Term Index (P)
Astrophysical terms and names of things beginning with the letter P.
P1
P3
P4
P6
P7
PA
PB
PC
PD
PE
PF
PG
PH
PI
PK
PL
PM
PN
PO
PP
PQ
PR
PS
PT
PU
PV
PW
PY
PZ
- P (phosphorus): metal, P, atomic number 15
- P: see rare designator prefixes
- p (peculiar galaxy): galaxy with out-of-the-ordinary features
- P Cygni: see P Cygni profile
- P Cygni profile: emission-line shape including a blue-shifted absorption feature
- P orbital: see electron orbital
- P-Cam: see Fred Young Submillimeter Telescope
- P-CMBcam: see Fred Young Submillimeter Telescope
- P-curve: see PCA analysis
- P-dot (period derivative): rate of change in the period of an orbit or rotation
- P-L: see Palomar-Leiden Survey
- P-L relation: see Cepheid variable
- p-mode: see asteroseismology
- p-nuclei: see p-process
- P-P chain (proton-proton chain): type of fusion reaction chain turning hydrogen into helium
- P-P space: see position-position-velocity space
- P-P-P space: see position-position-velocity space
- data cube: three-dimensional array of numerical data
- P-P-V space (position-position-velocity space): 3D space concept using velocity as one of the three dimensions
- P-Pdot diagram: diagram comparing the rotation and the slowing of pulsars
- p-process: synthesis of elements through proton capture
- rp-process: synthesis of elements through repeated proton capture
- P-Spec: see Fred Young Submillimeter Telescope
- P-V: see wavefront error
- P-V space: see position-position-velocity space
- P1640: see Hale Telescope
- P18: see Palomar Observatory
- P3K: see Hale Telescope
- P48 (Palomar 48 Inch Telescope): 48 inch Schmidt telescope at Palomar Observatory
- P60 (Palomar 60-inch Telescope): 60 inch telescope at Palomar Observatory
- CorMASS: near-infrared spectrograph
- P7: see Mercator Telescope
- P500: see cluster radius
- PA (position angle): indication of a direction across the celestial sphere
- PA: see POINT-AGAPE
- Pa: see atm
- PACE: see SELENE
- PACS: see Herschel Space Observatory
- PEP: survey aimed at star formation in early times
- PACS Evolutionary Probe (PEP): survey aimed at star formation in early times
- pAGB (post-AGB star): stellar-evolution phase between AGB and white dwarf
- PAH (polycyclic aromatic hydrocarbon): hydrocarbons consisting of meshes of benzene rings
- PAH emissions: infrared emission from polycyclic aromatic hydrocarbons in gas clouds
- pair breaking and formation: see Cooper pair
- pair instability
- pair production: creation of a particle/antiparticle pair
- pair telescope: telescope that detects gamma rays via pair production
- pair-instability supernova: type of large supernova
- PAIRITEL
- Pal (Palomar Globular Clusters): list of 15 globular clusters found in POSS plates
- paleomagnetism: ancient magnetic fields and their characteristics
- PALFA: Arecibo search for pulsars
- Pallas: see asteroid
- PALM-3000: see Hale Telescope
- PALMS: survey to find exoplanets for direct imaging
- Palomar: see Palomar Globular Clusters
- Palomar 1.5 m Telescope (Palomar 60-inch Telescope): 60 inch telescope at Palomar Observatory
- Palomar 18 inch Schmidt Camera: see Palomar Observatory
- Palomar 48 (Palomar 48 Inch Telescope): 48 inch Schmidt telescope at Palomar Observatory
- Palomar 48 Inch Telescope: 48 inch Schmidt telescope at Palomar Observatory
- Palomar 48-inch Schmidt (Palomar 48 Inch Telescope): 48 inch Schmidt telescope at Palomar Observatory
- Palomar 60-inch Telescope: 60 inch telescope at Palomar Observatory
- Palomar Digital Sky Survey: see Palomar Observatory Sky Survey
- Palomar Gattini-IR (Gattini-IR): IR transient survey telescope
- Palomar Globular Clusters: list of 15 globular clusters found in POSS plates
- Palomar high-redshift quasar surveys: 1980s Hale-telescope quasar searches using new technology
- Palomar Maps: see Parsamian Nebula Catalog
- Palomar Observatory: California observatory with Hale telescope
- Palomar Observatory Sky Survey: 1950s photographic plates from Palomar 48 inch telescope
- Palomar Observatory Sky Survey I (Palomar Observatory Sky Survey): 1950s photographic plates from Palomar 48 inch telescope
- Palomar Observatory Sky Survey II: see Palomar Observatory Sky Survey
- Palomar Planet Crossing Asteroid Survey (Planet Crossing Asteroid Survey): search for NEOs using small Palomar Schmidt Camera
- Palomar Proper Motion Survey (Luyten Palomar Survey): 1970s catalog of stars with high proper motion
- Palomar Testbed Interferometer: near-infrared interferometer experiment
- Palomar Transient Factory: survey designed to find transients
- Palomar-Green Catalog (Palomar-Green Survey): list of objects with excess ultraviolet light
- Palomar-Green Survey: list of objects with excess ultraviolet light
- Palomar-Haro-Luyten Catalog: 1960s catalog of faint blue stars
- Palomar-Leiden Survey: 1960s survey to identify distant asteroids
