Astrophysics (index) | about |

**F:****F-type star****(F)**: spectral type of star a bit hotter than then Sun

**F orbital:****electron orbital**: a nucleus's "locations" where an electron can orbit

**F-D statistics:****Bose-Einstein statistics**: possible distribution of particles not bound by Pauli exclusion

**f-mode:****asteroseismology**: study of stars through analysis of their pulsation

**F-number:****focal length**: length from optical element to focal plane

**F-stop:****focal length**: length from optical element to focal plane

**F-type star****(F)**: spectral type of star a bit hotter than then Sun**f-value:****oscillator strength**: fraction expressing QM's contribution to the probability of absorption

**f**_{sky}:**Fsky****(f**: fraction of the sky, e.g., what a survey covers_{sky})

**Faber-Jackson relation****(FJR)**: relation between elliptical galaxy luminosity and stellar velocity dispersion**Fabry-Pérot interferometer****(FPI)**: type of chromatic-dispersing interferometer**facility:****observatory**: facility for astronomical observation

**facula**: bright spot on a planet or the Sun**failed binary**: like a binary star but one not achieve the mass of a star**failed binary system:****failed binary**: like a binary star but one not achieve the mass of a star

**Faint Images of Radio Sky at Twenty Centimeters:****USS Sources**: catalog of sources with steep spectral index

**Faint Images of the Radio Sky at Twenty-centimeters:****FIRST**: 1990s radio survey

**Faint Infrared Grism Survey****(FIGS)**: survey to identify redshift of distant galaxies**Fairall:****Fairall Galaxy List****(Frl,Fairall)**: 1977 list of galaxies with bright nuclei

**Fairall Galaxy List****(Frl,Fairall)**: 1977 list of galaxies with bright nuclei**fallback supernova:****core collapse supernova**: supernova resulting from the collapse of the core of a star

**false vacuum**: apparent QM vacuum**Fanaroff-Riley classification**: a classification of the radio characteristics of radio sources**far infrared****(FIR)**: infrared radiation with wavelengths in the 30-450um range**BLAST**: balloon-borne 1.8m submillimeter telescope**confusion limit**: limit on telescope imaging due to too many sources in the same region**Herschel Space Observatory**: infrared observatory-satellite with 3.5 meter reflector**Origins Space Telescope****(OST)**: concept for future very large space IR telescope**SPICA**: plan for a future space IR telescope**STARFIRE**: planned balloon-borne 2.5m telescope and spectroscope

**Far Infrared and Submillimetre Telescope:****Herschel Space Observatory**: infrared observatory-satellite with 3.5 meter reflector

**far ultraviolet:****Far Ultraviolet Spectroscopic Explorer****(FUSE)**: early 2000s space telescope for short-wavelength ultraviolet**ultraviolet****(UV)**: electromagnetic radiation, wavelength 10-400 nm

**Far Ultraviolet Space Telescope:****FAUST**: 1990s ultraviolet space telescope used on two shuttle missions

**Far Ultraviolet Spectroscopic Explorer****(FUSE)**: early 2000s space telescope for short-wavelength ultraviolet**far-infrared astronomy:****far infrared****(FIR)**: infrared radiation with wavelengths in the 30-450um range

**Faraday effect:****Faraday rotation**: rotation of optical polarization by a medium in a magnetic field

**Faraday rotation**: rotation of optical polarization by a medium in a magnetic field**Farnese Atlas:****Hipparchus**: Greek astronomer who developed concept of magnitude

**FAST**: Arecibo-like 500m telescope in deployment in China**fast Fourier transform****(FFT)**: efficient algorithm for calculating a discrete Fourier transform**Fast Fourier Transform Telescope**: proposed all-digital telescope with synthetic aperture

**Fast Fourier Transform Telescope**: proposed all-digital telescope with synthetic aperture**Fast Infrared Exoplanet Spectroscopy Survey Explorer:****FINESSE**: planned space mission for exoplanet spectrography

