User:Iceblock/Oxford Dictionary of Astronomy

A

 * Å -> angstrom
 * AAO -> Anglo-Australian Observatory
 * AAS -> American Astronomical Society
 * AAT -> Anglo-Australian Telescope
 * AAVSO -> American Association of Variable Star Observers
 * A band
 * Abell Catalogue
 * Abell cluster
 * Abell radius
 * constant of aberration -> annual aberration
 * optical aberration
 * aberration of starlight
 * ablation
 * ablation age
 * absolute magnitude
 * 1
 * 2
 * absolute temperature -> thermodynamic temperature
 * absolute zero
 * absorption
 * absorption coefficient
 * absorption edge
 * absorption line
 * absorption nebula -> dark nebula
 * absorption spectrum
 * abundance -> abundance of elements
 * Acamar
 * acceleration of free fall
 * accretion
 * accretion disk
 * ACE -> Advanced Composition Explorer
 * Achernar
 * Achilles
 * achondrite
 * achromatic
 * achromatism
 * A-class asteroid
 * acronical
 * Acrux -> Alpha Crucis
 * active galactic nucleus
 * active optics
 * active prominence
 * active region
 * John Couch Adams
 * Walter Sydney Adams
 * Adams Ring
 * adaptive optics
 * Adhara
 * adiabatic process
 * Adonis
 * Adrastea (moon)
 * ADS -> Aitken Double Star Catalogue
 * Advanced Composition Explorer
 * ACE
 * advance of perihelion
 * advection
 * aeon
 * aerial -> antenna
 * aerobraking
 * aerolite -> stony meteorite
 * aeronomy
 * aerosol
 * Ae star
 * aether -> ether
 * afocal
 * afterglow
 * AGB star -> asymptotic giant branch star
 * Agena -> Hadar -> Beta Centauri
 * agglutinate
 * AGILE
 * AGK
 * AGN -> active galactic nucleus
 * Ahnighito meteorite -> Cape York meteorite
 * airglow
 * airmass
 * air shower -> cosmic-ray shower
 * George Biddell Airy
 * Airy disk
 * Robert Grant Aitken
 * Aitken Double Star Catalogue
 * AI Velorum star
 * AJ -> Astronomical Journal
 * Akari
 * Albategnius -> al-Battani
 * al-Battani -> Battani
 * albedo
 * albedo feature
 * Albireo
 * Alcor
 * Alcyone
 * Aldebaran
 * Alderamin
 * Alexandra family
 * ALEXIS
 * Hannes Olof G&ouml;sta Alfv&eacute;n
 * Alfv&eacute;n surface
 * Alfv&eacute;n wave
 * Algenib
 * Algieba
 * Algol
 * Algol star
 * Algonquin Radio Observatory
 * Alhena
 * aliasing
 * alidade
 * Alioth
 * Alkaid
 * Allegheny Observatory
 * Allende meteorite
 * Allen Telescope Array
 * all-sky camera
 * ALMA -> Atacama Large Millimeter Array
 * Almaak
 * Almagest
 * almanac
 * almucantar
 * Alnair
 * Alnath
 * Alnilam
 * Alnitak
 * &alpha; -> right ascension
 * Alpha Capricornid meteors
 * Alpha Centauri
 * Alpha Crucis
 * Alpha Cygnid meteors
 * Alpha Cygni star
 * alpha particle
 * Alphard
 * Alpha Scorpiid meteors
 * Alpha2 Canum Venaticorum star
 * Alphekka
 * Alpheratz
 * Alrescha
 * Alshain
 * al-Sufi -> Sufi
 * Altair
 * altazimuth mounting
 * altitude
 * al-Tusi -> Tusi
 * aluminizing
 * Amalthea
 * Viktor Amazaspovich Ambartsumian
 * ambipolar diffusion
 * AM Canum Venaticorum star
 * American Association of Variable Star Observers
 * American Astronomical Society
 * Ames Research Center
 * AM Herculis star
 * Amor group
 * amplitude
 * 1
 * 2
 * Am star
 * anaemic spiral galaxy
 * analemma
 * Ananke
 * anastigmatic
 * Anaxagoras
 * Anaximander
 * Andromeda
 * Andromeda Galaxy
 * Andromedid meteors
 * Anglo-Australian Observatory
 * Anglo-Australian Telescope
 * Anders Jonas &Aring;ngstr&ouml;m
 * angstrom
 * angular acceleration
 * angular diameter
 * angular distance -> angular separation
 * angular momentum
 * angular resolution
 * angular separation
 * angular velocity
 * anisotropy
 * Ankaa
 * annealing
 * annual aberration
 * annual equation
 * annual inequality -> annual equation
 * annual parallax
 * annual variation
 * annular eclipse
 * anomalistic month
 * anomalistic year
 * anomalous Cepheid
 * anomalous iron
 * anomaly
 * anorthosite
 * ANS -> Astronomical Netherlands Satellite
 * ansa
 * ansae
 * antapex -> solar apex
 * Antares
 * antenna
 * Antennae
 * antenna pattern
 * antenna temperature
 * anthelion
 * anthelion radiant
 * anthropic principle
 * anticentre -> galactic anticentre
 * anti-dwarf nova
 * antimatter
 * antitail
 * Antlia
 * Eugène Michael Antoniadi
 * Antoniadi scale
 * Antu
 * ap-
 * apo-
 * Apache Point Observatory
 * apastron
 * aperture
 * aperture efficiency
 * aperture ratio
 * aperture synthesis
 * APEX -> Atacama Pathfinder Experiment
 * apex -> solar apex
 * aphelion
 * Aphrodite Terra
 * ApJ -> Astrophysical Journal
 * aplanatic
 * apoapsis
 * apocentre
 * apochromatic
 * apodization
 * apogee
 * apohele
 * Apollo group
 * Apollonius of Perga
 * Apollo project
 * apparent diameter -> angular diameter
 * apparent magnitude
 * apparent noon
 * apparent place
 * apparent retrogression
 * apparent sidereal time
 * apparent solar time
 * apparition
 * appulse
 * apse -> apsides
 * apsis -> apsides
 * apsidal motion
 * apsides
 * Ap star
 * Apus
 * Aquarid meteors
 * Aquarius
 * aqueous alteration
 * Aquila
 * Ara
 * arachnoid
 * François Arago
 * Dominique François Jean Arago
 * Arago ring
 * arc
 * archaeoastronomy
 * arch filament system
 * arc minute -> minute of arc
 * arcmin -> minute of arc
 * arc second -> second of arc
 * arcsec -> second of arc
 * Arcturus
 * arcus
 * area photometer
 * Arecibo Observatory
 * Comet Arend–Roland (C/1956 R1)
 * areo-
 * Friedrich Wilhelm August Argelander
 * Argelander step method
 * Argo Navis
 * argon–potassium method -> potassium–argon method
 * argument of perihelion
 * Argyre Planitia
 * Ariel
 * Ariel satellites
 * Aries
 * first point of Aries
 * Aristarchos Telescope
 * Aristarchus of Samos
 * Aristotle
 * Arizona meteor crater -> meteor crater
 * Arizona Radio Observatory
 * ARO
 * AR Lacertae star
 * armillary sphere
 * arm population
 * Arneb
 * array
 * 1
 * 2
 * artificial satellite
 * ASCA
 * ascending node
 * Asclepius
 * ashen light
 * ASP -> Astronomical Society of the Pacific
 * aspect
 * aspheric
 * stellar association
 * Association of Universities for Research in Astronomy
 * AURA
 * A star
 * asterism
 * asteroid
 * asteroid belt
 * asteroseismology
 * asthenosphere
 * astigmatism
 * Astraea
 * astration
 * astrobiology
 * astrobleme
 * astrochemistry
 * astrodynamics
 * astrograph
 * Astrographic Catalogue
 * astrolabe
 * astrology
 * astrometric binary
 * astrometry
 * astronavigation
 * Astronomer Royal
 * Astronomer Royal for Scotland
 * The Astronomical Almanac
 * Astronomical Journal
 * AJ
 * Astronomical Netherlands Satellite
 * ANS
 * Astronomical Society of the Pacific
 * ASP
 * astronomical triangle
 * astronomical twilight
 * astronomical unit
 * AU
 * astronomy
 * Astronomy and Astrophysics
 * A&A -> Astronomy and Astrophysics
 * astrophotography
 * Astrophysical Journal
 * astrophysics
 * ASTROSAT
 * astrum
 * Asuka -> ASCA
 * asymptotic giant branch star
 * AGB star
 * Atacama Large Millimeter Array
 * ALMA
 * Atacama Pathfinder Experiment
 * APEX
 * ataxite
 * Aten group
 * Atlas
 * atmosphere
 * atmospheric extinction
 * atmospheric refraction
 * atmospheric scattering -> atmospheric extinction -> Mie scattering -> Rayleigh scattering
 * atmospheric window
 * ATNF -> Australia Telescope National Facility
 * atom
 * atomic clock
 * atomic time
 * Atria
 * attenuation
 * 1
 * 2
 * AU -> astronomical unit
 * aubrite
 * Auger shower -> cosmic-ray shower
 * augmentation
 * AURA -> Association of Universities for Research in Astronomy
 * Auriga
 * Aurora programme
 * aurora
 * auroral oval
 * auroral substorm -> substorm
 * Australia Telescope National Facility
 * ATNF
 * australite
 * autocorrelation
 * autocorrelator
 * autoguider
 * autoionization
 * autumnal equinox -> equinox
 * averted vision
 * Avior
 * axion
 * optical axis
 * axis of rotation
 * azimuth
 * Azophi -> al-Sufi

B

 * BAA -> British Astronomical Association
 * Wilhelm Heinrich Walter Baade
 * Walter Baade
 * Baade's Window
 * Baade–Wesselink method
 * Harold Delos Babcock
 * Horace Welcome Babcock
 * background noise
 * background radiation
 * backscattering
 * Bailey type
 * Francis Baily
 * Baily's beads
 * Baker–Schmidt telescope
 * Baldwin effect
 * Balmer limit
 * Balmer lines -> Balmer series
 * Balmer series
 * band
 * bandpass filter
 * bandwidth
 * bar
 * barium star
 * Barlow lens
 * Edward Emerson Barnard
 * Barnard's Loop
 * Barnard's Star
 * barn-door mount -> Scotch mount
 * Barnes–Evans relationship
 * barred spiral galaxy
 * barrel distortion
 * Barringer Crater -> meteor crater
 * barycentre
 * Barycentric Celestial Reference System
 * barycentric coordinates
 * Barycentric Coordinate Time
 * Barycentric Dynamical Time
 * baryon
 * baryon star
 * basalt
 * basaltic achondrite
 * baseline
 * impact basin
 * Muammad ibn Jabir al-Battani
 * Ba II star -> barium star
 * Bautz–Morgan class
 * Johann Bayer
 * Bayer letters
 * B band
 * B-class asteroid
 * BCRS -> Barycentric Celestial Reference System
 * BD -> Bonner Durchmusterung
 * Beagle
 * beam
 * beaming
 * beamwidth
 * beat Cepheid
 * Becklin–Neugebauer Object (BN Object)
 * Becrux -> Beta Crucis
 * bediasite
 * Beehive Cluster -> Praesepe
 * Belinda
 * Bellatrix
 * Susan Jocelyn Bell Burnell
 * Jocelyn Bell Burnell
 * Belt of Orion
 * Benetnasch -> Alkaid
 * Comet Bennett (C/1969 Y1)
 * bent-pillar mounting
 * BepiColombo
 * BeppoSAX
 * Berkeley–Illinois–Maryland Association Array (BIMA Array)
 * Friedrich Wilhelm Bessel
 * Besselian day numbers
 * Besselian elements
 * Besselian epoch
 * Besselian year
 * Be star
 * B(e) star
 * Beta Canis Majoris star -> Beta Cephei star
 * Beta Cephei star
 * Beta Crucis
 * beta decay
 * Beta Lyrae star
 * beta particle
 * Beta Persei star -> Algol star
 * Beta Pictoris
 * Beta Regio
 * Beta Taurid meteors
 * Betelgeuse
 * Hans Albrecht Bethe
 * Bethe–Weizs&auml;cker cycle -> carbon–nitrogen cycle
 * Bianca
 * Bianchi cosmology
 * biconcave lens
 * biconvex lens
 * Comet 3D/Biela
 * Bielid meteors -> Andromedid meteors
 * Big Bang theory
 * Big Bear Solar Observatory
 * Big Crunch
 * Big Dipper
 * billitonite
 * BIMA Array
 * binary galaxy
 * binary pulsar
 * binary star
 * binding energy
 * binoculars
 * Jean-Baptiste Biot
 * bipolar group
 * bipolar nebula
 * bipolar outflow
 * birefringent filter
 * Birmingham Solar Oscillations Network
 * BiSON -> Birmingham Solar Oscillations Network
 * black body
 * black-body radiation
 * black drop
 * black dwarf
 * Black Eye Galaxy
 * black hole
 * Black Widow Pulsar -> binary pulsar
 * blazar
 * Blaze Star
 * Blazhko effect
 * BL Herculis star
 * blink comparator
 * Blinking Planetary
 * BL Lacertae object
 * BL Lac object
 * bloomed lens
 * blooming
 * 1
 * 2
 * blue clearing
 * blue compact dwarf galaxy
 * blue giant
 * blue Moon
 * 1
 * 2
 * Blue Planetary
 * blue populous cluster -> Large Magellanic Cloud
 * blueshift
 * blue straggler
 * B magnitude
 * BN Object -> Becklin–Neugebauer Object
 * Johann Elert Bode
 * Bode's law
 * Bartholomeus Jan Bok
 * Bartholomeus 'Bart' Jan Bok
 * Bok globule -> globule
 * bolide
 * bolometer
 * bolometric correction
 * bolometric magnitude
 * Boltzmann constant
 * George Phillips Bond
 * William Cranch Bond
 * Bond albedo
 * Hermann Bondi
 * Bonner Durchmusterung
 * Bo&ouml;tes
 * boson
 * Boss General Catalogue
 * GC
 * boundary layer
 * bound–bound transition
 * bound–free transition
 * Bouwers telescope
 * Ira Sprague Bowen
 * Bowen fluorescence
 * bow shock
 * Bp star
 * Brackett series
 * James Bradley
 * Bragg crystal spectrometer
 * Tycho Brahe
 * Brans–Dicke theory
 * breccia
 * bremsstrahlung
 * bridge (astronomy)
 * bright nebula
 * brightness temperature
 * Bright Star Catalogue
 * British Astronomical Association
 * broad-band photometry
 * Brocchi's Cluster
 * Comet 16P/Brooks 2 -> Jupiter comet family
 * Ernest William Brown
 * brown dwarf
 * B star
 * Bubble Nebula
 * Budrosa family
 * Bug Nebula
 * bump Cepheid
 * Geoffrey Ronald Burbidge
 * Eleanor Margaret Burbidge
 * burst (astronomy)
 * Butcher–Oemler effect
 * Butler matrix
 * Butterfly Cluster
 * butterfly diagram
 * Butterfly Nebula
 * BV photometry
 * Bw star
 * BY Draconis star
 * Byurakan Astrophysical Observatory

