Term Index (O)

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Term Index (O)

O:
- O-type star (O): star with spectral characteristics of above 30000 K
- Ohio Radio Survey (OSS): 1960s radio survey by Ohio State University
- oxygen (O): element, O, atomic number 8
O star:
- O-type star (O): star with spectral characteristics of above 30000 K
OΣ:
- Struve Catalogs: two catalogs of double stars
OΣΣ:
- Struve Catalogs: two catalogs of double stars
O-class:
- O-type star (O): star with spectral characteristics of above 30000 K
O-class star:
- O-type star (O): star with spectral characteristics of above 30000 K
O-type star (O): star with spectral characteristics of above 30000 K
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 type (O5): spectral type of star with a temperature of about 45000 K
O5 spectral type (O5): spectral type of star with a temperature of about 45000 K
OAC:
- Astrocats: software to create and manage an astronomy catalog
OAO:
- Orbiting Astronomical Observatory (OAO): series of 1960s-1970s NASA space telescopes
OAO-1:
- Orbiting Astronomical Observatory (OAO): series of 1960s-1970s NASA space telescopes
OAO-2:
- Orbiting Astronomical Observatory (OAO): series of 1960s-1970s NASA space telescopes
OAO-3:
- Orbiting Astronomical Observatory (OAO): series of 1960s-1970s NASA space telescopes
OAO-B:
- Orbiting Astronomical Observatory (OAO): series of 1960s-1970s NASA space telescopes
OASIS:
- William Herschel Telescope (WHT): 4.2 meter telescope in the Canary Islands
OB association: stellar association with O or B class stars
- OB star: a hot star with class O or early B
- stellar association: like a large open cluster but even less tightly bound
OB star: a hot star with class O or early B
- OB association: stellar association with O or B class stars
OB supergiant:
- supergiant: very large giant star
Oberon:
- moon: a planet's natural satellite, such as Earth's
- Uranus: second outer-most solar system planet
object:
- astronomical object: planet, star, galaxy, etc.
- LDN 1689: dense core within the Rho Ophiuchi Cloud Complex
- moon: a planet's natural satellite, such as Earth's
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,SMBBH,SMBHB): 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
- candidate companion (CC): 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
- cloud: higher-density region of space
- comet: Sun-orbiting object with coma and possible tail
- compact object (CO): dense astronomical body such as white dwarf or denser
- damocloid: minor planet with a comet-like orbit
- 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
- filament: linear volume of high molecular gas density within a galaxy
- galaxy: gravitationally-bound group of stars
- galaxy cloud: substructure of a supercluster
- 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,HHO): type of glowing nebula near protostars
- HI supershell: shells of HI hundreds of parsecs
- 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
- Mars crosser (MC,MCA): asteroid with an orbit that crosses that of Mars
- 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): 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
- 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 (PPD): disk of dust and gas around a young star or protostar
- protoplanetary nebula (PPN): short AGB phase before planetary nebula
- pseudobulge: like a galaxy bulge only flatter
- pulsar (PSR): type of astronomical body with EMR in regular cycles of seconds or less
- quasar (QSO): distant, bright object that appears something like a star
- radio source (RS): something in the sky generating radio signal
- 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 (SGR): object that produces repeated gamma ray bursts
- SSSB (SB): solar system body smaller than a dwarf planet
- stellar stream: long group of co-moving stars
- stellar-mass black hole: black hole that is a stellar remnant
- 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
- supershell: very large ISM shell-shaped region
- telluric star: star of known spectrum used for calibration
- trans-Neptunian object (TNO): minor planet beyond Neptune
- transitional disk: disk with inner part cleared
- X-ray burster (XRB): neutron star binary producing nova-like bursts
- X-ray source: something in the sky generating X-ray signal
objective lens:
- refracting telescope: telescope using lenses rather than mirrors to magnify
objects:
- astronomical catalog: lists of observed astronomical bodies and their characteristics
- coeval: the same age
- demographics: statistics of characteristics within a group
- natural astronomical telescopes: use of an astronomical body as a telescope
- phase curve: brightness of an object according to its phase angle
- rare designator prefixes: designator prefixes generally used for only a few objects
- rotation period: time it takes an astronomical body to revolve
- SIMBAD: online database of astronomical objects
oblateness:
- J₂: geopotential coefficient regarding a planet's oblateness
obliquity: angle between an object's rotational and orbital axes
obscured fraction:
- obscured fraction-luminosity relation: relation between AGN luminosity and surrounding dust IR emission
obscured fraction-luminosity relation: relation between AGN luminosity and surrounding dust IR emission
observable universe: that part of the universe that we can conceivably observe
- particle horizon: furthest point from which light can reach us
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
observational astronomy: term covering observation
observatories:
- observational astronomy: term covering observation
observatorio:
- observatory: facility for astronomical observation
Observatorio del Roque de los Muchachos:
- Roque de los Muchachos Observatory (ORM,LPO,NHO): 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