**fast radio burst****(FRB)**: astronomical high energy radio pulses of a few milliseconds**fast shock:****shock wave**: abrupt propagating disturbance in a fluid

**fast-spinning Earth model:****Moon formation**: process by which the Moon and other moons formed

**FAUST**: 1990s ultraviolet space telescope used on two shuttle missions**FDM:****finite difference method****(FDM)**: means of estimating calculus and differential equation solutions

**Fe:****iron****(Fe)**: metal, Fe, atomic number 26

**FEA:****finite element method****(FEM,FEA)**: computational method for PDEs suited to physical problems

**feature:****spectral feature**: recognizable feature of a spectrum

**feedback:****star formation feedback**: mechanisms whereby star formation regulates its own rate

**Feedback in Realistic Environments:****FIRE Simulations**: high resolution simulation of galaxies

**feldspar:****basalt**: an igneous rock type that shows rapid cooling

**FEM:****finite element method****(FEM,FEA)**: computational method for PDEs suited to physical problems

**Fenton Hill Observatory:****Fermi****(FGST,GLAST)**: satellite for studying gamma rays**Fermi energy:****electron degeneracy**: the condition of electrons supported solely by the Pauli exclusion principle

**Fermi Gamma-ray Space Telescope:****Fermi****(FGST,GLAST)**: satellite for studying gamma rays

**Fermi-Dirac distribution:****Bose-Einstein statistics**: possible distribution of particles not bound by Pauli exclusion

**Fermi-Dirac statistics:****Bose-Einstein statistics**: possible distribution of particles not bound by Pauli exclusion**particle**: very small thing

**Fermi-LAT:****Fermi****(FGST,GLAST)**: satellite for studying gamma rays

**fermion:****Bose-Einstein statistics**: possible distribution of particles not bound by Pauli exclusion**neutrino****(ν)**: light, electrically neutral elementary particle**particle**: very small thing**Pauli exclusion principle**: fermions in a quantum system cannot have identical quantum numbers**spin****(m**: an angular-momentum quantum number_{s})

**Ferrel cell:****Hadley cell**: circulation pattern of up at the equator, out, down, and back

**ferromagnetism:****magnetic field**: magnetic force as distributed over a space

**FFT:****fast Fourier transform****(FFT)**: efficient algorithm for calculating a discrete Fourier transform**Fast Fourier Transform Telescope**: proposed all-digital telescope with synthetic aperture

**FFT Telescope:****Fast Fourier Transform Telescope**: proposed all-digital telescope with synthetic aperture

**FGI:****QUIJOTE**: survey to measure the polarization of the CMB

**FGK star**: a star of class F, G, or K**FGM:****THEMIS**: set of satellites studying the Earth's magnetic field

**FGS:****James Webb Space Telescope****(JWST)**: future space-based 6.5 meter infrared telescope

**FGST:****Fermi****(FGST,GLAST)**: satellite for studying gamma rays

**fiber positioner**: machine to set up fibers in multi-object spectrograph**Fick's laws:****diffusion**: the spreading of particles toward an even distribution

**Fickian diffusion:****diffusion**: the spreading of particles toward an even distribution

**fictitious force:****inertial reference frame**: frame of reference where no force means no acceleration

**field**: adjective meaning "in this field of view but unrelated"**Darcy velocity field**: vector field indicating a kind of seepage in a porous medium**field of view****(FOV)**: angular measure of how much an optical instrument can view**magnetosphere**: area around an object where its magnetic field dominates**mathematical field**: function of three variables, potentially representing space**multipole expansion**: series expansion of a function over the surface of a sphere**Reynolds decomposition**: mathematical separation of average and fluctuating parts of a quantity**survey field**: portion of the celestial sphere where a survey's observations aim

**field brown dwarf:****field**: adjective meaning "in this field of view but unrelated"

**field galaxy**: galaxy not in a cluster or group**field lines**: lines showing the pattern of a mathematical field**field object:****field**: adjective meaning "in this field of view but unrelated"