C

 * Caelum
 * Calar Alto Observatory
 * caldera
 * calendar
 * calendar year
 * Caliban
 * California Nebula
 * Callippus
 * Callisto
 * Caloris Basin
 * Caltech Submillimeter Observatory
 * CSO
 * Calypso (moon)
 * Cambridge Optical Aperture Synthesis Telescope
 * COAST
 * Camelopardalis
 * William Wallace Campbell
 * Canada–France–Hawaii Telescope
 * canale
 * canali
 * Martian canals
 * Cancer
 * Tropic of Cancer
 * Canes Venatici
 * Canis Major
 * Canis Minor
 * Annie Jump Cannon
 * Canopus
 * cantaloupe terrain
 * Capella
 * Cape Photographic Durchmusterung
 * Cape photometry
 * Cape RI photometry -> Kron–Cousins RI photometry
 * Cape York meteorite
 * Caph
 * Tropic of Capricorn
 * Capricornid meteors
 * Capricornus
 * captured rotation -> synchronous rotation
 * Carafe Galaxy
 * carbonaceous chondrite
 * carbon burning
 * carbon cycle -> carbon–nitrogen cycle
 * carbon flash
 * carbon–nitrogen cycle (CN cycle)
 * carbon star
 * Carina
 * Carina Arm
 * Carina Dwarf Galaxy
 * Carina–Sagittarius Arm
 * CARMA -> Combined Array for Research in Millimeter-wave Astronomy
 * Carme
 * Carnegie Observatories
 * Carpo
 * Richard Christopher Carrington
 * Carrington heliographic coordinates
 * Carrington rotation
 * Carte du Ciel
 * Cartesian coordinates
 * Cartwheel Galaxy
 * Cassegrain telescope
 * Cassini
 * Giovanni Domenico Cassini
 * Jacques Cassini
 * Cassini Division
 * Cassini–Huygens
 * Cassiopeia
 * Cassiopeia A
 * Castalia
 * Castor
 * cataclysmic binary
 * cataclysmic variable
 * catadioptric system
 * Catalina Sky Survey
 * catalogue equinox
 * catena
 * catoptric system
 * Cat's Eye Nebula
 * cavus
 * CCD -> charge-coupled device
 * CCD spectrometer
 * C-class asteroid
 * cD Galaxy
 * CDM -> cold dark matter
 * CDS -> Centre de Donn&eacute;es astronomiques de Strasbourg
 * celestial axis
 * celestial coordinates
 * celestial equator
 * Celestial Intermediate Reference System
 * celestial latitude
 * celestial longitude
 * celestial mechanics
 * celestial meridian
 * celestial pole
 * celestial sphere
 * Centaur group
 * Centaurus
 * Centaurus A
 * Center for Astrophysics
 * Central Bureau for Astronomical Telegrams
 * central meridian
 * central peak
 * Centre de Donn&eacute;es astronomiques de Strasbourg
 * centre of gravity
 * centre of inertia
 * centre of mass
 * centrifugal force
 * centripetal force
 * Cepheid instability strip
 * Cepheid variable
 * Cepheus
 * Cerenkov counter
 * Cerenkov radiation
 * Ceres
 * Cerro Pach&oacute;n
 * Cerro Paranal
 * Cerro Tololo Inter-American Observatory
 * Cetus
 * CfA -> Harvard–Smithsonian Center for Astrophysics
 * CGRO -> Compton Gamma Ray Observatory
 * Chamaeleon
 * Chandler period
 * Chandler wobble
 * Subrahmanyan Chandrasekhar
 * Chandrasekhar limit
 * Chandrasekhar-Sch&ouml;nberg limit
 * Chandra X-ray Observatory
 * Chandrayaan-1
 * Chang'e
 * chaos
 * chaotic orbit
 * chaotic terrain
 * CHARA Array
 * charge
 * charge-coupled device
 * Charon
 * chasma
 * chassignite
 * chemical element
 * chemosphere
 * Chicxulub
 * CHIPSat
 * Chiron
 * Ernst Florens Friedrich Chladni
 * chondrite
 * chondrule
 * chopper
 * chopping secondary
 * William Henry Mahoney Christie
 * chromatic aberration
 * chromosphere
 * chromospheric network
 * Chryse Planitia
 * CH star
 * Circinus
 * Circlet
 * circular velocity
 * circumpolar
 * circumstellar maser
 * circumstellar matter
 * Cirrus Nebula -> Veil Nebula
 * CIRS -> Celestial Intermediate Reference System
 * cislunar
 * civil time
 * civil twilight
 * civil year
 * Alexis Claude Clairaut
 * Alvan Clark
 * classical Cepheid
 * clast
 * clathrate
 * CLEAN
 * Clementine
 * James Clerk Maxwell
 * C line
 * clock drive -> drive
 * clock star
 * closed universe
 * Clown Face Nebula -> Eskimo Nebula
 * Cluster
 * star cluster -> globular cluster
 * star cluster -> open cluster
 * cluster, star -> star cluster
 * cluster of galaxies
 * cluster variable -> RR Lyrae star
 * CMB -> cosmic microwave background
 * CME -> coronal mass ejection
 * CM relation -> colour–magnitude relation
 * CN band
 * CN cycle -> carbon–nitrogen cycle
 * CNO cycle -> carbon–nitrogen–oxygen cycle
 * CN star
 * Coalsack
 * coaltitude
 * COAST
 * Coathanger
 * COBE
 * Cocoon Nebula
 * cocoon star
 * CoD -> C&oacute;rdoba Durchmusterung
 * coded mask
 * coelostat
 * coesite
 * coherence
 * coherence bandwidth
 * colatitude
 * cold camera
 * cold dark matter
 * collapsar
 * colles
 * collimation
 * collimation error
 * collimator
 * Colombo Gap
 * colorimetry -> colour index
 * colour -> colour index
 * colour excess
 * colour index
 * colour–luminosity relation -> colour–magnitude relation
 * colour–magnitude relation
 * colour temperature
 * Columba
 * column density
 * colure
 * cometary coma
 * optical coma
 * Coma Berenices
 * Coma Cluster
 * Coma Star Cluster
 * Coma–Virgo Cluster -> Virgo Cluster
 * Combined Array for Research in Millimeter-wave Astronomy
 * combined magnitude
 * comes
 * comet
 * cometary globule
 * comet family
 * comet-seeker
 * commensurability
 * Andrew Ainslie Common
 * common envelope binary
 * common proper motion
 * compact galaxy
 * compact object
 * compact source
 * comparator
 * comparison spectrum
 * composite-spectrum binary
 * Compton effect
 * Compton Gamma Ray Observatory
 * Compton–Getting effect
 * Compton scattering -> Compton effect
 * Compton upscattering -> inverse Compton scattering
 * Concordia family
 * Cone Nebula
 * confusion
 * conic section
 * conjunction
 * constant of aberration -> annual aberration
 * constellation
 * constructive interference -> interference
 * contact binary
 * continuous creation
 * continuous spectrum
 * continuum
 * stellar convection
 * convective envelope
 * convective equilibrium
 * convective overshoot -> overshooting
 * convective zone
 * convergent point
 * converging lens
 * convolution
 * Thomas Cooke
 * cooled camera -> cold camera
 * cooling flow
 * coorbital
 * Coordinated Universal Time
 * coordinate systems -> celestial coordinates
 * coordinate time
 * Copernican system
 * Nicolaus Copernicus
 * Copernicus satellite
 * Coprates
 * Cor Caroli
 * Cordelia
 * C&oacute;rdoba Durchmusterung
 * planetary core
 * stellar core
 * core collapse
 * 1
 * 2
 * Coriolis force
 * corona
 * 1
 * 2
 * 3
 * Corona Australis
 * Corona Borealis
 * coronagraph
 * coronal bright point
 * coronal condensation
 * coronal hole
 * coronal lines
 * coronal loop
 * coronal mass ejection
 * coronal plume
 * coronal rain
 * COROT
 * co-rotation
 * corpuscular radiation
 * 1
 * 2
 * corrector plate
 * correlation detection
 * correlation function
 * correlation receiver
 * correlator
 * Corvus
 * COS-B
 * cosmic abundance
 * Cosmic Background Explorer
 * cosmic background radiation -> cosmic microwave background
 * CBR -> cosmic background radiation
 * cosmic censorship
 * cosmic dust
 * cosmic microwave background
 * cosmic rays
 * cosmic-ray shower
 * cosmic scale factor
 * cosmic string
 * cosmic texture
 * cosmic year
 * cosmochemistry -> astrochemistry
 * cosmological constant
 * cosmological distance scale
 * cosmological principle
 * cosmology
 * cosmos
 * Cosmos satellites
 * COSPAR
 * coud&eacute; focus
 * Couder telescope
 * counterglow -> gegenschein
 * Philip Herbert Cowell
 * c.p.m. -> common proper motion
 * Crab Nebula
 * Crab Pulsar
 * Crater
 * crater
 * crater chain
 * crater counting
 * cr&ecirc;pe ring
 * crepuscular rays
 * crescent
 * Cressida
 * Crimean Astrophysical Observatory
 * critical density
 * Andrew Claude de la Cherois Crommelin
 * cross-axis mounting
 * crossing time
 * cross-wire micrometer
 * crown glass
 * crust
 * Crux
 * cryostat
 * cryovolcanism
 * C star
 * CTIO -> Cerro Tololo Inter-American Observatory
 * Cubewano
 * culmination
 * curvature of field
 * curvature of space -> curvature of spacetime
 * curvature of spacetime
 * curvature radiation
 * curve of growth
 * cusp
 * cusp gap
 * Cybele group
 * cyclotron maser
 * cyclotron radiation
 * Cygnus
 * Cygnus A
 * Cygnus Loop
 * Cygnus Rift
 * Cygnus X-1
 * Cynthian
 * Cytherean

D

 * Dactyl
 * Dall–Kirkham telescope
 * Damocles
 * Damocloid
 * Andr&eacute; Danjon
 * Danjon astrolabe
 * Danjon scale
 * dark adaptation
 * dark energy
 * dark galaxy
 * dark matter
 * dark nebula
 * daughter isotope
 * Davida
 * David Dunlap Observatory
 * Raymond Davis, Jr
 * William Rutter Dawes
 * Dawes limit
 * Dawn
 * day
 * Daylight Saving Time -> Summer Time
 * day number
 * 1
 * 2
 * D-class asteroid
 * DCT -> Discovery Channel Telescope
 * DDO classification
 * DDO photometry
 * dec. -> declination
 * deceleration parameter
 * Comet de Ch&eacute;seaux (C/1743 X1)
 * declination
 * declination axis
 * deconvolution
 * decoupling
 * dedispersion
 * Deep Impact
 * deep-sky object
 * Deep Space Network
 * Deep Space 1
 * defect of illumination
 * deferent
 * deflection of light
 * degeneracy
 * degenerate star
 * degree of arc
 * degrees of freedom
 * Deimos
 * delay line
 * Delphinus
 * &delta; -> declination
 * delta -> declination
 * Delta Aquarid meteors
 * Delta Cepheid star -> classical Cepheid
 * Delta Delphini star
 * Delta Scuti star
 * delta T
 * &Delta;T
 * Demon Star
 * Deneb
 * Deneb Kaitos
 * Denebola
 * William Frederick Denning
 * density parameter
 * density wave
 * descending node
 * Desdemona
 * Willem de Sitter
 * de Sitter universe
 * Despina
 * destructive interference -> interference
 * detached binary
 * deuterium
 * G&eacute;rard Henri de Vaucouleurs
 * dewar
 * dew cap
 * D galaxy
 * diagonal
 * diamond ring
 * Diana Chasma
 * dichotomy
 * dichroic mirror
 * Robert Henry Dicke
 * Dicke radiometer
 * Dicke switch
 * dielectronic recombination
 * differential rotation
 * differentiation
 * diffraction
 * diffraction grating
 * diffraction-limited
 * diffraction pattern
 * diffraction rings
 * diffuse interstellar bands
 * diffuse nebula
 * diogenite
 * Dione
 * dioptric system
 * Diphda -> Deneb Kaitos
 * dipole
 * 1
 * 2
 * 3
 * dipole antenna
 * Dirac cosmology
 * directivity
 * direct motion
 * dirty snowball
 * disconnection event
 * Discovery Channel Telescope
 * Discovery Program
 * dish antennae
 * disk galaxy
 * disk population
 * disparition brusque -> filament
 * dispersion
 * 1
 * 2
 * dispersion measure
 * distance modulus
 * distortion
 * diurnal
 * diurnal aberration
 * diurnal inequality
 * diurnal libration
 * diurnal motion
 * diurnal parallax
 * diverging lens
 * D layer
 * D lines
 * dMe star
 * Dobsonian telescope
 * Dog Star
 * John Dollond
 * domain wall
 * dome
 * Dominion Astrophysical Observatory
 * Dominion Radio Astrophysical Observatory
 * Comet Donati (C/1858 L1)
 * Christian Johann Doppler
 * Doppler broadening
 * Doppler effect -> Doppler shift
 * dopplergram
 * Doppler shift
 * Dorado
 * dorsum
 * Double Cluster
 * Double Double
 * double-lined binary
 * double-mode variable
 * double pulsar
 * double quasar
 * double star
 * doublet
 * 1
 * 2
 * DQ Herculis star
 * Draco
 * draconic month
 * Draconid meteors -> Giacobinid meteors
 * Drake equation
 * Henry Draper
 * Draper
 * drawtube
 * Johan Ludvig Emil Dreyer
 * drifting sub-pulse
 * drift scan
 * drive
 * D star
 * Dubhe
 * Dumbbell Nebula
 * dust
 * dust tail -> cometary tail
 * duty cycle
 * dwarf Cepheid
 * dwarf galaxy
 * dwarf nova
 * dwarf planet
 * dwarf spheroidal galaxy
 * dwarf star
 * dwarf variable
 * Dwingeloo galaxy
 * Dwingeloo Radio Observatory
 * dynamical equinox
 * dynamical friction
 * dynamical parallax
 * dynamical time
 * dynamo
 * Frank Watson Dyson

