Term Index (E)
Astrophysical terms and names of things beginning with the letter E.
EA
EB
EC
ED
EE
EF
EG
EH
EI
EJ
EK
EL
EM
EN
EO
EP
EQ
ER
ES
ET
EU
EV
EX
EY
- E (eclipsing binary): binary star system detected by variations in magnitude
- E (electric field): electric force as distributed over a space
- E: see ESO/Uppsala Survey of the ESO (B) Atlas
- E: see HEAO-2
- e
- E and B Experiment (EBEX): balloon-based CMB polarization survey
- E ring: see Enceladus
- E+A galaxy (post-starburst galaxy): galaxy indicating star formation some time back
- E-CDFS
- MIGHTEE: radio survey of four established deep fields
- e-e bremsstrahlung: see bremsstrahlung
- E-ELT (European Extremely Large Telescope): 39-meter telescope under construction
- E-Elt
- e-folding (e-folding time): time to increase by a factor of e
- e-folding time: time to increase by a factor of e
- e-ion bremsstrahlung: see bremsstrahlung
- e-MERLIN: see MERLIN
- E-mode: see polarization modes
- CMB polarization: effects of scattering and lensing on the CMB
- EBEX: balloon-based CMB polarization survey
- QUaD: survey to measure the polarization of the CMB
- E-THEMIS: see Europa Clipper
- e-VLBI (electronic very-long-baseline interferometry): real-time VLBI using electronic links
- Eh (reduction potential): measure of a chemical species' tendency to acquire electrons
- e+ (positron): electron-like antimatter particle with electric charge of +1
- e- (electron): type of lepton that is stable and has an electric charge of -1
- EA: see variable star
- EA Observatory (East Asian Observatory): operator of JCMT
- EAAE (European Association for Astronomy Education): promotes science education
- EACOA (East Asian Core Observatories Association): promotes astronomy
- EAGLE: simulation of galaxy formation and evolution
- EAGLE: see European Extremely Large Telescope
- EAGLE Project
- EAGLE: simulation of galaxy formation and evolution
- EAO (East Asian Observatory): operator of JCMT
- EAPSNET (East-Asian Planet Search Network): initiative to find exoplanets
- early: see spectral class
- early dark energy: see dark energy
- early M dwarf: see M dwarf
- Early Release Science: see James Webb Space Telescope
- early universe: from the Big Bang to recombination
- early-type galaxy: see galaxy
- early-type nitrogen-rich Wolf-Rayet: see Wolf-Rayet star
- early-type star: see spectral class
- Earth: third solar system planet from the Sun
- Earth (Earth analog): planet with characteristics of Earth
- Earth analog: planet with characteristics of Earth
- Earth atmospheric pressure: see atm
- Earth mass: see mass
- solar mass: mass unit representing the mass of the Sun
- Earth rotation aperture synthesis (Earth rotation synthesis): using the Earth's rotation to observe with various interferometry baselines
- Earth rotation synthesis: using the Earth's rotation to observe with various interferometry baselines
- Earth science
- Earth term: see pulsar timing array
- Earth Trojan
- 2010 TK7: asteroid that is an Earth Trojan
- Earth-crossing asteroid: see near-Earth object
- Earth-sized VLBI: ground-based VLBI with near-maximal baseline
- Earth-skimming: see TAMBO
- earthlight (earthshine): reflected and emitted electromagnetic radiation from Earth
- earthquake: see quake
- Earths: see extra-solar planet
- earthshine: reflected and emitted electromagnetic radiation from Earth
- EAS (European Astronomical Society): European organization
- EAS Job Directory: directory of astrophysics jobs
- East Asian Core Observatories Association: promotes astronomy
- East Asian Observatory: operator of JCMT
- East-Asian Planet Search Network: initiative to find exoplanets
- EB: see CMB polarization
- EB: see variable star
- Ebb: see GRAIL
- EBEX: balloon-based CMB polarization survey
- EBHIS: see Galactic All-sky Survey
- EBIT (electron beam ion trap): lab instrument to create ions for study
- EBL (extragalactic background light): electromagnetic radiation from star formation and AGNs
- EBLM: see rare designator prefixes
- EBM: see one dimensional climate model
- eBOSS: see Baryon Oscillation Spectroscopic Survey
- eBOSS: see Sloan Digital Sky Survey
- EC: see Palomar-Green Survey
- EC: see stellar cluster
- ECA: see near-Earth object
- eccentric anomaly: see mean anomaly
- eccentric Jupiter: see giant planet
- eccentricity: degree to which an orbit is non-circular
- comet: Sun-orbiting object with coma and possible tail
- DQ Tau: young binary star system
- EXOSAT: 1980s European space X-ray telescope
- Haumea: dwarf planet discovered in 2004
- HD 80606 b: hot Jupiter discovered in 2001
- orbital element: parameters describing an orbit
- Planet Nine: theoretical planet beyond Neptune
- Pluto: dwarf planet formerly listed as one of the nine planets
- Sedna: distant solar system planetoid discovered in 2003
- Solar Orbiter: space probe investigating the Sun's surface and the heliosphere
- eccentricity-type resonance: see orbital resonance
- ECDFS (Extended Chandra Deep Field-South Survey): 1100 square arcminute X-ray survey
- DEVILS: visible-light spectrographic survey of 56k distant galaxies
- echelette grating: see grating
- echelle grating: see grating
- HARPS: high-precision spectrograph for exoplanet searches
- immersion grating: grating where light is within the material
- WINERED: near-infrared non-cryogenic spectrograph
- eclipse (secondary eclipse): eclipse of a body that also transits
- eclipse: see occultation
- celestial event: something astronomical occurring visibly in the sky
- transit: a celestial body passing between another and an observer
- eclipse mapping: using eclipse light curves to map surface features
- eclipse season: see solar eclipse
- eclipse timing offset: see secondary eclipse
- eclipsing Algol: see variable star
- eclipsing Beta Lyrae: see variable star
- eclipsing binary: binary star system detected by variations in magnitude
- ecliptic: path of the Sun on the celestial sphere as seen from Earth
- ecliptic coordinate system: celestial coordinate system system based upon Earth's orbital plane
- ecliptic latitude: see ecliptic coordinate system
- ecliptic longitude: see ecliptic coordinate system
- ecliptic plane (ecliptic): path of the Sun on the celestial sphere as seen from Earth
- Ecliptic Plane Input Catalog: see K2
- ecliptic pole: see ecliptic coordinate system
- ECM: see Europa Clipper
- ECO: see RESOLVE
- ECSN: see core collapse supernova
- EDD (Extragalactic Distance Database): online database of distance-related measures of galaxies
- Eddington accretion rate: see Eddington luminosity
- Eddington accretion rate: see accretion
- Eddington approximation: approximation of a star's internal EMR's divergence from isotropic
- Eddington bias: selection bias from mistaking something common for something rare
- Eddington limit (Eddington luminosity): maximum luminosity at which radiation force overcomes gravity
- Eddington luminosity: maximum luminosity at which radiation force overcomes gravity
- Eddington ratio: see Eddington luminosity
- Eddington valve (kappa mechanism): stellar instability caused by opacity increasing with temperature
- Eddington-Barbier relation: see source function
- eddy: see turbulence
- EDE: see dark energy
- EDG: see double star designation
- EDGES: survey aiming at highly-redshifted 21-cm detection
- Edgeworth-Kuiper Belt (Kuiper Belt): further part of solar system beyond Neptune
- Edgeworth-Kuiper Belt object: see Kuiper Belt
- EDI: see Magnetospheric Multiscale Mission
- TripleSpec: near-infrared spectrograph on the Hale Telescope
- EDM (electron degenerate matter): dense matter such as that in white dwarf
- education
- EE: see CMB polarization
- EE cosmic rays: see cosmic rays
- EECR: see cosmic rays
- EECRs
- EELG: see emission line galaxy
- EELT (European Extremely Large Telescope): 39-meter telescope under construction
- EF Eridani: binary star including a substellar object
- EF Eridani B: see EF Eridani
- effective elastic thickness (elastic thickness): measure of the thickness of a sagging layer of a planet surface
- effective field theory: type of useful simplification of a field theory
- effective number of neutrinos: see neutrino
- effective radius: radius of a galaxy within which 1/2 the light is emitted
- effective temperature: temperature of an equivalent black body in terms of total radiation
- Effelsberg 100-m Radio Telescope: German large single-dish radio telescope
- Effelsberg Radio Telescope
- Effelsberg-Bonn HI Survey: see Galactic All-sky Survey
- effusion: see supercritical fluid
- EFI
- THEMIS: set of satellites studying the Earth's magnetic field
- EFOSC2: see ESO 3.6m Telescope
- EFOSC2: see New Technology Telescope
- PESSTO: NTT survey following up on transients
- EFT (effective field theory): type of useful simplification of a field theory
- EGB (cosmic gamma ray background): gamma-ray radiation seen everywhere
- EGB: see rare designator prefixes
- EGCR: see cosmic rays
- EGG (evaporating gas globule): very small dense cloud of hydrogen and dust