**field of view****(FOV)**: angular measure of how much an optical instrument can view**field of vision:****field of view****(FOV)**: angular measure of how much an optical instrument can view

**field planet:****field**: adjective meaning "in this field of view but unrelated"

**field spectrometer:****spectroscopy**: measurement of the strengths of different electromagnetic wavelengths

**field star**: star that is not part of a star cluster**fields:****mathematical field**: function of three variables, potentially representing space

**FIGS:****Faint Infrared Grism Survey****(FIGS)**: survey to identify redshift of distant galaxies

**filament**: linear volume of high molecular gas density within a galaxy**Nessie**: star forming filament found in the Orion star forming region

**filled ice:****clathrate**: crystal lattice with voids that can trap molecules

**filter**: optical device to filter out part of the EMR spectrum**B**: photometric filter for blue light**G band**: band of visible light around 5100 angstroms**I band**: photometric filter for near infrared light**passband**: range of electromagnetic wavelengths that a filter allows**R band**: band of visible light around 6500 angstroms**U**: photometric filter for ultraviolet light**V**: photometric filter for visible light

**filters:****JHK photometric system****(JHK)**: system to classify stars according to near-infrared colors**passband**: range of electromagnetic wavelengths that a filter allows**photometric system**: specification of a set of filters/passbands**photometry**: studying starlight through bandpass filters**sensitivity function****(S)**: function of wavelength giving the sensitivity of an instrument

**final data release:****data release****(DR)**: publication or distribution of a set of data from a survey

**final parsec problem**: lack of a convincing theory on how SMBHs can reach each other**fine structure**: spectral lines due to electron spin and relativistic effects**fine structure constant:****fine structure**: spectral lines due to electron spin and relativistic effects

**fine structure line:****fine structure**: spectral lines due to electron spin and relativistic effects

**FINESSE**: planned space mission for exoplanet spectrography**finger of God distortion:****redshift space**: concept of space using redshift as the radial dimension

**finite difference method****(FDM)**: means of estimating calculus and differential equation solutions**finite element analysis:****finite element method****(FEM,FEA)**: computational method for PDEs suited to physical problems

**finite element method****(FEM,FEA)**: computational method for PDEs suited to physical problems**finite volume method****(FVM)**: computational method to PDEs especially suited to fluid dynamics**finite-volume method:****MITgcm**: well-known general circulation model

**FIR:****far infrared****(FIR)**: infrared radiation with wavelengths in the 30-450um range

**FIRAS:****Cosmic Background Explorer****(COBE)**: 1989 satellite for observing the CMB

**FIRE:****Magellan Telescopes**: pair of 6.5m optical telescopes in Chile

**FIRE Simulations**: high resolution simulation of galaxies**Fireworks Galaxy:****NGC 6946**: face-on spiral galaxy

**FIRST**: 1990s radio survey**Herschel Space Observatory**: infrared observatory-satellite with 3.5 meter reflector**USS Sources**: catalog of sources with steep spectral index

**first galaxies**: targeted highest red-shift galaxies showing little or no metal**first light**: initial demonstration that a telescope works**first order perturbation problem:****perturbation theory**: breaking an equation into a solvable part and approximatable part

**first point of Aries:****equinox**: times when tilt of Earth is neither toward or away from the Sun

**FIS:****AKARI**: Japanese space infrared telescope

**fission:****fusion**: formation of an atomic nucleus nuclei from multiple smaller nuclei**quantum number**: number representing a conserved quantity**strong force**: force that holds quarks and nuclei together

**FITS:****SPECTRE**: an interactive spectrum analysis software package

**Five Hundred Meter Aperture Spherical Telescope:****FAST**: Arecibo-like 500m telescope in deployment in China

**fixed star**: star that does not change position in the celestial sphere**FJR:****Faber-Jackson relation****(FJR)**: relation between elliptical galaxy luminosity and stellar velocity dispersion