E

 * Eagle Nebula
 * early-type galaxy
 * early-type star
 * Earth
 * Earth coorbital asteroid -> Apollo group -> Aten group
 * Earth-crossing asteroid -> Amor group
 * Earth-approaching asteroid
 * earthlight -> earthshine
 * eccentric anomaly
 * eccentricity
 * echelle grating
 * echelle spectrograph
 * E-class asteroid
 * eclipse
 * eclipse season
 * eclipse year
 * eclipsing binary
 * ecliptic
 * ecliptic coordinates
 * ecliptic latitude
 * ecliptic limits
 * ecliptic longitude
 * ecliptic pole
 * E corona
 * Arthur Stanley Eddington
 * Eddington limit
 * Edgeworth–Kuiper Belt -> Kuiper Belt
 * E-ELT -> European Extremely Large Telescope
 * effective aperture
 * effective area
 * effective focal length
 * effective temperature
 * Effelsberg Radio Observatory
 * Egg Nebula
 * Albert Einstein
 * Einstein coefficient
 * Einstein Cross
 * Einstein–de Sitter universe
 * Einstein Observatory
 * Einstein ring
 * Einstein shift -> gravitational redshift
 * ejecta
 * Elara
 * E layer
 * electromagnetic radiation
 * electromagnetic spectrum
 * electron
 * electron degeneracy
 * electron density
 * electron scattering opacity
 * electron temperature
 * electronvolt
 * chemical element
 * optical element
 * elementary particle
 * abundance of elements
 * orbital elements
 * E line
 * Ellerman bomb
 * ellipse
 * ellipsoid
 * ellipsoidal variable
 * elliptic aberration -> E-terms
 * elliptical galaxy
 * ellipticity -> oblateness
 * Elnath -> Alnath
 * elongation
 * 1
 * 2
 * Eltanin -> Etamin
 * Elysium Planitia
 * emersion
 * emission
 * emission line
 * emission nebula
 * emission spectrum
 * emissivity
 * photographic emulsion
 * Enceladus
 * Comet 2P/Encke
 * Johann Franz Encke
 * Encke Division
 * energy level
 * English mounting
 * Enif
 * Ensisheim meteorite
 * enstatite chondrite
 * entrainment
 * entropy
 * envelope (astronomy)
 * eon -> aeon
 * Eos family
 * epact
 * Ep galaxy
 * ephemeris
 * Ephemeris Time
 * epicycle
 * Epimetheus
 * epoch
 * e-process
 * Epsilon Aurigae
 * equant
 * equation (astronomy)
 * equation of light
 * equation of the centre
 * equation of the equinoxes
 * equation of the origins
 * equation of time
 * equator
 * equatorial bulge
 * equatorial coordinates
 * equatorial horizontal parallax
 * equatorial mounting
 * equinoctial colure
 * equinox
 * equipotential surface
 * equivalence principle
 * equivalent focal length
 * equivalent width
 * Equuleus
 * ERA -> Earth rotation angle
 * Eratosthenes
 * Erfle eyepiece
 * ergosphere
 * Eridanus
 * Eris
 * Eros
 * eruptive binary
 * eruptive prominence
 * eruptive variable
 * ESA -> European Space Agency
 * escape velocity
 * Eskimo Nebula
 * ESO -> European Southern Observatory
 * ET -> Ephemeris Time
 * Eta Aquarid meteors
 * Eta Carinae
 * Eta Carinae Nebula
 * etalon
 * Etamin
 * E-terms
 * ether
 * eucrite
 * Eudoxus of Cnidus
 * Leonhard Euler
 * Eunomia family
 * Europa
 * European Extremely Large Telescope
 * European Southern Observatory
 * European Space Agency
 * European VLBI Network
 * EUV -> extreme ultraviolet
 * EUVE -> Extreme Ultraviolet Explorer
 * eV -> electronvolt
 * evection
 * evening star
 * event horizon
 * Evershed effect
 * EVN -> European VLBI Network
 * evolved star
 * excitation
 * excitation temperature
 * exit cone
 * exit pupil
 * EX Lupi star
 * exobiology -> astrobiology
 * ExoMars
 * exoplanet -> extrasolar planet
 * EXor -> EX Lupi star
 * Exosat
 * exosphere
 * expanding universe
 * Explorer
 * exposure age
 * extended source
 * 1
 * 2
 * atmospheric extinction
 * interstellar extinction
 * extragalactic nebula -> galaxy
 * extrasolar planet
 * extreme Population I star
 * extreme ultraviolet
 * Extreme Ultraviolet Explorer
 * extrinsic variable
 * eye lens
 * eyepiece
 * eye relief

F

 * Faber–Jackson relation
 * David Fabricius
 * Johann Fabricius
 * Johannes Fabricius
 * Fabry lens
 * Fabry–Perot interferometer
 * facula
 * 1
 * 2
 * fall
 * falling star -> meteor
 * False Cross
 * Fanaroff–Riley class
 * fan beam
 * Faraday effect
 * far infrared
 * farrum
 * far ultraviolet
 * Far Ultraviolet Spectroscopic Explorer
 * Fast Auroral Snapshot Explorer
 * fast nova
 * Faulkes Telescopes
 * fault
 * F band
 * F-class asteroid
 * F corona
 * feed
 * fermion
 * fibrille
 * field curvature -> curvature of field
 * field equations
 * field flattener
 * field lens
 * field of view
 * field star
 * field stop
 * 53 Persei star
 * figure
 * filament
 * 1
 * 2
 * filamentary nebula
 * filar micrometer
 * filigree
 * filled aperture
 * filled-centre supernova remnant -> plerion
 * filter
 * 1
 * 2
 * filtergram
 * find
 * finder
 * fine structure
 * fireball
 * first contact
 * first point of Aries
 * first point of Libra
 * first quarter
 * Fish Mouth
 * fission
 * fission track
 * Fitzgerald contraction -> Lorentz–Fitzgerald contraction
 * fixed stars
 * FK
 * FK Comae Berenices star
 * John Flamsteed
 * Flamsteed numbers
 * solar flare
 * flare star
 * flash spectrum
 * flash star
 * flat
 * polar flattening
 * F layer
 * Williamina Paton Fleming
 * flexus
 * flickering
 * flint glass
 * flocculi
 * 1 -> mottles
 * 2 -> plages
 * Flora group
 * fluctus
 * flumen
 * fluorescence
 * fluorite
 * flux
 * flux collector
 * flux density
 * 1
 * 2
 * flux tube
 * flux unit
 * f/number
 * focal distance
 * focal length
 * focal plane
 * focal point
 * focal ratio
 * focal reducer
 * focal surface
 * optical focus
 * orbital focus
 * Fokker–Planck equation
 * folded dipole
 * following
 * Fomalhaut
 * footpoint -> coronal loop
 * forbidden line
 * Forbush effect
 * fork mounting
 * Fornax
 * Fornax A
 * Fornax Dwarf Galaxy
 * 47 Tucanae
 * forward scattering
 * fossa
 * Foucault test
 * four-colour photometry -> Str&ouml;mgren photometry
 * Fourier analysis
 * Fourier transform
 * Fourier transform spectrometer
 * fourth contact
 * William Alfred Fowler
 * Fp star
 * fractional method
 * frame dragging
 * frame of reference
 * Franklin-Adams charts
 * Joseph von Fraunhofer
 * Fraunhofer lines
 * Fred Lawrence Whipple Observatory
 * free–bound transition
 * free–free transition
 * frequency
 * frequency analysis -> Fourier analysis
 * Friedmann universe
 * fringe -> interference pattern
 * fringe pattern
 * f-spot
 * F star
 * FTS -> Fourier transform spectroscopy
 * full Moon
 * full-wave dipole
 * full width at half maximum
 * fundamental catalogue
 * fundamental mode
 * fundamental plane
 * fundamental star
 * fuor -> FU Orionis star
 * FUSE -> Far Ultraviolet Spectroscopic Explorer
 * fusion
 * fusion crust
 * future light cone -> light cone
 * FWHM -> full width at half maximum

G

 * g -> acceleration of free fall
 * G -> gravitational constant
 * Gacrux -> Gamma Crucis
 * Gaia
 * gain
 * galactic anticentre
 * galactic bulge
 * galactic centre
 * galactic cluster
 * galactic coordinates
 * galactic disk
 * galactic equator
 * galactic halo
 * galactic latitude
 * galactic longitude
 * galactic magnetic field
 * galactic nucleus
 * galactic plane
 * galactic pole
 * galactic rotation
 * galactic window
 * galactic year -> cosmic year
 * Galatea
 * Galaxy
 * galaxy
 * galaxy cannibalism
 * galaxy cluster
 * galaxy encounter
 * galaxy evolution
 * Galaxy Evolution Explorer
 * galaxy formation
 * galaxy merger
 * GALEX -> Galaxy Evolution Explorer
 * Galilean satellites
 * Galilean telescope
 * Galileo
 * Galileo Galilei
 * Galileo National Telescope
 * Galileo Regio
 * Johann Gottfried Galle
 * Galle Ring
 * Gamma Cassiopeiae star
 * Gamma Crucis
 * Gamma Doradus star
 * gamma-ray astronomy
 * gamma-ray background
 * gamma-ray burst
 * Gamma-ray Large Area Space Telescope
 * gamma rays
 * gamma-ray telescope
 * George Gamow
 * Ganymede
 * Sergei Illarionovich Gaposchkin -> Cecilia Payne-Gaposchkin
 * Garnet Star
 * gas giant -> giant planet
 * Gaspra
 * gas scintillation proportional counter
 * gas tail -> cometary tail
 * Carl Friedrich Gauss
 * Gaussian gravitational constant
 * G band
 * G-class asteroid
 * GCRS -> Geocentric Celestial Reference System
 * GCVS -> General Catalogue of Variable Stars
 * gegenschein
 * Geminga
 * Gemini
 * Geminid meteors
 * Gemini Observatory
 * Gemma -> Alphekka
 * General Catalogue of Variable Stars
 * general precession
 * general theory of relativity
 * Genesis
 * Geneva photometry
 * geo-
 * geocentric
 * Geocentric Celestial Reference System
 * geocentric coordinates
 * Geocentric Coordinate Time
 * geocentric equatorial parallax
 * geocentric parallax
 * geocorona
 * geodesic
 * geodesy
 * Geographos
 * geoid
 * geomagnetic storm
 * geomagnetism
 * geometrical albedo
 * geometrical libration -> optical libration
 * georgiaite
 * geostationary orbit
 * geosynchronous orbit
 * geotail -> magnetotail
 * germanium detector
 * German mounting
 * GHA
 * ghost crater
 * Ghost of Jupiter
 * Riccardo Giacconi
 * Giacobinid meteors
 * Comet 21P/Giacobini–Zinner
 * giant branch
 * Giant Magellan Telescope
 * Giant Metrewave Radio Telescope
 * giant molecular cloud
 * giant planet
 * giant star
 * gibbous
 * Gienah
 * David Gill
 * Ginga
 * Giotto
 * GLAST -> Gamma-ray Large Area Space Telescope
 * Glauke
 * glitch
 * Global Oscillation Network Group
 * globular cluster
 * globule
 * GMAT -> Greenwich Mean Astronomical Time
 * GMC -> giant molecular cloud
 * GMST -> Greenwich Mean Sidereal Time
 * GMT -> Greenwich Mean Time
 * GMT -> Giant Magellan Telescope
 * gnomon
 * Goddard Space Flight Center
 * G&ouml;del universe
 * Thomas Gold
 * Goldstone
 * GONG -> Global Oscillation Network Group
 * John Goodricke
 * GoTo telescope
 * Benjamin Apthorp Gould
 * Gould's Belt
 * graben
 * interplanetary grains
 * interstellar grains
 * Granat
 * grand unified theory
 * Gran Telescopio Canarias
 * granulation
 * graticule -> reticle
 * grating -> diffraction grating
 * grating spectrometer
 * gravitation
 * gravitational acceleration
 * gravitational collapse
 * gravitational constant
 * gravitational deflection
 * gravitational energy
 * gravitational field
 * gravitational force
 * gravitational instability
 * gravitational lens
 * gravitational mass
 * gravitational radiation
 * gravitational wave
 * graviton
 * gravity assist
 * gravity gradient
 * Gravity Probe B
 * grazing-incidence telescope
 * grazing occultation
 * GRB -> gamma-ray burst
 * Great Attractor
 * Great Bear -> Ursa Major
 * great circle
 * Great Dark Spot
 * greatest brilliancy
 * greatest elongation
 * Great Observatories
 * Great Red Spot
 * Great Rift
 * Great September Comet (C/1882 R1)
 * Great Wall
 * Green Bank
 * Green Bank Telescope
 * green flash
 * greenhouse effect
 * Greenwich hour angle
 * Greenwich Mean Astronomical Time
 * Greenwich Mean Sidereal Time
 * Greenwich Mean Time
 * Greenwich meridian
 * Greenwich Observatory
 * Greenwich sidereal date
 * Greenwich Sidereal Time
 * Gregorian calendar
 * Gregorian telescope
 * James Gregory
 * Comet 26P/Grigg–Skjellerup
 * grism
 * grooved terrain
 * Grotrian diagram
 * ground state
 * GRS -> Great Red Spot
 * Howard Grubb
 * Grus
 * GST -> Greenwich Sidereal Time
 * G star
 * GTC -> Gran Telescopio Canarias
 * Guardians
 * guest star
 * guider
 * guide star
 * guide telescope
 * Gum Nebula
 * GUT -> grand unified theory
 * GW Virginis star -> ZZ Ceti star
 * gyrofrequency
 * gyrosynchrotron radiation