- EGG: see rare designator prefixes
- EGGR: see rare designator prefixes
- EGM: see rare designator prefixes
- EGO (European Gravitational Observatory): gravitational wave observatory in Italy
- EGP: see extra-solar planet
- egress duration: see transiting planet
- EGRET: see Compton Gamma Ray Observatory
- EGS (Extended Groth Strip): region of sky searched for distant galaxies
- CEERS: JWST early release observation program covering the EGS
- DEEP2: redshift survey of 60,000 galaxies
- EGSD2: see DEEP2
- EH (event horizon): surface-shape around a black hole through which light cannot escape
- EHB: see horizontal branch
- EHB star: see horizontal branch
- EHe: see helium star
- EHT (Event Horizon Telescope): growing VLBI network
- EIC: see rare designator prefixes
- EIE: Italian engineering company that produces astronomical equipment
- EIE ALMA Prototype Antenna (ARO 12m Telescope): twelve meter microwave telescope at KPNO
- EIE Group
- eigen-basis: see eigen-decomposition
- eigen-decomposition: useful type of factoring a matrix into the product of three
- eigenvalue: ratio between a vector and a linear transformation of that vector
- eigenmode: vibration mode of an oscillator where all parts move at the same frequency
- eigenmode decomposition
- eigenmode: vibration mode of an oscillator where all parts move at the same frequency
- eigenmode expansion
- eigenmode: vibration mode of an oscillator where all parts move at the same frequency
- eigenvalue: ratio between a vector and a linear transformation of that vector
- eigenvector: see eigenvalue
- Eight-Burst Nebula (NGC 3132): PN of interest in southern sky
- Einstein angle: see gravitational microlensing
- Einstein coefficients: a substance's probabilities of emission and absorption
- Einstein delay: EMR delay due to relativistic effects of environment and motion
- Einstein gravitational constant: see gravitational constant
- Einstein gravity (general relativity): formula relating gravity, space, time, and mass
- Einstein Observatory (HEAO-2): 1978 X-ray observatory space mission
- Einstein parallax: see gravitational microlensing
- Einstein Probe: Chinese X-ray space observatory
- Einstein radius: see gravitational microlensing
- Einstein ring: see gravitational lensing
- Einstein ring: see gravitational microlensing
- Einstein Telescope: concept for a larger LIGO-like GW detector
- Einstein's equation: see general relativity
- Einstein's field equation: see general relativity
- cosmological constant: force counteracting the universe's inward gravitational pull
- Lambda-CDM model: Big-Bang cosmological model with a cosmological constant and cold dark matter
- wCDM: Big-Bang cosmological model with constant cosmological equation of state
- Einstein-Boltzmann equation: see CMBFAST
- Einstein-de Sitter model: universe tuned to the smallest expansion that continues forever
- Einstein-de Sitter universe (Einstein-de Sitter model): universe tuned to the smallest expansion that continues forever
- Einstein-Rosen bridge: see wormhole
- EIS: see Europa Clipper
- EIS: see Magnetospheric Multiscale Mission
- EIS: see rare designator prefixes
- Eisenberg-Pearson telescope: see Korsch telescope
- EIT: see Solar and Heliospheric Observatory
- EJASA (Electronic Journal of the Astronomical Society of the Atlantic): online journal during the 1990s
- ejecta: material ejected from something
- ejection: forcing or throwing something out
- EKBO: see Kuiper Belt
- El Niño
- Kelvin waves: pressure and gravity waves formed by Coriolis force and a barrier
- El Universo en palabras: Series of audios produced by Astroaccesible
- ELAIS: see Infrared Space Observatory
- ELAIS-N1: see Infrared Space Observatory
- ELAIS-N2: see Infrared Space Observatory
- ELAIS-N3: see Infrared Space Observatory
- ELAIS-S1: see Infrared Space Observatory
- ELAIS-S2: see Infrared Space Observatory
- ELAN: see Lyman-alpha blob
- elastic scattering: see scattering
- elastic thickness: measure of the thickness of a sagging layer of a planet surface
- electric dipole radiation: EMR generated by an oscillating electric dipole
- electric field: electric force as distributed over a space
- electric force: see Coulomb's law
- electric potential: see electric field
- electric thruster: see ion engine
- electricity
- electromagnetic induction (magnetic induction): voltage across a conductor induced by changing magnetic field
- electromagnetic ion cyclotron wave: see plasma wave
- electromagnetic radiation: radiation such as light, radio, X-rays
- black body: idealized object that reflects no light
- electromagnetic spectrum: spectrum of EMR
- electromagnetic waves (electromagnetic radiation): radiation such as light, radio, X-rays
- electromagnetism: electricity and magnetism and their interaction
- electromotive force: force that drives an electric current
- electron: type of lepton that is stable and has an electric charge of -1
- electron: see particle
- baryon: protons, neutrons, and other three-quark particles
- beta decay: radioactivity such that an electron or positron is emitted
- ionization fraction: a substance's ratio of unattached electrons to nuclei
- lepton: elementary particle with 1/2 integer spin such as electron
- plasma frequency: frequency of electron plasma oscillation
- positron: electron-like antimatter particle with electric charge of +1
- radioactive decay: changes in atomic nuclei that happen over time
- spark chamber: type of ion detector
- standard model: model of elementary particles including quarks
- supersymmetry: extension to standard model of particle physics
- tau neutrino: neutrino flavor that becomes a tau particle during interactions
- electron beam ion trap: lab instrument to create ions for study
- electron capture: combination of an electron with a proton
- electron capture supernova: supernova from collapse of iron-free stellar cores
- electron capture supernova: see core collapse supernova
- electron column density: see column density
- electron degeneracy: electrons set free of atoms by the Pauli exclusion principle
- electron degeneracy pressure: see electron degeneracy
- degeneracy: general word meaning a violation of normal rules
- electron pressure: the electron contribution to pressure within a plasma
- neutron star: stellar remnant consisting entirely of solar masses of neutrons
- electron degenerate matter: dense matter such as that in white dwarf
- electron degenerate matter: see electron degeneracy
- electron excitation (atomic excitation): electrons above the ground state within atoms
- electron fraction: see ionization fraction
- electron fraction: see r-process
- electron neutrino: see tau neutrino
- electron orbital: a nucleus's "locations" where an electron can orbit
- electron pressure: the electron contribution to pressure within a plasma
- electron relaxation: see atomic excitation
- electron scattering: any process that changes the course of an electron
- electron screening: reduction of effective charge of a nucleus by nearby electrons
- electron shell: radius-level around an atomic nucleus at which electrons can orbit
- electron subshell: see electron shell
- electron volt: very small unit of energy
- photon: quantum of light, i.e., light as a particle
- photon energy: the energy carried by a single photon
- electron-ion bremsstrahlung: see bremsstrahlung
- electron-positron plasma: see Faraday rotation
- electron-volt
- gamma rays: electromagnetic radiation, wavelength 10 picometers and less
- X-ray: electromagnetic radiation, wavelength 0.01 to 10 nanometers
- electronegativity
- oxidation state: number of electrons loaned out by an atom in an ionic bond
- electronic
- Electronic Journal of the Astronomical Society of the Atlantic: online journal during the 1990s
- electronic very-long-baseline interferometry: real-time VLBI using electronic links
- electronics
- electrons
- Cooper pair: pair of electrons sharing a particular type of bond
- Fermi sea: atom's minimal-energy electrons filling its lower shells
- electrostatic barrier: the problem that dust grains will repel and not join to form planet seeds
- barrier: challenging issue regarding planet formation
- electrostatic bond
- ice: solid state of water
- electrostatic ion cyclotron wave: see plasma wave
- electroweak: single conception including both electromagnetic and weak forces
- electroweak force: see electroweak
- WIMP: proposed particle comprising dark matter
- element: class of atom based on its number of protons
- aluminum: element, Al, atomic number 13
- calcium: element, Ca, atomic number 20
- carbon: element, C, atomic number 6
- helium: non-metallic element, He, atomic number 2
- hydrogen: most prominent element, atomic number 1
- iron: metal, Fe, atomic number 26
- lithium: metal, Li, atomic number 3
- magnesium: element, Mg, atomic number 12
- neon: element, Ne, atomic number 10
- nickel: metal, Ni, atomic number 28
- nitrogen: metal, N, atomic number 7
- oxygen: element, O, atomic number 8
- phosphorus: metal, P, atomic number 15
