Term Index (O)
Astrophysical terms and names of things beginning with the letter O.
O1
O2
O3
O4
O5
OA
OB
OC
OD
OE
OF
OG
OH
OI
OK
OL
OM
ON
OO
OP
OR
OS
OT
OU
OV
OW
OX
OZ
- O (O-type star): star with spectral characteristics of above 30000 K
- O (oxygen): element, O, atomic number 8
- O: see Ohio Radio Survey
- O star (O-type star): star with spectral characteristics of above 30000 K
- OΣ: see Struve Catalogs
- OΣΣ: see Struve Catalogs
- O-class: see O-type star
- O-class star (O-type star): star with spectral characteristics of above 30000 K
- O-type star: star with spectral characteristics of above 30000 K
- O1: see LIGO
- O1/O2 Catalog: see Gravitational Wave Transient Catalog
- O2: see LIGO
- O3: see LIGO
- O3a Catalog: see Gravitational Wave Transient Catalog
- O3b Catalog: see Gravitational Wave Transient Catalog
- O4: see LIGO
- O5 (O5 spectral type): spectral type of star with a temperature of about 45000 K
- O5 spectral type: spectral type of star with a temperature of about 45000 K
- OAC: see Astrocats
- OAO (Okayama Astrophysical Observatory): observatory at Mt. Chikurinji
- OAO (Orbiting Astronomical Observatory): series of 1960s-1970s NASA space telescopes
- OAO-1: see Orbiting Astronomical Observatory
- OAO-2: see Orbiting Astronomical Observatory
- OAO-3: see Orbiting Astronomical Observatory
- OAO-B: see Orbiting Astronomical Observatory
- OASIS: see William Herschel Telescope
- OB association: stellar association including O and/or early B class stars
- OB star: a hot star with class O or early B
- OB association: stellar association including O and/or early B class stars
- OB supergiant: see supergiant
- Oberon: see Uranus
- moon: a planet's natural satellite, such as Earth's
- object (astronomical object): planet, star, galaxy, etc.
- LDN 1527: dark nebula in Taurus
- LDN 1689: dense core within the Rho Ophiuchi Cloud Complex
- moon: a planet's natural satellite, such as Earth's
- Oumuamua: small body that passed through the solar system in 2017
- object type
- accretion disk: disk around an astronomical body of material that is accreting
- asteroid: minor planet without comet characteristics
- binary minor planet: minor planet with another body orbiting it
- binary SMBH: co-orbiting supermassive black holes
- black hole: region of such high mass that light cannot escape
- bright nebula: cloud that gives off or reflects light
- bulge: denser group of stars within a larger group
- candidate companion: possible object apparently orbiting a known object
- centaur: asteroid-like body orbiting among the outer planets
- circumplanetary disk: disk of dust and gas around a planet
- circumstellar disk: disk or ring shaped accumulation of matter around a star
- circumstellar envelope: shell-like cloud surrounding a star
- cloud: higher-density region of space
- comet: Sun-orbiting object with coma and possible tail
- compact object: dense astronomical body such as white dwarf or denser
- damocloid: minor planet with a comet-like orbit
- damped Lyman alpha absorber: object producing broadened lines in a Lyman alpha forest
- dark nebula: cloud that obscures stars behind it
- decretion disk: disk around an astronomical body of its ejected material
- dwarf planet: round like a planet, only smaller
- emission nebula: nebula that emits light such as an HII region or PN
- emission-line object: source of interest due to an emission line
- filament: linear volume of high molecular gas density within a galaxy
- galactic worm: high density streak of HI perpendicular to galactic plane
- galaxy: gravitationally-bound group of stars
- galaxy cloud: substructure of a supercluster
- galaxy cluster: large group of galaxies gravitationally-bound to the group
- galaxy filament: thread-like formations of galaxies, 50 to 80 megaparsecs
- globular cluster: spherical group of stars orbiting a galaxy
- Herbig-Haro object: type of glowing nebula near protostars
- HI supershell: large shells bordered by HI regions
- host: object such as star around which something is orbiting or drawn to
- host galaxy: galaxy associated with a particular object or transient
- host planet: the planet associated with a moon or ring, etc.