H

 * HA -> hour angle
 * Hadar
 * Hadley circulation
 * Hadley Rille
 * hadron
 * hadron era
 * HAEBE -> Herbig Ae/Be star
 * Haedi -> Kids
 * Haig mount -> Scotch mount
 * Hakucho
 * halation
 * HALCA
 * George Ellery Hale
 * Comet Hale–Bopp (C/1995 01)
 * Hale Observatories
 * Hale's law -> bipolar group
 * Hale telescope
 * half-life
 * half-wave dipole
 * half-width -> full width at half maximum
 * Asaph Hall
 * Edmond Halley
 * Halley-family comet
 * Halley's Comet
 * atmospheric halo
 * galactic halo
 * halo CME
 * halo orbit
 * halo population
 * H&alpha;
 * Hamal
 * H and K lines
 * Hanle effect
 * hard X-rays
 * Haro galaxy
 * Hartebeesthoek Radio Astronomy Observatory
 * HartRAO -> Hartebeesthoek Radio Astronomy Observatory
 * Hartmann test
 * Haruka -> HALCA
 * Harvard classification
 * Harvard College Observatory
 * Harvard Revised Photometry
 * Harvard–Smithsonian Center for Astrophysics
 * harvest Moon
 * Hat Creek Radio Observatory
 * Hathor
 * Haute-Provence Observatory
 * Stephen William Hawking
 * Hawking radiation
 * Hayabusa
 * Hayashi track
 * Haystack Observatory
 * HCG -> Hickson compact group
 * HD Catalogue -> Henry Draper Catalogue
 * cometary head
 * head–tail galaxy
 * HEAO -> High Energy Astrophysical Observatory
 * heat death of the Universe
 * Heaviside layer -> E layer
 * heavy element
 * heavy-metal star
 * Hebe
 * Hektor
 * Helene
 * heli- -> Sun
 * helio- -> Sun
 * heliacal rising and setting
 * heliocentric
 * 1
 * 2
 * heliocentric coordinates
 * heliocentric latitude
 * heliocentric longitude
 * heliocentric parallax -> annular parallax
 * heliographic coordinates
 * heliometer
 * heliopause
 * helioseismology
 * heliosheath
 * heliosphere
 * Helios probes
 * heliostat
 * helium burning
 * helium flash
 * helium shell flash
 * helium star
 * Helix Nebula
 * Hellas Planitia
 * helmet streamer -> streamer
 * Helmholtz–Kelvin contraction
 * hemispherical albedo
 * Henry Draper Catalogue
 * Henyey track
 * Hephaistos
 * Heraclides of Pontus
 * Herbig Ae/Be star
 * Herbig–Haro object
 * Hercules
 * Hercules Cluster
 * Hercules X-1
 * Herculina
 * Hermes
 * Caroline Lucretia Herschel
 * Karoline Lucretia Herschel -> Caroline Lucretia Herschel
 * John Frederick William Herschel
 * Frederick William Herschel -> William Herschel
 * Friedrich Wilhelm Herschel -> William Herschel
 * William Herschel
 * Herschelian telescope
 * Comet 35P/Herschel–Rigollet
 * Herschel Space Observatory
 * Hertha family -> Nysa family
 * hertz
 * Ejnar Hertzsprung
 * Hertzsprung gap
 * Hertzsprung–Russell diagram
 * Victor Francis Hess
 * HESSI -> Ramaty High-energy Solar Spectroscopic Imager
 * HETE-2 -> High Energy Transient Explorer-2
 * Johannes Hevelius
 * Antony Hewish
 * hexahedrite
 * HH object -> Herbig–Haro object
 * Hickson compact group
 * Hidalgo
 * hierarchical cosmology
 * High Energy Astrophysical Observatory
 * high-energy astrophysics
 * High-Energy Transient Explorer-2
 * lunar highlands
 * high-speed photometry
 * high-velocity cloud
 * high-velocity star
 * Hilda group
 * George William Hill
 * Himalia
 * Hind's Crimson Star
 * Hind's Variable Nebula
 * Hinode
 * Hinotori
 * Hipparchus of Nicaea
 * Hipparcos
 * Hirayama family
 * Hiten
 * H line -> H and K lines
 * H magnitude
 * Hoba West meteorite
 * Hobby–Eberly Telescope
 * Hohmann orbit
 * Holmberg radius
 * homogeneity
 * homology
 * Homunculus Nebula
 * H I region
 * Hooker Telescope
 * horizon
 * horizontal branch
 * horizontal coordinates
 * horizontal parallax
 * horizontal refraction
 * horn antenna
 * Horologium
 * Jeremiah Horrocks
 * Jeremiah Horrox -> Jeremiah Horrocks
 * Horsehead Nebula
 * horseshoe mounting
 * Horseshoe Nebula
 * horseshoe orbit
 * horst
 * hot Big Bang
 * hot dark matter
 * hot Jupiter
 * hot spot
 * 1
 * 2
 * hour angle
 * hour circle
 * Hourglass Nebula
 * howardite
 * Fred Hoyle
 * HPBW -> half-power beamwidth
 * half-power beamwidth -> beamwidth
 * HR diagram -> Hertzsprung–Russell diagram
 * HR number
 * HSO -> Herschel Space Observatory
 * HST -> Hubble Space Telescope
 * H20 maser
 * H II region
 * Edwin Powell Hubble
 * Hubble classification
 * Hubble constant
 * Hubble diagram
 * Hubble flow
 * Hubble law
 * Hubble parameter -> Hubble constant
 * Hubble radius
 * Hubble–Sandage variable
 * Hubble Space Telescope
 * Hubble's Variable Nebula
 * Hubble time
 * William Huggins
 * Hendrik ('Henk') Christoffel van de Hulst
 * Milton Lasell Humason
 * hummocky terrain
 * Humphreys series
 * Hungaria group
 * hunter's Moon
 * Huygenian eyepiece
 * Christiaan Huygens
 * Huygens Gap
 * Huygens probe
 * Hyades
 * Comet Hyakutake (C/1996 B2)
 * Hydra
 * hydrocarbon
 * hydrogen
 * hydrogen burning
 * hydrogen emission region
 * hydrogen ion
 * hydrogen line -> 21-centimetre line
 * hydrogen spectrum
 * hydrostatic equilibrium
 * hydroxyl
 * Hydrus
 * Hygiea
 * hyperbola
 * hyperbolic comet
 * hyperbolic orbit
 * hyperbolic velocity
 * hyperboloid
 * hyperfine structure
 * hypergiant star
 * Hyperion
 * hypernova
 * hyperon
 * hypersensitization
 * hypersthene achondrite -> diogenite
 * hypervelocity impact
 * Hz -> hertz
 * HZ43

I

 * Iapetus
 * IAU -> International Astronomical Union
 * IC -> Index Catalogue
 * Icarus
 * ICE -> International Cometary Explorer
 * ICRF -> International Celestial Reference Frame
 * ICRS -> International Celestial Reference System
 * Ida
 * IGM -> intergalactic medium
 * igneous
 * IGY -> International Geophysical Year
 * Comet Ikeya–Seki (C/1965 S1)
 * Comet Ikeya–Zhang (153P/)
 * illuminance
 * IMAGE -> Imager for Magnetopause-to-Aurora Global Exploration
 * image intensifier -> image tube
 * Image Photon Counting System
 * Imager for Magnetopause-to-Aurora Global Exploration
 * image tube
 * imaging photometer -> area photometer
 * I magnitude
 * Imbrium Basin
 * immersion
 * impact crater
 * impactite
 * impersonal astrolabe -> Danjon astrolabe
 * inclination
 * 1
 * 2
 * Index Catalogue
 * indochinite
 * Indus
 * inequality
 * inert gas -> noble gas
 * inertial coordinate system
 * inertial mass
 * inertial reference frame
 * infall velocity
 * inferior conjunction
 * inferior planet
 * inflationary universe
 * Infrared Astronomical Satellite
 * infrared astronomy
 * infrared cirrus
 * infrared excess
 * infrared photometry
 * infrared radiation
 * infrared source
 * Infrared Space Observatory
 * infrared telescope
 * infrared window
 * initial mass function
 * Robert Thorburn Ayton Innes
 * Innisfree meteorite
 * insolation
 * instability strip
 * Institut de Radio Astronomie Millim&eacute;trique
 * INT -> Isaac Newton Telescope
 * INTEGRAL -> International Gamma-Ray Astrophysics Laboratory
 * integrated magnitude
 * integration time
 * intensity
 * intensity interferometer
 * interacting binary
 * interacting galaxy
 * Interamnia
 * interference
 * 1
 * 2
 * interference filter
 * interference pattern
 * interferometer
 * intergalactic absorption
 * intergalactic magnetic field
 * intergalactic medium
 * intermediate-band photometry
 * intermediate-population star
 * intermediate-type star
 * International Astronomical Union
 * International Atomic Time
 * International Celestial Reference Frame
 * International Celestial Reference System
 * International Cometary Explorer
 * International Date Line
 * International Gamma-Ray Astrophysics Laboratory
 * International Geophysical Year
 * International Sun–Earth Explorer
 * International Sunspot Number
 * International Ultraviolet Explorer
 * International Years of the Quiet Sun
 * interplanetary matter
 * interplanetary scintillation
 * interpulse
 * interstellar absorption
 * interstellar maser
 * interstellar matter
 * interstellar molecule
 * interstellar reddening -> interstellar absorption
 * interstellar scintillation
 * interstellar wind
 * intrinsic colour index
 * intrinsic variable
 * invariable plane
 * inverse Compton effect
 * inverse Compton scattering -> inverse Compton effect
 * inverse P Cygni profile -> P Cygni profile
 * inverse-square law
 * inversion layer -> atmospheric transparency
 * Io (moon)
 * iodine cell
 * ion
 * ionization
 * ionization equilibrium
 * ionization front
 * ionization potential
 * ionization temperature
 * ionopause
 * ionosphere
 * ionospheric scintillation
 * ion tail -> cometary tail
 * Iota Aquarid meteors
 * IPCS -> Image Photon Counting System
 * IQSY -> International Years of the Quiet Sun
 * IR -> infrared
 * IRAM -> Institut de Radio Astronomie Millim&eacute;trique
 * IRAS -> Infrared Astronomical Satellite
 * Comet IRAS–Araki–Alcock (C/1983 H1)
 * Iris (asteroid)
 * iron meteorite
 * iron peak
 * irradiance
 * irradiation
 * 1
 * 2
 * irregular galaxy
 * irregular variable
 * IRTF -> NASA Infrared Telescope Facility
 * Isaac Newton Group
 * Isaac Newton Telescope
 * ISEE -> International Sun–Earth Explorer
 * Ishtar Terra
 * ISM -> interstellar matter -> interstellar medium
 * ISO (observatory) -> Infrared Space Observatory
 * isochron
 * isochrone
 * isophotal wavelength
 * isophote
 * isotherm
 * isothermal process
 * isothermal region
 * isotope
 * isotropy
 * IUE -> International Ultraviolet Explorer
 * Izar

J

 * James Clerk Maxwell Telescope
 * James Webb Space Telescope
 * jansky
 * Karl Guthe Jansky
 * (Pierre) Jules C&eacute;sar Janssen
 * Janus (moon)
 * JCMT -> James Clerk Maxwell Telescope
 * JD -> Julian Date
 * James Hopwood Jeans
 * Jeans length
 * Jeans mass
 * jet (astronomical objects)
 * Jet Propulsion Laboratory
 * Jewel Box
 * Jilin meteorite
 * J magnitude
 * Job's Coffin
 * Jodrell Bank Observatory
 * Johnson photometry
 * Johnson Space Center
 * Joint Astronomy Centre
 * Harold Spencer Jones
 * joule
 * Jovian planet
 * JPL -> Jet Propulsion Laboratory
 * Julian calendar
 * Julian Date
 * Julian day number
 * Julian epoch
 * Juliet (moon)
 * Juno (asteroid)
 * Jupiter (planet)
 * Jupiter–family comet
 * JWST -> James Webb Space Telescope

K

 * K -> kelvin scale
 * Immanuel Kant
 * Kappa Crucis Cluster -> Jewel Box cluster
 * Kappa Cygnid meteors
 * kappa mechanism
 * Jacobus Cornelius Kapteyn
 * Kapteyn Selected Areas
 * Kapteyn's Star
 * Kaus Australis
 * K corona
 * K-correction
 * Keck Telescopes
 * Keeler Gap
 * Kellner eyepiece
 * Lord (William Thomson) Kelvin
 * Kelvin–Helmholtz contraction -> Helmholtz–Kelvin contraction
 * kelvin scale
 * Kennedy Space Center
 * Kepler (satellite)
 * Johannes Kepler
 * Johann Kepler -> Johannes Kepler
 * Keplerian telescope
 * Kepler's equation
 * Kepler's laws
 * Kepler's Star
 * Kerr black hole
 * Keyhole Nebula
 * Keystone
 * Kids (asterism)
 * kinematic parallax
 * kinetic energy
 * kinetic temperature
 * Gustav Robert Kirchhoff
 * Kirchhoff's laws
 * Kirin meteorite -> Jilin meteorite
 * Daniel Kirkwood
 * Kirkwood gaps
 * Kitt Peak National Observatory
 * Kleinmann–Low Nebula
 * KL Nebula -> Kleinmann–Low Nebula
 * K line -> H and K lines
 * K magnitude
 * knife-edge test -> Foucault test
 * Kochab
 * Comet Kohoutek (C/1973 E1)
 * K&ouml;nig eyepiece -> Erfle eyepiece
 * Koronis family
 * KPNO -> Kitt Peak National Observatory
 * Kracht group
 * Kramers opacity
 * KREEP
 * Kreutz sungrazer
 * Kron–Cousins RI photometry
 * Kruskal diagram
 * K star
 * Kueyen
 * Gerard Peter Kuiper
 * Kuiper Airborne Observatory
 * Kuiper Belt