- Palomar-Leiden Trojan survey: see Palomar-Leiden Survey
- Palomar-Quest Sky Survey
- Palomar-Quest Survey
- PAMELA: cosmic ray detector attached to satellite
- Pampa la Bola: see Llano de Chajnantor Observatory
- Pan: see shepherd moon
- Pan-Andromeda Archaeological Survey (PAndAS): survey of M31 and M33
- Pan-STARRS: set of survey telescopes
- Pan-STARRS 1: see Pan-STARRS
- Pan-STARRS MDS: see Medium Deep Survey
- Pan-STARRS Object: see Pan-STARRS
- Pan-STARRS1: see Pan-STARRS
- PanCAKE: see JWST ETC
- PanCam: see Rosalind Franklin
- Pancam: see Mars Exploration Rover
- PanCET: HST UV/optical/NIR survey of selected exoplanets
- panchromatic: involving all colors, i.e., all wavelengths
- Panchromatic Comparative Exoplanet Treasury (PanCET): HST UV/optical/NIR survey of selected exoplanets
- Panchromatic Hubble Andromeda Treasury (PHAT): HST survey of M31 stars
- PAndAS: survey of M31 and M33
- Pandeia (JWST ETC): Python-based exposure time calculator for JWST
- Pandeia Coronagraphy Advanced Kit for Extractions: see JWST ETC
- Pandora: see shepherd moon
- PANIC: see Magellan Telescopes
- Panoramic Imaging Survey of Centaurus and Sculptor: survey of extended halos of two nearby galaxies
- Panoramic Survey Telescope and Rapid Response System (Pan-STARRS): set of survey telescopes
- Pantheon: catalog of well-checked Type Ia supernovae
- Pantheon sample (Pantheon): catalog of well-checked Type Ia supernovae
- Pantheon supernovae (Pantheon): catalog of well-checked Type Ia supernovae
- PAO (Pierre Auger Observatory): cosmic-ray observatory in Argentina
- PAPA: see Aditya-L1
- PAPER: radio interferometer for 21-cm measurement
- Par: see Parsamian Nebula Catalog
- parabola: see conic section
- parabolic mirror
- paraboloid: circularly-symmetric 3D surface based on parabola
- spheroid: sphere-like shape that is flattened or elongated
- paradigm
- relativity: physics models accommodating the constancy of the speed of light
- parallax: angle due to different lines of sight
- parallax angle: see parallax
- parameter retrieval (retrieval): determining parameters through observation and modeling
- parameterized post-Newtonian formalism: method of approximating GR-based gravity from Newtonian gravity
- Paranal Observatory: ESO Atacama observatory with ESO VLT
- Parenago: see rare designator prefixes
- parent nuclide: see radioactive dating
- parent nuclide: see radioactive decay
- Parker Probe (Parker Solar Probe): space probe investigating solar corona
- Parker Solar Probe: space probe investigating solar corona
- Parker wind: model of the solar wind
- Parker wind model (Parker wind): model of the solar wind
- Parkes 210ft Telescope (Parkes Observatory): Australian observatory with large single-dish radio telescope
- Parkes 64m Telescope (Parkes Observatory): Australian observatory with large single-dish radio telescope
- HIPASS: HI survey carried out 1997 to 2002
- Parkes Catalog: catalog of from 1960s-1990 of radio sources in southern hemisphere
- Parkes HI Zone of Avoidance Shallow Survey: see Parkes HI Zone of Avoidance Survey
- Parkes HI Zone of Avoidance Survey: radio survey to identify galaxies hidden by the zone of avoidance
- Parkes Multibeam Pulsar Survey: late 1990s radio survey in search of pulsars
- Parkes Observatory: Australian observatory with large single-dish radio telescope
- Parkes Pulsar Timing Array: group of pulsars timed by Parkes Observatory
- Parkes Telescope (Parkes Observatory): Australian observatory with large single-dish radio telescope
- Parkes-MIT-NRAO Surveys: 1990 southern-hemisphere radio surveys
- Parque Astron*oacute;mico Atacama: see Llano de Chajnantor Observatory
- Parsamian: see Parsamian Nebula Catalog
- Parsamian Nebula Catalog: 1965 list of nebulae
- parsec: about 3.26 light-years
- ParselTongue: see Astronomical Image Processing System
- partial derivative: see partial differential equation
- partial differential equation: equation constructed as if the variables differentiated are independent
- partial ionization zone: portion of some stars where gas is partially ionized
- kappa mechanism: stellar instability caused by opacity increasing with temperature
- partial pressure: see number density
- partial vapor pressure
- particle: very small thing
- particle: see cosmic dust
- alpha particle: essentially a helium nucleus produced by radioactivity
- astrophysical neutrino: neutrino from other than Earth or the usual sources
- axion: proposed light, electrically neutral elementary particle
- baryon: protons, neutrons, and other three-quark particles
- electron: type of lepton that is stable and has an electric charge of -1
- graviton: quantum of gravity
- hyperon: exotic type of baryon
- Lee-Weinberg bound: lower limit on mass of heavy lepton