**FK5:****Catalogues of Fundamental Stars**: series of astrometric catalogs from 19th century on

**Flagship Mission:****Lynx**: concept for space X-ray observatory

**Flagship Missions:****NASA**: includes space-based astronomy research

**FLAMES:****European Southern Observatory Very Large Telescope****(ESO VLT,VLT)**: four 8.2-meter optical telescopes in Chile that can act together**VLT-FLAMES Tarantula Survey****(VFTS)**: VLT spectroscopic survey of massive stars

**Flamsteed designation**: star designation system dating from 1700s**FLAO:****Large Binocular Telescope****(LBT)**: dual 8.4 meter telescope in Arizona

**flare spray:****solar eruption**: sudden brightening of the Sun**solar flare**: sudden brightening of the Sun

**flare star:****variable star**: star that varies in magnitude

**flaring state:****stellar flare**: sudden brightening of a star

**FLASH**: hydrodynamic simulation system**Flash Center for Computational Science:****FLASH**: hydrodynamic simulation system

**flat universe:****critical density****(ρ**: density of the universe which leaves it flat_{c})

**flatness problem:****inflation**: theorized rapid expansion of the very early universe

**Flexible Image Transport System:****SPECTRE**: an interactive spectrum analysis software package

**Flexible Modeling System:****TAM**: non-gray-RT 3D model of Titan's atmosphere

**FLITECAM:****SOFIA**: aircraft-based infrared observatory

**Flora:****asteroid family**: set of asteroids based on similar orbits

**FLS:****Spitzer Space Telescope****(SST)**: a satellite with infrared telescope

**fluence:****flux**: flow rate per unit area

**fluffy CAI:****CAI**: calcium/aluminum specs in chondrites

**fluid dynamics:****Brunt-Väisälä frequency**: natural frequency of buoyancy waves**Darcy velocity field**: vector field indicating a kind of seepage in a porous medium**dead zone**: area within a disk where normal things don't happen**discontinuous Galerkin method**: computational method for PDEs handling discontinuities**expansion fan**: the "sound" of a supersonic flow flowing around a convex corner**finite element method****(FEM,FEA)**: computational method for PDEs suited to physical problems**finite volume method****(FVM)**: computational method to PDEs especially suited to fluid dynamics**gas flow**: dynamics of gas, plasma, i.e., compressible fluids**Godunov scheme**: computational fluid dynamics method**gravity wave**: wave in fluid where restoring force is gravity**hydrodynamic equations**: equations describing the dynamics of fluids**hydrodynamics**: study of liquids in motion**Kolmogorov spectrum**: energy spectrum of the eddies of different sizes in a turbulent fluid**Mach number**: ratio of a flow with the speed of sound**MagIC**: numerical code to for fluid dynamics including dynamos**magnetohydrodynamics****(MHD)**: dynamics of electrically conducting fluids**magnetorotational instability****(MRI)**: instability in the fluid of a disk from MHD effects**mixing length theory**: tractable simplified model of convection**Navier-Stokes equations****(NS equations)**: equations that describe fluid dynamics**permeability****(κ,k)**: ability of a material to allow fluids to pass through it**PLUTO Code**: fluid-dynamic simulation code**radiation hydrodynamics****(RHD)**: hydrodynamics plus the affects of EMR**ram pressure**: pressure on a body moving through a fluid**Reynolds decomposition**: mathematical separation of average and fluctuating parts of a quantity**Reynolds number****(Re)**: measure reflecting a fluid system's propensity to turbulence**Richardson number****(Ri)**: measure of fluid stability consisting of ratio of buoyancy and shear**Rossby number****(Ro)**: ratio of inertial to Coriolis force**shock wave**: abrupt propagating disturbance in a fluid**Stokes number****(Stk,St)**: measure of a particle's tendency to flow the flow of a fluid**Taylor-Proudman theorem**: theorem regarding movement through a rotating fluid**Toomre Q parameter****(Q)**: stability criterion for differentially rotating disks**turbulence**: irregular flow of a fluid**turbulent pressure**: pressure component due to the presence of turbulence**vortensity****(PV)**: ratio of vorticity to mass density