L

 * labes
 * labyrinthus
 * Nicolas Louis de Lacaille
 * Lacerta
 * Lacertid -> BL Lacertae object
 * lacus
 * Lagoon Nebula
 * Joseph Louis de Lagrange(-Tournier)
 * Lagrangian point
 * l'Aigle meteorite shower
 * Joseph J&eacute;r&ocirc;me (Le Fran&ccedil;ais) de Lalande
 * Lalande 21185
 * Lambda Bo&ouml;tis star
 * Lambda Eridani star
 * La Palma -> Roque de los Muchachos Observatory
 * Pierre Simon de Laplace
 * Laplacian plane
 * Large Binocular Telescope
 * Large Magellanic Cloud
 * Large Millimeter Telescope
 * large-scale structure
 * Large Synoptic Survey Telescope
 * Larissa
 * Las Campanas Observatory
 * laser
 * Laser Interferometer Space Antenna
 * La Silla Observatory
 * William Lassell
 * Lassell ring
 * last contact
 * last quarter
 * La Superba
 * late heavy bombardment
 * late-type galaxy
 * late-type star
 * latitude
 * latitude variation
 * LBV -> luminous blue variable
 * L dwarf
 * leap second
 * leap year
 * least circle of confusion -> astigmatism -> spherical aberration
 * Henrietta Swan Leavitt
 * Leda (moon)
 * Georges &Eacute;douard Lema&icirc;tre
 * Lema&icirc;tre universe
 * lens
 * Lense–Thirring effect -> frame dragging
 * gravitational lens
 * lenticula
 * lenticular galaxy
 * Leo (constellation)
 * Leo Minor (constellation)
 * Leonid meteors
 * lepton
 * lepton era
 * Lepus
 * Leto family
 * Urbain Jean Joseph Le Verrier <-> Urbain Jean Joseph Leverrier
 * Le Verrier Ring
 * Comet Lexell (D/1770 L1)
 * LHA -> local hour angle
 * Libra (constellation)
 * first point of Libra
 * libration
 * libration point -> Lagrangian point
 * Lick Observatory
 * light
 * speed of light
 * light bucket -> flux collector
 * light cone
 * light-curve
 * light pollution
 * light pressure -> radiation pressure
 * light time
 * light year
 * limb
 * limb brightening
 * limb darkening
 * limiting magnitude
 * 1
 * 2
 * Lincoln Near-Earth Asteroid Research
 * Bertil Lindblad
 * Lindblad resonance
 * linea
 * LINEAR
 * line blanketing
 * line broadening
 * line of apsides
 * line of inversion -> magnetic inversion line
 * line of nodes
 * line profile
 * liner
 * line ratio
 * line receiver
 * line spectrum
 * linewidth
 * line wing
 * lingula
 * LISA -> Laser Interferometer Space Antenna
 * LISA Pathfinder
 * Lissajous orbit
 * lithium star
 * lithosiderite -> stony-iron meteorite
 * lithosphere
 * Little Dipper
 * Little Dumbbell
 * Liverpool Telescope
 * L magnitude
 * LMC -> Large Magellanic Cloud
 * LMT -> Large Millimeter Telescope
 * lobate ridge
 * lobate scarp
 * lobe
 * 1
 * 2
 * local arm
 * local bubble
 * Local Group
 * local hour angle
 * local mean time
 * local sidereal time
 * local standard of rest
 * local supercluster
 * local thermodynamic equilibrium
 * local time
 * Lockman hole
 * (Joseph) Norman Lockyer
 * lodranite
 * LOFAR -> Low Frequency Array
 * LONEOS -> Lowell Observatory Near-Earth Object Search
 * long-baseline interferometry
 * longitude
 * longitude at the epoch
 * longitude of perigee
 * longitude of perihelion
 * longitude of the ascending node
 * long-period comet
 * long-period variable
 * lookback time
 * loop prominence
 * Lorentz–Fitzgerald contraction
 * Lorentz transformation
 * Lost City meteorite
 * (Alfred Charles) Bernard Lovell
 * Lovell Telescope
 * Percival Lowell
 * Lowell Observatory
 * Lowell Observatory Near-Earth Object Search
 * lower culmination
 * Low Frequency Array
 * low-luminosity star
 * low-mass star
 * low surface brightness galaxy
 * low-velocity star
 * LRO -> Lunar Reconnaissance Orbiter
 * LSR -> local standard of rest
 * LSST -> Large Synoptic Survey Telescope
 * LST -> local sidereal time
 * LTP -> lunar transient phenomenon
 * luminosity
 * luminosity class
 * luminosity evolution -> galaxy evolution
 * luminosity function
 * luminosity–volume test
 * luminous arc
 * luminous blue variable
 * Luna (Moon probes)
 * lunar eclipse
 * lunar inequality
 * Lunar Module
 * Lunar Orbiter
 * lunar parallax
 * Lunar Prospector
 * Lunar Reconnaissance Orbiter
 * lunar theory -> lunar inequality
 * lunar transient phenomenon
 * lunation
 * Knut Emil Lundmark
 * lunisolar precession
 * lunitidal interval
 * Lunokhod
 * Lupus
 * Lutz–Kelker bias
 * Willem ('William') Jacob Luyten
 * l.y. -> light year
 * Lydia family
 * Lyman-&alpha; forest
 * Lyman-break Galaxy
 * Lyman limit
 * Lyman series
 * Lynx (constellation)
 * Bernard Ferdinand Lyot
 * Lyot filter -> birefringent filter
 * Lyra (constellation)
 * Lyrid meteors
 * Lysithea

M

 * m -> apparent magnitude
 * M -> Messier Catalogue
 * M -> absolute magnitude
 * MACHO
 * Mach's principle
 * macrospicules
 * macroturbulence
 * macula
 * Maffei Galaxies
 * Magdalena Ridge Observatory
 * Magellan
 * Magellanic Clouds
 * Magellanic Stream
 * Magellan Telescopes
 * magma
 * magnetar
 * magnetic inversion line
 * magnetic monopole
 * magnetic star
 * magnetic storm -> geomagnetic storm
 * magnetic variable
 * magnetobremsstrahlung
 * magnetogram
 * magnetohydrodynamics
 * magnetopause
 * magnetosheath
 * magnetosphere
 * magnetotail
 * magnification
 * magnitude
 * magnitude of an eclipse
 * main beam
 * main-belt asteroid -> asteroid belt
 * main lobe -> main beam
 * main sequence
 * major axis
 * Maksutov telescope
 * Malin-1
 * Malmquist bias
 * manganese–mercury star -> mercury–manganese star
 * manganese star
 * mantle
 * many-body problem -> n-body problem
 * mare (astronomy)
 * Maria family
 * Mariner
 * Mariner Valley -> Valles Marineris
 * Markab
 * Markarian galaxy
 * Mars (planet)
 * Marsden group
 * Mars Exploration Rover
 * Mars Express
 * Mars Global Surveyor
 * Marshall Space Flight Center
 * Mars Odyssey (2001 Mars Odyssey)
 * Mars Pathfinder
 * Mars probes
 * Mars Reconnaissance Orbiter
 * mascon
 * maser
 * maser amplifier
 * maser source
 * Nevil Maskelyne
 * mass
 * mass defect
 * mass discrepancy
 * mass function
 * mass loss
 * mass–luminosity relation
 * mass–radius relation
 * mass ratio
 * mass-to-light ratio
 * mass transfer
 * John Cromwell Mather
 * matter era
 * Mauna Kea Observatories
 * (Edward) Walter Maunder
 * Maunder minimum
 * maximum-entropy method
 * James Clerk Maxwell
 * Maxwell Gap
 * Maxwell Montes
 * Maxwell Telescope -> James Clerk Maxwell Telescope
 * Mayall Telescope
 * McDonald Observatory
 * McIntosh scheme -> sunspot
 * M-class asteroid
 * McMath–Pierce Solar Telescope
 * MDM Observatory
 * mean anomaly
 * mean daily motion
 * mean density of matter
 * mean equator
 * mean equinox
 * mean motion
 * mean parallax -> statistical parallax
 * mean place
 * mean pole
 * mean position -> mean place
 * mean sidereal time
 * mean solar day
 * mean solar time
 * mean sun
 * mean time
 * medium-band photometry
 * megamaser
 * megaregolith
 * Megrez
 * Melipal
 * meniscus lens
 * meniscus Schmidt telescope
 * Menkalinan
 * Menkar
 * Mensa (constellation)
 * mensa (planets)
 * Donald Howard Menzel
 * Merak
 * Mercury
 * mercury-manganese star
 * Mercury Surface, Space Environment, Geochemistry, and Ranging
 * celestial meridian
 * terrestrial meridian
 * meridian angle
 * meridian astronomy
 * meridian circle
 * meridian passage -> meridian transit
 * meridian telescope -> meridian circle -> transit circle -> transit instrument
 * meridian transit
 * MERLIN -> Multi-Element Radio-Linked Interferometer Network
 * meson
 * mesopause
 * mesosiderite
 * mesosphere
 * MESSENGER -> Mercury Surface, Space Environment, Geochemistry, and Ranging
 * Charles Joseph Messier
 * Messier Catalogue
 * Me star
 * metagalaxy
 * metal
 * metallic hydrogen
 * metal-poor star
 * metal-rich star
 * metastable state
 * meteor
 * Meteor Crater
 * meteorite
 * meteoroid
 * meteor shower
 * meteor storm
 * meteor stream
 * meteor swarm
 * methanol maser
 * Metis
 * Metonic cycle
 * Meudon Observatory
 * Meyer group
 * MHD -> magnetohydrodynamics
 * Miaplacidus
 * Mice (galaxies)
 * Albert Abraham Michelson
 * Michelson interferometer
 * Michelson–Morley experiment
 * Michelson stellar interferometer -> stellar interferometer
 * microchannel plate detector
 * microdensitometer
 * microlensing
 * micrometeorite
 * micrometer (measuring instrument)
 * micrometre
 * micron
 * micropore optics
 * Microscopium (constellation)
 * microturbulence
 * Microvariability and Oscillations of Stars
 * microvariable
 * microwave background radiation
 * microwaves
 * Midcourse Space Experiment
 * Mie scattering
 * Milky Way
 * millimetre-wave astronomy
 * millimetre waves
 * millisecond pulsar
 * Mills cross
 * Edward Arthur Milne
 * Milne–Eddington approximation
 * Mimas (moon)
 * Mimosa -> Beta Crucis
 * Hermann Minkowski
 * Rudolph Leo Bernhard Minkowski
 * minor axis
 * minor planet -> asteroid
 * Minor Planet Center
 * Mintaka
 * minute
 * minute of arc <-> arcmin
 * Mira
 * Mirach
 * Miranda (moon)
 * Mira star
 * Mirphak
 * mirror
 * mirror blank
 * Mirzam
 * missing mass
 * Maria Mitchell
 * Mittenzwey eyepiece
 * mixing ratio
 * Mizar
 * MJD -> Modified Julian Date
 * MK classification -> Morgan–Keenan classification
 * MKK classification -> Morgan–Keenan classification
 * M magnitude
 * MMT Observatory
 * mock Moon -> parselene
 * mock Sun -> parhelion
 * Modified Julian Date
 * moldavite
 * molecular cloud
 * molecular hydrogen
 * molecular line
 * molecule
 * Molonglo Radio Observatory
 * moment of inertia
 * MONET -> Monitoring Network of Telescopes
 * Monitoring Network of Telescopes
 * monocentric eyepiece
 * Monoceros (constellation)
 * monochromatic light
 * monochromatic magnitude
 * monochromator
 * Monogem Ring
 * monopole -> magnetic monopole
 * mons (planets)
 * month
 * Monthly Notices of the Royal Astronomical Society
 * Mont M&eacute;gantic Observatory -> Observatoire du Mont-M&eacute;gantic
 * Moon
 * Mopra Observatory
 * Moreton wave
 * William Wilson Morgan
 * Morgan–Keenan classification
 * Morgan's classification
 * morning star
 * MOST -> Microvariability and Oscillations of Stars
 * mottles
 * Mount Graham International Observatory
 * mounting
 * Mount Palomar Observatory -> Palomar Observatory
 * Mount Stromlo and Siding Spring Observatories
 * Mount Wilson classification -> sunspot
 * Mount Wilson Observatory
 * moustache -> Ellerman bomb
 * moving cluster
 * MRAO -> Mullard Radio Astronomy Observatory
 * M region
 * MRO -> Magdalena Ridge Observatory
 * MSSSO -> Mount Stromlo and Siding Spring Observatories
 * MS star
 * 1
 * 2
 * M star
 * MSX -> Midcourse Space Experiment
 * Mu Cephei star
 * Mullard Radio Astronomy Observatory
 * Johann M&uuml;ller -> Regiomontanus
 * multi-beam receiver
 * Multi-Element Radio-Linked Interferometer Network
 * multiple star
 * multiplet
 * multi-ringed basin -> impact basin
 * multiverse
 * muon
 * mural circle
 * Musca (constellation)

N

 * nadir
 * Nagler eyepiece
 * Naiad
 * Nal detector
 * naked eye
 * naked singularity
 * nakhlite
 * Nan&ccedil;ay Radio Astronomy Observatory
 * nanometre
 * Naos
 * narrow-band photometry
 * NASA -> National Aeronautics and Space Administration
 * NASA Infrared Telescope Facility
 * Nasir Eddin -> al-Tusi
 * Nasser Eddin -> al-Tusi
 * Nasmyth focus
 * National Aeronautics and Space Administration
 * National Astronomy and Ionosphere Center -> Arecibo Observatory
 * National Optical Astronomy Observatory
 * National Radio Astronomy Observatory
 * National Solar Observatory
 * National Space Science Data Center
 * The Nautical Almanac
 * nautical twilight
 * n-body problem
 * NEA -> near-Earth asteroid
 * neap tide
 * near-Earth asteroid
 * Near-Earth Asteroid Tracking
 * near infrared
 * NEAR Shoemaker
 * near ultraviolet
 * NEAT -> Near-Earth Asteroid Tracking
 * nebula
 * nebula filter
 * nebular line
 * nebular variable
 * nebulosity
 * negative eyepiece
 * negative lens -> diverging lens
 * Neptune (planet)
 * Nereid (moon)
 * Neumann lines
 * neutral hydrogen
 * neutral hydrogen line -> 21-centimetre line
 * neutral point
 * neutrino
 * neutrino astronomy
 * neutron
 * neutron degeneracy
 * neutron star
 * Simon Newcomb
 * New General Catalogue
 * New Horizons
 * New Millennium Program
 * new Moon
 * New Style date
 * New Technology Telescope
 * newton
 * Isaac Newton
 * Newtonian–Cassegrain telescope
 * Newtonian focus
 * Newtonian telescope
 * Newton's law of gravitation
 * Newton's laws of motion
 * N galaxy
 * NGC -> New General Catalogue
 * nickel–iron meteorite -> iron meteorite
 * Nicol prism
 * nightglow -> airglow
 * night sky brightness
 * night vision
 * Nix Olympica -> Olympus Mons
 * NLC -> noctilucent clouds
 * nm -> nanometre
 * N magnitude
 * NOAO -> National Optical Astronomy Observatory
 * Nobeyama Radio Observatory
 * noble gas
 * noctilucent clouds
 * nocturnal
 * nodal line
 * node
 * nodical month -> draconic month
 * non-baryonic matter
 * non-gravitational force
 * non-radial pulsation
 * non-thermal radiation
 * Nordic Optical Telescope
 * Norma (constellation)
 * normal astrograph
 * North America Nebula
 * Northern Coalsack -> Great Rift
 * Northern Cross -> Cygnus (constellation)
 * northern lights -> aurora (astronomy)
 * North Galactic Spur
 * north polar distance
 * North Polar Sequence
 * North Star -> Polaris
 * nova
 * nova-like variable
 * NPD -> north polar distance
 * NRAO -> National Radio Astronomy Observatory
 * NS -> New Style date
 * NSO -> National Solar Observatory
 * NSSDC -> National Space Science Data Center
 * N star -> carbon star
 * NTT -> New Technology Telescope
 * Nubecula Major -> Magellanic Clouds
 * Nubecula Minor -> Magellanic Clouds
 * nuclear fusion
 * nuclear reaction
 * nuclear time-scale
 * nucleon
 * nucleosynthesis
 * atomic nucleus
 * cometary nucleus
 * galactic nucleus
 * null geodesic
 * number evolution -> galaxy evolution
 * Nunki
 * nutation
 * nutation in right ascension -> equation of the equinoxes
 * Nysa family