- host star: the star associated with a planetary system
- infrared source: astronomical object producing observable infrared
- integrated flux nebula: fuzzy illuminated nebula within Milky Way halo
- intergalactic HI cloud: cloud of HI not within any galaxy
- intermediate-mass black hole: black hole between stellar mass and supermassive
- jet: stream of matter from an astronomical body
- Keplerian disk: disk whose motion follows Kepler's laws
- large quasar group: structure consisting of a collection of quasars
- long-period comet: comet with an orbital period of more than 200 years
- Lyman-alpha blob: Lyman-alpha emitting cloud larger than a galaxy
- MACHO: proposed astronomical objects comprising dark matter
- Mars crosser: asteroid with an orbit that crosses that of Mars
- meteorite: rock found on Earth that is the remnant of a meteor
- meteoroid: rocky object in solar system, smaller than an asteroid
- microquasar: stellar-sized black hole with quasar-like activity
- millisecond pulsar: pulsar spinning with a period in the range of milliseconds
- minor planet: lesser solar system body without comet characteristics
- moon: a planet's natural satellite, such as Earth's
- near-Earth object: object orbiting the Sun that passes close to Earth
- nebula: cloud of dust and gas
- neutrino hotspot: region of sky from which significant neutrinos have been detected
- odd radio circle: extragalactic ring-shaped radio source noticed in 2020
- oligarch: term for large planetesimals that dominate
- planet: round object orbiting a star that clears out its own orbital path
- planetary embryo: object that may grow into a future planet
- planetary mass object: has the mass of a planet
- planetary nebula: glowing gas shell ejected by a red giant
- planetesimal: object held together by gravity that combines with others to form planets
- planetoid: an asteroid or physically similar body
- plutoid: Pluto-like dwarf planet
- point source: celestial object that focuses to a point or single Airy disk
- primordial black hole: black holes forming at the most dense volumes when inflation ceased
- protoplanet: simplest, least-developed object classified as a planet
- protoplanetary disk: disk of dust and gas around a young star or protostar
- protoplanetary nebula: short AGB phase before planetary nebula
- pseudobulge: like a galaxy bulge only flatter
- pulsar: type of astronomical body with EMR in regular cycles of seconds or less
- pulsar wind nebula: type of nebula generated by a young pulsar
- quasar: distant, bright object that appears something like a star
- quasi-satellite: body that orbits near another though they aren't bound
- radio source: astronomical object producing observable radio
- RAMBO: proposed astronomical objects comprising dark matter
- reflection nebula: nebula made visible by light it scatters from nearby stars
- ring system: disk or set of rings orbiting a planet
- shell: hollow shaped region of some kind of ISM
- soft gamma repeater: object that produces repeated gamma-ray bursts
- solar system object: the Sun, solar system planets, minor planets, comets, and moons
- source: astronomical object producing some observed signal
- SSSB: solar system body smaller than a dwarf planet
- star: astronomical body shining from fusion energy
- stellar stream: long group of co-moving stars
- stellar-mass black hole: black hole that is a stellar remnant
- subsatellite: object orbiting a moon
- supercluster: cluster of galaxy clusters
- supermassive black hole: black hole with a mass of millions to billions of solar masses
- supernova remnant: nebula of debris resulting from a supernova
- supershell: very large ISM shell-shaped region
- telluric star: star of known spectrum used for calibration
- Tolman VII object: theoretical object adhering to exact GR solution
- trans-Neptune object: minor planet beyond Neptune
- transitional disk: disk with inner part cleared
- very low luminosity object: term sometimes used for protostars with luminosity less than 0.1 solar
- vulcanoid: theoretical asteroid orbiting within Mercury's orbit
- WIT: "what is it" for an unexplainable object
- X-ray burster: neutron star binary producing nova-like bursts
- X-ray pulsar: pulsar producing X-rays from accretion
- X-ray source: astronomical object producing observable X-ray
- objective lens: see refracting telescope
- objects
- oblate spheroid: see spheroid
- oblateness: see J2
- obliquity: angle between an object's rotational and orbital axes