- silicon: metal, Si, atomic number 14
- sodium: metal, Na, atomic number 11
- sulfur: metal, S, atomic number 16
- titanium: metal, Ti, atomic number 22
- element sedimentation: see sedimentation
- elemental sedimentation: see sedimentation
- elements
- atomic number: number of protons in an atomic nucleus
- fusion: formation of an atomic nucleus nuclei from multiple smaller nuclei
- mass number: number of nucleons in an atomic nucleus
- elevation range: measure of how high and low a telescope can be pointed
- ELF (Enceladus Life Finder): mission to search for life on Saturn moon Enceladus
- ELF (extremely low frequency): electromagnetic radiation, frequency 3 Hz to 30 Hz
- ELF (ultraluminous infrared galaxy): a galaxy emitting a more far infrared than an LIRG
- ELF: see Colossus Telescope
- ELG (emission line galaxy): a galaxy type characterized by emission lines
- REBELS: survey of star-forming galaxies during the reionization
- ELHC: see EROS
- Elias: see rare designator prefixes
- Elias 2-27: much-studied YSO
- ELIRG: see luminous infrared galaxy
- eLISA (New Gravitational Wave Observatory): past proposal for space mission to detect gravitational waves
- ellipse: see conic section
- ellipsoid: see spheroid
- paraboloid: circularly-symmetric 3D surface based on parabola
- ellipsoidal variable: binary star elongated by gravity
- elliptical
- elliptical galaxies
- elliptical galaxy: ellipsoidal-shaped galaxy
- ellipticity: degree to which a body's shape is un-spherical
- ELM Survey: survey of extremely-low-mass white dwarfs
- ELODIE
- elongation: see heliocentric system
- Elqui stream
- ELT (European Extremely Large Telescope): 39-meter telescope under construction
- ELT (extremely large telescope): optical telescope with a 20+ meter aperture
- ELT-CAM (MICADO): camera planned for E-ELT
- ELT-CAM: see European Extremely Large Telescope
- ELT-HARMONI (HARMONI): spectrograph planned for E-ELT
- ELT-HIRES: see European Extremely Large Telescope
- ELT-IFU (HARMONI): spectrograph planned for E-ELT
- ELT-IFU: see European Extremely Large Telescope
- ELT-MIDIR: see European Extremely Large Telescope
- ELT-MOS: see European Extremely Large Telescope
- EM (electromagnetism): electricity and magnetism and their interaction
- EM radiation (electromagnetic radiation): radiation such as light, radio, X-rays
- embedded cluster: see stellar cluster
- embedded lens: see gravitational lensing
- embryo (planetary embryo): object that may grow into a future planet
- EME
- eigenmode: vibration mode of an oscillator where all parts move at the same frequency
- emergent gravity (entropic gravity): MOND-like theory of gravity
- EMF (electromotive force): force that drives an electric current
- EMIC: see plasma wave
- EMIR: see Gran Telescopio Canarias
- EMIR: see IRAM 30m Telescope
- EMIR Multi-line Probe of the ISM Regulating Galaxy Evolution (EMPIRE Survey): survey of gas in M51a to follow up PAWS
- Emirates Mars Mission (Hope Probe): UAE Mars orbiter currently studying Mars
- EMIRS: see Hope Probe
- emission: addition of photons to a beam of EMR
- emission band: see spectral band
- emission coefficient: measure of how much light a substance emits
- emission line: narrow frequency-region of a spectrum with higher intensity
- emission line galaxy: a galaxy type characterized by emission lines
- REBELS: survey of star-forming galaxies during the reionization
- emission line nebula (emission nebula): nebula that emits light such as an HII region or PN
- emission line tomography (line tomography): using double-peaked spectral lines to place constituents of a disk
- emission nebula: nebula that emits light such as an HII region or PN
- emission redshift: see redshift
- emission spectroscopy
- emission-line object: source of interest due to an emission line
- emission-line star: general term for a star exhibiting stronger-than-usual emission lines
- emissive photodissociation: see photodissociation
- emissivity: measure of a material's efficiency at radiating thermal radiation
- emissivity index: see spectral index
- EMMI: see New Technology Telescope
- EMP (Ephemerides of Minor Planets): annual catalog on minor planet positions
- EMP: see Population III
- EMPG (extremely metal poor galaxy): galaxy of interest for its very low metallicity
- EMPIRE Survey: survey of gas in M51a to follow up PAWS
- EMR (electromagnetic radiation): radiation such as light, radio, X-rays
- 21-cm experiment: search for redshifted 21-cm hydrogen emission lines
- AB system: monochromatic magnitude calibration based upon absolute values
- absolute magnitude: magnitude as would be seen from 10 parsecs
- absorption: removal of photons from a beam of EMR
- absorption coefficient: measure of how much light a substance absorbs
- active galactic nucleus: central region of a galaxy with extremely high luminosity
- AGN corona: plasma surrounding or near an AGN
- airglow: glow from a planet's atmosphere
- albedo: measure of reflectance
- anomalous cosmic rays: cosmic rays with unexpectedly low energies
- aperture: opening through which light passes
- aperture synthesis: interferometry to simulate a larger aperture telescope
- apparent magnitude: magnitude as seen from Earth adjusted for Earth atmosphere
- atmospheric window: frequency bands within which the atmosphere passes EMR
- Auger effect: atom's emission of an electron along with a photon
- aurora: light produced by atmosphere and solar wind
- B: photometric filter for blue light
- bandwidth: number of hertz between minimum and maximum frequencies
- beam: portion of a sky that a radio telescope is viewing
- black body: idealized object that reflects no light
- black-body radiation: EMR with a characteristic spectrum due to the temperature of a body
- blue shift: shortening of wavelengths due to Doppler effects
- bolometer: instrument measuring heat produced by radiation
- bolometric correction: difference between an object's bolometric and visual magnitudes
- bolometric luminosity: total luminosity of an object at all wavelengths
- bolometric magnitude: absolute magnitude of all wavelengths
- bremsstrahlung: photon emission when a charged particle is decelerated
- brightness temperature: temperature of an equivalent black body in terms of spectral radiance
- broad line region: AGN region producing broader lines
- cavity-enhanced absorption spectroscopy: passing a beam through a gas multiple times to amplify absorption lines
- CCD: type of electronic device to detect light
- Cherenkov radiation: radiation from the shock of a charged particle passing through a medium
- chirp: burst of signal rising or falling in frequency
- circular polarization ratio: ratio of circular polarization handedness in reflected radar signal
- CMB lensing: gravitational lensing of the CMB
- color index: a number that characterizes the color of an object
- color temperature: temperature-measure of a source based on a color index
- color-period diagram: means of comparing periods of stars at various wavelengths
- column density: measure of the matter through which EMR is passing
- Compton reflection: recognizable emission due to a gas or plasma's Compton scattering
- Compton scattering: photon collision with a charged particle that emits a different photon
- continuum emission: continuous spectrum such as black-body radiation or bremsstrahlung
- cooling function: function relating a gas's cooling rate to its temperature
- cosmic background radiation: electromagnetic radiation coming from every direction
- cosmic infrared background: widespread infrared radiation not associated with known sources
- cosmic microwave background: microwave radiation coming from every direction
- cosmic optical background: widespread optical radiation not associated with known sources
- cosmic X-ray background: X-ray radiation coming from outside the Milky Way
- cosmological redshift: redshift of distant objects due to the Hubble expansion
- cross dispersion spectrograph: echelle spectrograph with additional disperser crosswise to the first
- CTIS: imaging spectrometer using CT algorithm to sort out overlapping orders
- curvature radiation: synchrotron-like radiation when particles follow curved field lines
- cyclotron radiation: radiation emitted when charged particles are accelerated
- detective quantum efficiency: measure of instrument's ability to create images
- differential spectroscopy: analysis of the comparison of two spectrographs
- diffuse emission: electromagnetic radiation not confined to a point source
- dispersion measure: to what degree an EMR signal's lower frequencies are delayed
- distance modulus: apparent magnitude minus absolute magnitude
- Doppler broadening: broadening of spectral lines due to movement of the sources of photons
- Doppler shift: wave frequency difference due to relative velocity difference with source
- Earth-sized VLBI: ground-based VLBI with near-maximal baseline
- earthshine: reflected and emitted electromagnetic radiation from Earth
