Term Index (O)
- O:
- O-type star (O): type of star with about 50 times the mass of the Sun
- Ohio Radio Survey: 1960s radio survey by Ohio State University
- oxygen (O): element, O, atomic number 8
- OΣ:
- O-class:
- O-type star (O): type of star with about 50 times the mass of the Sun
- O-type star (O): type of star with about 50 times the mass of the Sun
- O1:
- LIGO: pair of observatories to detect gravitational waves
- O2:
- LIGO: pair of observatories to detect gravitational waves
- O3:
- LIGO: pair of observatories to detect gravitational waves
- O5:
- O5 spectral class (O5): type of star with about 50 times the mass of the Sun
- OAC:
- Astrocats: software to create and manage an astronomy catalog
- OASIS:
- OB association: stellar association with O or B class stars
- OB star: a hot star with class O or B
- Oberon:
- moon: a planet's natural satellite, such as Earth's
- Uranus: second outer-most solar system planet
- object:
- LDN 1689: dense core within the Rho Ophiuchi Cloud Complex
- moon: a planet's natural satellite, such as Earth's
- ring system: disk or set of rings orbiting a planet
- telluric star: star of known spectrum used for calibration
- object type:
- accretion disk: disk around an astronomical body of material that is accreting
- asteroid: minor planet without comet characteristics
- binary minor planet (BMP): minor planet with another body orbiting it
- binary SMBH (BSMBH): co-orbiting supermassive black holes
- black hole (BH): region of such high mass that light cannot escape
- bulge: denser group of stars within a larger group
- 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
- comet: Sun-orbiting object with coma and possible tail
- compact object: dense astronomical body such as white dwarf or denser
- 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
- filament: linear volume of high molecular gas density within a galaxy
- galaxy: gravitationally-bound group of stars
- galaxy cluster (CL): large group of galaxies gravitationally-bound to the group
- globular cluster (GC): spherical group of stars orbiting a galaxy
- Herbig-Haro object (HH): illuminated nebula from colliding jets
- HI supershell: bubbles of HI hundreds of light-years across
- jet: stream of matter from an astronomical body
- Keplerian disk: disk whose motion follows Kepler's laws
- long-period comet: comet with an orbital period of more than 200 years
- MACHO: proposed astronomical objects comprising dark matter
- meteoroid: rocky object in solar system, smaller than an asteroid
- microquasar: stellar-sized black hole with quasar-like activity
- millisecond pulsar (MSP): 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 (NEO): object orbiting the Sun that passes close to Earth
- nebula: cloud of dust and gas
- 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 (PMO): has the mass of a planet
- planetary nebula (PN, PNe): gas shell ejected by a red giant
- planetesimal: objects held together by gravity that combine to form planets
- planetoid: an asteroid or physically similar body
- plutoid: Pluto-like dwarf planet
- protoplanet: simplest, least-developed object classified as a planet
- protoplanetary disk (PPD): disk of dust and gas around a young star or protostar
- protoplanetary nebula (PPN): AGB phase before planetary nebula
- pulsar (PSR): astronomical body whose electromagnetic radiation displays a cycle
- quasar (QSO): distant, bright object that appears something like a star
- radio source (RS): something in the sky generating radio signal
- reflection nebula: nebula made visible by light it scatters from nearby stars
- soft gamma repeater (SGR): object that produces repeated gamma ray bursts
- SSSB: solar system body smaller than a dwarf planet
- subsatellite: object orbiting a moon
- supermassive black hole (SMBH): black hole with a mass of millions to billions of solar masses
- supernova remnant (SNR): nebula of debris resulting from a supernova
- trans-Neptunian object (TNO): minor planet beyond Neptune
- transitional disk: disk with inner part cleared
- objects:
- oblateness:
- J2: geopotential coefficient regarding a planet's oblateness
- obliquity: angle between an object's rotational and orbital axes
- observable universe:
- observation:
- band shifting: effect of redshift on photometry
- dropout: means of identifying distant galaxies
- field: adjective meaning "in this field of view but unrelated"
- striae: parallel ridges
- surface density (Σ): quantity such as mass per surface area
- synthetic field method (SFM): method of testing galaxy opacity
- telluric star: star of known spectrum used for calibration
- tracer: chemical whose presence indicates the presence of another chemical
- Observation Run 1:
- LIGO: pair of observatories to detect gravitational waves
- Observation Run 2:
- LIGO: pair of observatories to detect gravitational waves
- Observation Run 3:
- LIGO: pair of observatories to detect gravitational waves
- observatorio:
- Observatorio del Roque de los Muchachos:
- observatory: facility for astronomical observation
- observed color index:
- color index: a number that characterizes the color of an object
- observed wavelength:
- rest wavelength: normal wavelength observed when not moving in relation to the source
- occultation: one celestial body hiding another from an observer
- occultation observations: gathering astronomical information through measuring occultations
- occultation spectroscopy:
- occulter:
- coronagraph: telescope feature to block light from a specific body
- Exo-S: a study on the concept of a starshade mission
- New Worlds Mission: plan for space occulter to facilitate the view of exoplanets
- occulting bar: telescope feature to block light from a specific body
- starshade: spacecraft to block light from a specific body
- occulting bar: telescope feature to block light from a specific body
- ocean world:
- oceanic carbon cycle:
- octopole:
- octupole:
- octupole level:
- octupole term:
- ODE:
- off the shell:
- mass shell: conceptual volume of mass shaped like a hollow sphere
- off-axis telescope:
- OGLE: survey searching for microlensing transients
- OGS:
- HEAO-2: 1978 x-ray observatory space mission
- OH:
- hydroxyl (OH): compound of hydrogen and oxygen, one atom each
- OH/IR source: AGB star with strong OH maser
- OH maser:
- OH/IR source: AGB star with strong OH maser
- OH/IR star:
- OHIO:
- Ohio Radio Survey: 1960s radio survey by Ohio State University
- Ohio Sky Survey:
- Ohio State University Radio Observatory:
- Ohmic heating:
- OIR: a spectral "band name" for both visible light and infrared
- Olbers' paradox: argument using the dark of the sky regarding the nature of the universe
- oligarch: term for large planetesimals that dominate
- oligarch growth:
- oligarch: term for large planetesimals that dominate
- oligarch theory:
- OM:
- XMM-Newton: x-ray observatory-satellite operated by ESA
- OMC:
- OMEGA:
- Omega Centauri: large globular cluster
- OmegaCAM:
- on the shell:
- mass shell: conceptual volume of mass shaped like a hollow sphere
- ONC:
- one dimensional climate model: atmospheric model ignoring all horizontal motion
- one dimensional model:
- one meter barrier:
- Ontario:
- Oort Cloud: cloud of comets and minor planets around the solar system
- comet: Sun-orbiting object with coma and possible tail
- Oort constants: two constants characterizing local Milky-Way motion
- Ooty Radio Telescope (ORT): cylindrical radio telescope in India
- opacity: a measure of opaqueness of a material
- Open Astronomy Catalog:
- Astrocats: software to create and manage an astronomy catalog
- open cluster: group of stars within a galaxy apparently formed by a single cloud
- open Dragone:
- open Dragone telescope:
- Open Kilonova Catalog:
- Astrocats: software to create and manage an astronomy catalog
- open magnetic field lines:
- Open Supernova Catalog:
- Astrocats: software to create and manage an astronomy catalog
- open universe:
- open-Dragone design:
- OpenSpace: visualization software aimed at astrophysical data
- Oph-L 1689:
- LDN 1689: dense core within the Rho Ophiuchi Cloud Complex
- Ophelia:
- Ophiuchus Molecular Cloud:
- opposition: positioning of two astronomical objects 180 degrees apart in the sky
- optical:
- optical and infrared:
- OIR: a spectral "band name" for both visible light and infrared
- optical axis: center line through an optical instrument
- optical depth (τ): a measure of opaqueness of a path of light
- optical depth to the EOR:
- Lambda-CDM model (ΛCDM,LCDM): Big-Bang cosmological model with a cosmological constant and cold dark matter
- optical double: two stars that look like one with naked eye
- Optical Gravitational Lensing Experiment:
- OGLE: survey searching for microlensing transients
- optical interferometer: interferometer of visible light
- optical interferometry:
- optical segmentation:
- optical thickness:
- optically thick:
- optically thin:
- optically violent variable quasar:
- blazar: very compact variable quasar
- optics: science and technology regarding visible light
- OPTIMOS:
- orange dwarf:
- orbit:
- orbit plot: graphic showing the path of an orbit as a line
- orbital:
- orbital element: parameters describing an orbit
- orbital inclination: angle between plane of an orbit and a reference plane
- minimum mass (m sin i): measured bound on the mass of an exoplanet
- 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
- 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:
- J2: geopotential coefficient regarding a planet's oblateness
- orbital plot:
- orbit plot: graphic showing the path of an orbit as a line
- orbital resonance: tendency of orbits of two bodies to remain in a simple pattern
- orbital speed: speed of an orbiting body around the barycenter of a system
- Orbiting Solar Observatory 7:
- OSO 7: 1970s observatory-satellite for viewing the Sun
- orbits:
- order-of-magnitude:
- dex: a number or factor's log base 10
- orders-of-magnitude:
- dex: a number or factor's log base 10
- ordinary differential equation:
- ORFEUS SPAS:
- ORFEUS Telescope:
- ORFEUS-SPAS 1:
- ORFEUS-SPAS 2:
- organization:
- Origins Space Telescope (OST): concept for future very large space IR telescope
- Orion: well-known constellation in the northern hemisphere
- Orion A:
- Orion Arm:
- spiral arm: long, winding visible structure within a spiral galaxy
- Orion B:
- Orion Cluster:
- Orion Complex:
- 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 Nebula (M42, NGC 1976): easily observed nebula that includes SF regions
- Orion Nebula Cluster (ONC): open cluster in the constellation Orion
- Orion Spur:
- spiral arm: long, winding visible structure within a spiral galaxy
- Orion Trapezium Cluster:
- ORP:
- ORT:
- orthogonal transfer CCD:
- OSC:
- Astrocats: software to create and manage an astronomy catalog
- OSCA:
- Oschin Telescope:
- oscillator strength: fraction expressing QM's contribution to the probability of absorption
- OSIRIS:
- OSIRIS-REx: planned space mission to return a sample of an asteroid
- OSO 7: 1970s observatory-satellite for viewing the Sun
- OSSE:
- OSSOS:
- OST:
- OSURO:
- OTCCD:
- Other Worlds Laboratory (OWL): group researching planets and moons
- outer Lindblad resonance:
- Outer Solar System Origins Survey (OSSOS): survey searching for trans-Neptune objects
- outflow:
- outgassing:
- Overwhelmingly Large Telescope (OWL): 100m telescope plan
- OVRO:
- OVRO 40 Meter Telescope:
- OVV quasar:
- blazar: very compact variable quasar
- Owens Valley Long Wavelength Array:
- Owens Valley Radio Observatory (OVRO): group of radio telescopes in California near the VLBA
- OWL:
- Oxford SWIFT:
- oxidation:
- oxidation number:
- oxidation state: number characterizing atoms of a compound as ions
- oxidation/reduction potential:
- oxidation/reduction reaction:
- oxide:
- geochemistry: the chemistry of the Earth, planets, and moons
- oxidizing agent:
- oxygen (O): element, O, atomic number 8
- oxygen burning:
- oxygen lines: spectral lines specific to oxygen
- oxygen-neon-magnesium white dwarf:
- white dwarf: stellar remnant of mostly electron-degenerate matter
- ozone:
- earthshine: reflected and emitted electromagnetic radiation from Earth
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