- obs. (observatory): facility for astronomical observation
- obscured fraction: see obscured fraction-luminosity relation
- obscured fraction-luminosity relation: relation between AGN luminosity and surrounding dust IR emission
- obscured star formation
- observable: any physical phenomenon that you can detect
- observable universe: that part of the universe that we can conceivably observe
- observation
- Observation Run 1: see LIGO
- Observation Run 2: see LIGO
- Observation Run 3: see LIGO
- observational astronomy: term covering observation
- Observatoire de la Côte d'Azur (Côte d'Azur Observatory): French astronomical research organization
- observatories
- observatorio (observatory): facility for astronomical observation
- Observatorio de Calar Alto (Calar Alto Observatory): observatory on mountain in mainland Spain
- Observatorio del Roque de los Muchachos (Roque de los Muchachos Observatory): observatory at La Palma in the Canary Islands
- Observatorio del Teide (Teide Observatory): observatory on Mount Teide in the Canary Islands
- observatory: facility for astronomical observation
- Observatory of Madrid
- observed color index: see color index
- observed wavelength: see rest wavelength
- observing program (astronomical survey): project collecting astronomical data
- OC (open cluster): group of stars within a galaxy apparently formed by a single cloud
- OCA (Côte d'Azur Observatory): French astronomical research organization
- occlusion: see occultation
- occultation: one celestial body hiding another from an observer
- occultation observations: gathering astronomical information through measuring occultations
- occultation spectrography: see spectroscopy
- occultation spectroscopy: see transit spectroscopy
- occultations
- occulter: see coronagraph
- occulter: see occulting bar
- Exo-S: a study on the concept of a starshade mission
- New Worlds Mission: plan for space occulter to facilitate the view of exoplanets
- starshade: spacecraft to block light from a specific body
- occulting bar: telescope feature to block light from a specific body
- ocean planet (water world): planet with substantial liquid water
- ocean world (water world): planet with substantial liquid water
- oceanic carbon cycle
- Ocl: see rare designator prefixes
- OCO (Oort Cloud Object): object in Oort Cloud such as a comet
- OCPP: see Pioneer Venus Orbiter
- octopole: see multipole expansion
- octupole: see multipole expansion
- octupole level: see multipole expansion
- octupole term
- odd radio circle: extragalactic ring-shaped radio source noticed in 2020
- ODE: see partial differential equation
- ODI: see WIYN 3.5m Telescope
- Odyssey: research supercomputer at Harvard sometimes used for astrophysics simulations
- Oe star: see Be star
- OEC (Open Exoplanet Catalogue): independently maintained list of known exoplanets
- OEFD: see Pioneer Venus Orbiter
- OETP: see Pioneer Venus Orbiter
- off the shell: see mass shell
- off-axis telescope: telescope
- OFTI: see orbitize
- OGBD: see Pioneer Venus Orbiter
- OGC (Ogle Galaxy Catalog): catalog of luminous galaxies
- OGLE: survey searching for microlensing transients
- Ogle Galaxy Catalog: catalog of luminous galaxies
- OGLE-2005-BLG-390L: see OGLE-2005-BLG-390Lb
- OGLE-2005-BLG-390Lb: probable rocky planet orbiting red dwarf
- OGS: see HEAO-2
- OH (hydroxyl): one hydrogen atom and one oxygen atom bound together
- OH airglow: see airglow
- OH maser
- Oh-My-God Particle: extremely energetic particle from space detected in 1991
- OH/IR source: AGB star with strong OH maser
- OH/IR star (OH/IR source): AGB star with strong OH maser
- OHIO: see Ohio Radio Survey
- Ohio
- IMB: 1980s neutrino detector
- Ohio Radio Survey: 1960s radio survey by Ohio State University
- Ohio Sky Survey (Ohio Radio Survey): 1960s radio survey by Ohio State University
- Ohio State University Radio Observatory
- ohm: see siemens
- Ohm's law: see telegrapher's equations
- ohm-meter: see siemens
- Ohmic heating: heating resulting from an electric current through a material
- OHP 1.93 m
- OHS: see Subaru Telescope
- OIG: see Telescopio Nazionale Galileo
- OIMS: see Pioneer Venus Orbiter
- OIR: "band name" that means both visible light and infrared
- OIR: see Pioneer Venus Orbiter
- OIR-dark galaxy: see dropout
- Okayama Astrophysical Observatory: observatory at Mt. Chikurinji
- Oke-Gunn photometric system (griz photometric system): photometric system designed for electronic sensors