**fluid mechanics:****baroclinicity**: measure of misalignment of fluid density and pressure**hydrostatic equilibrium**: state of a fluid body when forces are such that the fluid is at rest**Kelvin-Helmholtz instability****(KHI)**: waves forming from velocity shear**Navier-Stokes equations****(NS equations)**: equations that describe fluid dynamics**RT instability**: result of lighter fluid pushing a heavier fluid

**fluorescence**: mechanism by which molecules emit a longer wavelength than they absorb**biofluorescence**: common fluorescence in organisms to dissipate harmful UV radiation**Compton reflection**: recognizable emission due to a gas or plasma's Compton scattering**K-line**: iron X-ray line**polycyclic aromatic hydrocarbon****(PAH)**: hydrocarbons consisting of meshes of benzene rings

**fluorescence protection:****biofluorescence**: common fluorescence in organisms to dissipate harmful UV radiation

**fluorescent protein:****biofluorescence**: common fluorescence in organisms to dissipate harmful UV radiation

**fluoride:****geochemistry**: the chemistry of the Earth, planets, and moons

**fluorine:****geochemistry**: the chemistry of the Earth, planets, and moons

**flux**: flow rate per unit area**Gini/M20**: an automatable method of detecting whether a galaxy has recently merged**PCA analysis**: an automatable method of determining galaxy morphology**solar constant**: flux from the Sun at 1 AU**spectral flux density****(S)**: flux or power of radiation per unit area per unit wavelength

**flux density:****flux**: flow rate per unit area**spectral flux density****(S)**: flux or power of radiation per unit area per unit wavelength

**flux reconstruction****(FR)**: numerical approach emphasizing joining the subdivisions**flux rope**: rope-shaped structure in magnetic fields associated with coronal mass ejections**FLWO:****Fred Lawrence Whipple Observatory****(FLWO)**: observatory near Amado, Arizona

**FM:****frequency modulation****(FM)**: changing the frequency of a signal's carrier**rare designator prefixes**: designator prefixes generally used for only a few objects

**FMOS:****multi-object spectrograph**: device to record the spectrum of multiple targets simultaneously**Subaru Telescope**: 8.2 meter telescope in Hawaii

**FMS:****TAM**: non-gray-RT 3D model of Titan's atmosphere

**FOC:****Hubble Space Telescope****(HST)**: observatory-satellite with 2.4 meter reflective telescope

**focal length**: length from optical element to focal plane**focal plane**: plane within optical system at which an image is in focus**focal plane array****(FPA)**: array of receivers at the focus of a radio telescope**focal point:****focal plane**: plane within optical system at which an image is in focus

**focal ratio:****focal length**: length from optical element to focal plane**focal plane**: plane within optical system at which an image is in focus

**FOCAS:****Subaru Telescope**: 8.2 meter telescope in Hawaii

**focus:****focal plane**: plane within optical system at which an image is in focus

**foe**: unit of energy on the order of a supernova's output**Fokker-Planck equation**: shows likelihood of velocity over time of a disturbed particle**stellar dynamics**: stars' gravitational interaction

**Fokker-Planck limit:****stellar dynamics**: stars' gravitational interaction

**forbidden line**: lines that quantum mechanics disallows for the most part**forbidden mechanism:****forbidden line**: lines that quantum mechanics disallows for the most part

**forbidden transition:****forbidden line**: lines that quantum mechanics disallows for the most part

**FORCAST:****SOFIA**: aircraft-based infrared observatory

**forced libration:****foreground subtraction**: removing unwanted sources of EMR in intensity mapping**FORNAX**: hydrodynamics simulation software**Fornax Cluster:****galaxy cluster****(CL)**: large group of galaxies gravitationally-bound to the group**Virgo Supercluster**: supercluster including the Local Group

**Fornax Wall:****galaxy filament**: thread-like formations of galaxies, 50 to 80 megaparsecs

**FORS2:****European Southern Observatory Very Large Telescope****(ESO VLT,VLT)**: four 8.2-meter optical telescopes in Chile that can act together