- lepton: elementary particle with 1/2 integer spin such as electron
- neutralino: proposed type of particle that might include WIMPs
- neutrino: light, electrically neutral elementary particle
- neutron: type of baryon that is stable and has no electric charge
- pion: first type of meson discovered
- plasmon: quasiparticle that is quantum of plasma vibration
- positron: electron-like antimatter particle with electric charge of +1
- proton: type of baryon that is stable and has an electric charge of +1
- quark: type of elementary particle incorporated in protons and neutrons
- tau neutrino: neutrino flavor that becomes a tau particle during interactions
- WIMP: proposed particle comprising dark matter
- particle accelerator: see particle physics
- particle density
- mass density: mass per unit volume, as opposed to particle density
- particle horizon: furthest point from which light can reach us
- particle mixing (quantum mixing): means by which one particle spontaneously changes to another
- particle number: number of particles
- particle physics: physics such as carried out in accelerators
- effective field theory: type of useful simplification of a field theory
- freeze-out: particles existing long-term after a decoupling
- quark: type of elementary particle incorporated in protons and neutrons
- Particle Physics and Astronomy Research Council: former UK science agency
- particle spectrometer: device to determine the characteristics of incoming particles
- particle-antiparticle annihilation
- antimatter: similar to normal matter but with opposite electrical charge
- particle-in-cell simulation (PIC simulation): method used in simulating plasma
- particles
- partition function: scale factor for Boltzmann factors
- partitioning
- Partiview: visualization software aimed at 4D data
- parts per million: method of expressing a small ratio
- PARVI: see Hale Telescope
- pascal: see atm
- Paschen
- Paschen series: hydrogen lines for electrons settling from n > 3 to n = 3
- Paschen series: hydrogen lines for electrons settling from n > 3 to n = 3
- hydrogen: most prominent element, atomic number 1
- PASJ (Publications of the Astronomical Society of Japan): bimonthly journal
- PASP (Publications of the Astronomical Society of the Pacific): monthly journal
- passband: range of electromagnetic wavelengths that a filter allows
- passive dust: dust in a model that is influenced but does not influence
- passive dust model (passive dust): dust in a model that is influenced but does not influence
- past
- PAT: see superconducting tunnel junction
- Pathways to Discovery in Astronomy and Astrophysics for the 2020s: see decadal survey
- patterned ground: see polygonal ground
- Paul Wild Observatory
- Pauli exclusion principle: fermions in a quantum system cannot have identical quantum numbers
- PAVO: see CHARA
- Pavo-Indus Supercluster
- PAWS: survey of GMCs in M51a
- Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA): cosmic ray detector attached to satellite
- PB: see rare designator prefixes
- PB-2: see POLARBEAR
- PBF: see Cooper pair
- PBH (primordial black hole): black holes forming at the most dense volumes when inflation ceased
- PBL (planetary boundary layer): low level of atmosphere affected by ground
- PC: see Palomar high-redshift quasar surveys
- PC: see rare designator prefixes
- pc (parsec): about 3.26 light-years
- PCA (principal component analysis): statistical strategy of devising independent variables
- PCA: see RXTE
- PCA analysis: an automatable method of determining galaxy morphology
- telluric line: absorption line in ground observation due to Earth atmosphere
- PCA analysis: an automatable method of determining galaxy morphology
- PCAS (Planet Crossing Asteroid Survey): search for NEOs using small Palomar Schmidt Camera
- PCC: see POEMMA
- PCEB (post-common-envelope binary): binary star system showing unusual stellar evolution
- PCS (Penrose Compton scattering): type of Compton scattering within a black hole's ergosphere
- PCS: see Hubble Space Telescope
- PdBI (Plateau de Bure Interferometer): 6-dish interferometer in French Alps
- PHIBSS: survey of CO in distant galaxies
- PdBI Arcsecond Whirlpool Survey (PAWS): survey of GMCs in M51a
- PDE (partial differential equation): equation constructed as if the variables differentiated are independent
- PDF (probability density function): shows probability of taking a particular value from a continuous range
- PDM (phase dispersion minimization): particular method of finding periodic components in signal
- Pdot (period derivative): rate of change in the period of an orbit or rotation
- PDR: review checking initial design with requirements
- PDR (photodissociation region): cloud of partially-ionized atomic hydrogen
- PDR: see photodissociation
- PDS (Pico dos Dias Survey): survey aimed to find T-Tauri stars
- PDS: see BeppoSAX
