Term Index (M)
- M:
- M band:
- infrared (IR): electromagnetic radiation, wavelength .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 type of star with a temperature in the vicinity of 2500K
- m sin i:
- minimum mass (m sin i): measured bound on the mass of an exoplanet
- M-class:
- M-type star (M): spectral type of star with a temperature in the vicinity of 2500K
- M-type star (M): spectral type of star with a temperature in the vicinity of 2500K
- 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:
- 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
- PAndAS: survey of M31 and M33
- POINT-AGAPE: survey of M31 for microlensing
- SKHB: survey of globular clusters in M31
- M33:
- M42:
- Orion Nebula (M42, NGC 1976): easily observed nebula that includes SF regions
- 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
- M87*:
- M94:
- M20:
- Gini/M20: an automatable method of detecting whether a galaxy has recently merged
- M500:
- Mbol:
- Mc:
- chirp mass (Mc): 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
- 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
- machine learning:
- MACHO: proposed astronomical objects comprising dark matter
- 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: explosive event larger than a nova and smaller than a supernova
- MACS:
- 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:
- MAG/ER:
- MagAO:
- MagE:
- Magellan Planet Search Program:
- Magellan Telescopes: pair of 6.5m optical telescopes in Chile
- Magellanic Clouds:
- Magellanic Clouds Photometric Survey (MCPS): UBVI survey of the Magellanic Clouds
- Magellanic spiral galaxy:
- Magellanic Stream:
- MagIC: numerical code to for fluid dynamics including dynamos
- magma ocean: presumed to occur early in Earth history and potentially on exoplanets
- magnesium:
- 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 diffusivity:
- Reynolds number (Re): measure reflecting a fluid system's propensity to turbulence
- magnetic dipole radiation: EMR naturally generated by a spinning magnetic dipole
- 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 strength (H): a field associated with magnetism
- magnetic flux (B): 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:
- magnetism:
- magnetized molecular cloud:
- magnetizing field:
- magneto-brems:
- magneto-bremsstrahlung:
- magneto-plasma system:
- magnetoacoustic wave:
- magnetobremsstrahlung:
- magnetohydrodynamics (MHD): dynamics of electrically conducting fluids
- magnetometer: instrument to measure the strength of a magnetic field
- 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
- DQ Tau: young binary star system
- 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 sequence:
- main sequence fitting: cluster star distance determined through fitting with the H-R diagram
- main sequence galaxy:
- main sequence star: star burning hydrogen into helium in its center
- 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 merger:
- Makemake:
- Malin:
- Malmquist bias: selection bias from detecting only the brighter objects
- MaNGA:
- MANIFEST:
- manifold:
- MAP:
- MARCI:
- MARDI:
- Mariner:
- Mars: well-explored planet in the solar system
- Mariner 10:
- Mercury: inner-most and smallest planet in the solar system
- Mark:
- Mark II (MKII): 38m 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 in planning
- Mars: well-explored planet in the solar system
- Mars 2020 Rover:
- Mars Exploration Rover (MER): mission to Mars with two rovers
- Mars Express: Mars probe launched by ESA in 2003
- Mars Global Surveyor (MGS): Mars probe launched by NASA in 1996
- Mars Phoenix:
- Phoenix: Mars probe launched by NASA in 2007 with lander
- 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
- MARSIS:
- MarsWRF: Mars-oriented general circulation model
- Martian Moons Exploration:
- MMX: Japanese probe to bring back a sample of a Martian moon
- MARVELS:
- MARVELS Spectrograph:
- mas:
- arcsecond (arcsec,sec): 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): 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
- 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 loading: moving gas gaining mass from clouds or stars
- mass loss: a star's reduction in mass
- mass number:
- 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:
- 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:
- 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 Cluster Survey (MACS): survey of distant clusters evident in ROSAT X-ray data
- massive compact halo object:
- MACHO: proposed astronomical objects comprising dark matter
- MAST: archive of data from surveys and missions
- Mastcam-Z:
- materials:
- mathematical field: function of three variables, potentially representing space
- mathematics:
- MATISSE:
- matrix:
- 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 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 Observatories (MKO): observatories on Mauna Kea in Hawaii
- 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
- 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 (B): total magnetism passing through a surface
- Maxwell's equations: four equations describing electricity and magnetism
- Maxwell-Boltzmann distribution: distribution of velocities of gas particles
- Maxwell-Boltzmann statistics:
- Maxwell-Faraday equation:
- Mayall:
- Mayall 4m Telescope: 4m reflector telescope at Kitt Peak
- Mazurek's law: the effect of tweaking parameters is counterbalanced by feedback
- MB:
- MB20:
- MBA:
- MBAC:
- MBJD:
- Julian date (JD): time in days since noon UT November 24 4714 BC Gregorian
- Mbol:
- MBS:
- MC:
- HEAO-1: 1977 X-ray observatory space mission
- MCAL:
- AGILE: Italian space gamma-ray observatory
- MCC:
- McDonald Observatory:
- Hobby-Eberly Telescope (HET): 9.2 meter telescope in Texas
- NEWS: planned near-infrared spectrometer on Discovery Channel Telescope
- MCG:
- MCINN:
- MCMC:
- MCPS:
- MCS:
- MDI:
- MDR:
- MDR/SRR: planning step for a NASA mission
- MDR/SRR: planning step for a NASA mission
- MDSCC:
- mean anomaly: angle describing an object's position within an elliptical orbit
- 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:
- 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:
- MEarth Project (MEarth): automated observatories monitoring nearby red dwarfs for transits
- MEarth-South:
- 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 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
- 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
- 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
- column density: measure of the matter through which EMR is passing
- completeness: measure of how many of a survey's objects of a certain magnitude have been detected
- 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
- distance modulus (u): 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
- 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
- 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
- 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
- Holmberg radius: a measure of size of galaxy based on surface brightness
- illumination: measure of light energy producing a telescope's image
- insolation: solar energy received per unit area in given time
- intensity: power reaching a surface from a specific source
- irradiance: 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 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
- 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): a field associated with magnetism
- magnetic flux (B): 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
- number density: number of objects per volume
- opacity: 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
- 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
- plate scale: relation between angle and distance across an image
- pointing error (PE): discrepancy in telescope's aim
- position angle: indication of a direction across the celestial sphere
- Poynting vector (S): measures directional energy flux density
- projected separation: minimal distance between two distant objects close to each other
- 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
- 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
- redshift (z): change to longer wavelengths due to Doppler affects
- 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
- 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 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 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: way to describe polarization state
- Strehl ratio: measure of optical aberration
- surface abundance: quantity such as mass per surface area
- surface brightness: brightness per unit area of a surface
- systemic velocity: average velocity of grouped objects, such as a galaxy
- temperature: measure of heat in matter
- thermal inertia: a measure of a material's ability to absorb heat through conduction
- Thomson optical depth: a measure of affects of Thomson scattering
- 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 telescope's distortion of incoming waves
- wavelength: an alternative description of an electromagnetic wave's frequency or photon energy
- 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 probe launched by NASA in 2007 with lander
- mechanics:
- mechanisms:
- MEDA:
- Medicina Radio Observatory:
- medium:
- cosmic dust: cosmic dust is dust in space such as interstellar dust
- 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
- MegaCam:
- megaflare:
- megajansky:
- jansky (Jy): unit of measurement of spectral flux density
- 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:
- Melotte:
- Melotte 25:
- Melotte Catalog: 1915 catalog of open and globular clusters
- memory burst:
- MEMS:
- MEMS accelerometer:
- MEMS gravimeter:
- MER:
- MER-A:
- MER-B:
- Mercator Telescope: 1.2m telescope in the Canary Islands
- HERMES: four-channel spectrograph on the Anglo-Australian Telescope
- Mercury: inner-most and smallest planet in the solar system
- merger:
- mergers:
- black hole merger: two black holes meeting and forming one
- 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: 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
- meridian: circle around the Earth passing through both poles
- meridional current:
- meridional flow: north-south air circulation
- MEROPE:
- meson:
- baryon: protons, neutrons, and other three-quark particles
- particle: very small thing
- pion (π): first type of meson discovered
- mesopause:
- mesosphere:
- 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 15 (M15): globular cluster with collapsed core
- Messier 31:
- Andromeda (M31): spiral galaxy in the Local Group