O

 * OAO -> Orbiting Astronomical Observatory
 * OB association
 * Oberon
 * object glass
 * objective
 * objective grating
 * objective prism
 * oblateness
 * oblate spheroid -> spheroid
 * oblique rotator
 * obliquity of the ecliptic
 * Observatoire du mont M&eacute;gantic
 * observatory
 * occultation
 * occulting bar
 * occulting disk
 * oceanus
 * OC star
 * octahedrite
 * Octans (constellation)
 * ocular -> eyepiece
 * Oe star
 * off-axis guider
 * Of star
 * o.g. -> object glass
 * OH–IR source
 * OH line
 * OH maser
 * OHP -> Haute-Provence Observatory
 * Heinrich Wilhelm Matth&auml;us Olbers
 * Olbers' paradox
 * Old Style date
 * Oljato (asteroid)
 * Olympus Mons
 * O magnitude
 * Omega Centauri
 * Omega Nebula
 * Onsala Space Observatory
 * ON star
 * Jan Hendrik Oort
 * Oort Cloud
 * Oort's constants
 * Oosterhoff group
 * Ootacamund Radio Astronomy Centre
 * opacity
 * open cluster
 * open universe
 * Ophelia (moon)
 * Ophiuchid meteors
 * Ophiuchus (constellation)
 * Ernst Julius &Ouml;pik
 * Oppenheimer–Volkoff limit
 * Opportunity (Mars rover)
 * opposition (astronomy)
 * opposition effect
 * optical axis
 * optical depth
 * optical double
 * optical flat
 * optical glass
 * optical interferometer
 * optical libration
 * optical pathlength
 * optical pulsar
 * optical thickness -> optical depth
 * optical wedge
 * optics
 * orbit
 * orbital elements
 * orbital velocity
 * Orbiting Astronomical Observatory
 * Orbiting Solar Observatory
 * ordinary chondrite
 * organic molecule
 * Orgueil meteorite
 * Orientale Basin
 * Orion (constellation)
 * Orion Arm
 * Orion Association
 * Orionid meteors
 * Orion Molecular Clouds
 * Orion Nebula
 * Orion Spur
 * Orion variable
 * ORM -> Roque de los Muchachos Observatory
 * orrery
 * orthoscopic eyepiece
 * OS -> Old Style date
 * oscillating universe
 * osculating elements
 * osculating orbit
 * OSO -> Orbiting Solar Observatory
 * O star
 * OT -> Teide Observatory
 * outgassing
 * 1
 * 2
 * overcontact binary
 * oversampling
 * overshooting
 * overtone mode
 * OVV quasar -> optically violently variable quasar -> blazar
 * Owens Valley Radio Observatory
 * Owl Nebula
 * oxygen burning
 * ozonosphere

P

 * PA -> position angle
 * PAH -> polycyclic aromatic hydrocarbon
 * pair annihilation
 * pair production
 * palimpsest
 * Pallas (asteroid)
 * pallasite
 * Palomar Observatory
 * Palomar Observatory Sky Survey
 * palus
 * Pan (moon)
 * Pandora (moon)
 * Pan-STARRS
 * parabola
 * parabolic antenna
 * parabolic comet
 * parabolic orbit
 * parabolic velocity
 * paraboloid
 * parallactic angle
 * parallactic ellipse
 * parallactic inequality
 * parallactic motion
 * parallax
 * parametric amplifier
 * Paranal Observatory
 * paraxial
 * parent isotope
 * parfocal
 * parhelion
 * Paris Observatory
 * Parkes Observatory
 * parsec
 * parselene
 * William Parsons -> Third Earl of Rosse
 * partial eclipse
 * particle -> elementary particle
 * pascal (unit)
 * Paschen–Back effect
 * Paschen series
 * Pasiphae (moon)
 * passband
 * past light cone -> light cone
 * patera
 * pathlength -> optical pathlength
 * Paul Wild Observatory
 * Pavo (constellation)
 * Cecilia Helena Payne-Gaposchkin
 * pc -> parsec
 * P-class asteroid
 * P Cygni line profile
 * P Cygni star -> S Doradus star
 * Peacock (star)
 * peculiar galaxy
 * peculiar motion
 * peculiar star
 * peculiar velocity
 * pedestal crater
 * Peekskill meteorite
 * Pegasus (constellation)
 * Pele
 * Pelican Nebula
 * Penrose process
 * penumbra
 * 1
 * 2
 * penumbral eclipse
 * Arno Allan Penzias
 * perfect cosmological principle
 * peri-
 * periapsis
 * periastron
 * periastron effect
 * pericentre
 * perigee
 * perihelion
 * time of perihelion passage
 * orbital period
 * period–age relation
 * period–colour relation
 * period–density relation
 * periodic comet
 * periodic orbit
 * periodic perturbation
 * period–luminosity–colour relation
 * period–luminosity relation
 * period–mass relation
 * period–radius relation
 * period–spectrum relation
 * Perseid meteors
 * Perseus (constellation)
 * Perseus A
 * Perseus Arm
 * Perseus Cluster
 * personal equation
 * perturbation
 * Petzval surface
 * Pfund series
 * PHA -> Potentially Hazardous Asteroid
 * Phad
 * Phaethon (asteroid)
 * phase
 * 1
 * 2
 * phase angle
 * phased array
 * phase defect
 * phase diagram
 * phase difference
 * phase rotator
 * phase-switching interferometer
 * phase transition -> inflationary universe
 * Phecda -> Phad
 * Pherkad
 * Phillips bands
 * Phobos (moon)
 * Phobos probes
 * Phocaea group
 * Phoebe (moon)
 * Phoenicid meteors
 * Phoenix (constellation)
 * Phoenix (Mars lander)
 * Pholus (asteroid)
 * photino
 * photocathode
 * photocell -> photoelectric cell
 * photocentre
 * 1
 * 2
 * photoconductive cell
 * photodissociation
 * photodissociation region
 * photoelectric cell
 * photoelectric magnitude
 * photoelectric photometer
 * photographic amplification
 * photographic emulsion
 * photographic magnitude
 * photographic zenith tube
 * photoheliograph
 * photoionization
 * photometer
 * photometric binary
 * photometric parallax
 * photometric standard -> standard star
 * photometry
 * photomultiplier
 * photon
 * photon sphere
 * photopolarimeter -> polarimeter
 * photosphere
 * photovisual magnitude
 * photovoltaic detector
 * physical albedo -> geometrical albedo
 * physical double
 * physical libration
 * Giuseppe Piazzi
 * Pic du Midi Observatory
 * Edward Charles Pickering
 * William Henry Pickering
 * Pickering Series
 * Pico Veleta
 * Pictor (constellation)
 * pincushion distortion
 * Pinwheel Galaxy
 * pion
 * Pioneer
 * Pioneer Venus
 * Pipe Nebula
 * Pisces (constellation)
 * Piscid meteors
 * Piscis Austrinid meteors
 * Piscis Austrinus (constellation)
 * pitch angle
 * pixel
 * plage
 * Planck (spacecraft)
 * Planck constant
 * Planck era
 * Planck's law
 * planemo
 * planet
 * planetarium
 * planetary aberration
 * planetary aspect -> aspect
 * planetary migration
 * planetary nebula
 * planetary precession
 * planetesimal
 * planetoid -> asteroid -> Giuseppe Piazzi
 * planetology
 * planisphere
 * planitia
 * planoconcave lens
 * planoconvex lens
 * planum
 * John Stanley Plaskett
 * Plaskett's Star
 * plasma
 * plasmapause
 * plasmasphere
 * plasma tail -> cometary tail
 * Plateau de Bure
 * plate centre
 * plate constants
 * plate-measuring machine
 * plate scale
 * plate tectonics
 * Platonic year
 * PLC relation -> period–luminosity–colour relation
 * Pleiades
 * plerion
 * Pl&ouml;ssl eyepiece
 * Plough (asterism)
 * PL relation -> period–luminosity relation
 * plume
 * 1
 * 2
 * Plutino
 * Pluto
 * P magnitude
 * Pockels cell
 * Norman Robert Pogson
 * Pogson ratio
 * Pogson scale
 * Pogson step method
 * (Jules) Henri Poincar&eacute;
 * Pointers
 * point source
 * point-spread function
 * polar -> AM Herculis star -> DQ Herculis star
 * polar axis
 * polar cap
 * polar diagram
 * polar distance
 * polar flattening
 * polarimeter
 * polarimetry -> polarization
 * Polaris
 * polarization
 * polar motion
 * polar orbit
 * polar plume -> coronal plume
 * polar ring galaxy
 * polar sequence
 * polar wandering
 * pole
 * pole star
 * Pollux
 * polycyclic aromatic hydrocarbon
 * John Pond
 * Jean Louis Pons
 * stellar population
 * Population I
 * Population II
 * Population III
 * pore
 * Porrima
 * Porro prism
 * Portia (moon)
 * positional astronomy -> astrometry -> meridian astronomy
 * position angle
 * position-angle effect
 * position circle
 * position micrometer -> filar micrometer
 * positive lens -> converging lens
 * POSS -> Palomar Observatory Sky Survey
 * post-nova
 * potassium–argon method
 * potential hazardous asteroid
 * power spectrum
 * Poynting–Robertson effect
 * PPM Star Catalogue
 * p-process
 * Praesepe
 * preceding
 * precession
 * precession constant
 * precession of the equinoxes
 * precursor pulse
 * pre-nova
 * pressure broadening
 * Pr&iacute;bram meteorite
 * primary cosmic ray
 * primary minimum
 * primary mirror
 * prime focus
 * prime meridian
 * prime vertical
 * primordial fireball
 * primordial galaxy
 * Principia
 * principle of equivalence -> equivalence principle
 * prism
 * prismatic astrolabe
 * probable error
 * Procyon
 * prograde motion -> direct motion
 * prolate spheroid -> spheroid
 * Prometheus (moon)
 * prominence
 * prominence spectroscope
 * promontorium
 * proper motion
 * proper time
 * proplyd
 * proportional counter
 * Prospero (moon)
 * Proteus (moon)
 * protogalaxy
 * proton
 * proton–proton reaction
 * protoplanet
 * protoplanetary nebula
 * 1
 * 2
 * protostar
 * protosun
 * Proxima Centauri
 * p-spot
 * Ptolemaic system
 * Ptolemy <-> Claudius Ptolemaeus
 * Publications of the Astronomical Society of the Pacific
 * Puck (moon)
 * Pulcherrima -> Izar
 * pulsar
 * pulsating variable
 * pulsation mode
 * pulse broadening
 * pulse profile
 * pulse width
 * Pup (Sirius B)
 * pupil
 * Puppid–Velid meteors
 * Puppis (constellation)
 * Purkinje effect
 * PV Telescopii star
 * Pyxis
 * PZT -> photographic zenith tube

Q

 * Q-class asteroid
 * Q magnitude
 * QSO -> quasi-stellar object
 * QSS -> quasi-stellar radio source
 * quadrant
 * Quadrantid meteors
 * quadrature
 * quadrupole
 * quantum
 * quantum cosmology
 * quantum efficiency
 * quantum gravitation
 * quantum theory
 * Quaoar
 * quark
 * quark star
 * quasar
 * quasi-stellar object
 * quasi-stellar radio source
 * quiescent prominence
 * quiet sun
 * quintessence -> dark energy