- PDS 456
- PDS 70: T-Tauri star with protoplanetary disk and protoplanet
- PDS 70b: see PDS 70
- PDS 70c: see PDS 70
- PE (pointing error): discrepancy in telescope's aim
- PE (potential energy): an object's energy that can be released
- Pe: see rare designator prefixes
- pE (reduction potential): measure of a chemical species' tendency to acquire electrons
- pea (pea galaxy): small greenish galaxy
- pea galaxy: small greenish galaxy
- peak amplitude (amplitude): the height of a wave
- peak epoch (peak star-formation epoch): around 10 billion years ago when star formation peaked
- peak epoch of star formation (peak star-formation epoch): around 10 billion years ago when star formation peaked
- peak galaxy-formation epoch: see peak star-formation epoch
- peak star-formation epoch: around 10 billion years ago when star formation peaked
- peak star-formation era (peak star-formation epoch): around 10 billion years ago when star formation peaked
- peak-to-peak amplitude: see amplitude
- peak-to-valley wavefront error: see wavefront error
- Pearson moment
- kurtosis: measure of the probability of a distribution's tails
- Pearson's chi-squared test (chi-squared test): statistical significance test
- pebble: term sometimes used for solid objects from cm to meter size
- pebble accretion: accretion of pebble-sized solids to a planetary embryo
- pebble accretion: see accretion
- pebble accretion: see planet formation
- pebble: term sometimes used for solid objects from cm to meter size
- pebble isolation mass: see isolation mass
- pec (peculiar galaxy): galaxy with out-of-the-ordinary features
- peculiar
- spectral type: classification of stars based upon spectral features
- peculiar galaxy: galaxy with out-of-the-ordinary features
- peculiar galaxy: see galaxy merger
- NGC 7727: irregular galaxy with two SMBHs
- peculiar motion (peculiar velocity): velocity with respect to local rest
- peculiar star (chemically peculiar star): star with SED showing presence metals unusual for stars
- peculiar velocity: velocity with respect to local rest
- peculiar velocity diagram: see velocity-metallicity relation
- Peking University
- Kavli Institute: any of a number of science institutes supported by Kavli Foundation
- Pellet: see rare designator prefixes
- Pencil Nebula: see Vela supernova remnant
- Penrose Compton scattering: type of Compton scattering within a black hole's ergosphere
- Penrose mechanism (Penrose process): process by which energy can be extracted from black hole's rotation
- Penrose pair production: see Penrose Compton scattering
- Penrose photoproduction process: see Penrose Compton scattering
- Penrose Process
- Penrose process: process by which energy can be extracted from black hole's rotation
- PEP: survey aimed at star formation in early times
- PEP: see JUICE
- PEP: see photometry
- PEPE: see Deep Space 1
- PEPSI: see Large Binocular Telescope
- PEPSSI: see New Horizons
- periapse: see apsis
- periapsis: see apsis
- eccentricity: degree to which an orbit is non-circular
- mean anomaly: angle describing an object's position within an elliptical orbit
- periastron: see apsis
- pericenter: see apsis
- pericentric passage: see quenched galaxy
- perigalacticon: see apsis
- perigee: see apsis
- perihelion: see apsis
- period: see frequency
- period derivative: rate of change in the period of an orbit or rotation
- P-Pdot diagram: diagram comparing the rotation and the slowing of pulsars
- period-luminosity relation: see Cepheid variable
- period-luminosity-color relation: see Cepheid variable
- period-mean density relation: see Cepheid variable
- Period04: software to identify periods in time series data
- periodic table of the elements: see atomic number
- Perkins Telescope: see Lowell Observatory
- Mimir: multi-function near-infrared instrument on Perkins Telescope
- permafrost
- Mars: well-explored planet in the solar system
- polygonal ground: crack pattern in ground forming polygons due to freezing
- permeability: ability of a material to allow fluids to pass through it
- Perseus Arm: see spiral arm
- Perseus Cluster: large galaxy cluster in the Perseus-Pisces Supercluster
- galaxy cluster: large group of galaxies gravitationally-bound to the group
- Perseus Complex: see Taurus-Auriga Complex
- Perseus Molecular Cloud: see Taurus-Auriga Complex
- Perseus-Pisces Supercluster: nearby supercluster
- Perseverance: see Mars 2020
- MMRTG: power source for space probes
- perturbation: see perturbation theory
- J2: geopotential coefficient regarding a planet's oblateness
- perturbation theory: breaking an equation into a solvable part and approximable part
- Peru
- TAMBO: concept for neutrino detector in valley in Peru
- peryton: see fast radio burst
- PESSTO: NTT survey following up on transients
- PETIT: see atmospheric model
