechanism for generating magnetic fields around astronomical bodies
- mho:
- siemens (S): SI unit of electrical conductance
- MHS:
- Mars 2020: Mars rover mission currently on Mars after 2021 landing
- MI:
- MICADO: camera planned for E-ELT
- MICAS:
- Michelle:
- Michelson interferometer: device to measure small changes in distance or light speed
- Michelson-Morley experiment:
- relativity: physics models accommodating the constancy of the speed of light
- micro black hole:
- black hole (BH): region of such high mass that light cannot escape
- primordial black hole: black holes forming at the most dense volumes when inflation ceased
- micro-arcsecond:
- arcsecond (arcsec,sec,second of arc): a 3600th of an angular degree
- micro-bolometer:
- bolometer: instrument measuring heat produced by radiation
- microarcseconds:
- arcsecond (arcsec,sec,second of arc): a 3600th of an angular degree
- microelectromechanical systems:
- MicroFUN (μFUN): observers following up on microlensing events in the galactic bulge
- microgal:
- Gal: gravimetry unit of the effect of a planet's gravity
- microkelvin:
- kelvin (K): temperature scale starting at absolute zero
- microlensing:
- microlensing event:
- Microlensing Follow-up Network:
- MicroFUN (μFUN): observers following up on microlensing events in the galactic bulge
- Microlensing Observations in Astrophysics:
- MOA: search for microlensing events
- Microlensing Planet Search (MPS): program to follow up on microlensing detections
- MicrOmega-IR:
- micrometeorite:
- meteoroid: rocky object in solar system, smaller than an asteroid
- micrometeoroid:
- meteoroid: rocky object in solar system, smaller than an asteroid
- microquasar: stellar-sized black hole with quasar-like activity
- Microrover Flight Experiment:
- microsatellite:
- CHIPSat: small satellite to investigate ISM plasma
- microturbulence:
- Microvariability and Oscillations of Stars:
- CSA: includes astronomical research
- MOST: 2000s observatory-satellite looking for stellar oscillations
- microvariable:
- 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:
- microwave astronomy:
- microwave: electromagnetic radiation, frequency 300 MHz to 300 GHz
- millimeter astronomy: observation and analysis at wavelengths on the order of a millimeter
- microwave KID:
- KID: type of sensitive electronic device to detect light
- microwave radio astronomy:
- microwave: electromagnetic radiation, frequency 300 MHz to 300 GHz
- microwave radiometer:
- microwave source:
- microwave: electromagnetic radiation, frequency 300 MHz to 300 GHz
- radio source (RS): something in the sky generating radio signal
- mid infrared (MIR,mid-IR): infrared radiation with wavelengths in the 7.5-25 μm range
- mid-IR:
- mid infrared (MIR,mid-IR): infrared radiation with wavelengths in the 7.5-25 μm range
- Mid-scale Dark Energy Spectroscopic Instrument:
- Mid-scale Innovations Program:
- NSF AST: US government astronomical research funding division
- MIDAS:
- Rosetta: space probe that visited a comet
- Midcourse Space Experiment (MSX): 1990s space telescope
- middle ultraviolet:
- ultraviolet (UV): electromagnetic radiation, wavelength 10-400 nm
- MIDEX:
- FINESSE: planned space mission for exoplanet spectrography
- NASA: includes space-based astronomy research
- SPHEREx: all-sky spectral survey space-mission plan
- STAR-X: concept for a future X-ray space telescope
- Swift: satellite for studying gamma-ray bursts
- MIDI:
- Mie scattering: scattering of light by large particles
- Mie theory:
- MIGHTEE: radio survey of four established deep fields
- migration:
- MIKE:
- Mikheyev-Smirnov-Wolfenstein effect (MSW effect): neutrino oscillation between three flavors
- Mikulski Archive For Space Telescopes:
- MAST: archive of data from surveys and missions
- MIL:
- 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:
- Milky Way subgroup: the Milky Way and its satellites
- Milky-Way demographics:
- Millennium Galaxy Catalogue (MGC): 2000s catalog of 10,000 galaxies
- milli flux unit:
- jansky (Jy): unit of measurement of spectral flux density
- milli-arcsecond:
- arcsecond (arcsec,sec,second of arc): a 3600th of an angular degree
- millibar:
- milligal:
- Gal: gravimetry unit of the effect of a planet's gravity
- millijansky:
- jansky (Jy): unit of measurement of spectral flux density
- millikelvin:
- kelvin (K): temperature scale starting at absolute zero
- millimeter:
- Millimeter Anisotropy Experiment Imaging Array:
- MAXIMA: 1998-1999 balloon-borne 1.3-meter millimeter telescope
- Millimeter Array:
- millimeter astronomy: observation and analysis at wavelengths on the order of a millimeter
- microwave: electromagnetic radiation, frequency 300 MHz to 300 GHz
- millimeter wave:
- microwave: electromagnetic radiation, frequency 300 MHz to 300 GHz
- millimeter astronomy: observation and analysis at wavelengths on the order of a millimeter
- millimeter wave astronomy:
- Millimeter-wave Intensity Mapping Experiment (mmIME): project to map CO an [CII]
- millimeter/submillimeter astronomy:
- million-body problem:
- N-body problem: calculating the paths of gravitationally-interacting celestial objects
- millisecond magnetar:
- magnetar: neutron star with a strong magnetic field
- millisecond pulsar (MSP): pulsar spinning with a period in the range of milliseconds
- millitorr:
- torr: unit of pressure approximating a millimeter of mercury on Earth
- Mills:
- Mills Cross Array:
- MSH Catalog (MSH): 1950s catalog of radio sources from a Mills Cross survey
- Mills Cross Radio Telescope:
- MSH Catalog (MSH): 1950s catalog of radio sources from a Mills Cross survey
- Milne-Eddington model:
- MIMA:
- Mimas:
- moon: a planet's natural satellite, such as Earth's
- Saturn: second largest planet in the solar system
- MIMI:
- Cassini: explorer spacecraft sent to Saturn
- Mimir: multi-function near-infrared instrument on Perkins Telescope
- MIMIZUKU:
- MIMOS II:
- MIMOS-II:
- min:
- arcsecond (arcsec,sec,second of arc): a 3600th of an angular degree
- MINECO:
- mini black hole:
- black hole (BH): region of such high mass that light cannot escape
- mini gas giant:
- 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-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:
- Mini-RF:
- Mini-TES:
- miniature black hole:
- black hole (BH): region of such high mass that light cannot escape
- primordial black hole: black holes forming at the most dense volumes when inflation ceased
- Miniature X-ray Solar Spectrometer:
- CUBIXSS: solar spectrometer satellite concept
- minimum mass (m sin i): measured bound on the mass of an exoplanet
- minimum mass solar nebula:
- solar nebula: cloud of gas and dust that formed the solar system
- minimum orbit intersection distance (MOID): smallest distance between paths of two orbiting bodies
- miniTAO:
- Minkowski diagram:
- Minkowski metric:
- metric: mathematical generalization of the concept of distance
- Minkowski space:
- spacetime: four dimensions: time and the three space dimensions
- minor 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
- planetoid: an asteroid or physically similar body
- Pluto: dwarf planet formerly listed as one of the nine planets