- Eddington approximation: approximation of a star's internal EMR's divergence from isotropic
- effective temperature: temperature of an equivalent black body in terms of total radiation
- Einstein coefficients: a substance's probabilities of emission and absorption
- electric dipole radiation: EMR generated by an oscillating electric dipole
- electromagnetic spectrum: spectrum of EMR
- electron volt: very small unit of energy
- electronic very-long-baseline interferometry: real-time VLBI using electronic links
- emission: addition of photons to a beam of EMR
- emission coefficient: measure of how much light a substance emits
- equation of radiative transfer: equation describing energy transfer by EMR
- equilibrium temperature: temperature a planet would have if it were an externally-heated black body
- European VLBI Network: consortium of radio telescopes to coordinate VLBI efforts
- extended source: term for astronomical object covering some area of the sky
- extinction: the absence of any radiation from an astronomical object because all is absorbed or scattered
- extragalactic background light: electromagnetic radiation from star formation and AGNs
- extreme ultraviolet: electromagnetic radiation in the range of 10-124 nm
- extremely low frequency: electromagnetic radiation, frequency 3 Hz to 30 Hz
- far infrared: infrared radiation with wavelengths in the 30-450 μm range
- fast radio burst: astronomical high energy radio pulses of a few milliseconds
- fluorescence: emission from a molecule excited by absorption
- flux: flow rate per unit area
- flux density: measure of the strength of a radio signal
- foreground subtraction: removing unwanted sources of EMR in intensity mapping
- frequency: number of cycles per unit of time, such as waves per second
- frequency modulation: changing the frequency of a signal's carrier
- G band: band of visible light around 5100 angstroms
- g-r color: difference between SDSS g' and r' magnitudes
- galaxy SED: SED of a galaxy, sometimes synthesized from photometric surveys
- gamma rays: electromagnetic radiation, wavelength 10 picometers and less
- gamma-ray burst: short flash of gamma rays apparently from outside our galaxy
- Geiger-avalanche photodiode: type of solid state photon sensor
- gravitational lensing: focusing electromagnetic radiation by gravitational force
- gravitational microlensing: gravitational lensing by "small" objects such as individual stars and planets
- gravitational redshift: redshift due to GR effects of gravity
- gray body: ideal object that reflects the same fraction of light at any wavelength
- GRB-supernova: supernova that produces a GRB
- greenhouse effect: mechanism that boosts temperature through selective blocking of EMR
- griz photometric system: photometric system designed for electronic sensors
- Gunn-Peterson trough: spectral feature in EMR from redshift 6+
- GZK limit: limit on energy of cosmic rays
- Hanle effect: effect of magnetic field on the polarization of emitted photons
- Hawking radiation: EMR theorized to be emitted by black holes, powered by their mass
- high frequency: electromagnetic radiation, frequency 3-30 MHz
- I band: passband for near-infrared light
- imaging Fourier transform spectroscopy: Michelson-interferometer-based imaging spectroscopy
- imaging spectrometer: device to capture spectrum point-by-point of an image
- infrared: light with wavelength too long for our eyes to sense
- infrared cirrus: cirrus-cloud-like infrared emissions from dust, etc.
- infrared excess: more infrared than that of a star's typical spectrum
- integral field spectrograph: spectrograph that captures images
- integral field unit: instrument to allow a spectrograph to capture data over a 2D field
- intensity: power reaching a surface from a specific source
- intensity mapping: measure of cosmic matter density
- interferometer: device detecting EMR properties using interference between waves
- interstellar radiation field: EMR throughout the "empty" space of a galaxy
- ionizing radiation: radiation with photon energy sufficient to ionize
- irradiance: EMR power reaching a surface
- jansky: unit of measurement of spectral flux density
- JHK photometric system: system to classify stars according to near-infrared colors
- K band: atmospheric window centered around 2.2 microns, or 136 THz
- K correction: correction to magnitude for redshift
- Kirchhoff's law of thermal radiation: for an object in thermodynamic equilibrium, emissivity equals absorptance
- Kirchhoff's laws: laws regarding the source of spectral lines
- light curve: changing intensity of light from a transient
- line shape function: function describing the shape of a spectral line
- long gamma-ray burst: GRB lasting more than two seconds
- low-surface-brightness galaxy: galaxies less bright than those historically identified
- luminosity: measure of brightness
- Lyman-Werner photon: ultraviolet photon with proper energy to excite molecular hydrogen
- magnetic dipole radiation: EMR naturally generated by a spinning magnetic dipole
- magnitude: a logarithmic measure of brightness
- maser: electromagnetic radiation amplified by stimulated emission
- microchannel array: electronic device to EMR
- microwave: electromagnetic radiation, frequency 300 MHz to 300 GHz
- mid infrared: infrared radiation with wavelengths in the 7.5-25 μm range
- MKO photometric system: 2000s system covering near infrared
- monochromatic luminosity: luminosity at a specific wavelength
- multi-object spectrograph: device to record the spectrum of multiple targets simultaneously
- multipole expansion: series expansion of a function over the surface of a sphere
- narrow line region: AGN region producing narrower lines
- near infrared: electromagnetic radiation in the range of 750-2500 nm
- non-thermal: regarding radiation other than black-body
- non-thermal emission: EMR not due to a body's heat
- observational astronomy: term covering observation
- OIR: "band name" that means both visible light and infrared
- opacity: a measure of opaqueness of a material
- optical depth: a measure of opaqueness of a path of light
- optics: science and technology regarding visible light
- oscillator strength: fraction expressing QM's contribution to the probability of absorption
- passband: range of electromagnetic wavelengths that a filter allows
- Penrose Compton scattering: type of Compton scattering within a black hole's ergosphere
- phase curve: brightness of an object according to its phase angle
- photochemistry: study of the chemical effects of light
- photodiode: class of solid state device to detect EMR
- photoevaporation: dispersal of a gas from UV radiation
- photographic magnitude: magnitude derived from photographic plate
- photoionization: photon striking neutral atom expelling an electron
- photometer: instrument measuring brightness
- photometric redshift: method of estimating redshift without spectroscopy
- photometric system: specification of a set of filters/passbands
- photomultiplier tube: electronic device to detect light
- photon counting: sensing EMR down to the photon level
- photon energy: the energy carried by a single photon
- photon noise: variation in light measurement due to its quantum nature
- Planck function: yields black-body spectrum curve
- polarimetry: measurement of polarization of EMR
- polarization: property of waves that oscillate in a particular direction
- polarization modes: curl- and divergent-like components of CMB polarization patterns
- post-starburst galaxy: galaxy indicating star formation some time back
- Poynting vector: measures directional energy flux density
- Q band: name for EMR frequency-range on the order of 45 GHz
- quantum efficiency: measure of instrument's ability to sense EMR
- quenched galaxy: galaxy currently producing minimal stars
- R band: band of visible light around 6500 angstroms
- radar: probe based on reflecting radio waves
- radiance: measure of EMR to/from a solid angle through an area
- radiant flux: measure of brightness
- radiation hydrodynamics: hydrodynamics plus the effects of EMR
- radiation pressure: the pressure exerted by electromagnetic radiation
- radiation zone: region of a star transmitting energy through radiative diffusion
- radiative flux: power passing through a unit area
- radiative transfer: energy transfer in the form of electromagnetic radiation
- radiative transfer code: computer model of a gas's radiative transfer
- radiative transfer model: models of radiative transfer, often computerized
- radio: electromagnetic radiation, frequency 3 kHz to 300 GHz
- radiometer: device for measuring radiant flux
- Rayleigh scattering: wave scattering by particles smaller than the wavelength
- Rayleigh-Jeans law: yields approximation of black-body curve useful at low frequencies
- reddening: red appearance of astronomical objects because blue light is attenuated by dust
- redshift: change to longer wavelengths due to Doppler effects
- redshift space: concept of space using redshift as the radial dimension