- OL: see double star designation
- Olbers' paradox: argument using the dark of the sky regarding the nature of the universe
- oligarch: term for large planetesimals that dominate
- isolation mass: mass of an oligarch after accreting all nearby planetesimals
- oligarch theory: see oligarch
- oligarch theory: see planet formation
- oligarchic accretion: see oligarch
- oligarchic growth: see oligarch
- olivine
- methane: compound of one carbon and 4 hydrogen atoms
- OLR: see Lindblad resonance
- Olympus Mons: see Mars
- OM: see XMM-Newton
- OMAG: see Pioneer Venus Orbiter
- OMAyA: see Large Millimeter Telescope
- OMC: see INTEGRAL
- OMC: see Orion Molecular Cloud Complex
- OMEGA: see Mars Express
- Omega Centauri: large globular cluster
- Omega-Prime
- OmegaCAM: see VLT Survey Telescope
- OMM 1.6m
- SIMP: 2000s infrared proper-motion survey
- on the shell: see mass shell
- On-Orbit Servicing, Assembly and Manufacturing: see OSAM-1
- ONC (Orion Nebula Cluster): open cluster in the constellation Orion
- ONC: see Hayabusa2
- one dimensional climate model: atmospheric model ignoring all horizontal motion
- one dimensional model: see three dimensional model
- one meter barrier (meter size barrier): a barrier to planet formation on the order of a meter diameter
- ONMS: see Pioneer Venus Orbiter
- Onsala: see rare designator prefixes
- Ontario
- Oo: see rare designator prefixes
- Oort Cloud: cloud of distant comets surrounding the solar system
- comet: Sun-orbiting object with coma and possible tail
- Oort Cloud Object: object in Oort Cloud such as a comet
- Oort constants: two constants characterizing local Milky-Way motion
- Ooty Radio Telescope: cylindrical radio telescope in India
- Ooty Wide Field Array: see Ooty Radio Telescope
- OPA: see Pioneer Venus Orbiter
- opacity: a measure of opaqueness of a material
- OPAG (Outer Planets Assessment Group): NASA forum to provide input to long-term planning of outer planets missions
- OPE: see Giotto
- Open Astronomy Catalog: see Astrocats
- open cluster: group of stars within a galaxy apparently formed by a single cloud
- open Dragone telescope: see Dragone telescope
- Open Exoplanet Catalogue: independently maintained list of known exoplanets
- Open Kilonova Catalog: see Astrocats
- open magnetic field lines
- Open Supernova Catalog: see Astrocats
- MOSFiT: code to match light-curves with light-curve models
- Open TDE Catalog: see tidal disruption event
- open universe: see critical density
- open-Dragone design: see Dragone telescope
- OpenSpace: visualization software aimed at astrophysical data
- Oph-L 1689 (LDN 1689): dense core within the Rho Ophiuchi Cloud Complex
- Ophelia: see shepherd moon
- Ophiuchus Molecular Cloud (Rho Ophiuchi Cloud Complex): nebula that is a nearby star-forming region
- OPI: see double star designation
- Opportunity: see Mars Exploration Rover
- opposition: positioning of two astronomical objects 180 degrees apart in the sky
- optical
- optical and infrared (OIR): "band name" that means both visible light and infrared
- optical astronomy: see visible light
- optical axis: center line through an optical instrument
- optical coma
- optical counterpart: see counterpart
- optical depth: a measure of opaqueness of a path of light
- optical depth to the EOR: see Lambda-CDM model
- optical double: double star where the two are not gravitationally bound
- optical fiber
- optical filter (filter): optical device to filter out part of the EMR spectrum
- Optical Gravitational Lensing Experiment (OGLE): survey searching for microlensing transients
- optical interferometer: interferometer of visible light
- optical interferometry: see optical interferometer
- optical segmentation: see segmented mirror
- optical SFR: see star formation rate
- optical star formation rate: see star formation rate
- optical telescope assembly: see Hubble Space Telescope
- optical thickness (optical depth): a measure of opaqueness of a path of light
- optical transient: transient evident from visible light observation
- optical transient source: see optical transient
- optical violent variable quasar
- 3C 279: striking variable quasar
- optical window: see atmospheric window
- optically thick: see optical depth
- optically thin: see optical depth
- optically violent variable quasar: see blazar
- optics: science and technology regarding visible light
- OPTIMOS: see European Extremely Large Telescope
- Optopus
- ORAD: see Pioneer Venus Orbiter
- orange dwarf: see K-type star