R

 * RA -> right ascension
 * radar astronomy
 * radar meteor
 * radial pulsation
 * radial velocity
 * radial-velocity spectrometer
 * radian
 * radiant
 * radiation
 * radiation belt
 * radiation era
 * radiation laws -> Planck's law -> Stefan–Boltzmann law -> Wien's displacement law
 * radiation pressure
 * radiation temperature
 * radiative equilibrium
 * radiative recombination -> free–bound transition
 * radiative transfer
 * radiative zone
 * radioactive age dating
 * radio astrometry
 * RadioAstron
 * radio astronomy
 * radio galaxy
 * radiogenic
 * radioheliograph
 * radio interferometer
 * radio jet -> jet (astronomy)
 * radio meteor
 * radiometer
 * radiometric dating -> radioactive age dating
 * radionuclide
 * radio source
 * radio star
 * radio telescope
 * radio waves
 * radio window
 * radius–luminosity relation
 * radius of curvature
 * radius vector
 * Raman effect
 * Ramaty High-Energy Solar Spectroscopic Imager
 * rampart crater
 * Ramsden disk
 * Ramsden eyepiece
 * Ranger (Moon probes)
 * RAS -> Royal Astronomical Society
 * Rasalgethi
 * Rasalhague
 * Ra-Shalom (asteroid)
 * R association
 * raster
 * raster scan
 * RAS thread
 * RATAN-600
 * Rayleigh criterion
 * Rayleigh–Jeans formula
 * Rayleigh limit -> Rayleigh criterion
 * Rayleigh number
 * Rayleigh scattering
 * crater rays
 * R Canis Majoris star
 * R-class asteroid
 * R Coronae Borealis star
 * Grote Reber
 * receiver
 * 1
 * 2
 * reciprocity failure
 * recombination
 * recombination epoch
 * recombination line
 * rectangular coordinates
 * recurrent nova
 * recycled pulsar
 * reddening
 * red dwarf
 * red giant
 * Red Planet -> Mars (planet)
 * redshift
 * redshift–distance relation
 * redshift–magnitude relation
 * Red Spot -> Great Red Spot
 * reduced proper motion
 * red variable
 * reference frame -> frame of reference
 * reference star
 * reflectance spectrum
 * reflecting telescope
 * reflection effect
 * reflection grating
 * reflection nebula
 * reflection variable
 * reflector -> reflecting telescope
 * refracting telescope
 * atmospheric refraction
 * refractive index
 * refractor -> refracting telescope
 * refractory
 * regio
 * Regiomontanus
 * regmaglypt
 * regolith
 * regression of nodes
 * Regulus
 * relative orbit
 * relative sunspot number
 * relativistic beaming
 * relativistic velocity
 * relativity
 * relaxation time
 * remote sensing
 * r&eacute;seau
 * residuals
 * resolution -> resolving power
 * resolving power
 * resonance
 * resonance line
 * resonant scattering
 * rest mass
 * restricted three-body problem
 * retardation
 * retardation plate -> wave plate
 * reticle
 * Reticulum (constellation)
 * reticulum (planets)
 * retrograde motion
 * reversing layer
 * revolution
 * RFT -> richest-field telescope
 * RGO -> Royal Greenwich Observatory
 * RGU photometry
 * Rhea (moon)
 * RHESSI -> Ramaty High-Energy Solar Spectroscopic Imager
 * Rho Cassiopeiae star
 * Rho Ophiuchi Nebula
 * Richardson–Lucy algorithm
 * richest-field telescope
 * Rigel
 * right ascension
 * Rigil Kentaurus -> Alpha Centauri
 * rille (Moon)
 * rima
 * planetary ring
 * ring arcs
 * ring galaxy
 * Ring Nebula
 * rise time
 * rising
 * George Willis Ritchey
 * Ritchey–Chr&eacute;tien telescope
 * R magnitude
 * Robertson–Walker metric
 * Roche limit
 * Roche lobe
 * ROE -> Royal Observatory, Edinburgh
 * Ole Christensen R&ouml;mer
 * Olaus Christensen R&ouml;mer -> Ole Christensen R&ouml;mer
 * Ronchi test
 * Rood–Sastry type
 * roof prism
 * Roque de los Muchachos Observatory
 * Rosalind (moon)
 * Rosat
 * Rosetta
 * Rosette Nebula
 * Frank Elmore Ross
 * Third Earl of Rosse <-> William Parsons
 * Rosseland mean opacity
 * Bruno Benedetto Rossi
 * Rossiter effect
 * Rossi X-ray Timing Explorer
 * rotating variable
 * rotation
 * rotation curve
 * rotation effect -> Rossiter effect
 * rotation measure
 * Royal Astronomical Society
 * Royal Greenwich Observatory
 * Royal Observatory, Edinburgh
 * r-process
 * RR Lyrae star
 * RRs variable -> Delta Scuti star
 * RR Telescopii star
 * RS Canum Venaticorum star
 * R star -> carbon star
 * Rubin–Ford effect
 * runaway star
 * rupes
 * Henry Norris Russell
 * Russell–Vogt theorem -> Vogt–Russell theorem
 * RV Tauri star
 * RW Aurigae star
 * RXTE -> Rossi X-ray Timing Explorer
 * Martin Ryle
 * Ryle Telescope

S

 * SAAO -> South African Astronomical Observatory
 * Sabik
 * Sachs–Wolfe effect
 * Sacramento Peak Observatory
 * Carl Edward Sagan
 * Sagitta (constellation)
 * Sagittarius (constellation)
 * Sagittarius A
 * Sagittarius Arm
 * Sagittarius Dwarf Galaxy
 * Saha ionization equation
 * Sakigake
 * Salpeter function -> initial mass function
 * Salpeter process -> triple-alpha process
 * SALT -> South African Large Telescope
 * SAMPEX -> Solar, Anomalous, and Magnetospheric Particle Explorer
 * Allan Rex Sandage
 * SAO -> Smithsonian Astrophysical Observatory
 * SAO Catalog -> Smithsonian Astrophysical Observatory Star Catalog
 * saros
 * SAS -> Small Astronomy Satellite
 * satellite
 * Saturn (planet)
 * Saturn Nebula
 * scale height
 * scattered-disk object
 * scatter ellipse
 * scattering
 * Scheat
 * Schechter function
 * Schedar -> Shedir
 * Christoph Scheiner
 * Giovanni Virginio Schiaparelli
 * schiefspiegler telescope
 * Maarten Schmidt
 * Schmidt camera
 * Schmidt–Cassegrain telescope
 * Sch&ouml;nberg–Chandrasekhar limit -> Chandrasekhar–Sch&ouml;nberg limit
 * Schr&ouml;ter effect
 * (Samuel) Heinrich Schwabe
 * Karl Schwarzschild
 * Schwarzschild black hole
 * Schwarzschild radius
 * Schwarzschild telescope
 * Comet 29P/Schwassmann–Wachmann 1
 * scintillation
 * scintillation counter
 * S-class asteroid
 * Sco-Cen Association
 * scopulus
 * Scorpius (constellation)
 * Scorpius X-1
 * Scotch mount
 * SC star -> S star
 * SCT -> Schmidt–Cassegrain telescope
 * Sculptor (constellation)
 * Sculptor group
 * Scutum (constellation)
 * SDO -> Solar Dynamics Observatory
 * S Doradus star
 * SDSS photometry
 * Search for Extraterrestrial Intelligence
 * Seashell Galaxy
 * season
 * (Pietro) Angelo Secchi
 * Secchi classification
 * second
 * leap second
 * secondary cosmic ray
 * secondary crater
 * secondary minimum
 * secondary mirror
 * second contact
 * second of arc
 * secular
 * secular acceleration
 * secular parallax
 * secular perturbation
 * secular variable
 * seeing
 * segmented mirror
 * selected areas -> Kapteyn Selected Areas
 * selective absorption
 * Selene (Moon probe)
 * selenology
 * self-absorption
 * semidetached binary
 * semidiameter
 * semi-forbidden line -> forbidden line
 * semimajor axis
 * semiregular variable
 * sensitivity
 * separation
 * Serpens (constellation)
 * Serrurier truss
 * Setebos
 * SETI -> Search for Extraterrestrial Intelligence
 * setting
 * setting circle
 * Seven Sisters -> Pleiades
 * Sextans (constellation)
 * sextant
 * Carl Keenan Seyfert
 * Seyfert galaxy
 * Seyfert's Sextet
 * Shack–Hartmann test -> Hartmann test
 * shadow bands
 * shadow transit
 * Shapiro delay
 * Harlow Shapley
 * Shapley Concentration -> supercluster
 * shatter cone
 * Shaula
 * Shedir
 * shell burning
 * shell galaxy
 * shell star
 * shepherd moon
 * shergottite
 * shield volcano
 * shock metamorphism
 * Eugene Merle Shoemaker
 * Comet Shoemaker–Levy 9 (D/1993 F2)
 * shooting star -> meteor
 * short-period comet
 * short-period variable
 * Sickle (asterism)
 * side lobe
 * sidereal
 * sidereal day
 * sidereal month
 * sidereal period
 * sidereal rate
 * sidereal time
 * sidereal year
 * siderite -> iron meteorite
 * siderolite -> stony-iron meteorite
 * siderophyre
 * siderostat
 * Siding Spring Observatory
 * Sigma Octantis
 * signal-to-noise ratio -> sensitivity
 * Sikhote–Alin meteorite
 * silicon burning
 * silicon star
 * silvering
 * SIMBAD
 * SIM PlanetQuest
 * single-lined binary
 * singularity
 * Sinope (moon)
 * sinuous rille
 * sinus
 * SiO maser
 * Sirius
 * Sirrah
 * Willem de Sitter
 * SI units
 * six-colour system
 * 61 Cygni
 * SKA -> Square Kilometre Array
 * sky brightness
 * Skylab
 * Earl Carl Slipher
 * Vesto Melvin Slipher
 * Sloan Digital Sky Survey
 * slow nova
 * slow pulsator
 * SMA -> Submillimeter Array
 * Small Astronomy Satellite
 * small circle
 * Small Magellanic Cloud
 * SMART-1
 * SMC -> Small Magellanic Cloud
 * Smithsonian Astrophysics Observatory
 * Smithsonian Astrophysics Observatory Star Catalog
 * SMM -> Solar Maximum Mission
 * George Fitzgerald Smoot III
 * SNC meteorites
 * SNR -> supernova remnant
 * SNU -> solar neutrino unit
 * SOAR -> Southern Astrophysical Research telescope
 * SOFIA -> Stratospheric Observatory for Infrared Astronomy
 * soft gamma-ray repeater
 * soft X-rays
 * SO galaxy -> lenticular galaxy
 * SOHO -> Solar and Heliospheric Observatory
 * Sojourner
 * Solar, Anomalous, and Magnetospheric Particle Explorer
 * solar activity
 * Solar and Heliospheric Observatory
 * solar antapex
 * solar apex
 * solar atmosphere
 * solar constant
 * solar cycle -> sunspot cycle
 * solar day
 * Solar Dynamics Observatory
 * solar dynamo
 * solar eclipse
 * solar flare
 * solar interior
 * solar irradiance
 * solar mass
 * solar maximum
 * Solar Maximum Mission
 * solar minimum
 * solar motion
 * solar nebula
 * solar neutrino unit
 * Solar Orbiter
 * solar oscillations -> helioseismology
 * solar parallax
 * Solar System
 * solar telescope
 * solar–terrestrial relations
 * Solar Terrestrial Relations Observatory
 * solar time
 * solar tower
 * solar wind
 * solar year
 * solid Schmidt telescope
 * solstice
 * solstitial colure
 * Sombrero Galaxy
 * Sothic cycle
 * source count
 * South African Astronomical Observatory
 * South Atlantic Anomaly
 * Southern African Large Telescope
 * Southern Astrophysical Research Telescope
 * Southern Cross
 * southern lights
 * Southern Reference Stars
 * Southern Sky Survey
 * South Pole Aitken Basin
 * curvature of space -> curvature of spacetime
 * space motion
 * space probe
 * space reddening -> interstellar absorption
 * Space Telescope Science Institute
 * spacetime
 * space velocity
 * Spacewatch
 * space weather
 * spallation
 * spark chamber
 * spec. -> speculum metal
 * Special Astrophysical Observatory
 * special theory of relativity
 * speckle interferometry
 * spectral classification
 * spectral index
 * spectral line
 * spectral type
 * spectrogram
 * spectrograph
 * spectroheliogram
 * spectroheliograph
 * spectrohelioscope
 * spectrometer
 * spectrophotometer
 * spectrophotometry
 * spectropolarimetry
 * spectroscope
 * spectroscopic binary
 * spectroscopic parallax
 * spectroscopy
 * spectrum
 * 1
 * 2
 * spectrum binary
 * spectrum variable -> Alpha2 Canum Venaticorum
 * speculum metal
 * Harold Spencer Jones
 * spherical aberration
 * spherical albedo -> Bond albedo
 * spherical astronomy
 * spherical coordinates
 * spheroid
 * Spica
 * spicule
 * spider
 * spin
 * spinar
 * spin casting
 * Spindle Galaxy
 * spin-down
 * spin–orbit coupling
 * spin temperature
 * spiral arm
 * spiral galaxy
 * Spirit (Mars rover)
 * Lyman Spitzer, Jr
 * Spitzer Space Telescope
 * spokes
 * sporadic meteor
 * Gustav Friedrich Wilhelm Sp&ouml;rer
 * Sp&ouml;rer minimum
 * Sp&ouml;rer's law
 * spray
 * spring equinox -> vernal equinox
 * Springfield mounting
 * spring tide
 * s-process
 * sputtering
 * Square Kilometre Array
 * Square of Pegasus
 * SS Cygni
 * SS Cygni star
 * SS433
 * S star
 * ST -> standard time
 * standard atmosphere
 * standard epoch
 * standard solar model
 * standard star
 * standard time
 * standstill
 * star
 * starburst galaxy
 * star cluster
 * star count
 * Stardust
 * Stark broadening
 * starquake
 * starspot
 * star streaming
 * static limit
 * static universe
 * stationary point
 * 1
 * 2
 * statistical parallax
 * steady-state theory
 * Stefan–Boltzmann constant
 * Stefan–Boltzmann law
 * Stefan's law -> Stefan–Boltzmann law
 * stellar association
 * stellar atmosphere
 * stellar evolution
 * stellar interferometer
 * stellar population
 * stellar structure
 * stellar wind
 * Stephano (moon)
 * Stephan's Quintet
 * step method -> Argelander step method -> Pogson step method
 * steradian
 * STEREO -> Solar Terrestrial Relations Observatory
 * stereo comparator
 * Steward Observatory
 * stishovite
 * Stokes parameters
 * Stonyhurst heliographic coordinates
 * stony-iron meteorite
 * stony meteorite
 * stratigraphy
 * stratopause
 * stratosphere
 * Stratospheric Observatory for Infrared Astronomy
 * streamer
 * Strehl ratio
 * strewn field
 * 1
 * 2
 * string -> cosmic string
 * Bengt Georg Daniel Str&ouml;mgren
 * Str&ouml;mgren photometry
 * Str&ouml;mgren sphere
 * strontium star
 * Struve
 * Friedrich Georg Wilhelm von Struve
 * Otto Struve
 * Otto Wilhelm Struve
 * STScI -> Space Telescope Science Institute
 * style
 * Subaru Telescope
 * subatomic particle -> elementary particle
 * subdwarf
 * subgiant
 * subluminous star
 * sublunar point
 * Submillimeter Array
 * Submillimeter Wave Astronomy Satellite
 * submillimetre astronomy
 * sub-pulse
 * subsolar point
 * substellar object
 * substellar point
 * substorm
 * sudden ionospheric disturbance
 * Abd al-Raman al-Sufi
 * Suisei
 * sulcus
 * summer solstice -> solstice
 * Summer Time
 * Summer Triangle
 * Sun
 * sundial
 * sundog -> parhelion
 * Sunflower galaxy
 * sungrazer -> Kreutz sungrazer
 * sunrise
 * sunset
 * sunskirter
 * sunspot
 * sunspot cycle
 * Sunyaev–Zel'dovich effect
 * supercluster
 * supergalactic plane
 * supergiant
 * supergiant elliptical
 * supergranulation
 * superheterodyne receiver
 * superhump -> SU Ursae Majoris star
 * superior conjunction
 * superior planet
 * superluminal velocity
 * supermassive black hole
 * supermassive star
 * supermaximum -> SU Ursae Majoris star
 * supernova
 * Supernova 1987A
 * supernova remnant
 * super-rotation
 * super-Schmidt telescope
 * superstring theory
 * supersynthesis
 * surface brightness
 * surface gravity
 * surface temperature
 * surge prominence
 * Surveyor (space probes)
 * SU Ursae Majoris star
 * Suzaku
 * S Vulpeculae star
 * Swan bands
 * Swan Nebula -> Omega Nebula
 * SWAS -> Submillimeter Wave Astronomy Satellite
 * Swift (satellite)
 * Comet 109P/Swift–Tuttle
 * Sword Hand of Perseus
 * Sword of Orion
 * SX Arietis star
 * SX Phoenicis star
 * Sycorax (moon)
 * symbiotic star
 * synchronous orbit
 * synchronous rotation
 * syndyname
 * synodic
 * synodic month
 * synodic period
 * Syrtis Major
 * Systems I, II, and III
 * syzygy