- relativistic beaming: directional relativistic effect on light from relativistic speeds
- relativistic speed: a substantial fraction of the speed of light
- rest wavelength: normal wavelength observed when not moving in relation to the source
- Sagnac effect: an effect of the movement of light beams regarding their interference
- scattering: changing the direction of a particle's movement
- Schuster-Schwarzschild model: simplified model of a star's production of absorption lines
- self-absorption: EMR absorption by the same substance that emitted it
- sensitivity function: function of wavelength giving the sensitivity of an instrument
- short gamma-ray burst: GRB lasting less than two seconds
- solar constant: flux from the Sun at 1 AU
- source function: measure indicating the effect of a material on EMR passing through
- specific intensity: intensity per unit wavelength or frequency
- spectral energy distribution: function or plot of brightness at each wavelength in the spectrum
- spectral flux density: flux or power of radiation per unit area per unit wavelength
- spectral index: power by which an object's flux depends on frequency
- spectral line energy distribution: function or plot of brightness of lines in a spectrum
- spectral resolution: measure of a spectrograph's ability to resolve features of the spectrum
- spectral signature: spectral characteristics indicating the emitting material and conditions
- spectral temperature: temperature-measure of a source based on a spectrum
- spectrograph: device to record the spectrum of incoming light
- spectrography: charting the strengths of different electromagnetic wavelengths
- spectrometer: device to measure light by wavelength across its spectrum
- spectrometry: measuring the strengths of different electromagnetic wavelengths
- spectropolarimetry: measurement of light's polarization by wavelength
- spectroscope: device to study the spectrum of incoming light
- spectroscopy: measurement of light with various electromagnetic wavelengths
- speed of light: fundamental constant measured as the speed at which light travels
- starburst galaxy: galaxy forming stars at a very high rate
- Stark effect: electric field influence on spectral lines
- stimulated emission: emission triggered by received photons
- Stokes parameters: means of describing a polarization state
- Strömgren photometric system: four-color photometric system devised in 1950s
- submillimeter galaxy: galaxy that produces significant submillimeter radiation
- subradio: electromagnetic radiation, frequency below 3 kHz
- super low frequency: electromagnetic radiation, frequency 30 Hz to 300 Hz
- superconducting tunnel junction: type of Josephson junction usable in EMR sensors
- supernova light curve: changing intensity of light following a supernova
- superradiance: exotic quantum-mechanics light-amplification phenomenon
- surface brightness: brightness per unit area of a surface
- surface of last scattering: sphere around us from which CMB photons are just reaching us
- synchrotron radiation: radiation emitted when high-speed charged particles are accelerated
- synchrotron self-Compton: charged particle cloud scattering its own synchrotron-produced photons
- thermal bremsstrahlung: type of EMR produced by thin, hot plasma
- thermal dust emission: glow of dust heated by stars or AGNs
- thermal emission: EMR due to a body's heat
- Thomson optical depth: a measure of effects of Thomson scattering
- Thomson scattering: elastic scattering of photons by a charged particle
- tired light: an alternate theory explaining the cosmological redshift
- transit spectroscopy: spectroscopy through an exoplanet's transit
- transmission spectroscopy: spectrum of radiation passing through a substance
- tremendously low frequency: presumably electromagnetic radiation, frequency below 3 Hz
- two-stream approximation: approximation of a star's internal EMR's divergence from isotropic
- U: photometric filter for ultraviolet light
- UBV photometric system: commonly-cited photometric system for describing stars' colors
- ugriz photometric system: photometric system used for SDSS
- ultra low frequency: electromagnetic radiation, frequency 300 Hz to 3 kHz
- ultra-high-energy gamma rays: energetic gamma rays with more than 100 TeV photon energy
- ultraviolet: electromagnetic radiation, wavelength 10-400 nm
- UVOIR: a spectral "band name" covering UV, visible light, and IR
- V: photometric filter for visible light
- Vega system: magnitude calibration such that Vega has zero magnitude
- very low frequency: electromagnetic radiation, frequency 3-30 kHz
- very-high-energy gamma rays: energetic gamma rays with 100 GeV to 100 TeV photon energy
- very-long-baseline interferometry: interferometry based upon storing timing data at each telescope
- visible light: electromagnetic radiation that our eyes can sense
- wavelength: distance over which a repeating wave repeats
- wavenumber: reciprocal of wavelength
- weak lensing: slight lensing detected in random patterns of distant objects
- Wien approximation: yields approximation of black body curve useful at short wavelengths
- Wien's displacement law: relates temperature to wavelength of maximum emission
- X-ray: electromagnetic radiation, wavelength 0.01 to 10 nanometers
- X-ray flash: short flash of X-rays
- XEUV: electromagnetic radiation in the range of 0.15-124 nm
- Zeeman effect: magnetic field influence on spectral lines
- Zeeman-Doppler imaging: technique for imaging stellar magnetic fields
- EMRI (extreme mass ratio inspiral): inspiraling pair of objects with mass ratio beyond 10,000
- EMU: see Australian Square Kilometre Array Pathfinder
- EMUS: see Hope Probe
- ENA (energetic neutral atom): high-speed neutral atom
- ENACS (ESO Nearby Abell Cluster Survey): 1990s spectroscopy and photometry survey of galaxy clusters
- Enceladus: Saturn moon considered possible carrier of life
- Enceladus Life Finder: mission to search for life on Saturn moon Enceladus
- Saturn: second largest planet in the solar system
- Enceladus Orbilander: concept for a NASA mission to Enceladus
- Encke-type comet: see long-period comet
- endothermic reaction: reaction that absorbs heat
- energetic neutral atom: high-speed neutral atom
- energetic particle: see solar energetic particle
- energy: physical state needed to do something
- energy balance model: see one dimensional climate model
- energy density: energy per unit volume
- energy spectral density: see magnetic energy spectrum
- energy spectral density: see spectral density
- ENG: see double star designation
- engineering
- Engineering and Physical Sciences Research Council: UK agency for scientific research, including astronomy
- engineering first light: see first light
- England
- Enhanced MERLIN: see MERLIN
- Enhanced X-ray Timing and Polarization (eXTP): plan for a space X-ray telescope
- Enlil
- WSA-Enlil: computer model of heliosphere for space weather prediction
- enormous Lyman-alpha nebula: see Lyman-alpha blob
- Enriched Xenon Observatory (EXO): experiment to detect neutrinoless double beta decay in xenon
- enrichment mode: see mass spectrometer
- entropic gravity: MOND-like theory of gravity
- entropy: relative measure of the amount of usable energy available
- envelope (atmosphere): gas surrounding astronomical object
- Environmental Context: see RESOLVE
- EnVision: planned 2030s ESA Venus orbiter
- Enzo: hydrodynamic simulation system
- eon (gigayear): a billion years
- EOR (epoch of reionization): time when the universe's neutral hydrogen atoms ionized
- EoR (epoch of reionization): time when the universe's neutral hydrogen atoms ionized
- EoR-Spec: see Fred Young Submillimeter Telescope
- EoS (equation of state): equation relating temperature, pressure, and volume
- Eos
- EOVSA
- EP (Einstein Probe): Chinese X-ray space observatory
- EP: see photodissociation
- EPA: see Giotto
- EPAC: see Ulysses
- EPAM: see Advanced Composition Explorer
- EPAS: see International Cometary Explorer
- EPD: see Galileo
- EPD: see Solar Orbiter
- EPDP: see SMART-1
- Ephemerides of Minor Planets: annual catalog on minor planet positions
- ephemeris: information on the position of a celestial body in the sky over time
- ephemeris time
- time standard: method of designating points in time and quantifying time periods
- EPIC: see DISCOVR
- EPIC: see K2
- EPIC: see XMM-Newton
- EPIC 201912552: see K2-18b
- EPIC 201912552b (K2-18b): super-Earth in a habitable zone
- EPICS: see European Extremely Large Telescope
- epicycle: small circular motion around a large circular motion
- epicyclic frequency: frequency of oscillation in an accretion disk
- epicycle: small circular motion around a large circular motion
- spiral galaxy: flat galaxy with spiraling arms
- Epimetheus: see shepherd moon
- episodic star formation: see star formation
- EPO: "education and public outreach"
- EPOCh
- EPOXI: mission using Deep Impact for further exploration