- orbit
- orbit plot: graphic showing the path of an orbit as a line
- orbital (electron orbital): a nucleus's "locations" where an electron can orbit
- orbital decay: gradual reduction in radius of an orbit
- orbital eccentricity (eccentricity): degree to which an orbit is non-circular
- orbital element: parameters describing an orbit
- Orbital Express: see Autonomous Space Transport Robotic Operations
- orbital inclination: angle between plane of an orbit and a reference plane
- orbital period: length of time for an orbiting object to complete one cycle
- mean anomaly: angle describing an object's position within an elliptical orbit
- period derivative: rate of change in the period of an orbit or rotation
- sidereal: relative to the fixed position of the stars
- synodic period: period until a planet returns to the same position relative to the Sun
- Orbital perturbation analysis: see J2
- orbital plane: see orbital element
- orbital plot (orbit plot): graphic showing the path of an orbit as a line
- orbital radius: see semi-major axis
- orbital resonance: tendency of orbits of multiple bodies to remain in a simple pattern
- orbital speed: speed of an orbiting body around the barycenter of a system
- Orbiting Astronomical Observatory: series of 1960s-1970s NASA space telescopes
- Orbiting Solar Observatory 7 (OSO 7): 1970s observatory-satellite for viewing the Sun
- Orbiting Solar Observatory 8 (OSO 8): 1970s observatory-satellite for viewing the Sun
- Orbiting Wide-angle Light Collectors: space mission concept to detect cosmic rays through Earth atmosphere light flashes
- orbitize: planet orbit-fitting software for direct image observations
- orbits
- Orbits for the Impatient: see orbitize
- ORC (odd radio circle): extragalactic ring-shaped radio source noticed in 2020
- Orcus
- order: see grating
- order: see spherical harmonics
- order-of-magnitude (dex): a number or ratio's log base 10
- orders-of-magnitude: see dex
- ordinary differential equation: see partial differential equation
- ORFEUS SPAS
- ORFEUS Telescope
- ORFEUS-SPAS 1
- ORFEUS-SPAS 2
- organization
- Origins Space Telescope: concept for 2030s large space IR telescope
- Orion: well-known constellation in the northern hemisphere
- Orion (Orion space telescopes): two Russian 1970s UV space telescopes
- Orion A: see Orion Molecular Cloud Complex
- Orion Arm: see spiral arm
- Orion B: see Orion Molecular Cloud Complex
- Orion Bar: see Orion Nebula
- Orion Bridge
- Orion Cluster (Orion Nebula Cluster): open cluster in the constellation Orion
- Orion Complex (Orion Molecular Cloud Complex): group of molecular clouds with star-forming regions
- Orion Disks: protoplanetary disks visible in front of Orion Nebula
- Orion Molecular Cloud Complex: group of molecular clouds with star-forming regions
- Orion Molecular Clouds (Orion Molecular Cloud Complex): group of molecular clouds with star-forming regions
- Orion Nebula: easily-observed nebula that includes SF regions
- COUP: survey of X-ray sources in the Orion Nebula
- Orion Disks: protoplanetary disks visible in front of Orion Nebula
- Trapezium Cluster: open cluster of stars in Orion Nebula
- Orion Nebula Cluster: open cluster in the constellation Orion
- Orion space telescopes: two Russian 1970s UV space telescopes
- Orion spacecraft: see Space Launch System
- Orion Spur: see spiral arm
- Orion Trapezium Cluster (Trapezium Cluster): open cluster of stars in Orion Nebula
- Orion variable: see variable star
- Orion-1: see Orion space telescopes
- Orion-2: see Orion space telescopes
- Orion-Cygnus Arm: see spiral arm
- ORM (Roque de los Muchachos Observatory): observatory at La Palma in the Canary Islands
- OROCHI: see MMX
- ORP (reduction potential): measure of a chemical species' tendency to acquire electrons
- ORPA: see Pioneer Venus Orbiter
- orphan afterglow: see gamma-ray burst
- orphan GRB afterglow: see gamma-ray burst
- Orphan stream: stellar stream wrapping around the Milky Way
- orrery: mechanical device to simulate the solar system
- ORT (Ooty Radio Telescope): cylindrical radio telescope in India
- orthogonal transfer CCD: see image stabilization
- OSAM
- OSAM-1: prototype space robot for servicing satellites
- OSAM-1: prototype space robot for servicing satellites
- OSAM-2: see OSAM-1
- OSC: see Astrocats
- MOSFiT: code to match light-curves with light-curve models
- OSCA: see William Herschel Telescope
- Oschin Schmidt (Palomar 48 Inch Telescope): 48 inch Schmidt telescope at Palomar Observatory