- Baksan Neutrino Observatory (BNO): Russian underground particle detector
- Borexino: European underground neutrino observatory
- Cerro Tololo Inter-American Observatory (CTIO): NOAO observatory in Chile with Blanco telescope
- Cosmic Explorer: concept for a very large LIGO-like GW detector
- Dominion Radio Astrophysical Observatory (DRAO): radio observatory in British Columbia, Canada
- East Asian Observatory (EAO): operator of JCMT
- Einstein Telescope: concept for a larger LIGO-like GW detector
- European Gravitational Observatory (EGO): gravitational wave observatory in Italy
- European Southern Observatory (ESO): organization operating telescopes in the southern hemisphere
- EUSO-SPB: balloon-born cosmic ray observatory
- Fenton Hill Observatory (FHO): New Mexico GRB-oriented astronomical observatory
- Fred Lawrence Whipple Observatory (FLWO): observatory near Amado, Arizona
- Gemini Observatory: pair of telescopes in Hawaii and Chile
- GEO600: ground-based gravitational-wave detector in Germany
- Green Bank Observatory (GBO): radio observatory in West Virginia including GBT
- Haleakala Observatory: observatory on Maui, Hawaii
- High Altitude Observatory (HAO): NCAR unit observing and monitoring the Sun
- IceCube: neutrino detector at the South Pole
- IMB: 1980s neutrino detector
- Interstellar Boundary Explorer (IBEX): satellite observing the ISM/heliosphere boundary
- Jodrell Bank Observatory (JBO): radio observatory in England
- KAGRA: gravitational wave detector in Japan preparing for operation
- Kamioka Observatory: Japanese underground particle detector
- Kitt Peak National Observatory (KPNO): NRAO observatory in Arizona with Mayall telescope
- La Silla Observatory (LSO): Atacama-desert observatory run by ESO
- La Silla Paranal Observatory (LPO): manages three ESO observatory sites in Chile
- Las Campanas Observatory (LCO): observatory in southern Atacama Desert
- Las Cumbres Observatory (LCO): world-wide network of telescopes
- Lick Observatory: California observatory of long standing
- LIGO: pair of observatories to detect gravitational waves
- LIGO-India: planned gravitational wave detector in India
- LISA: proposed space mission to detect gravitational waves
- LiteBIRD: planned spacecraft to map CMB polarization
- Llano de Chajnantor Observatory: group of observatories on a high plateau of the Atacama Desert
- Long Baseline Array (LBA): radio interferometer using Australian telescopes
- Lowell Observatory: Arizona observatory of long standing
- Mauna Kea Observatories (MKO): observatories on Mauna Kea in Hawaii
- National Astronomical Observatory of Japan (NAOJ): Japanese astronomy organization
- National Optical Astronomy Observatory (NOAO): past US optical astronomy organization
- National Radio Astronomy Observatory (NRAO): US radio astronomy organization
- National Solar Observatory (NSO): US government sponsored solar observatory
- New Gravitational Wave Observatory (NGO): past proposal for space mission to detect gravitational waves
- NOIRLab: US optical/infrared astronomy organization
- Owens Valley Radio Observatory (OVRO): group of radio telescopes in California near the VLBA
- Palomar Observatory: California observatory with Hale telescope
- Paranal Observatory: ESO Atacama observatory with ESO VLT
- Pierre Auger Observatory (PAO): cosmic-ray observatory in Argentina
- POEMMA: planned space cosmic-ray neutrino observatory
- Queen's University Radio Observatory (QRO): early radio astronomy facility near Kingston, Ontario
- Roque de los Muchachos Observatory (ORM,LPO,NHO): observatory at La Palma in the Canary Islands
- Siding Spring Observatory (SSO): observatory in New South Wales, Australia
- Simons Observatory (SO): CMB observatory on Atacama Desert
- South African Astronomical Observatory (SAAO): South African observatory with SALT telescope
- Spektr-RG (SRG, SXG): Russian-German X-ray observatory launched in 2019
- TAMA 300: small prototype gravitational wave detector in Japan
- TD-1A: 1970s European observatory-satellite with UV telescopes
- Teide Observatory: observatory on Mount Teide in the Canary Islands
- Telescope Array Project (TA): cosmic-ray observatory aiming for extremely energetic particles
- Tonantzintla Surveys (Ton): surveys providing early images of quasars and Seyfert galaxies
- Tunka experiment: Russian Cherenkov detector aimed at cosmic rays and gamma rays
- USNO: observatory obtaining astronomical data for Naval use
- Vainu Bappu Observatory (VBO): observatory in southern India
- Very Long Baseline Array (VLBA): radio interferometer stretching 8000 km
- Virgo: ground-based gravitational-wave detector in Italy
- Wilkinson Microwave Anisotropy Probe (WMAP): spacecraft that measured variations in the cosmic background radiation
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
observing program:
- astronomical survey: project to collect uniform astronomical data across the sky
OC:
- open cluster (OC): group of stars within a galaxy apparently formed by a single cloud
occlusion:
- occultation: one celestial body hiding another from an observer
occultation: one celestial body hiding another from an observer
- occultation observations: gathering astronomical information through measuring occultations
occultation observations: gathering astronomical information through measuring occultations
occultation spectroscopy:
- earthshine: reflected and emitted electromagnetic radiation from Earth
- exoplanet eclipse light curve: graph of light as an exoplanet transits in front of its star
- secondary eclipse: eclipse of a body that also transits
- transit spectroscopy: spectroscopy through an exoplanet's transit
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 planet:
- water world: planet with substantial liquid water
ocean world:
- hydrology: study of the movement of water
- water world: planet with substantial liquid water
oceanic carbon cycle:
- carbon dioxide (CO₂): compound of carbon atom and two oxygen atoms
Ocl:
- rare designator prefixes: designator prefixes generally used for only a few objects
OCPP:
- Pioneer Venus Orbiter (PVO): NASA Venus probe launched 1978
octopole:
- multipole expansion: series expansion of a function over the surface of a sphere
octupole:
- multipole expansion: series expansion of a function over the surface of a sphere
- perturbation theory: breaking an equation into a solvable part and approximable part
octupole level:
- multipole expansion: series expansion of a function over the surface of a sphere
octupole term:
- perturbation theory: breaking an equation into a solvable part and approximable part
ODE:
- partial differential equation (PDE): equation constructed as if the variables differentiated are independent
ODI:
- WIYN 3.5m Telescope: Kitt Peak telescope run by university collaboration with NOAO
Oe star:
- Be star: early star with Balmer emission lines
OEC:
- Open Exoplanet Catalogue (OEC): independently maintained list of known exoplanets
OEFD:
- Pioneer Venus Orbiter (PVO): NASA Venus probe launched 1978
OEFP:
- Pioneer Venus Orbiter (PVO): NASA Venus probe launched 1978
off the shell:
- mass shell: conceptual volume of mass shaped like a hollow sphere
off-axis telescope: telescope
- Herschelian telescope: type of off-axis reflector telescope
OGBD:
- Pioneer Venus Orbiter (PVO): NASA Venus probe launched 1978
OGLE: survey searching for microlensing transients
OGLE-2005-BLG-3290Lb: exoplanet orbiting a binary star
OGLE-2005-BLG-390L:
- OGLE-2005-BLG-3290Lb: exoplanet orbiting a binary star
OGS:
- HEAO-2: 1978 X-ray observatory space mission
OH:
- hydroxyl (OH): neutral compound of hydrogen and oxygen, one atom each
- OH/IR source: AGB star with strong OH maser
OH airglow:
- airglow: glow from a planet's atmosphere
OH maser:
- OH/IR source: AGB star with strong 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:
- IMB: 1980s neutrino detector
- Ohio Radio Survey (OSS): 1960s radio survey by Ohio State University
Ohio Radio Survey (OSS): 1960s radio survey by Ohio State University
Ohio Sky Survey:
- Ohio Radio Survey (OSS): 1960s radio survey by Ohio State University
Ohio State University Radio Observatory:
- Ohio Radio Survey (OSS): 1960s radio survey by Ohio State University
ohm:
- siemens (S): SI unit of electrical conductance
Ohm's law:
- telegrapher's equations: two equations describing a transmission line
ohm-meter:
- siemens (S): SI unit of electrical conductance
Ohmic heating: heating resulting from an electric current through a material
- inflated radii: exceptionally large radii of some hot Jupiters
OHP 1.93 m:
- 51 Pegasi b (51 Peg b): first exoplanet found orbiting a main sequence star
- HD 189733 b: hot Jupiter orbiting an orange dwarf
- HD 209458 b: hot Jupiter discovered in 1999
OHS:
- Subaru Telescope: 8.2 meter telescope in Hawaii
OIMS:
- Pioneer Venus Orbiter (PVO): NASA Venus probe launched 1978
OIR: a spectral "band name" for both visible light and infrared
- Pioneer Venus Orbiter (PVO): NASA Venus probe launched 1978
OL:
- double star designation: systems and format of double star designators
Olbers' paradox: argument using the dark of the sky regarding the nature of the universe
oligarch: term for large planetesimals that dominate
oligarch theory:
- oligarch: term for large planetesimals that dominate
- planet formation: process by which planets form
oligarchic accretion:
- oligarch: term for large planetesimals that dominate
oligarchic growth:
- oligarch: term for large planetesimals that dominate
olivine:
- methane (CH₄): compound of one carbon and 4 hydrogen atoms
Olympus Mons:
- Mars: well-explored planet in the solar system
OM:
- XMM-Newton: X-ray observatory-satellite operated by ESA
OMAG:
- Pioneer Venus Orbiter (PVO): NASA Venus probe launched 1978
OMC:
- INTEGRAL: European gamma ray observatory-satellite
- Orion Molecular Cloud Complex: group of molecular clouds with star forming regions
OMEGA:
- Mars Express: Mars probe launched by ESA in 2003
Omega Centauri: large globular cluster
Omega-Prime:
- Munich Near-Infrared Cluster Survey (MUNICS): 1990s-2000s galaxy cluster survey
OmegaCAM:
- VLT Survey Telescope (VST): survey telescope located at the VLT site
OMM 1.6m:
- SIMP: 2000s infrared proper-motion survey
on the shell:
- mass shell: conceptual volume of mass shaped like a hollow sphere
On-Orbit Servicing:
- OSAM-1: prototype space robot for servicing satellites
ONC:
- Orion Nebula Cluster (ONC): open cluster in the constellation Orion
one dimensional climate model: atmospheric model ignoring all horizontal motion
one dimensional model:
- one dimensional climate model: atmospheric model ignoring all horizontal motion
- subgrid-scale physics: shortcuts handling physics on a smaller scale than a simulation's grid
- three dimensional model: computer simulation handling variation in all three dimensions
one meter barrier:
- meter size barrier: a barrier to planet formation on the order of a meter diameter
ONMS:
- Pioneer Venus Orbiter (PVO): NASA Venus probe launched 1978
Ontario:
- Canadian Institute for Theoretical Astrophysics (CITA,ICAT): national research organization at University of Toronto
- Queen's University Radio Observatory (QRO): early radio astronomy facility near Kingston, Ontario
Oo:
- rare designator prefixes: designator prefixes generally used for only a few objects
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
OPA:
- Pioneer Venus Orbiter (PVO): NASA Venus probe launched 1978
opacity (κ): a measure of opaqueness of a material
- absorption coefficient: measure of how much light a substance absorbs
OPE:
- Giotto: 1980s space mission carrying out a Comet Halley flyby
Open Astronomy Catalog:
- Astrocats: software to create and manage an astronomy catalog
open cluster (OC): group of stars within a galaxy apparently formed by a single cloud
- Hyades Cluster: nearest open cluster
- NGC 346: open cluster in SMC
- Orion Nebula Cluster (ONC): open cluster in the constellation Orion
- Pleiades (M45): visible open cluster with seven B-stars
- stellar dynamics: stars' gravitational interaction
- Trapezium Cluster: open cluster of stars in Orion Nebula
open Dragone:
- Dragone telescope: off-axis reflector telescope type that preserves polarization
open Dragone telescope:
- Dragone telescope: off-axis reflector telescope type that preserves polarization
Open Exoplanet Catalogue (OEC): independently maintained list of known exoplanets
Open Kilonova Catalog:
- Astrocats: software to create and manage an astronomy catalog
open magnetic field lines:
- curvature radiation: synchrotron-like radiation when particles follow curved field lines
Open Supernova Catalog:
- Astrocats: software to create and manage an astronomy catalog
- MOSFiT: code to match light-curves with light-curve models
Open TDE Catalog:
- tidal disruption event (TDE,TDF): star pulled apart by black hole tidal forces
open universe:
- critical density (ρ_c): density of the universe which leaves it flat
open-Dragone design:
- Dragone telescope: off-axis reflector telescope type that preserves polarization
OpenSpace: visualization software aimed at astrophysical data
Oph-L 1689:
- LDN 1689: dense core within the Rho Ophiuchi Cloud Complex
Ophelia:
- shepherd moon: small moon at outer edge of a ring
Ophiuchus Molecular Cloud:
- Elias 2-27: much-studied YSO
- Rho Ophiuchi Cloud Complex: nebula that is a nearby star-forming region
OPI:
- double star designation: systems and format of double star designators
Opportunity:
- Mars Exploration Rover (MER): mission to Mars with two rovers
opposition: positioning of two astronomical objects 180 degrees apart in the sky
optical:
- visible light: electromagnetic radiation, wavelength 390-750 nm
optical and infrared:
- OIR: a spectral "band name" for both visible light and infrared
optical astronomy:
- visible light: electromagnetic radiation, wavelength 390-750 nm
optical axis: center line through an optical instrument
- astigmatism: focusing differently according to direction across the focal plane
- off-axis telescope: telescope
optical coma:
- aberration: types of flaws in telescope images
optical counterpart:
- counterpart: image found at same coordinates using different EMR
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: double star where the two are not gravitationally bound
- binary star: system of two stars co-orbiting
optical fiber:
- fiber positioner: machine to set up fibers in multi-object spectrograph
Optical Gravitational Lensing Experiment:
- OGLE: survey searching for microlensing transients
optical interferometer: interferometer of visible light
- CHARA: optical interferometer
- COAST: optical interferometer in England
- European Southern Observatory Very Large Telescope (ESO VLT,VLT): four 8.2-meter optical telescopes in Chile that can act together
- GI2T: optical interferometer in France
- IOTA: past optical interferometer in Arizona
- Keck Observatory: observatory in Hawaii with two 10-meter reflectors
- Large Binocular Telescope (LBT): dual 8.4 meter telescope in Arizona
- MRO Interferometer (MROI): optical interferometer in New Mexico
- Narrabri Stellar Intensity Interferometer (NSII): 1960s optical interferometer for measuring stellar diameters
- Navy Precision Optical Interferometer (NPOI): optical interferometer in Arizona
- Palomar Testbed Interferometer (PTI): near-infrared interferometer experiment
- SUSI: optical interferometer in Australia
optical interferometry:
- interferometry: analysis of superimposed EMR waves
- optical interferometer: interferometer of visible light
optical segmentation:
- segmented mirror: a telescope mirror formed of array of smaller mirrors
optical SFR:
- star formation rate (SFR): rate at which material such as gas is turned into stars
optical star formation rate:
- star formation rate (SFR): rate at which material such as gas is turned into stars
optical telescope assembly:
- Hubble Space Telescope (HST): observatory-satellite with 2.4 meter reflective telescope
optical thickness:
- optical depth (τ): a measure of opaqueness of a path of light
optical violent variable quasar:
- 3C 279: striking variable quasar
optical window:
- atmospheric window: frequency bands within which the atmosphere passes EMR
optically thick:
- optical depth (τ): a measure of opaqueness of a path of light
optically thin:
- cooling function: function relating a gas's cooling rate to its temperature
- optical depth (τ): a measure of opaqueness of a path of light
optically violent variable quasar:
- blazar: very compact variable quasar
optics: science and technology regarding visible light
- aberration: types of flaws in telescope images
- adaptive optics (AO): optical instruments that dynamically adapt to atmospheric distortion
- Airy disk: image pattern an optical system produces from light from a point
- angular magnification: a magnification measure for a magnifier with an eyepiece
- angular resolution: measure of a telescope's ability to distinguish spatial detail
- aperture masking interferometry (AMI): interferometry using a mask in front of the telescope
- aperture synthesis: interferometry to simulate a larger aperture telescope
- atmospheric window: frequency bands within which the atmosphere passes EMR
- blended spectra: an observed spectrum comprising light from multiple objects
- cavity-enhanced absorption spectroscopy (CEAS): passing a beam through a gas multiple times to amplify absorption lines