- epoch: when an object was at a particular set of celestial coordinates
- epoch B1900.0
- epoch: when an object was at a particular set of celestial coordinates
- epoch B1950.0: midnight 1/1/1950 GMT as used as a time reference
- epoch: when an object was at a particular set of celestial coordinates
- epoch folding (data folding): locating periods in data by trial
- epoch J2000.0: noon 1/1/2000 GMT as used as a time reference
- epoch: when an object was at a particular set of celestial coordinates
- epoch of galaxy assembly (epoch of galaxy formation): before z=1, when many galaxies formed
- epoch of galaxy formation: before z=1, when many galaxies formed
- epoch of recombination (recombination): time when the universe's ionized hydrogen atoms neutralized
- epoch of reionization: time when the universe's neutral hydrogen atoms ionized
- EDGES: survey aiming at highly-redshifted 21-cm detection
- PAPER: radio interferometer for 21-cm measurement
- SARAS: survey aiming at highly-redshifted 21-cm detection
- EPOXI: mission using Deep Impact for further exploration
- Deep Impact: mission to create and observe an impact with a comet
- EPPS: see MESSENGER
- EPS merger trees
- Epsilon Eridani: third nearest visible star system in sky
- Epsilon Ind A ab: see Epsilon Indi
- Epsilon Indi: nearby star system including two brown dwarf companions
- EPSRC (Engineering and Physical Sciences Research Council): UK agency for scientific research, including astronomy
- EPTA (European Pulsar Timing Array): European collaboration of radio telescopes
- EPTA+: see European Pulsar Timing Array
- EQ (equatorial coordinate system): latitude/longitude-like system for the celestial sphere
- equant: see epicycle
- equation
- equation of radiative transfer: equation describing energy transfer by EMR
- equation of state: equation relating temperature, pressure, and volume
- Equation of State: Supernovae Trace Cosmic Expansion (ESSENCE): survey using supernova data to study dark energy
- Equator: see circle of latitude
- equatorial
- equatorial coordinate system: latitude/longitude-like system for the celestial sphere
- equatorial coordinates: see equatorial coordinate system
- J2000.0 equinox: equinox as of the J2000.0 epoch used as a positional reference
- equatorial Kelvin wave: see Kelvin waves
- equatorial mount: telescope mount with axis parallel to Earth's
- equatorial Rossby wave: see Kelvin waves
- equatorial wave: see Kelvin waves
- equilibrium condensation model: chemical model explaining solar system planet abundances
- equilibrium temperature: temperature a planet would have if it were an externally-heated black body
- equilibrium-limited weathering: see weathering
- equinox: point-in-time when tilt of Earth is neither toward nor away from the Sun
- J2000.0 equinox: equinox as of the J2000.0 epoch used as a positional reference
- equipment
- bandpass filter: device to filter away all but a band of frequencies
- drogue chute: parachute to slow something moving at high speed
- filter: optical device to filter out part of the EMR spectrum
- ion engine: type of electrical spacecraft engine
- mirror support cell: units in a telescope that support the mirror
- MMRTG: power source for space probes
- plate: product of astronomical photography
- Space Launch System: launch rocket in development, e.g., for future astronomical projects
- equipotential surface: see gravitational potential model
- equivalent aperture: see aperture
- equivalent elastic thickness (elastic thickness): measure of the thickness of a sagging layer of a planet surface
- equivalent width: see line broadening
- ER: see Lunar Prospector
- era of reionization (epoch of reionization): time when the universe's neutral hydrogen atoms ionized
- eRASS: see eROSITA
- eRASSt: see eROSITA
- eRASSU: see eROSITA
- erg: CGS unit of energy
- energy: physical state needed to do something
- ergosphere: type of region of space around rotating black hole
- black hole: region of such high mass that light cannot escape
- frame dragging: region of space dragged into rotation by a rotating object
- Penrose process: process by which energy can be extracted from black hole's rotation
- ERIC (European Research Infrastructure Consortium): science and technology initiative
- Eridanus II
- Eridanus Supervoid
- void: empty spaces between large scale structures
- Eridanus Void
- ERIS: see European Southern Observatory Very Large Telescope
- Eris
- ERNE: see Solar and Heliospheric Observatory
- ERO (extremely red object): class of galaxies showing more infrared than visible light
- EROS: search for MACHOs
- Eros
- EROS-1
- EROS-2
- erosion
- ablation: erosion of the surface of an object
- weathering: changes in surface due to contact with atmosphere
- erosion barrier: see planet formation
- eROSITA: Russian/German space X-ray telescope launched in 2019
- eRosita: see Spektr-RG
- eROSITA all-sky survey: see eROSITA
- error bar: feature of a graph to indicate accuracy
- ERS: see James Webb Space Telescope
- eruptive variable star: see variable star
- ES: see double star designation
- Es-Birm: see rare designator prefixes
- ESA (European Space Agency): NASA-like international space organization in Europe
- ARIEL: planned space mission for exoplanet spectrography
- ATHENA: planned ESA X-ray space telescope
- BepiColombo: mission to Mercury
- Cassini: explorer spacecraft sent to Saturn
- CHEOPS: space telescope in development to measure radii of exoplanets
- COROT: observatory-satellite to look for transiting exoplanets and stellar oscillations
- Darwin: past plan for space telescopes acting as an interferometer
- EnVision: planned 2030s ESA Venus orbiter
- ESA Vigil: plan for space-weather warning satellite at L5
- Euclid: survey observatory-satellite to measure dark energy
- EURECA: 1990s ESA satellite with a number of experiments
- ExoMars: program to search for signs of life on Mars
- EXOSAT: 1980s European space X-ray telescope
- Gaia: astrometry survey satellite launched in 2013
- Giotto: 1980s space mission carrying out a Comet Halley flyby
- Herschel Space Observatory: infrared observatory-satellite with 3.5-meter reflector
- Hipparcos: ESA astrometry space observatory circa 1990
- Infrared Space Observatory: 1990s 60-cm infrared space telescope
- INTEGRAL: European gamma ray observatory-satellite
- International Ultraviolet Explorer: 1980s ultraviolet space telescope
- James Webb Space Telescope: 6.5-meter infrared space telescope at L2
- JUICE: mission to Jupiter in development
- LISA: proposed space mission to detect gravitational waves
- Mars Express: Mars probe launched by ESA in 2003
- New Gravitational Wave Observatory: past proposal for space mission to detect gravitational waves
- Planck: microwave telescope in space
- PLATO: planned observatory-satellite aimed at finding exoplanets
- Rosalind Franklin: Mars rover in development for 2028 launch
- Rosetta: space probe that visited a comet
- SMART-1: Swedish lunar orbiter operational 2003-2006
- Solar and Heliospheric Observatory: satellite observing the Sun
- Solar Orbiter: space probe investigating the Sun's surface and the heliosphere
- Spacelab: reusable laboratory that was an optional Space Shuttle payload
- THEMIS: set of satellites studying the Earth's magnetic field
- THESEUS: plan for X-ray/Gamma-ray transient space mission
- Trace Gas Orbiter: ESA and Russian Mars orbiter-probe launched in 2016
- Venus Express: Venus probe launched by ESA in 2005
- XMM-Newton: X-ray observatory-satellite operated by ESA
- XRISM: X-ray space telescope launched in 2023
- ESA Vigil: plan for space-weather warning satellite at L5
- escape fraction: fraction of ionizing photons escaping a body
- escape parameter (Jeans parameter): ratio measuring a tendency of an atmosphere to escape
- escape velocity: minimal velocity that allows something to overcome a body's gravity
- Escorial: see rare designator prefixes
- ESD: see spectral density
- ESEX: see ARGOS
- ESI: see Keck Observatory
- ESIS: EUV spectrograph for solar corona observation
- ESO (European Southern Observatory): organization operating telescopes in the southern hemisphere
- ESO: see ESO/Uppsala Survey of the ESO (B) Atlas
- ESO (B) Atlas
- ESO 137-001: barred spiral galaxy in the Abell 3627 cluster
- ESO 3.6m Telescope: reflector telescope at La Silla
- ESO 97-G13 (Circinus Galaxy): nearest Seyfert galaxy
- ESO B plates
- ESO FWO
- ESO Nearby Abell Cluster Survey: 1990s spectroscopy and photometry survey of galaxy clusters
- ESO plate: see plate
- ESO Quick Blue Survey
- ESO Schmidt Telescope: 1 meter telescope in Chile with a wide field-of-view
- ESO VLT (European Southern Observatory Very Large Telescope): four 8.2-meter optical telescopes in Chile that can act together
- ESO-HA: see rare designator prefixes
- ESO/SERC Southern Sky Atlas: see UK Schmidt Survey
- ESO/SERC Survey (UK Schmidt Survey): photographic survey of the southern hemisphere sky
- ESO/Uppsala Survey of the ESO (B) Atlas: 1970s southern all-sky survey