- Petzval field curvature (field curvature): focusing to a curved surface rather than a plane
- PF-QHY: see William Herschel Telescope
- Pf1: see Green Bank Telescope
- PF2: see Green Bank Telescope
- PFA: see eXTP
- PFC: see Isaac Newton Telescope
- PFC: see POEMMA
- PFCam: see Shane Telescope
- PFIP: see William Herschel Telescope
- Pfleiderer: see rare designator prefixes
- PFS (Subaru PFS): multi-object spectrograph in development for the Subaru telescope
- PFS: see Magellan Telescopes
- PFS: see Mars Express
- PFS: see Subaru Telescope
- PFS: see Venus Express
- PFS Subaru Strategic Program: see Subaru PFS
- PFUEI: see Hale Telescope
- Pfund series: hydrogen lines for electrons settling from n > 5 to n = 5
- hydrogen: most prominent element, atomic number 1
- PG (Palomar-Green Survey): list of objects with excess ultraviolet light
- PG 1159 star: star in transition between planetary nebula and white dwarf
- PG 1159-035: see PG 1159 star
- PG 1302-102: galaxy possibly with binary SMBH
- PGC (Principal Galaxies Catalog): modern catalog of more than 70k galaxies
- LEDA: galaxy database with observation data
- PGC 10217
- PGC 3234374 (Comet Galaxy): unique spiral galaxy in cluster Abell 2667
- PGC 63287 (Sagittarius Dwarf Irregular Galaxy): most distant galaxy in the Local Group
- PGC 9892: see IC 342
- PGC54559 (Hoag's Object): peculiar ring galaxy
- PH (Planet Hunters): crowdsourcing website to identify galaxy types from surveys
- pH (acidity): measure of the activity of hydrogen ions in a solution
- PH3: see phosphorus
- PHA: see near-Earth object
- PHANGS: set of surveys of nearby galaxies
- Phantom Galaxy (Messier 74): easily-observed spiral galaxy
- PHARO: see Hale Telescope
- phase: see phase curve
- phase angle: view angle of reflected light implied by the phase of the Moon
- phase curve: brightness of an object according to its phase angle
- phase curve: brightness of an object according to its phase angle
- phase dispersion minimization: particular method of finding periodic components in signal
- phase integral: see phase space
- phase line: see phase space
- phase plane: see phase space
- phase plate: filter that changes the phase of light passing through
- phase space: space of all possible states of a system
- phase transition: transformation from one state of matter to another
- phased array: method of using a set of antennas directionally
- phased array feed: see phased array
- PHAT: HST survey of M31 stars
- PHEBUS: see GRANAT
- PHI: see Solar Orbiter
- PHIBSS: survey of CO in distant galaxies
- PHIBSS1 (PHIBSS): survey of CO in distant galaxies
- PHIBSS2: see PHIBSS
- Philae: see Rosetta
- Phillips relation
- Phillips relationship
- PHL (Palomar-Haro-Luyten Catalog): 1960s catalog of faint blue stars
- PHO: see near-Earth object
- Phobos
- Mars: well-explored planet in the solar system
- MMX: Japanese probe to bring back a sample of a Martian moon
- moon: a planet's natural satellite, such as Earth's
- Phocaea
- PHOENIX (PHOENIX stellar model): computer model of a stellar photosphere
- BT-Settl: model atmosphere of small stars and brown dwarfs
- Phoenix: Mars polar-region probe launched by NASA in 2007 with lander
- Phoenix: see Gemini Observatory
- PHOENIX code (PHOENIX stellar model): computer model of a stellar photosphere
- PHOENIX stellar model: computer model of a stellar photosphere
- Phoenix stream
- Pholus
- centaur: asteroid-like body orbiting among the outer planets
- phone number: colloquial expression for coordinates
- phonon: see quasiparticle
- phosphine: see phosphorus
- phosphor: see fluorescence
- phosphorescence: see fluorescence
- phosphorus: metal, P, atomic number 15
- phoswich: see BeppoSAX
- photino: see supersymmetry
- photo-electric photometer: see photometer
- photo-electric photometry: see photometer
- photo-z (photometric redshift): method of estimating redshift without spectroscopy
- photocathode: type of device producing free electrons from photons
- photocell
- photodiode: class of solid state device to detect EMR
- photochemistry: study of the chemical effects of light
- photodecomposition (photodissociation): chemical reaction in which photons break chemical bonds
- photodiode: class of solid state device to detect EMR
- photodisintegration: breakdown of a nucleus by a gamma ray
- photodissociation: chemical reaction in which photons break chemical bonds
- radiolysis: similar to photodissociation from higher energy photons
- photodissociation clouds: see photodissociation
- photodissociation front (photodissociation region): cloud of partially-ionized atomic hydrogen
- photodissociation region: cloud of partially-ionized atomic hydrogen
- photodissociation region: see HII region
- photodissociation region: see photodissociation
- photoelectric effect: see photoionization