- circular polarization ratio (CPR): ratio of circular polarization handedness in reflected radar signal
- coherent light: beam of light at a single frequency
- collimator: device to align beams of light
- coma: aberration where points of light show a tail
- deformable mirror (DM): mirror that can be flexed for fine control
- differential spectroscopy: analysis of the comparison of two spectrographs
- diffraction: effect of an obstacle on a wave
- diffraction limited: telescope limited only by the laws of diffraction
- diffractive interstellar scintillation (DISS): diffraction of star light by the ISM
- etalon: two parallel reflective surfaces separating light according to wavelength
- exit pupil: size of the image as presented to the eye
- extreme adaptive optics (ExAO): high-performance version of AO system
- Fabry-Pérot interferometer (FPI): type of chromatic-dispersing interferometer
- Faraday rotation: rotation of optical polarization by a medium in a magnetic field
- field of view (FOV): angular measure of how much an optical instrument can view
- focal length: length from optical element to focal plane
- focal plane: plane within optical system at which an image is in focus
- grazing incidence optics (GIO): optics that avoid large changes to the angle of rays
- grism: combination of a grating and a prism
- interferometer: device detecting properties of electromagnetic waves by detecting interference between waves
- Kramers opacity law: opacity's relation to density and temperature
- linearly variable filter (LVF): filter whose passband varies over one spatial dimension
- lucky imaging: method of combining short-term images to yield better resolution
- Lyot stop: optical element to block unwanted light within instruments
- Mie scattering: scattering of light by large particles
- opacity (κ): a measure of opaqueness of a material
- optical axis: center line through an optical instrument
- optical depth (τ): a measure of opaqueness of a path of light
- phase plate: filter that changes the phase of light passing through
- point-spread function (PSF): function describing an optical system's response to a point of light
- pointing error (PE): discrepancy in telescope's aim
- polarization: property of waves that oscillate in a particular direction
- PSF fitting: untangling airy disks to gain effective resolution
- Rayleigh scattering: wave scattering by particles smaller than the wavelength
- real image: image that shows on a screen placed at its location
- refractive interstellar scintillation (RISS): refraction of star light by the ISM
- Rosseland mean opacity: a useful weighted average of opacities at all the wavelengths
- scintillometry: measuring of twinkling
- seeing: apparent blurring and twinkling of objects seen through atmosphere
- shift-and-add: common speckle-suppression technique
- Snell's law: optical principle of refraction
- speckle imaging: method of combining short-term images to yield better resolution
- speckle suppression: methods of reducing noise in telescope observations
- speckles: image flaws such as extraneous spots
- stacking: combining images of the same object
- Strehl ratio: measure of optical aberration
- Thomson optical depth (τ_T,τ): a measure of effects of Thomson scattering
- transit spectroscopy: spectroscopy through an exoplanet's transit
- transmission spectroscopy: spectrum of radiation passing through a substance
- wavefront error (WFE): measure of a class of telescope distortion
OPTIMOS:
- European Extremely Large Telescope (E-ELT,ELT): 39-meter telescope under construction
Optopus:
- ESO Nearby Abell Cluster Survey (ENACS): 1990s spectroscopy and photometry survey of galaxy clusters
ORAD:
- Pioneer Venus Orbiter (PVO): NASA Venus probe launched 1978
orange dwarf:
- K-type star (K): spectral class of star a bit cooler than the Sun
- red dwarf: small, cool main-sequence star
orbit:
- conic section: orbit shapes, like the intersection of a plane and cone
- Keplerian orbit: orbit following a perfect ellipse or other conic section
- orbital element: parameters describing an 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 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
- 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:
- J₂: geopotential coefficient regarding a planet's oblateness
orbital plane:
- orbital element: parameters describing an orbit
orbital plot:
- orbit plot: graphic showing the path of an orbit as a line
orbital resonance: tendency of orbits of multiple bodies to remain in a simple pattern
- tidal locking: locked rotation of an orbiting body
orbital speed: speed of an orbiting body around the barycenter of a system
Orbiting Astronomical Observatory (OAO): series of 1960s-1970s NASA space telescopes
Orbiting Solar Observatory 7:
- OSO 7: 1970s observatory-satellite for viewing the Sun
Orbiting Wide-angle Light Collectors (OWL): planned space mission to detect cosmic rays through Earth atmosphere light flashes
orbits:
- apsis: closest or furthest point in an eccentric orbit
- barycenter: center of mass of two orbiting bodies
- conic section: orbit shapes, like the intersection of a plane and cone
- corotation resonance (CR): an orbital resonance with the same frequency as the orbit
- eccentricity (e): degree to which an orbit is non-circular
- epicycle: small circular motion around a large circular motion
- epicyclic frequency: frequency of oscillation in an accretion disk
- extreme mass ratio inspiral (EMRI): inspiraling pair of objects with mass ratio beyond 10,000
- halo orbit: type of orbit around an instable Lagrangian point
- hardness: measure of the binding energy of a binary
- Hill radius: radius of gravitational influence of a body
- Hill stability: planetary orbits which will remain in the same order