- ESO594-G004 (Sagittarius Dwarf Irregular Galaxy): most distant galaxy in the Local Group
- Esp: see double star designation
- ESPaDOnS: see Canada-France-Hawaii Telescope
- ESPRESSO: see European Southern Observatory Very Large Telescope
- ESRO (European Space Research Organisation): 1960s-1970s European collaboration
- Cos-B: 1970s satellite for studying gamma rays
- TD-1A: 1970s European observatory-satellite with UV telescopes
- ESSENCE: survey using supernova data to study dark energy
- ESTEC: see European Space Agency
- ESTRACK: see European Space Agency
- ET (Einstein Telescope): concept for a larger LIGO-like GW detector
- eta car (Eta Carinae): variable star
- Eta Carinae: variable star
- Eta Carinae Nebula (Carina Nebula): HII region with stars and nebulae of interest
- Eta Orionis
- Orion: well-known constellation in the northern hemisphere
- etalon: two parallel reflective surfaces separating light according to wavelength
- ETC (exposure time calculator): app to calculate time to carry out an observation
- etendue: measure of how wide and deep a telescope observes
- ETG: see galaxy
- ethane: see hydrocarbon
- ethene (ethylene): compound of two carbon and four hydrogen atoms
- ether: see relativity
- ethylene: compound of two carbon and four hydrogen atoms
- ethyne (acetylene): compound of two carbon and two hydrogen atoms
- ETNO
- EU: see EURECA
- Euclid: survey observatory-satellite to measure dark energy
- Euclidean metric: see metric
- EUI: see Solar Orbiter
- Euler method
- Euler's formula: formula relating exponentials to trigonometric functions
- Fourier series: type of series able to approximate a periodic function
- Euler's identity: see Euler's formula
- Euler's number
- Eulerian code: see stellar structure
- Eunomia
- EURECA: 1990s ESA satellite with a number of experiments
- Europa: well-known Jupiter moon
- Europa Clipper: NASA Europa space probe launched in 2024
- Europa Lander: plan for a late 2020s Europa probe landing on the surface
- Europa Multiple Flyby Mission (Europa Clipper): NASA Europa space probe launched in 2024
- Europe
- European
- European Association for Astronomy Education: promotes science education
- European Astronomical Society: European organization
- European Extremely Large Telescope: 39-meter telescope under construction
- European Gravitational Observatory: gravitational wave observatory in Italy
- European Large Area ISO Survey: see Infrared Space Observatory
- European Pulsar Timing Array: European collaboration of radio telescopes
- European Research Infrastructure Consortium: science and technology initiative
- European Retrievable Carrier (EURECA): 1990s ESA satellite with a number of experiments
- European Southern Observatory: organization operating telescopes in the southern hemisphere
- European Southern Observatory Very Large Telescope: four 8.2-meter optical telescopes in Chile that can act together
- European Space Agency: NASA-like international space organization in Europe
- European Space Research and Technology Centre: see European Space Agency
- European Space Research Organisation: 1960s-1970s European collaboration
- Cos-B: 1970s satellite for studying gamma rays
- European Space Research Organization
- TD-1A: 1970s European observatory-satellite with UV telescopes
- European Space Tracking: see European Space Agency
- European VLBI Network: consortium of radio telescopes to coordinate VLBI efforts
- European X-ray Observatory Satellite (EXOSAT): 1980s European space X-ray telescope
- europium
- EUSO: see EUSO-SPB
- EUSO-2: see EUSO-SPB
- EUSO-SPB: balloon-borne cosmic ray observatory
- EUSO-SPB2: see EUSO-SPB
- EUV (extreme ultraviolet): electromagnetic radiation in the range of 10-124 nm
- EUV: see IMAGE
- CHIPS: small satellite to investigate ISM plasma
- ionizing radiation: radiation with photon energy sufficient to ionize
- EUV From Earth and Space: see OSO 8
- EUV Snapshot Imaging Spectrograph (ESIS): EUV spectrograph for solar corona observation
- EUVE (Extreme Ultraviolet Explorer): 1990s ultraviolet space telescope
- EUVI: see STEREO
- EUVIP: see ARGOS
- eV (electron volt): very small unit of energy
- energy: physical state needed to do something
- gamma rays: electromagnetic radiation, wavelength 10 picometers and less
- photon: quantum of light, i.e., light as a particle
- photon energy: the energy carried by a single photon
- X-ray: electromagnetic radiation, wavelength 0.01 to 10 nanometers
- evaluation
- evaporating gas globule: very small dense cloud of hydrogen and dust
- evaporation: particles escaping, e.g., liquid molecules escaping as gas
- evaporation valley: see Fulton gap
- evaporation valley: see super-Earth
- EVCC: see Virgo Cluster Catalog
- EVE: see Solar Dynamics Observatory
- event
- 1947 sunspot: largest sunspot ever recorded
- 775 AD event: apparent solar eruption, based upon tree-ring evidence
- AT2018cow: unusual 2018 optical transient
- Big Bang: theoretical event when the universe expanded from a point
- Big Crunch: theoretical end of universe drawn together by gravity
- Carrington event: solar storm September 1-3 1859
- epoch of reionization: time when the universe's neutral hydrogen atoms ionized
- Great Debate: historical debate regarding the nature of galaxies
- GW170817: 2017 gravitational wave detection from a neutron star merger
- Kepler's Supernova: Type Ia supernova observed in 1604 by Johannes Kepler
- late heavy bombardment: time after solar system planet-formation when many impacts occurred
- Oh-My-God Particle: extremely energetic particle from space detected in 1991
- recombination: time when the universe's ionized hydrogen atoms neutralized
- SN 1572: Type Ia supernova noted in 1572 by Tycho Brahe
- SN 185: supernova recorded in China in AD 185
- SN 1987A: supernova in February 1987 rare for being visible by the naked eye
- SN 2014J: Type Ia supernova in Messier 82, the Cigar Galaxy
- solar eclipse: eclipse consisting of the Moon blocking the Sun from view
- stellar merger: two stars combining into one
- event horizon: surface-shape around a black hole through which light cannot escape
- Event Horizon Telescope: growing VLBI network
- event type
- EVLA (Very Large Array): radio telescope in New Mexico
- EVN (European VLBI Network): consortium of radio telescopes to coordinate VLBI efforts
- evolution (stellar evolution): the pattern of a star's changing structure over its life
- Evolution and Assembly of Galaxies and their Environments (EAGLE): simulation of galaxy formation and evolution
- Evolutionary Map of the Universe: see Australian Square Kilometre Array Pathfinder
- evolutionary track: H-R diagram track of the life of a star
- Evryscope: automated array of telescopes to uncover transients
- Ex-MORA: see MORA
- exaFLOP
- ExAO (extreme adaptive optics): high-performance version of AO system
- exascale computing: exaFLOP computing capability, i.e., quintillion FLOPs
- EXCEED: see Hisaki
- excess kurtosis: see kurtosis
- exchange: see binary star
- excitation (atomic excitation): electrons above the ground state within atoms
- excitation (state of excitation): energy level of something above the minimum
- excitation temperature: see temperature
- excited state: see atomic excitation
- excited state: see state of excitation
- EXCLAIM: planned balloon-borne 70-cm telescope with spectrometers
- EXES: see SOFIA
- EXI: see Hope Probe
- exit pupil: size of the image as presented to the eye
- EXO: experiment to detect neutrinoless double beta decay in xenon
- EXO: see EXOSAT
- EXO-200: see EXO
- Exo-C: see Exo-S
- exo-Earth: Earth-like exoplanet
- Earth analog: planet with characteristics of Earth
- GJ 1132 b: Earth-like extrasolar planet discovered in 2015
- Kepler-186f: Earth-like exoplanet in a star's habitable zone
- TOI 700 d: Earth-sized exoplanet in a habitable zone
- Exo-Kuiper Belt: see Kuiper Belt
- Exo-S: a study on the concept of a starshade mission
- Exo-starshade (Exo-S): a study on the concept of a starshade mission
- exobase: see exosphere
- exobiology (astrobiology): study of extra-terrestrial life
- Exobiology on Mars (ExoMars): program to search for signs of life on Mars
- exocomet: see falling evaporating body
- ExoCTK: collection of software for exoplanet observation and analysis
- exoearth (exo-Earth): Earth-like exoplanet
- EXOFAST: code to match model parameters with exoplanet observation data
- ExoFOP: site to facilitate exoplanet follow-up observation
- ExoFOP-K2: see ExoFOP
- ExoFOP-Kepler: see ExoFOP
- ExoFOP-TESS: see ExoFOP
- ExoLife Finder: see Colossus Telescope
- ExoMars: program to search for signs of life on Mars
- ExoMars: see Trace Gas Orbiter
- Mars: well-explored planet in the solar system
- Rosalind Franklin: Mars rover in development for 2028 launch
- ExoMars Rover (Rosalind Franklin): Mars rover in development for 2028 launch
- ExoMars TGO (Trace Gas Orbiter): ESA and Russian Mars orbiter-probe launched in 2016
- ExoMars Trace Gas Orbiter (Trace Gas Orbiter): ESA and Russian Mars orbiter-probe launched in 2016