- electron: type of lepton that is stable and has an electric charge of -1
- scintillator: instrument part designed to respond to high-energy photons
- photoelectric photometry: see photometry
- photoelectron: see electron
- photoevaporation: dispersal of a gas from UV radiation
- Fulton gap: planets with radius 1.5 to 2 Earth radii are rare
- photofission: see photodisintegration
- photographic magnitude: magnitude derived from photographic plate
- photographic plate (plate): product of astronomical photography
- plate scale: relation between angle and distance across an image
- photographic zenith tube: telescope permanently mounted to the zenith
- photography
- photoheating
- photoionization: photon striking neutral atom expelling an electron
- photoluminescence: see fluorescence
- photolysis (photodissociation): chemical reaction in which photons break chemical bonds
- photometer: instrument measuring brightness
- Photometric LSST Astronomical Time-series Classification Challenge
- photometric parallax: see spectroscopic parallax
- BATC: photometric survey of Milky Way stars
- photometric redshift: method of estimating redshift without spectroscopy
- photometric system: specification of a set of filters/passbands
- photometric systems
- passband: range of electromagnetic wavelengths that a filter allows
- photometric Type Ia supernova: see Type Ia supernova
- photometric-standard star: see photometry
- photometry: studying starlight using optical filters
- photomultiplier (photomultiplier tube): electronic device to detect light
- photomultiplier tube: electronic device to detect light
- photon: quantum of light, i.e., light as a particle
- baryon: protons, neutrons, and other three-quark particles
- particle: very small thing
- photon energy: the energy carried by a single photon
- quantum: minimal amount of something that triggers a reaction
- standard model: model of elementary particles including quarks
- supersymmetry: extension to standard model of particle physics
- photon counter: see photon counting
- photon counting: sensing EMR down to the photon level
- photon decoupling: see decoupling
- recombination: time when the universe's ionized hydrogen atoms neutralized
- photon energy: the energy carried by a single photon
- frequency: number of cycles per unit of time, such as waves per second
- photon: quantum of light, i.e., light as a particle
- wavelength: distance over which a repeating wave repeats
- photon epoch (radiation era): early-universe era when radiation pressure dominated
- recombination: time when the universe's ionized hydrogen atoms neutralized
- photon era (radiation era): early-universe era when radiation pressure dominated
- photon noise: variation in light measurement due to its quantum nature
- photon ring: see black hole shadow
- photon scattering: see scattering
- photon sphere: surface surrounding black hole where photons can orbit
- photon-assisted tunnelling: see superconducting tunnel junction
- photon-dominated region (photodissociation region): cloud of partially-ionized atomic hydrogen
- photon-dominated region: see photodissociation
- photon-photon pair production: see pair production
- photons
- photosphere: layer of star from which light propagates
- photospheric radius expansion: see X-ray burster
- PHR: see MASH Catalog of Planetary Nebulae
- PHWB: see wide binaries
- physical baryon density: see Lambda-CDM model
- physical cosmology: see cosmology
- physical dark matter density: see Lambda-CDM model
- physical double: see optical double
- physical field: physical property of some volume of space
- physical libration: see libration
- Enceladus: Saturn moon considered possible carrier of life
- physics
- 1H: hydrogen isotope with no neutrons
- absorption: removal of photons from a beam of EMR
- absorption coefficient: measure of how much light a substance absorbs
- Alfvén wave: a type of transverse wave along magnetic field lines in plasma
- alpha particle: essentially a helium nucleus produced by radioactivity
- angstrom: unit of length 10-10 meters
- anisotropy: directional-dependence such as temperature variation around the CMB
- anti-de Sitter space: type of curved space
- antimatter: similar to normal matter but with opposite electrical charge
- arXiv: website with physics paper preprints
- astrophysical neutrino: neutrino from other than Earth or the usual sources
- astrophysics: physics applied to astronomy
- atm: unit of pressure
- atomic excitation: electrons above the ground state within atoms
- atomic number: number of protons in an atomic nucleus
- Auger effect: atom's emission of an electron along with a photon
- axion: proposed light, electrically neutral elementary particle
- Axion Dark Matter Experiment: a search for axions as potential dark matter particles
- barycenter: center of mass of two orbiting bodies