**forward Fourier transform:****Fourier transform**: systematic method of breaking down functions into periodic components

**forward model**: model producing potential observable values from parameters**FOS:****Hubble Space Telescope****(HST)**: observatory-satellite with 2.4 meter reflective telescope

**fossil radio plasma:****radio relics**: clouds from past galaxy emitting radio synchrotron radiation

**four-body problem:****N-body problem**: calculating the paths of gravitationally-interacting celestial objects

**Four-shooter:****Hale Telescope**: 5.1m reflector telescope in California**Palomar Four-filter Survey****(PC)**: Hale telescope survey aimed at discovering high-redshift quasars

**Fourier analysis:****linear theory**: theory of operators satisfying the property of superposition

**Fourier domain:****Fourier space**: domain into which the Fourier transform maps a function

**Fourier series:****spectral method**: method of numerically solving differential equations

**Fourier series expansion:****angular power spectrum**: method of characterizing the CMB**Bernstein polynomial**: polynomial form capable of producing arbitrary shapes**multipole expansion**: series expansion of a function over the surface of a sphere

**Fourier space**: domain into which the Fourier transform maps a function**Fourier transform**: systematic method of breaking down functions into periodic components**FourStar:****Magellan Telescopes**: pair of 6.5m optical telescopes in Chile

**Fourth Cambridge Catalog of Radio Sources****(4C)**: 1960s catalog of northern hemisphere 178MHz sources**Fourth Cambridge Survey:****Fourth Cambridge Catalog of Radio Sources****(4C)**: 1960s catalog of northern hemisphere 178MHz sources

**FOV:****field of view****(FOV)**: angular measure of how much an optical instrument can view

**FPA:****focal plane array****(FPA)**: array of receivers at the focus of a radio telescope

**FPCS:****HEAO-2**: 1978 X-ray observatory space mission

**FPI:****Fabry-Pérot interferometer****(FPI)**: type of chromatic-dispersing interferometer

**FR:****flux reconstruction****(FR)**: numerical approach emphasizing joining the subdivisions

**FR classification:****Fanaroff-Riley classification**: a classification of the radio characteristics of radio sources

**FR-I:****Fanaroff-Riley classification**: a classification of the radio characteristics of radio sources

**FR-II:****Fanaroff-Riley classification**: a classification of the radio characteristics of radio sources

**fraction of the sky:****Fsky****(f**: fraction of the sky, e.g., what a survey covers_{sky})

**fractionation**: separation of compounds from a mixture**fractionation factor**: isotope quantity**fragmentation barrier**: the problem that the seeds of planets would break apart rather than merge**barrier**: challenging issue regarding planet formation**meter size barrier**: a barrier to planet formation on the order of a meter diameter

**frame dragging:****black hole****(BH)**: region of such high mass that light cannot escape**ergosphere**: type of region of space around rotating black hole

**frame of reference**: region, possibly in motion, from which something is observed/considered**reduced mass**: the reciprocal of the sum of the reciprocals of the masses of two objects**relativity**: physics models accommodating the constancy of the speed of light

**France:****CEA Service d'Astrophysique****(CEA SAp)**: French national astrophysics research institute**Centre de données astronomiques de Strasbourg****(CDS)**: repository of astronomical data**Centre national d'ètudes spatiales****(CNES)**: French space agency**Nançay Radio Telescope****(NRT)**: France large single-dish radio telescope**Northern Extended Millimeter Array****(NOEMA)**: large radio telescope array under construction in Europe**Plateau de Bure Interferometer****(PdBI)**: 6-dish interferometer in French Alps

**Frank Ross's Catalog****(Ross)**: high-proper-motion and variable stars catalogued by Frank Ross**Frank Ross's List:****Frank Ross's Catalog****(Ross)**: high-proper-motion and variable stars catalogued by Frank Ross