- innermost stable circular orbit (ISCO): border of region surrounding a BH in which orbits are unstable
- instability region: region around an object where orbits cannot persist
- Kepler radius: radius at which a particular velocity would orbit
- Kepler's laws: laws of the kinematics of orbits
- Keplerian orbit: orbit following a perfect ellipse or other conic section
- Kirkwood gap: gaps in asteroid orbital radii corresponding to Jupiter resonances
- Lagrange stability: a quality of some stable orbits
- Lagrangian point: points around two orbiting bodies where small objects can sit
- Laplace radius (r_L): a radius for a stable orbit of a satellite around a planet
- Laplace-Lagrange secular theory: theory of evolution of planetary orbits
- libration: oscillating motion of orbiting bodies relative to each other
- Lie transform: type of infinitesimal transform
- Lindblad torque: torque due to Lindblad resonances
- mass ratio (μ,q): ratio of masses of two objects such as a binary star
- mean anomaly: angle describing an object's position within an elliptical orbit
- minimum orbit intersection distance (MOID): smallest distance between paths of two orbiting bodies
- orbit plot: graphic showing the path of an orbit as a line
- orbital element: parameters describing an orbit
- 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
- 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
- period derivative: rate of change in the period of an orbit or rotation
- perturbation theory: breaking an equation into a solvable part and approximable part
- photon sphere: surface surrounding black hole where photons can orbit
- Poynting-Robertson effect: force slowing dust grains orbiting a star
- precession: periodic change in a body's rotation or orbit
- projected semi-major axis: semi-major axis projected onto line-of-sight or plane of the sky
- protected region: an area around a body where an orbit can be stable
- Q factor: measure of oscillator's damping
- retrograde hot Jupiter: large hot planet orbiting opposite the expected direction
- retrograde orbit: orbit opposite the usual direction
- Roche limit: nearest a body can orbit another and survive
- Roche lobe: region of a body's gravitational influence closest to its competitor
- secular: occurring slowly over a long period of time
- semi-major axis (a): maximum radius of an ellipse
- synchronous orbit: orbit with angular velocity matching the rotation of the orbited body
- tidal locking: locked rotation of an orbiting body
- tidal migration: interaction between tide and orbiting body that changes the orbit
- tidal Q: measure of orbital energy dissipated per orbit due to tidal forces
- Yarkovsky effect: force on spinning, orbiting objects from asymmetric radiation
- Yarkovsky-O'Keefe-Radzievskii-Paddack effect (YORP): rotational effect on asymmetric asteroids
Orcus:
- moon: a planet's natural satellite, such as Earth's
- trans-Neptunian object (TNO): minor planet beyond Neptune
order:
- interferometer: device detecting properties of electromagnetic waves by detecting interference between waves
- spherical harmonics: harmonic functions on the surface of a sphere
order-of-magnitude:
- dex: a number or ratio's log base 10
orders-of-magnitude:
- dex: a number or ratio's log base 10
ordinary differential equation:
- partial differential equation (PDE): equation constructed as if the variables differentiated are independent
ORFEUS SPAS:
- Interstellar Medium Absorption Profile Spectrograph (IMAPS): 1980s/1990s UV spectrometer
ORFEUS Telescope:
- Berkeley Extreme and Far-UV Spectrometer (BEFS): 1990s UV spectrometer used on two shuttle missions
- Tubingen Ultraviolet Echelle Spectrometer (TUES): 1990s UV spectrometer used on two Space Shuttle missions
ORFEUS-SPAS 1:
- Berkeley Extreme and Far-UV Spectrometer (BEFS): 1990s UV spectrometer used on two shuttle missions
- Interstellar Medium Absorption Profile Spectrograph (IMAPS): 1980s/1990s UV spectrometer
- Tubingen Ultraviolet Echelle Spectrometer (TUES): 1990s UV spectrometer used on two Space Shuttle missions
ORFEUS-SPAS 2:
- Berkeley Extreme and Far-UV Spectrometer (BEFS): 1990s UV spectrometer used on two shuttle missions
- Interstellar Medium Absorption Profile Spectrograph (IMAPS): 1980s/1990s UV spectrometer
- Tubingen Ultraviolet Echelle Spectrometer (TUES): 1990s UV spectrometer used on two Space Shuttle missions
organization:
- Academia Sinica Institute of Astronomy and Astrophysics (ASIAA,IAA): Taiwanese astrophysics research organization
- ACe consortium: corporations contracted to construct E-ELT
- ADEC: NASA unit to coordinate efforts of data archiving and dissemination
- Agenzia Spaziale Italiana (ASI): includes space-based astronomy research
- Association of Universities for Research in Astronomy (AURA): group of universities operating a number of observatories
- ASTRON: Netherlands radio astronomy research organization
- Astronet: European astronomy consortium
- Canadian Institute for Theoretical Astrophysics (CITA,ICAT): national research organization at University of Toronto
- Carl Sagan Institute (CSI): group researching finding life on other planets and moons
- CEA Service d'Astrophysique (CEA SAp): French national astrophysics research institute
- Center for Astrophysics (CfA): Harvard and Smithsonian research and education organization
- Centre de données astronomiques de Strasbourg (CDS): repository of astronomical data
- Centre national d'ètudes spatiales (CNES): French space agency
- CIG: initiative to produce Earth-science software
- CSA: includes astronomical research
- European Southern Observatory (ESO): organization operating telescopes in the southern hemisphere
- European Space Agency (ESA): NASA-like international space organization in Europe
- Goddard Space Flight Center (GSFC): NASA space research laboratory near Washington D.C.