- baryon: protons, neutrons, and other three-quark particles
- baryonic matter: ordinary matter made up of protons and neutrons
- beat frequency: frequency emerging from two other frequencies
- beta: ratio of plasma pressure to magnetic pressure
- beta decay: radioactivity such that an electron or positron is emitted
- Big Bang nucleosynthesis: creation of atomic nuclei in the very early universe
- bigravity: modifications to GR defining two metrics
- binding energy: energy needed to separate two objects
- Birkhoff's theorem: shows GR qualities of a spherically-symmetric mass
- black body: idealized object that reflects no light
- black hole: region of such high mass that light cannot escape
- black hole thermodynamics: science of black holes
- black-body radiation: EMR with a characteristic spectrum due to the temperature of a body
- black-hole information paradox: a behavior of black holes that appears to contradict physics
- blastwave: spherical shock wave from a small volume
- blended spectra: an observed spectrum comprising light from multiple objects
- Bogolyubov Institute for Theoretical Physics: Ukrainian research institute
- Bohr model: has electrons circling nucleus in quantized orbits
- bolometric luminosity: total luminosity of an object at all wavelengths
- Boltzmann constant: relates particle energy and temperature
- Boltzmann equation: equation relating atomic excitation to temperature
- Boltzmann transport equation: equation for evolving distribution of gas particles
- Bondi radius: radius within which a body moving through a medium will draw it in
- Bose-Einstein condensate: rare state of matter possible at cryogenic temperatures
- Bose-Einstein statistics: possible distribution of particles not bound by Pauli exclusion
- bow shock: shock wave of a magnetosphere through the surrounding medium
- brane: mathematical object with dimensions
- chemical equilibrium: state where chemical makeup is unchanging
- Cherenkov radiation: radiation from the shock of a charged particle passing through a medium
- Chern-Simons gravity: one type of modified general relativity
- chirp mass: a reduced-mass-like quantity that relates to gravitational waves
- circular polarization ratio: ratio of circular polarization handedness in reflected radar signal
- complex number: type of number that can be the square root of a negative number
- Compton scattering: photon collision with a charged particle that emits a different photon
- Compton wavelength: lower bound on a particle's possible de Broglie wavelength
- conformal field theory: a type of quantum field theory
- conservation law: property that remains unchanged by physical phenomena
- continuous gravitational wave: long-lasting repeating GWs such as from orbits
- continuum emission: continuous spectrum such as black-body radiation or bremsstrahlung
- convection: a heated fluid's flow due to its low density and buoyancy
- cooling function: function relating a gas's cooling rate to its temperature
- Coriolis force: apparent force in a rotating frame of reference
- cosmic string: rent in spacetime
- cosmic web: hypothesized structure of the dark matter throughout the universe
- cosmological constant: force counteracting the universe's inward gravitational pull
- cosmological time dilation: very distant events appear to take longer
- Coulomb's law: static electrical force relation
- cross section: "area" representation of probability of an interaction of particles
- Cryogenic Dark Matter Search: a search for a candidate dark matter particle
- Cryogenic Rare Event Search with Superconducting Thermometers: a search for a candidate dark matter particle
- CUORE: experiment to sense neutrinoless double beta decay
- curvature radiation: synchrotron-like radiation when particles follow curved field lines
- cyclotron radiation: radiation emitted when charged particles are accelerated
- cyclotron radiation emission spectroscopy: method of measuring the KE of beta particles
- dalton: mass unit used on atomic scale
- dark energy: energy theorized to accelerate the expansion of the universe
- dark matter: matter in galaxies and galaxy clusters suggested by their gravity
- dark matter filament: hypothesized type of long, thin volume of dark matter
- dark matter halo: hypothetical dark matter throughout and surrounding a galaxy
- de Broglie wavelength: wavelength of a particle's matter wave
- Debye length: length scale of screening effects within a plasma
- Deep Underground Neutrino Experiment: neutrino experiment under construction
- degeneracy: general word meaning a violation of normal rules
- degeneracy weight: number of quantum states with same energy level
- degree of ionization: fraction of material consisting of ions
- detonation: ignition propelled by a shock wave