- Messier 33:
- 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
- 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
- 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
- metallicity (Z): metal fraction of an object
- 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 stars:
- metal-rich stars:
- metal-silicate equilibrium:
- metallic helium:
- metal: in astrophysics, any element more massive than helium
- metallic hydrogen:
- 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
- neutrons from carbon-13: process by which neutrons are freed in the s process
- r-process: synthesization of elements through neutron capture faster than beta decay
- 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
- meteorite:
- CAI: calcium/aluminum specs in chondrites
- carbonaceous chondrite (C chondrite): stony meteorites with carbon compounds showing no melting
- chondrite: stony meteorites showing no melting
- meteoroid: rocky object in solar system, smaller than an asteroid
- meteoroid: rocky object in solar system, smaller than an asteroid
- 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
- 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
- mGal:
- 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
- MHS:
- MI:
- 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-arcsecond:
- arcsecond (arcsec,sec): a 3600th of an angular degree
- micro-bolometer:
- bolometer: instrument measuring heat produced by radiation
- microarcseconds:
- arcsecond (arcsec,sec): 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
- microlensing:
- EROS: search for MACHOs
- GMAN: collaboration to alert on microlensing transients
- gravitational lensing: focusing electromagnetic radiation by gravitational force
- gravitational microlensing: gravitational lensing by "small" objects such as individual stars and planets
- MACHO Project: survey searching out microlensing that could indicate a MACHO
- MicroFUN (μFUN): observers following up on microlensing events in the galactic bulge
- MOA: search for microlensing events
- OGLE: survey searching for microlensing transients
- POINT-AGAPE: survey of M31 for microlensing
- Probing Lensing Anomalies Network (PLANET): survey that recorded microlensing event lightcurves
- 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
- micrometeoroid:
- meteoroid: rocky object in solar system, smaller than an asteroid
- microquasar: stellar-sized black hole with quasar-like activity
- microsatellite:
- CHIPSat: small satellite to investigate ISM plasma
- Microvariability and Oscillations of Stars:
- CSA: includes astronomical research
- MOST: observatory-satellite to look for stellar oscillations
- microvariable:
- microwave: electromagnetic radiation, frequency 300MHz to 300GHz
- microwave amplification by stimulated emission of radiation:
- maser: electromagnetic radiation amplified by stimulated emission
- Microwave Anisotropy Probe:
- microwave astronomy:
- microwave: electromagnetic radiation, frequency 300MHz to 300GHz
- 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 kinetic inductance detector:
- KID: type of sensitive electronic device to detect light
- microwave radio astronomy:
- microwave: electromagnetic radiation, frequency 300MHz to 300GHz
- microwave radiometer:
- microwave source:
- microwave: electromagnetic radiation, frequency 300MHz to 300GHz
- mid infrared (MIR): infrared radiation with wavelengths in the 7.5um-25um 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
- 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
- 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
- Milagro: gamma ray telescope using Cherenkov radiation
- Milky Way: our galaxy
- Milky Way chemical evolution: process of the development of metals in the Milky Way
- Milky-Way demographics:
- milli flux unit:
- jansky (Jy): unit of measurement of spectral flux density
- milli-arcsecond:
- arcsecond (arcsec,sec): 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
- millimeter:
- Millimeter Array:
- millimeter astronomy: observation and analysis at wavelengths on the order of a millimeter
- microwave: electromagnetic radiation, frequency 300MHz to 300GHz
- 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 pulsar (MSP): pulsar spinning with a period in the range of milliseconds
- Mills:
- Mimas:
- moon: a planet's natural satellite, such as Earth's
- Saturn: second largest planet in the solar system
- MIMI:
- Cassini: explorer spaceship sent to Saturn
- Mimir: multi-function near-infrared instrument on Perkins Telescope
- MIMIZUKU:
- MIMOS II:
- min:
- arcsecond (arcsec,sec): a 3600th of an angular degree
- MINECO:
- mini gas giant:
- super-Earth: exoplanet more massive than Earth but substantially less than Neptune
- mini 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
- minimum mass (m sin i): measured bound on the mass of an exoplanet
- 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 planned sample-return mission
- 10199 Chariklo: largest minor planet in the outer solar system
- planetoid: an asteroid or physically similar body
- Pluto: dwarf planet formerly listed as one of the nine planets
- Minor Planet Center (MPC): organization collecting and organizing minor planet data
- minor planets:
- Mintaka:
- Orion: well-known constellation in the northern hemisphere
- minute:
- arcsecond (arcsec,sec): a 3600th of an angular degree
- MIPS:
- MIPSGAL:
- MIR:
- mid infrared (MIR): infrared radiation with wavelengths in the 7.5um-25um range
- 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
- misaligned gas:
- MISE:
- 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-based designator:
- missions:
- MDR/SRR: planning step for a NASA mission
- 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 class:
- MK luminosity class:
- MKID:
- KID: type of sensitive electronic device to detect light
- MKII:
- Mark II (MKII): 38m radio telescope in England
- Mkn:
- MKO:
- ML mapmaking:
- MlbO:
- MLE:
- MLO:
- Mly:
- light-year (ly): distance that light travels in a year
- MMA:
- mmIME:
- MMIRS:
- Magellan Telescopes: pair of 6.5m optical telescopes in Chile
- MMT: 6.5 meter telescope at Mt. Hopkins, Arizona
- MMO:
- MMR:
- MMRTG: power source for space probes
- 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
- MOA: search for microlensing events
- MOC:
- mock catalog: catalog of simulated astronomical bodies
- mode:
- model:
- model BH:
- model black hole:
- models:
- modern constellation:
- asterism: easily recognizable star pattern
- 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"
- MODS:
- Modular Open Source Fitter for Transients:
- Astrocats: software to create and manage an astronomy catalog
- modulation:
- MOIRCS:
- MOJAVE: program to monitor AGN jet radio brightness and polarization
- MOLA:
- molecular cloud: interstellar gas cloud including 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
- 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:
- 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
- monochromatic luminosity: luminosity at a specific wavelength
- monochromator:
- spectroscopy: measurement of the strengths of different electromagnetic wavelengths
- monolithic:
- monolithic mirror: telescope mirror made of one piece of material
- monopole:
- monsoon:
- monsoon trough:
- Monte Carlo:
- Hyperion: Monte Carlo radiative transfer code
- Monte Carlo method: mathematics and simulation using random samples
- Moon:
- Callisto: well-known Jupiter moon
- 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
- 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
- moonmoon:
- MOONS:
- Morgan classification: classification of galaxies by stellar spectrum and morphology
- N galaxy: galaxy with bright nucleus and faint surroundings
- Morgan's classification:
- Morgan-Keenan classification system:
- Morgan-Keenan luminosity class:
- MORIS:
- IRTF: Mauna Kea 3-meter infrared telescope
- morning width:
- Morphological Catalog of Galaxies:
- Morphological Catalogue of Galaxies (MCG): 1960s catalog from Palomar plates
- MOSAIC II:
- MOSFIRE:
- MOSFiT:
- Astrocats: software to create and manage an astronomy catalog
- MOST: observatory-satellite to look for stellar oscillations
- CSA: includes astronomical research
- 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
- moving group:
- moving mesh:
- AREPO: cosmology simulation using moving mesh technique
- moving-cluster method: method of measuring distance to a nearby star cluster
- MOXE:
- MP:
- USS Sources: catalog of sources with steep spectral index
- MPA:
- MeerKAT: new radio telescope in South Africa
- Mpc:
- HEAO-2: 1978 X-ray observatory space mission
- Minor Planet Center (MPC): organization collecting and organizing minor planet data
- parsec (pc): about 3.26 light-years
- MPG/ESO Telescope:
- MPI PAF:
- MPIA:
- MPIR:
- MPO:
- MR:
- MRC:
- USS Sources: catalog of sources with steep spectral index
- Mre:
- Reynolds number (Re): measure reflecting a fluid system's propensity to turbulence
- MRI:
- Mrk:
- Mrk 209:
- MRO:
- MRS:
- MS galaxy:
- MS-DESI:
- MSA:
- MMX: Japanese probe to bring back a sample of a Martian moon
- MSDESI:
- MSE:
- MSIP:
- NSF AST: US government astronomical research funding division
- MSL:
- MSP:
- Msun:
- solar mass (MSun,Msun): mass unit representing the mass of the Sun
- Sun: star at center of solar system
- MSW effect:
- Mt. Bigelow:
- Mt. John University Observatory:
- MOA: search for microlensing events
- Mt. Lemon:
- Mullard Radio Astronomy Observatory:
- Multi Mirror Telescope:
- MMT: 6.5 meter telescope at Mt. Hopkins, Arizona
- multi-conjugate AO:
- adaptive optics (AO): optical instruments that dynamically adapt to atmospheric distortion
- 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-site All-sky Camera:
- MASCARA: distributed array of telescopes to search for exoplanets
- multi-wavelength data:
- multichroic array:
- multichroic feedhorn array: radio array with sensors for two or more bands
- multilevel relaxation:
- 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 expansion: series expansion of a function over the surface of a sphere
- multipole magnetic field:
- Munich:
- muon:
- muon neutrino:
- MUPUS:
- Rosetta: space probe that visited a comet
- Murchison Radio-astronomy Observatory:
- Murchison Widefield Array (MWA): low frequency radio telescope
- MUSCLES: HST UV survey of some M Dwarfs that host exoplanets
- MUSE:
- MUSTANG: bolometer array on the Green Bank Telescope
- MUSTANG-2:
- MUV:
- ultraviolet (UV): electromagnetic radiation, wavelength 10-400 nm
- MWA:
- MWA-128:
- MWC:
- MWR:
- Mx:
- MXB:
index