**Fraunhofer diffraction:****diffraction**: effect of an obstacle on a wave

**Fraunhofer lines:****G band**: band of visible light around 5100 angstroms

**Fraunhofer's G band:****G band**: band of visible light around 5100 angstroms

**FRB:****fast radio burst****(FRB)**: astronomical high energy radio pulses of a few milliseconds

**FRB 121102:****fast radio burst****(FRB)**: astronomical high energy radio pulses of a few milliseconds

**Fred Lawrence Whipple Observatory****(FLWO)**: observatory near Amado, Arizona**Frederick C. Gillett Gemini Telescope:****Gemini Observatory**: pair of telescopes in Hawaii and Chile

**free electron:****galactic electron density**: density of electrons in the ISM

**free neutron:****neutron capture**: combination of an atomic nucleus and a neutron

**free neutron mean lifetime:****neutron capture**: combination of an atomic nucleus and a neutron

**free-bound emission:****recombination**: time when the universe's ionized hydrogen atoms neutralized

**free-fall time**: time it would take a body to collapse if unopposed**free-fall timescale:****free-fall time**: time it would take a body to collapse if unopposed**timescale****(t,τ)**: general length of time something takes

**free-floating:****field**: adjective meaning "in this field of view but unrelated"

**free-floating planet:****field**: adjective meaning "in this field of view but unrelated"

**free-free:****absorption**: removal of photons from a beam of EMR**Kramers opacity law**: opacity's relation to density and temperature

**free-free absorption:****bremsstrahlung**: photon emission when a charged particle is decelerated

**free-free radiation:****bremsstrahlung**: photon emission when a charged particle is decelerated**electron scattering**: any process that changes the course of an electron**spectral index****(α)**: power by which an object's flux depends on frequency

**Freeman law:****Freeman's law**: all spiral galaxy's have the same central surface brightness

**Freeman's law**: all spiral galaxy's have the same central surface brightness**frequency**: number of cycles per unit of time, such as waves per second**frequency domain:****Fourier space**: domain into which the Fourier transform maps a function

**frequency modulation****(FM)**: changing the frequency of a signal's carrier**frequentist statistics:****Bayesian statistics**: statistics method assigning probability to your belief

**Fresnel diffraction:****diffraction**: effect of an obstacle on a wave

**FRI:****Fanaroff-Riley classification**: a classification of the radio characteristics of radio sources

**Fried parameter:****seeing**: apparent blurring and twinkling of objects seen through atmosphere

**Friedmann equation:****Einstein-de Sitter model**: universe tuned to the smallest expansion that continues forever

**Friedmann model:****critical density****(ρ**: density of the universe which leaves it flat_{c})**Einstein-de Sitter model**: universe tuned to the smallest expansion that continues forever**redshift-angular size relation**: how observed size depends on redshift**scale factor****(a)**: relative size of the universe as a function of time

**Friedmann universe:****Einstein-de Sitter model**: universe tuned to the smallest expansion that continues forever

**FRII:****Fanaroff-Riley classification**: a classification of the radio characteristics of radio sources

**Frl:****Fairall Galaxy List****(Frl,Fairall)**: 1977 list of galaxies with bright nuclei

**front end:****back end instrument**: instruments of a telescope that process or combine signals

**front end instrument**: instruments of a telescope that detect and encode the signal**frost line:****snow line**: distance from protostar cool enough for water to condense

**FS:****rare designator prefixes**: designator prefixes generally used for only a few objects

**Fsky****(f**: fraction of the sky, e.g., what a survey covers_{sky})**FSPS:****stellar population synthesis code**: software to perform stellar population synthesis

**FU Ori:****FU Orionis star****(FUor)**: type of variable pre-main-sequence star

**FU Ori star:****FU Orionis star****(FUor)**: type of variable pre-main-sequence star

**FU Orionis:****FU Orionis star****(FUor)**: type of variable pre-main-sequence star

**FU Orionis object:****FU Orionis star****(FUor)**: type of variable pre-main-sequence star

**FU Orionis star****(FUor)**: type of variable pre-main-sequence star**pre-main-sequence star****(PMS)**: star not yet with a nuclear reaction