- Sedna: distant solar system planetoid discovered in 2003
- Minor Planet Center (MPC): organization collecting and organizing minor planet data
- minor planet moon:
- moon: a planet's natural satellite, such as Earth's
- minor planets:
- MINPA:
- Tianwen-1 (TW-1): Mars rover/orbiter mission currently orbiting Mars
- Mintaka:
- Orion: well-known constellation in the northern hemisphere
- minute:
- arcsecond (arcsec,sec,second of arc): a 3600th of an angular degree
- right ascension (RA): direction coordinate along celestial equator
- minute of arc:
- arcsecond (arcsec,sec,second of arc): a 3600th of an angular degree
- MinXSS:
- CUBIXSS: solar spectrometer satellite concept
- MIPS:
- MIPSGAL:
- MIR:
- mid infrared (MIR,mid-IR): infrared radiation with wavelengths in the 7.5-25 μm range
- Mira variable:
- MIRADAS:
- Miranda:
- moon: a planet's natural satellite, such as Earth's
- Uranus: second outer-most solar system planet
- MIRI:
- MIRI MRS:
- MIRIC-BLINC:
- MMT: 6.5 meter telescope at Mt. Hopkins, Arizona
- MIRO:
- Rosetta: space probe that visited a comet
- mirror:
- mirror cell:
- mirror support cell: units in a telescope that support the mirror
- MIRSI:
- IRTF: Mauna Kea 3-meter infrared telescope
- MIS:
- misaligned gas:
- MISC-T:
- miscibility:
- miscible:
- MISE:
- missing satellite problem:
- mission:
- EPOXI: mission using Deep Impact for further exploration
- K2: second Kepler mission that worked around failed equipment
- Mission Definition Review:
- MDR/SRR: planning step for a NASA mission
- Mission Definition Review/System Requirements Review:
- MDR/SRR: planning step for a NASA mission
- Mission of Opportunity:
- NASA: includes space-based astronomy research
- mission-based designator:
- missions:
- MDR/SRR: planning step for a NASA mission
- MIT:
- Kavli Institute: any of a number of science institutes supported by Kavli Foundation
- MIT Cosmic X-ray Experiment:
- OSO 7: 1970s observatory-satellite for viewing the Sun
- MIT General Circulation Model:
- MITgcm: well-known general circulation model
- MIT X-ray Burst Source Catalog (MXB): 1970s catalog of X-ray bursters
- MITgcm: well-known general circulation model
- mixing length:
- mixing length model:
- mixing length theory: tractable simplified model of convection
- mixing ratio: ratio of two components of a gas
- Mizuguchi-Dragone design:
- MJD:
- Julian date (JD): time in days since noon UT November 24 4714 BC Gregorian
- mJy:
- jansky (Jy): unit of measurement of spectral flux density
- mK:
- kelvin (K): temperature scale starting at absolute zero
- MK class:
- MK luminosity class:
- Mk1:
- Mk2:
- Mk3:
- Mk4:
- MKI:
- Kavli Institute: any of a number of science institutes supported by Kavli Foundation
- MKID:
- KID: type of sensitive electronic device to detect light
- MKII:
- Mark II (MKII): 38 m radio telescope in England
- MERLIN: VLBI array spread across England
- Mkn:
- MKO:
- MKO photometric system: 2000s system covering near infrared
- ML mapmaking:
- MLB:
- MlbO:
- MLE:
- MLF:
- mlmapper: software for maximum-likelihood mapmaking
- MLO:
- MLR:
- MLSO:
- Mly:
- light-year (ly): distance that light travels in a year
- MM:
- Tianwen-1 (TW-1): Mars rover/orbiter mission currently orbiting Mars
- MMA:
- mmIME:
- MMIRS:
- Magellan Telescopes: pair of 6.5 m optical telescopes in Chile
- MMT: 6.5 meter telescope at Mt. Hopkins, Arizona
- MMMI:
- Tianwen-1 (TW-1): Mars rover/orbiter mission currently orbiting Mars
- MMO:
- MMR:
- orbital resonance: tendency of orbits of multiple bodies to remain in a simple pattern
- MMRTG: power source for space probes
- MMS:
- MMSN:
- solar nebula: cloud of gas and dust that formed the solar system
- MMT: 6.5 meter telescope at Mt. Hopkins, Arizona
- MMT Observatory:
- MMT: 6.5 meter telescope at Mt. Hopkins, Arizona
- MMT Spectrograph:
- MMT: 6.5 meter telescope at Mt. Hopkins, Arizona
- MMT-pol:
- MMT: 6.5 meter telescope at Mt. Hopkins, Arizona
- MMTCam:
- MMT: 6.5 meter telescope at Mt. Hopkins, Arizona
- MMTO:
- MMT: 6.5 meter telescope at Mt. Hopkins, Arizona
- MMX: Japanese probe to bring back a sample of a Martian moon
- MO:
- Mars Observer (MO): failed 1992-1993 Mars orbiter mission
- NASA: includes space-based astronomy research
- MOA: search for microlensing events
- Mobile Anisotropy Telescope:
- QMAP: mid 1990s balloon-based CMB survey
- Mobile Astronomical System of Telescope Robot:
- MOC:
- mock catalog: catalog of simulated astronomical bodies
- mode:
- model:
- model BH:
- model black hole:
- models:
- modern constellation:
- asterism: easily recognizable star pattern
- modified GR:
- metric: mathematical generalization of the concept of distance
- modified Julian day:
- Julian date (JD): time in days since noon UT November 24 4714 BC Gregorian
- modified Newtonian dynamics (MOND): alternative theory of gravity addressing "dark matter"
- modified Urca process:
- MODS:
- Modular Open Source Fitter for Transients:
- Astrocats: software to create and manage an astronomy catalog
- Modular Open-Source Fitter for Transients:
- MOSFiT: code to match light-curves with light-curve models
- modulation:
- MOID:
- MOIRCS:
- MOJAVE: program to monitor AGN jet radio brightness and polarization
- mol:
- Avogadro's number (NA): roughly number of hydrogen atoms in a gram
- mole (mol): unit roughly the count of hydrogen atoms in a gram
- MOLA:
- mole (mol): unit roughly the count of hydrogen atoms in a gram
- molecular cloud: interstellar gas cloud that includes molecules
- CO to H2 factor (Xco,XCO): 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 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: CO survey of galaxies
- cold gas: gas cool enough to form galaxies and stars
- DeGaS-MC: GBT 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 (SFR): rate at which material such as gas is turned into stars
- molecular gas depletion time:
- galaxy: gravitationally-bound group of stars
- molecular gas fraction:
- gas fraction: fraction of a galaxy or cluster consisting of gas
- molecular handedness: mirror-imaged variants of some molecules
- molecular hydrogen:
- molecular hydrogen dissociation front (H2 dissociation front): point in a gas cloud where it is hot enough to dissociate hydrogen
- molecular orbital:
- molecular star formation law:
- Mollweide projection:
- HEALPix: type of map projection for spheres
- Mologlo Cross Telescope:
- UTMOST: telescope aiming to detect radio transients
- Molonglo Observatory Synthesis Telescope:
- UTMOST: telescope aiming to detect radio transients
- Molonglo Reference Catalog:
- USS Sources: catalog of sources with steep spectral index
- molten core:
- dynamo: mechanism for generating magnetic fields around astronomical bodies
- moment of inertia:
- moment of inertia factor: characterization of mass distribution within a planet
- MOND:
- 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
- monochromatic luminosity: luminosity at a specific wavelength
- monochromator:
- spectroscopy: measurement of light with various electromagnetic wavelengths
- monolithic:
- monolithic collapse:
- monolithic collapse model:
- monolithic mirror: telescope mirror made of one piece of material
- monopole:
- monsoon:
- monsoon trough:
- Monte Agliate Supernova and Asteroid Survey:
- Monte Carlo:
- Hyperion: Monte Carlo radiative transfer code
- Monte Carlo method: mathematics and simulation using random samples
- Moon:
- Callisto: well-known Jupiter moon
- complex crater: crater with central high-point
- Earth: third solar system planet from the Sun
- Enceladus: Saturn moon considered possible carrier of life
- Europa: well-known Jupiter moon
- Ganymede: well-known Jupiter moon
- GRAIL: 2011 NASA lunar orbiters to collect gravity data
- Io: well-known Jupiter moon
- LCROSS: space probe observing the lunar poles
- Lunar Reconnaissance Orbiter (LRO): space probe orbiting the Moon
- lunar swirl: swirly spot on the surface of the Moon
- lunar water: water on the moon
- moon: a planet's natural satellite, such as Earth's
- 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
- Titan: well-known Saturn moon
- Triton: Neptune's one significant moon
- Moon formation: process by which the Moon and other moons formed
- Moon mass:
- mass: object's quality that determines the effects of forces and gravity
- MoonKAM:
- GRAIL: 2011 NASA lunar orbiters to collect gravity data
- moonmoon:
- MOONS:
- Mopra Spectrometer:
- Mopra Telescope: Australian 22 m radio telescope
- MOPS:
- Moreton wave: type of wave moving across the chromosphere
- Moreton-Ramsey wave:
- Morgan classification: classification of galaxies by stellar spectrum and morphology
- N galaxy: galaxy with bright nucleus and faint surroundings
- Morgan galaxy classification:
- Morgan's classification:
- Morgan-Keenan classification system:
- Morgan-Keenan luminosity class:
- MORIS:
- IRTF: Mauna Kea 3-meter infrared telescope
- morning width:
- Morocco:
- TRAPPIST: ground-based automatic transiting planet finding telescope
- Morphological Catalog of Galaxies:
- Morphological Catalogue of Galaxies (MCG): 1960s catalog from Palomar plates
- morphological peculiarity:
- morphology:
- morphology-density relation: a galaxy is more likely to be elliptical if surrounded by galaxies
- MOSAIC:
- MOSAIC II:
- MOSES:
- ESIS: EUV spectrograph for solar corona observation
- MOSFIRE:
- MOSFiT: code to match light-curves with light-curve models
- Astrocats: software to create and manage an astronomy catalog
- MOST: 2000s observatory-satellite looking for stellar oscillations
- CSA: includes astronomical research
- UTMOST: telescope aiming to detect radio transients
- mount:
- Mount Graham:
- Mount Hopkins Observatory:
- Mount Palomar Observatory:
- Mount Sharp:
- Mount Stromlo Observatory:
- MACHO Project: survey searching out microlensing that could indicate a MACHO
- Mount Teide:
- Mount Wilson Observatory:
- moving cluster:
- moving group: observed group of stars with similar motion
- moving mesh:
- AREPO: cosmology simulation using moving mesh technique
- moving-cluster method: method of measuring distance to a nearby star cluster
- MOXE:
- Spektr-RG (SRG, SXG): Russian-German X-ray observatory launched in 2019
- MOXIE:
- Mars 2020: Mars rover mission currently on Mars after 2021 landing
- MOXSI:
- CUBIXSS: solar spectrometer satellite concept
- MP:
- USS Sources: catalog of sources with steep spectral index
- MPA:
- MeerKAT: new radio telescope in South Africa
- Mpc:
- MPF:
- MPG/ESO Telescope:
- MPI:
- MPI PAF:
- MPIA:
- MPIR:
- MPL:
- MPO:
- MPP:
- MPS:
- MR:
- MRC:
- Tianwen-1 (TW-1): Mars rover/orbiter mission currently orbiting Mars
- USS Sources: catalog of sources with steep spectral index
- Mre:
- Reynolds number (Re): measure reflecting a fluid system's propensity to turbulence
- MRFE:
- MRI:
- Mrk:
- Mrk 209:
- MRO:
- MRO Interferometer (MROI): optical interferometer in New Mexico
- MROI:
- MRP:
- MRS:
- MS:
- MS galaxy:
- MS lifetime:
- MS-DESI:
- MSA:
- MMX: Japanese probe to bring back a sample of a Martian moon
- MSC:
- Tianwen-1 (TW-1): Mars rover/orbiter mission currently orbiting Mars
- MSCD:
- Tianwen-1 (TW-1): Mars rover/orbiter mission currently orbiting Mars
- MSDESI:
- MSE:
- MSH:
- MSH Catalog (MSH): 1950s catalog of radio sources from a Mills Cross survey
- MSH Catalog (MSH): 1950s catalog of radio sources from a Mills Cross survey
- MSI:
- NEAR Shoemaker (NEAR): space mission aiming to return a sample of an asteroid
- MSIP:
- NSF AST: US government astronomical research funding division
- MSL:
- MSM:
- magnetar: neutron star with a strong magnetic field
- MMX: Japanese probe to bring back a sample of a Martian moon
- MSMFD:
- Tianwen-1 (TW-1): Mars rover/orbiter mission currently orbiting Mars
- MSP:
- MSS:
- Msun:
- solar mass (MSun,Msun): mass unit representing the mass of the Sun
- Sun: star at center of solar system
- MSW effect:
- MSX:
- Mt. Bigelow:
- Mt. John University Observatory:
- MOA: search for microlensing events
- Mt. Lemon:
- Mt. Stromlo 1.9 m telescope:
- MTL:
- mTorr:
- torr: unit of pressure approximating a millimeter of mercury on Earth
- Mu Columbae:
- O-type star (O): star with spectral characteristics of above 30000 K
- Mu Normae:
- O-type star (O): star with spectral characteristics of above 30000 K
- Mullard Radio Astronomy Observatory:
- 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-conjugate AO:
- adaptive optics (AO): optical instruments that dynamically adapt to atmospheric distortion
- Multi-Epoch Nearby Cluster Survey (MENeaCS): Type Ia supernova survey in clusters at z = 0.1
- 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 (MOONS): advanced spectrograph under development for VLT
- multi-object spectrograph: device to record the spectrum of multiple targets simultaneously
- multi-object spectrography:
- multi-object spectrometer:
- Multi-Order Solar EUV Spectrograph:
- ESIS: EUV spectrograph for solar corona observation
- Multi-site All-sky Camera:
- MASCARA: distributed array of telescopes to search for exoplanets
- multi-star system:
- star system: a gravitationally bound set of a few stars
- multi-wavelength data:
- multichroic array:
- multichroic feedhorn array: radio array with sensors for two or more bands
- multilevel relaxation:
- multiple expansion:
- Multiple Mirror Telescope:
- MMT: 6.5 meter telescope at Mt. Hopkins, Arizona
- multiple star:
- multiple star system:
- multiple-impact model:
- 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:
- multipole expansion: series expansion of a function over the surface of a sphere
- multipole magnetic field:
- multipole moment:
- multipole number:
- Multiwavelength Survey by Yale-Chile (MUSYC): optical/NIR survey of four deep fields
- Munich:
- Munich Near-Infrared Cluster Survey (MUNICS): 1990s-2000s galaxy cluster survey
- MUNICS:
- muon:
- muon neutrino:
- MUPUS:
- Rosetta: space probe that visited a comet
- mUrca:
- Murchison Radio-astronomy Observatory:
- Murchison Widefield Array (MWA): low frequency radio telescope
- MUSCLES: HST UV survey of some M Dwarfs that host exoplanets
- MUSE:
- MUSIC:
- MUSTANG: bolometer array on the Green Bank Telescope
- MUSTANG-2:
- MUSYC:
- MUV:
- ultraviolet (UV): electromagnetic radiation, wavelength 10-400 nm
- MWA:
- MWA-128:
- MWC:
- MWD:
- white dwarf (WD): stellar remnant of mostly electron degenerate matter
- MWM:
- MWR:
- Mx:
- MXB:
- MXRB:
- MYSO:
- Mz:
Index