- High Altitude Observatory (HAO): NCAR unit observing and monitoring the Sun
- Institut de radioastronomie millimétrique (IRAM): organized radio astronomy collaboration between France, Germany, and Spain
- Institute of Theoretical Astrophysics (ITA): Heidelberg research institute
- Instituto de Astrofísica de Canarias (IAC): research institute on Canary Islands
- International Astronomical Union (IAU,UAI): association of professional astronomers
- IPAC: Caltech group to collect and analyze infrared observations
- Isaac Newton Group of Telescopes (ING): three telescopes in Canary Islands
- Japan Aerospace Exploration Agency (JAXA): Japan agency includes astronomical research
- Kavli Institute: any of a number of science institutes supported by Kavli Foundation
- Max Planck Institute for Astronomy (MPIA): Heidelberg research institute
- Max Planck Institute for Radio Astronomy (MPIR): Bonn research institute
- Minor Planet Center (MPC): organization collecting and organizing minor planet data
- NASA: includes space-based astronomy research
- NASA Astrobiology Institute (NAI): research funding and coordination organization
- NASA Deep Space Network (NASA DSN,DSN): NASA's world-wide radio communication setup
- National Astronomical Observatory of Japan (NAOJ): Japanese astronomy organization
- National Optical Astronomy Observatory (NOAO): past US optical astronomy organization
- National Radio Astronomy Observatory (NRAO): US radio astronomy organization
- NOIRLab: US optical/infrared astronomy organization
- NSF AST: US government astronomical research funding division
- Other Worlds Laboratory (OWL): group researching planets and moons
- RECONS: consortium for research on stars near the Sun
- Roscosmos: Russian organization for space technology and research
- Space Telescope Science Institute (STScI): science operator of space telescopes
Origins Space Telescope (OST): concept for 2030s large space IR telescope
Orion: well-known constellation in the northern hemisphere
Orion A:
- Orion Molecular Cloud Complex: group of molecular clouds with star forming regions
Orion Arm:
- spiral arm: long, winding visible structure within a spiral galaxy
Orion B:
- Orion Molecular Cloud Complex: group of molecular clouds with star forming regions
Orion Cluster:
- Orion Nebula Cluster (ONC): 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 (M42, NGC 1976): easily observed nebula that includes SF regions
- Orion Disks: protoplanetary disks visible in front of Orion Nebula
- Trapezium Cluster: open cluster of stars in Orion Nebula
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:
- Trapezium Cluster: open cluster of stars in Orion Nebula
Orion variable:
- variable star: star that varies in magnitude
Orion-Cygnus Arm:
- spiral arm: long, winding visible structure within a spiral galaxy
ORM:
- Carlsberg Meridian Catalogue (CMC): series of astrometric catalogs from 19th century on
- Gran Telescopio Canarias (GTC): 10.4 meter telescope in the Canary Islands
- Instituto de Astrofísica de Canarias (IAC): research institute on Canary Islands
- Isaac Newton Group of Telescopes (ING): three telescopes in Canary Islands
- Isaac Newton Telescope (INT): 2.5 m telescope in Canary Islands
- MASCARA: distributed array of telescopes to search for exoplanets
- Mercator Telescope: 1.2 m telescope in the Canary Islands
- Roque de los Muchachos Observatory (ORM,LPO,NHO): observatory at La Palma in the Canary Islands
- Telescopio Nazionale Galileo (TNG): 3.58 m telescope in Canary Islands
OROCHI:
- MMX: Japanese probe to bring back a sample of a Martian moon
ORP:
- reduction potential (E_h,ORP,pE): measure of a chemical species' tendency to acquire electrons
ORPA:
- Pioneer Venus Orbiter (PVO): NASA Venus probe launched 1978
orphan afterglow:
- gamma-ray burst (GRB): short flashes of gamma rays apparently from outside our galaxy
orphan GRB afterglow:
- gamma-ray burst (GRB): short flashes of gamma rays apparently from outside our galaxy
Orphan stream: stellar stream wrapping around the Milky Way
orrery: mechanical device to simulate the solar system
ORT:
- Ooty Radio Telescope (ORT): cylindrical radio telescope in India
orthogonal transfer CCD:
- image stabilization: camera mechanism to compensate for movement
OSAM-1: prototype space robot for servicing satellites
OSC:
- Astrocats: software to create and manage an astronomy catalog
- MOSFiT: code to match light-curves with light-curve models
OSCA:
- William Herschel Telescope (WHT): 4.2 meter telescope in the Canary Islands
Oschin Schmidt:
- Palomar 48 Inch Telescope (P48): 48 inch Schmidt telescope at Palomar Observatory
Oschin Telescope:
- Palomar Transient Factory (PTF): survey designed to find transients
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
- minimum orbit intersection distance (MOID): smallest distance between paths of two orbiting bodies
OSIRIS:
- Gran Telescopio Canarias (GTC): 10.4 meter telescope in the Canary Islands
- HD 209458 b: hot Jupiter discovered in 1999
- Keck Observatory: observatory in Hawaii with two 10-meter reflectors