T

 * tachocline
 * tachyon
 * TAI -> Temps Atomique International -> International Atomic Time
 * cometary tail
 * tangential velocity
 * Tarantula Nebula
 * Tarazed
 * T association
 * Taurid meteors
 * Taurus
 * Taurus A
 * Taurus Molecular Clouds
 * Taurus Moving Cluster
 * Taurus X-1
 * TCB -> Barycentric Coordinate Time
 * T-class asteroid
 * TDB -> Temps Dynamique Barycentrique -> Barycentric Dynamical Time
 * T dwarf
 * Teapot (asterism)
 * Comet Tebbutt (C/1861 J1)
 * technetium star
 * tectonics
 * Teide Observatory
 * tektite
 * telecompressor
 * tele-extender
 * telescope
 * telescope drive -> drive
 * telescope mounting -> mounting
 * Telescopio Nazionale Galileo
 * Telescopium (constellation)
 * Telesto
 * telluric lines
 * tellurium
 * Comet 55P/Tempel–Tuttle
 * temperature
 * temperature minimum
 * Tenma
 * termination shock
 * terminator
 * terra
 * terracing
 * terrestrial age
 * Terrestrial Dynamical Time -> Terrestrial Time
 * terrestrial planet
 * Terrestrial Time
 * tesla
 * tessera
 * Tethys (moon)
 * Thalassa (moon)
 * Thales of Miletus
 * Tharsis Montes
 * Thebe (moon)
 * Themis family
 * Themisto (moon)
 * theory of everything -> grand unified theory
 * thermal bremsstrahlung -> free–free transition
 * thermal equilibrium
 * 1
 * 2
 * thermal radiation
 * thermocouple
 * thermodynamic equilibrium -> thermal equilibrium
 * thermodynamic temperature
 * thermopile
 * thermosphere
 * thinned chip
 * Third Cambridge Catalogue
 * third contact
 * third quarter -> last quarter
 * 30 Doradus -> Tarantula Nebula
 * Thirty Meter Telescope
 * tholus
 * William Thomson -> Lord Kelvin
 * Thomson scattering
 * three-body problem
 * three-colour photography -> astrophotography
 * three-colour photometry -> Johnson photometry
 * three-kiloparsec arm
 * Thuban
 * Thule (asteroid)
 * tidal bulge
 * tidal evolution
 * tidal force
 * tidal friction
 * tidal heating
 * tides
 * time
 * time dilation
 * time of perihelion passage
 * time zone
 * TiO bands
 * tip–tilt mirror
 * Tisserand parameter
 * Titan (moon)
 * Titania (moon)
 * Titius–Bode law -> Bode's law
 * TLP -> lunar transient phenomenon
 * TMT -> Thirty Meter Telescope
 * TNG -> Galileo National Telescope
 * TNO -> trans-Neptunian object
 * Toby Jug Nebula
 * Tolman test
 * Clyde William Tombaugh
 * topocentric
 * topocentric coordinates
 * Torino scale
 * Toro (asteroid)
 * torquetum
 * torus
 * total eclipse
 * totality
 * total magnitude -> integrated magnitude
 * total solar irradiance
 * Toutatis (asteroid)
 * TRACE -> Transition Region and Coronal Explorer
 * train (meteors)
 * transfer function
 * transfer lens
 * transfer orbit
 * transient lunar phenomenon -> lunar transient phenomenon
 * meridian transit
 * planetary transit
 * transit circle
 * transit instrument
 * transition probability
 * transition region
 * Transition Region and Coronal Explorer
 * transmission grating
 * trans-Neptunian object
 * atmospheric transparency
 * transverse velocity -> tangential velocity
 * Trapezium (star)
 * Triangulum (constellation)
 * Triangulum Australe (constellation)
 * Triangulum Galaxy
 * Trifid Nebula
 * trigonometric parallax
 * triple-alpha process
 * triplet (lens)
 * triquetrum
 * trischiefspiegler -> schiefspiegler telescope
 * Triton (moon)
 * Trojan asteroid
 * tropic
 * tropical month
 * tropical period
 * tropical year
 * Tropic of Cancer
 * Tropic of Capricorn
 * tropopause
 * troposphere
 * true anomaly
 * true equator
 * true equinox
 * true pole
 * Trumpler classification
 * Trumpler star
 * TT -> Terrestrial Time
 * T Tauri star
 * T Tauri wind
 * Tucana (constellation)
 * Tully–Fischer relation
 * Tunguska event
 * tuning-fork diagram
 * atmospheric turbulence
 * turnoff point
 * Nasir al-Din al-Tusi
 * Comet 41P/Tuttle–Giacobini–Kres&aacute;k
 * 21-centimetre line
 * twilight
 * twinkling
 * two-body problem
 * two-colour diagram
 * two-colour photometry -> BV photometry
 * Two-Micron All-Sky Survey
 * two-spectrum binary -> composite-spectrum binary
 * Tycho Brahe
 * Tycho Catalogue
 * Tychonic system
 * Tycho's Star
 * Type I supernova -> supernova
 * Type II supernova -> supernova

U

 * UBV photometry -> Johnson photometry
 * UBVRIJKL photometry -> Johnson photometry
 * U-class asteroid
 * U Geminorum star
 * Uhuru
 * UKIDSS -> UKIRT Infrared Deep-Sky Survey
 * UKIDSS photometry
 * UKIRT -> United Kingdom Infrared Telescope
 * UKIRT Infrared Deep-Sky Survey
 * UKST -> United Kingdom Schmidt Telescope
 * ultra-compact dwarf galaxy
 * ultra-luminous infrared galaxy
 * ultraviolet astronomy
 * ultraviolet excess star
 * ultraviolet photometry
 * ultraviolet radiation
 * Ulugh Beg
 * Ulysses (spacecraft)
 * U magnitude
 * umbra
 * 1
 * 2
 * Umbriel (moon)
 * undae
 * undersampling
 * Undina family
 * unfilled aperture
 * unit distance
 * United Kingdom Infrared Telescope
 * United Kingdom Schmidt Telescope
 * Universal Time
 * Universe
 * unsharp masking
 * upper culmination -> culmination
 * Upsilon Sagittarii star
 * Uranometria
 * Uranus
 * Urca process
 * ureilite
 * Harold Clayton Urey
 * Ursa Major
 * Ursa Major Moving Cluster
 * Ursa Minor
 * Ursid meteors
 * US Naval Observatory
 * USNO CCD Astrograph Catalog
 * UT -> Universal Time
 * UTC -> Universel Temps Coordonn&eacute; -> Coordinated Universal Time
 * Utopia Planitia
 * UU Herculis star
 * UV -> ultraviolet
 * uvby system -> Str&ouml;mgren photometry
 * UV Ceti star
 * UV Persei star
 * UXor -> UX Orionis star
 * UX Orionis star
 * UX Ursae Majoris star

V

 * vacuum energy
 * Valhalla (impact basin)
 * Valles Marineris
 * vallis
 * James Alfred Van Allen
 * Van Allen Belts
 * Van Biesbroeck's Star
 * Hendrik van de Hulst
 * van Maanen's Star
 * variable star
 * variation
 * 1
 * 2
 * variation of latitude -> latitude variation
 * vastitas
 * Vatican Advanced Technology Telescope
 * VBLUW photometry -> Walraven photometry
 * V-class asteroid
 * Vega (star)
 * Vega probes
 * Veil Nebula
 * Vela (constellation)
 * Vela pulsar
 * Vela Supernova Remnant
 * velocity curve
 * velocity dispersion
 * velocity–distance relation
 * Venera
 * Venus (planet)
 * Venus Express
 * VERITAS -> Very Energetic Radiation Imaging Telescope Array System
 * vernal equinox
 * vertical circle
 * Very Energetic Radiation Imaging Telescope Array System
 * Very Large Array
 * Very Large Telescope
 * Very Long Baseline Array
 * very long baseline interferometry
 * very slow nova -> RR Telescopii star
 * Very Small Array
 * Vesta (asteroid)
 * Viking (space probes)
 * VILGEN photometry
 * Vilnius photometry
 * violent relaxation
 * virga
 * Virginid meteors
 * Virgo (constellation)
 * Virgo A
 * Virgo Cluster
 * Virgo Supercluster -> local supercluster
 * virial theorem
 * Virtual Observatory
 * virtual particle
 * Visible and Infrared Survey Telescope for Astronomy
 * VISTA -> Visible and Infrared Survey Telescope for Astronomy
 * visual binary
 * visual magnitude
 * VLA -> Very Large Array
 * VLBA -> Very Long Baseline Array
 * VLBI -> very long baseline interferometry
 * VLBI Space Observatory Programme
 * VLT -> Very Large Telescope
 * V magnitude
 * Hermann Carl Vogt
 * Vogt–Russell theorem
 * void
 * Voigt profile
 * Volans
 * volatile
 * von Zeipel theorem
 * Voyager (space probes)
 * VSOP -> VLBI Space Observatory Programme
 * Vulcan (hypothetical planet)
 * Vulpecula (constellation)
 * VV Cephei star -> Zeta Aurigae star
 * VV Sculptoris star

W

 * walled plain
 * Walraven photometry
 * waning
 * Washington Double Star Catalog
 * Water Jar
 * water maser -> H2O maser
 * water of hydration
 * wavefront
 * waveguide
 * wavelength
 * wavenumber
 * wave plate
 * waxing
 * WC star -> Wolf–Rayet star
 * WDS -> Washington Double Star Catalog
 * weber
 * weird terrain
 * Carl Friedrich von Weizs&auml;cker
 * Werner lines
 * Comet West (C/1975 V1)
 * Westerbork Radio Observatory
 * Wezen
 * Fred Lawrence Whipple
 * Whipple Observatory -> Fred Lawrence Whipple Observatory
 * Whirlpool Galaxy
 * whistler
 * white dwarf
 * white hole
 * white-light corona
 * WHT -> William Herschel Telescope
 * Wide Field Infrared Survey Explorer
 * Widmanst&auml;tten pattern
 * Wielen dip
 * Wien's displacement law
 * Wild Duck Cluster
 * Wild's Triplet
 * Rupert Wildt
 * Wilkinson Microwave Anisotropy Probe
 * William Herschel Telescope
 * Robert Woodrow Wilson
 * Wilson–Bappu effect
 * Wilson effect
 * Comet 107P/Wilson–Harrington
 * WIMP
 * Wind (satellite)
 * winter solstice -> solstice
 * WISE -> Wide Field Infrared Survey Explorer
 * WIYN Telescope
 * WMAP -> Wilkinson Microwave Anisotropy Probe
 * W. M. Keck Observatory
 * WN star -> Wolf–Rayet star
 * Maximilian ('Max') Franz Joseph Cornelius
 * (Johann) Rudolf Wolf
 * Wolf diagram
 * Wolf–Lundmark–Melotte system
 * Wolf–Rayet star
 * Wolf sunspot number
 * Wolf 359
 * Wollaston prism
 * Wolter telescope
 * Richard van der Riet Woolley
 * world line
 * wormhole
 * Wright telescope
 * wrinkle ridge
 * WR star -> Wolf–Rayet star
 * W Serpentis star -> Algol star
 * W Ursae Majoris star
 * W Virginis star
 * Wyoming Infrared Observatory
 * WZ Sagittae star

X

 * XMM-Newton
 * X-ray astronomy
 * X-ray background
 * X-ray binary
 * X-ray bright point -> coronal bright point
 * X-ray burst
 * X-ray calorimeter
 * X-ray nova
 * X-ray pulsar
 * X-rays
 * X-ray source
 * X-ray telescope
 * X-ray Timing Explorer
 * X-ray transient
 * XTE -> Rossi X-ray Timing Explorer
 * XUV -> extreme ultraviolet

Y

 * Yagi antenna
 * Yale Bright Star Catalogue -> Bright Star Catalogue
 * Yarkovsky effect
 * Y dwarf
 * year
 * Yepun
 * Yerkes Observatory
 * Yerkes system
 * 1
 * 2
 * Y magnitude
 * Yohkoh
 * yoke mounting
 * YY Orionis star

Z

 * z -> redshift
 * ZAMS -> zero-age main sequence
 * Z Andromedae star
 * Zanstra method
 * ZC -> Zodiacal Catalogue
 * Z Camelopardalis star
 * ZD -> zenith distance
 * Zeeman effect
 * Zelenchukskaya
 * zenith
 * zenithal attraction
 * zenithal hourly rate
 * zenith distance
 * zenith telescope
 * zero-age horizontal branch
 * zero-age main sequence
 * Zeta Aurigae star
 * ZHR -> zenithal hourly rate
 * zirconium star -> S star
 * Z magnitude
 * zodiac
 * Zodiacal Catalogue
 * zodiacal dust
 * zodiacal light
 * Zond
 * zone catalogue
 * zone of avoidance
 * zone time
 * Zubenelgenubi
 * Z&uuml;rich relative sunspot number -> relative sunspot number
 * Fritz Zwicky
 * Zwicky Catalogue
 * ZZ Ceti star

Feature entries

 * active galactic nucleus
 * Big Bang theory
 * black hole
 * cosmic microwave background
 * cosmology
 * extrasolar planet
 * galaxy evolution
 * gamma-ray burst
 * nova
 * pulsar
 * quasar
 * redshift survey
 * Search for Extraterrestrial Intelligence
 * stellar evolution
 * supernova
 * time