**full width at half maximum****(FWHM)**: a measure of the width of a hump-shaped curve**fullerine:****polycyclic aromatic hydrocarbon****(PAH)**: hydrocarbons consisting of meshes of benzene rings

**fully ionized:****degree of ionization**: fraction of material consisting of ions

**Fulton gap**: planets with radius 1.5 to 2 Earth radii are rare**function:****angular power spectrum**: method of characterizing the CMB**conditional luminosity function****(CLF)**: function characterizing luminosity of galaxies with a given halo mass**conditional stellar mass function****(CSMF)**: function characterizing galaxies within a halo of a given mass**dense core mass function****(DCMF,CMF)**: function describing range of masses of dense cores**galaxy SED**: SED of a galaxy, sometimes synthesized from photometric surveys**halo mass function**: mass of distribution of dark matter**Hamiltonian**: mathematical transform useful in mechanics**initial mass function****(IMF)**: function describing initial mass of stars**line shape function**: function describing the shape of a spectral line**luminosity function****(LF)**: function giving number of stars or galaxies at different luminosities**mass function**: measure of binaries that constrains the masses**Navarro-Frenk-White profile****(NFW profile)**: a dark matter spatial mass distribution function**phase curve**: brightness of an object according to its phase angle**Planck function**: yields black body curve**point-spread function****(PSF)**: function describing an optical system's response to a point of light**probability density function****(PDF)**: shows probability of taking a particular value from a continuous range**Rayleigh-Jeans law**: yields approximation of black body curve**sensitivity function****(S)**: function of wavelength giving the sensitivity of an instrument**spectral density**: strength of power or energy as a function of frequency**spectral energy distribution****(SED)**: function or plot of brightness at each wavelength in the spectrum**spectral line energy distribution****(SLED)**: function or plot of brightness of lines in a spectrum**spectral power distribution****(SPD)**: function of power versus wavelength or frequency**stellar birth rate function**: function describing the birth rate of stars by mass**X-ray luminosity function****(XLF)**: maps X-ray luminosities to count of such sources

**function space:****basis function**: one of a set of functions used to approximate a function of interest

**fundamental ephemeris:****ephemeris**: information on the position of a celestial body in the sky over time

**fundamental plane**: three-way relation between elliptical galaxy characteristics**Funnelweb Survey:****TAIPAN**: multi-object spectrograph with robot fiber-positioner

**FUor:****FU Orionis star****(FUor)**: type of variable pre-main-sequence star**pre-main-sequence star****(PMS)**: star not yet with a nuclear reaction

**Furuhjelm:****rare designator prefixes**: designator prefixes generally used for only a few objects

**FUSE:****Far Ultraviolet Spectroscopic Explorer****(FUSE)**: early 2000s space telescope for short-wavelength ultraviolet

**fusion**: formation of an atomic nucleus nuclei from multiple smaller nuclei**CNO cycle**: fusion reaction chain turning hydrogen and nitrogen into helium and nitrogen**deuterium burning**: any fusion reaction starting with hydrogen**hydrogen burning**: any fusion reaction starting with hydrogen**neutrons from carbon-13**: process by which neutrons are freed in the s process**nuclear energy generation rate****(ε)**: fusion power per unit mass**proton-proton chain**: fusion reaction chain turning hydrogen into helium**quantum tunneling**: quantum mechanical effect of particles passing through a barrier**triple alpha process**: fusion reaction chain turning helium-4 into carbon

**FUV:****ultraviolet****(UV)**: electromagnetic radiation, wavelength 10-400 nm

**FVM:****finite volume method****(FVM)**: computational method to PDEs especially suited to fluid dynamics**MITgcm**: well-known general circulation model

**FWHM:****full width at half maximum****(FWHM)**: a measure of the width of a hump-shaped curve

**FX:****spectral correlator**: correlator that also functions as a spectrograph

**FX correlator:****spectral correlator**: correlator that also functions as a spectrograph

**FX spectrometer:****spectral correlator**: correlator that also functions as a spectrograph