- Rosetta: space probe that visited a comet
- SHARDS: GTC survey in GOODS-N field for quenched galaxies at z 1-2.3
- SOAR: 4.1 m reflector telescope in Chile
OSIRIS-REx: space mission aiming to return a sample of an asteroid
OSO 7: 1970s observatory-satellite for viewing the Sun
OSR:
- Tianwen-1 (TW-1): Mars rover/orbiter mission currently orbiting Mars
OSS:
- Ohio Radio Survey (OSS): 1960s radio survey by Ohio State University
- Origins Space Telescope (OST): concept for 2030s large space IR telescope
OSSE:
- Compton Gamma Ray Observatory (CGRO,GRO): 1990s space observatory for gamma ray observation
OSSOS:
- Outer Solar System Origins Survey (OSSOS): survey searching for trans-Neptune objects
OST:
- Origins Space Telescope (OST): concept for 2030s large space IR telescope
OSURO:
- Ohio Radio Survey (OSS): 1960s radio survey by Ohio State University
OTC:
- tidal disruption event (TDE,TDF): star pulled apart by black hole tidal forces
OTCCD:
- image stabilization: camera mechanism to compensate for movement
Other Worlds Laboratory (OWL): group researching planets and moons
OTS:
- Hubble Space Telescope (HST): observatory-satellite with 2.4 meter reflective telescope
- rare designator prefixes: designator prefixes generally used for only a few objects
Oukaïmeden Observatory:
- TRAPPIST: ground-based automatic transiting planet finding telescope
outer Lindblad resonance:
- Lindblad torque: torque due to Lindblad resonances
Outer Solar System Origins Survey (OSSOS): survey searching for trans-Neptune objects
outflow:
- star formation feedback: mechanisms whereby star formation regulates its own rate
outgassing:
- atmosphere formation: capture and modification of a planet's gases
OUVS:
- Pioneer Venus Orbiter (PVO): NASA Venus probe launched 1978
overdensity:
- Milky Way subgroup: the Milky Way and its satellites
- stellar overdensity: portion of galactic halo with more stars than normal
overfitting:
- Akaike information criterion (AIC): particular formula for comparison of statistical models
Overwhelmingly Large Telescope (OWL): 100 m telescope plan
OVRO:
- Owens Valley Radio Observatory (OVRO): group of radio telescopes in California near the VLBA
OVRO 40 Meter Telescope:
- Owens Valley Radio Observatory (OVRO): group of radio telescopes in California near the VLBA
OVV:
- 3C 279: striking variable quasar
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
Owens Valley Radio Observatory (OVRO): group of radio telescopes in California near the VLBA
OWL:
- EAGLE: simulation of galaxy formation and evolution
- Orbiting Wide-angle Light Collectors (OWL): planned space mission to detect cosmic rays through Earth atmosphere light flashes
- Other Worlds Laboratory (OWL): group researching planets and moons
- Overwhelmingly Large Telescope (OWL): 100 m telescope plan
Oxford SWIFT:
- Hale Telescope: 5.1 m reflector telescope in California
oxidation:
- atmosphere formation: capture and modification of a planet's gases
- oxidation state: number of electrons loaned out by an atom in an ionic bond
- reducing atmosphere: atmosphere lacking oxygen or other oxidizers
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 potential:
- reduction potential (E_h,ORP,pE): measure of a chemical species' tendency to acquire electrons
oxidation/reduction reaction:
- reducing atmosphere: atmosphere lacking oxygen or other oxidizers
oxide:
- geochemistry: the chemistry of the Earth, planets, and moons
oxidizing agent:
- reducing atmosphere: atmosphere lacking oxygen or other oxidizers
oxygen (O): element, O, atomic number 8
- alpha CO (α_CO): ratio of CO emissions to H₂
- carbon dioxide (CO₂): compound of carbon atom and two oxygen atoms
- carbon monoxide (CO): compound of carbon and oxygen, one atom each
- carbonate-silicate cycle: long-term cycle that sequesters Earth carbon
- geochemistry: the chemistry of the Earth, planets, and moons
- hydroxyl (OH): neutral compound of hydrogen and oxygen, one atom each
- neon burning: fusion reaction starting with neon
- nitrite (NO₂^-): ion of a nitrogen atom and two oxygen atoms with extra electron
- oxygen burning: fusion reaction starting with oxygen
- oxygen lines: spectral lines specific to oxygen
- silicate weathering feedback: feedback mechanism stabilizing carbon in Earth atmosphere
oxygen burning: fusion reaction starting with oxygen
- magnesium (Mg): element, Mg, atomic number 12
- nucleosynthesis: creation of atomic nuclei
- silicon (Si): metal, Si, atomic number 14
- sulfur (S): metal, S, atomic number 16
oxygen lines: spectral lines specific to oxygen
oxygen-burning shell:
- oxygen burning: fusion reaction starting with oxygen
oxygen-neon-magnesium white dwarf:
- white dwarf (WD): stellar remnant of mostly electron degenerate matter
oxygen-rich Wolf-Rayet:
- Wolf-Rayet star: type of star with broad emission bands
OzDES:
- Dark Energy Survey (DES): survey aimed at mapping the universe's expansion
ozone:
- earthshine: reflected and emitted electromagnetic radiation from Earth
ozone layer:
- Upper Atmosphere Research Satellite (UARS): 1990s spacecraft to observe Earth ozone layer

Index