- Oschin Telescope
- oscillator strength: fraction expressing QM's contribution to the probability of absorption
- osculating orbit (Keplerian orbit): orbit following a perfect ellipse or other conic section
- OSIRIS: see Gran Telescopio Canarias
- OSIRIS: see Keck Observatory
- OSIRIS: see Rosetta
- OSIRIS: see SOAR Telescope
- SHARDS: GTC survey in GOODS-N field for quenched galaxies at z = 1 to 2.3
- Osiris (HD 209458 b): hot Jupiter discovered in 1999
- OSIRIS-APEX: see OSIRIS-REx
- OSIRIS-REx: space mission aiming to return a sample of an asteroid
- 101955 Bennu: near-Earth asteroid that is the target of a sample-return mission
- CSA: includes astronomical research
- OSMOS: see Hiltner Telescope
- OSO 7: 1970s observatory-satellite for viewing the Sun
- OSO 8: 1970s observatory-satellite for viewing the Sun
- OSO H (OSO 7): 1970s observatory-satellite for viewing the Sun
- OSS (Ohio Radio Survey): 1960s radio survey by Ohio State University
- OSS: see Origins Space Telescope
- OSSE: see Compton Gamma Ray Observatory
- OSSOS (Outer Solar System Origins Survey): 2013-2017 survey that searched for trans-Neptune objects
- OST (Origins Space Telescope): concept for 2030s large space IR telescope
- OSURO
- OT (optical transient): transient evident from visible light observation
- OT source: see optical transient
- OTC: see tidal disruption event
- OTCCD: see image stabilization
- Other Worlds Laboratory: initiative researching planets and moons
- OTL: see rare designator prefixes
- OTS: see Hubble Space Telescope
- OTS: see optical transient
- OTS: see rare designator prefixes
- Oukaïmeden Observatory
- TRAPPIST: a ground-based automated transiting-planet finding telescope
- Oumuamua: small body that passed through the solar system in 2017
- outer belt: see Van Allen belts
- outer Lindblad resonance: see Lindblad resonance
- outer Lindblad resonance: see Lindblad torque
- Outer Planets Assessment Group: NASA forum to provide input to long-term planning of outer planets missions
- outer solar system
- Outer Solar System Origins Survey: 2013-2017 survey that searched for trans-Neptune objects
- outflow
- outgassing: see atmosphere formation
- outrigger: radio receiver some distance from main receiver for direction determination
- outside-in growth: see inside-out growth
- OUVS: see Pioneer Venus Orbiter
- overdensity (stellar overdensity): portion of galactic halo with more stars than normal
- overfitting: see Akaike information criterion
- Overwhelmingly Large Telescope: 100 m telescope plan
- OVRO (Owens Valley Radio Observatory): group of radio telescopes in California near the VLBA
- OVRO 40 Meter Telescope: see Owens Valley Radio Observatory
- OVRO-LWA: radio telescope in California
- OVRO-LWA: see Owens Valley Radio Observatory
- OVSA
- OVV
- 3C 279: striking variable quasar
- OVV quasar: see blazar
- Owens Valley Long Wavelength Array (OVRO-LWA): radio telescope in California
- Owens Valley Long Wavelength Array: see Owens Valley Radio Observatory
- Owens Valley Radio Observatory: group of radio telescopes in California near the VLBA
- Owens Valley Solar Array
- OWFA: see Ooty Radio Telescope
- OWL (Orbiting Wide-angle Light Collectors): space mission concept to detect cosmic rays through Earth atmosphere light flashes
- OWL (Other Worlds Laboratory): initiative researching planets and moons
- OWL (Overwhelmingly Large Telescope): 100 m telescope plan
- OWL: see Hayabusa2
- EAGLE: simulation of galaxy formation and evolution
- Oxford SWIFT: see Hale Telescope
- oxidation: see reducing atmosphere
- oxidation number (oxidation state): number of electrons loaned out by an atom in an ionic bond
- oxidation state: number of electrons loaned out by an atom in an ionic bond
- oxidation-reduction reaction: see reducing atmosphere
- oxidation/reduction potential (reduction potential): measure of a chemical species' tendency to acquire electrons
- oxide: see geochemistry
- oxidizing agent: see reducing atmosphere
- oxygen: element, O, atomic number 8
- oxygen burning: fusion reaction starting with oxygen
- oxygen lines: spectral lines specific to oxygen
- oxygen-burning shell: see oxygen burning
- oxygen-neon-magnesium white dwarf: see white dwarf
- oxygen-rich Wolf-Rayet: see Wolf-Rayet star
- oxygen-to-iron ratio: see alpha-enhanced
- OzDES: see Dark Energy Survey
- ozone
- earthshine: reflected and emitted electromagnetic radiation from Earth
- ozone layer
Index