- exomoon (exosatellite): natural satellite not in the solar system
- exoplanet (extra-solar planet): planet not in the solar system
- Exoplanet Characterization Toolkit (ExoCTK): collection of software for exoplanet observation and analysis
- exoplanet demographics (planet demographics): statistics regarding the number of planets
- exoplanet demographics: see demographics
- exoplanet eclipse light curve: graph of light as an exoplanet transits in front of its star
- Exoplanet Follow-up Observing Program (ExoFOP): site to facilitate exoplanet follow-up observation
- exoplanet occurrence rate (planet demographics): statistics regarding the number of planets
- Exoplanet Starshade (Exo-S): a study on the concept of a starshade mission
- exoplanet starshade (starshade): spacecraft to block light from a specific body
- exoplanet transit light curve (exoplanet eclipse light curve): graph of light as an exoplanet transits in front of its star
- exoplanets
- EXOSAT: 1980s European space X-ray telescope
- exosatellite: natural satellite not in the solar system
- exosphere: outer portion of atmosphere so thin that it is not gas-like
- ionosphere: layers of Earth atmosphere with significant ions
- exothermic reaction: see endothermic reaction
- exotic star: term for theoretical stars not made of atoms/ions
- Expérience pour la Recherche d'Objets Sombres (EROS): search for MACHOs
- Expanded Owens Valley Solar Array
- Expanded Very Large Array (Very Large Array): radio telescope in New Mexico
- expansion fan: the "sound" of a supersonic flow flowing around a convex corner
- expansion of the universe (Hubble expansion): ongoing expansion of the universe
- expectation bias: see selection bias
- expeditions
- experiment
- Experiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM): planned balloon-borne 70-cm telescope with spectrometers
- Experiment to Detect the Global EoR Signature (EDGES): survey aiming at highly-redshifted 21-cm detection
- Explorer 42 (Uhuru): 1970 X-ray space telescope
- Explorer 48 (Small Astronomy Satellite 2): 1970s NASA gamma ray space telescope
- Explorer 53 (Small Astronomy Satellite 3): 1970s NASA X-ray space telescope
- Explorer 57 (International Ultraviolet Explorer): 1980s ultraviolet space telescope
- Explorer 59 (International Cometary Explorer): 1980s space mission flying by comets
- Explorer 64 (Solar Mesophere Explorer): 1980s Earth atmospheric ozone research satellite
- Explorer 66 (Cosmic Background Explorer): 1989 satellite for surveying the CMB
- Explorer 67 (Extreme Ultraviolet Explorer): 1990s ultraviolet space telescope
- Explorer 69 (RXTE): space mission to time X-ray variations
- Explorer 71 (Advanced Composition Explorer): satellite collecting solar wind and cosmic rays
- Explorer 73 (TRACE): former solar observing satellite
- Explorer 75 (Wide Field Infrared Explorer): partly-failed 1999 infrared satellite
- Explorer 77 (Far Ultraviolet Spectroscopic Explorer): early 2000s space telescope for short-wavelength ultraviolet
- Explorer 78 (IMAGE): satellite mission to study magnetosphere
- Explorer 80 (Wilkinson Microwave Anisotropy Probe): spacecraft that measured variations in the cosmic background radiation
- Explorer 82 (CHIPS): small satellite to investigate ISM plasma
- Explorer 83 (Galaxy Evolution Explorer): observatory-satellite with 50-cm ultraviolet telescope
- Explorer 84 (Swift): satellite for studying gamma-ray bursts
- Explorer 91 (Interstellar Boundary Explorer): satellite observing the ISM/heliosphere boundary
- Explorer 92 (Wide-field Infrared Survey Explorer): infrared space telescope aimed at an all-sky survey
- Explorer 93 (NuSTAR): space telescope for high-energy X-rays
- Explorer 95 (Transiting Exoplanet Survey Satellite): observatory-satellite searching for transiting exoplanets
- Explorer 97 (IXPE): space observatory with X-ray polarimeters
- Explorer Program
- Explorers Program
- exponential growth: see runaway process
- exponential profile: see surface brightness profile
- Sérsic profile: model of the relative surface brightness across a galaxy
- exposure time: time spent acquiring a signal
- exposure time calculator: app to calculate time to carry out an observation
- EXPRES: Yale HRS spectrometer aimed at exoplanet detection
- EXPRES: see Lowell Discovery Telescope
- Extended Baryon Oscillation Spectroscopic Survey: see Baryon Oscillation Spectroscopic Survey
- Extended BOSS: see Baryon Oscillation Spectroscopic Survey
- Extended Chandra Deep Field-South: see Extended Chandra Deep Field-South Survey
- Extended Chandra Deep Field-South Survey: 1100 square arcminute X-ray survey
- extended GALEX Arecibo SDSS Survey: see GALEX Arecibo SDSS Survey
- Extended Groth Strip: region of sky searched for distant galaxies
- CEERS: JWST early release observation program covering the EGS
- DEEP2: redshift survey of 60,000 galaxies
- Groth Strip: region of sky in early HST survey
- extended planetary nebula: see planetary nebula
- Extended Roentgen Survey with an Imaging Telescope Array (eROSITA): Russian/German space X-ray telescope launched in 2019
- extended source: term for astronomical object covering some area of the sky
- externally dispersed interferometer
- TripleSpec: near-infrared spectrograph on the Hale Telescope
- extinct pulsar: see pulsar
- extinction: the absence of any radiation from an astronomical object because all is absorbed or scattered
- extinction coefficient: see extinction
- extinction curve: see extinction
- extinction efficiency factor: see extinction
- extinction event (mass extinction): event in which many species went extinct
- eXTP: plan for a space X-ray telescope
- XTP: past plan for a space X-ray telescope
- extra-background light
- CIBER: sounding-rocket survey of near-infrared background
- extra-solar planet: planet not in the solar system
- extragalactic astronomy: astronomy of other galaxies, galaxy clusters, AGNs, quasars, etc.
- extragalactic background light: electromagnetic radiation from star formation and AGNs
- extragalactic cosmic rays: see cosmic rays
- Extragalactic Distance Database: online database of distance-related measures of galaxies
- extragalactic distance scale: see cosmic distance ladder
- extragalactic gamma ray background (cosmic gamma ray background): gamma-ray radiation seen everywhere
- extragalactic nebula (galaxy): gravitationally-bound group of stars
- extrasolar giant planet: see extra-solar planet
- extrasolar moon (exosatellite): natural satellite not in the solar system
- Extrasolar Planet Observation and Characterization
- EPOXI: mission using Deep Impact for further exploration
- Extrasolar Planet Observation and Deep Impact Extended Investigation (EPOXI): mission using Deep Impact for further exploration
- Deep Impact: mission to create and observe an impact with a comet
- extrasolar satellite (exosatellite): natural satellite not in the solar system
- extremal black hole: see black hole model
- extreme adaptive optics: high-performance version of AO system
- extreme AO (extreme adaptive optics): high-performance version of AO system
- extreme emission line galaxy: see emission line galaxy
- extreme energy cosmic rays: see cosmic rays
- extreme helium star: see helium star
- extreme horizontal branch: see horizontal branch
- extreme horizontal branch star: see horizontal branch
- extreme Kuiper Belt object: see Kuiper Belt
- extreme luminous supergiant: see supergiant
- extreme mass ratio inspiral: inspiraling pair of objects with mass ratio beyond 10,000
- Extreme Precision Spectrometer (EXPRES): Yale HRS spectrometer aimed at exoplanet detection
- extreme trans-Neptune object
- extreme trans-Neptunian object
- extreme ultraviolet: electromagnetic radiation in the range of 10-124 nm
- Extreme Ultraviolet Explorer: 1990s ultraviolet space telescope
- Extreme Ultraviolet Spectroscope: see Hisaki
- Extreme Ultraviolet Spectroscope for Exospheric Dynamics: see Hisaki
- Extreme Universe Space Observatory: see EUSO-SPB
- Extreme Universe Space Observatory-Super-Pressure Balloon (EUSO-SPB): balloon-borne cosmic ray observatory
- extreme-energy cosmic rays
- Extremely Large Telescope (European Extremely Large Telescope): 39-meter telescope under construction
- extremely large telescope: optical telescope with a 20+ meter aperture
- extremely low frequency: electromagnetic radiation, frequency 3 Hz to 30 Hz
- extremely luminous far infrared galaxy (ultraluminous infrared galaxy): a galaxy emitting a more far infrared than an LIRG
- extremely luminous infrared galaxy: see luminous infrared galaxy
- extremely metal poor
- extremely metal poor galaxy: galaxy of interest for its very low metallicity
- extremely metal poor poor: see Population III
- extremely metal poor star
- extremely red object: class of galaxies showing more infrared than visible light
- extremely wide: see filter designator
- extrinsic S-star: see S-type star
- extrinsic variable: see variable star
- eye piece: see exit pupil
- eye relief: see exit pupil
Index