- deuterium: hydrogen isotope with one neutron
- DGP gravity: alternative theory of gravity addressing "dark energy"
- diffraction: an effect of the edge of an obstacle on a wave
- diffraction limited: telescope limited only by the laws of diffraction
- diffusion: the spreading of particles toward an even distribution
- dipole: field with two poles
- discontinuous Galerkin method: computational method for PDEs handling discontinuities
- Doppler shift: wave frequency difference due to relative velocity difference with source
- dynamical friction: drag produced by gravitational interaction with surrounding objects
- dynamical instability: situation where a perturbation makes itself larger
- dynamo: mechanism for generating magnetic fields around astronomical bodies
- e-folding time: time to increase by a factor of e
- Eddington approximation: approximation of a star's internal EMR's divergence from isotropic
- Eddington luminosity: maximum luminosity at which radiation force overcomes gravity
- effective field theory: type of useful simplification of a field theory
- effective temperature: temperature of an equivalent black body in terms of total radiation
- eigen-decomposition: useful type of factoring a matrix into the product of three
- eigenmode: vibration mode of an oscillator where all parts move at the same frequency
- eigenvalue: ratio between a vector and a linear transformation of that vector
- Einstein coefficients: a substance's probabilities of emission and absorption
- Einstein delay: EMR delay due to relativistic effects of environment and motion
- Einstein-de Sitter model: universe tuned to the smallest expansion that continues forever
- electric field: electric force as distributed over a space
- electromagnetic radiation: radiation such as light, radio, X-rays
- electromagnetic spectrum: spectrum of EMR
- electromagnetism: electricity and magnetism and their interaction
- electron: type of lepton that is stable and has an electric charge of -1
- electron degeneracy: electrons set free of atoms by the Pauli exclusion principle
- electron degenerate matter: dense matter such as that in white dwarf
- electron orbital: a nucleus's "locations" where an electron can orbit
- electron pressure: the electron contribution to pressure within a plasma
- electron scattering: any process that changes the course of an electron
- electron screening: reduction of effective charge of a nucleus by nearby electrons
- electron shell: radius-level around an atomic nucleus at which electrons can orbit
- electron volt: very small unit of energy
- electroweak: single conception including both electromagnetic and weak forces
- element: class of atom based on its number of protons
- emission: addition of photons to a beam of EMR
- emission coefficient: measure of how much light a substance emits
- endothermic reaction: reaction that absorbs heat
- energy: physical state needed to do something
- energy density: energy per unit volume
- entropic gravity: MOND-like theory of gravity
- entropy: relative measure of the amount of usable energy available
- equation of radiative transfer: equation describing energy transfer by EMR
- equation of state: equation relating temperature, pressure, and volume
- equilibrium temperature: temperature a planet would have if it were an externally-heated black body
- erg: CGS unit of energy
- evaporation: particles escaping, e.g., liquid molecules escaping as gas
- EXO: experiment to detect neutrinoless double beta decay in xenon
- expansion fan: the "sound" of a supersonic flow flowing around a convex corner
- f(R) gravity: class of modifications to general relativity
- false vacuum: apparent QFT vacuum
- field lines: lines showing the pattern of a mathematical field
- finite difference method: means of estimating calculus and differential equation solutions
- finite element method: computational method for PDEs suited to physical problems
- finite volume method: computational method for PDEs especially suited to fluid dynamics
- flavor: subtype of some type of particle
- fluorescence: emission from a molecule excited by absorption
- flux: flow rate per unit area
- flux freezing: magnetic field lines becoming attached to plasma they pass through
- forbidden line: spectral line that quantum mechanics disallows for the most part
- fractionation: separation of one chemical mixture into others
- fractionation factor: isotope-related ratio
- frame of reference: region, possibly in motion, from which something is observed/considered
- free streaming: particles moving long distances without disturbance
- Friedmann model: type of model of universe incorporating general relativity
- fusion: formation of an atomic nucleus nuclei from multiple smaller nuclei
- Gamow peak: relative speed most likely to cause atoms to fuse within a gas
- gas flow: dynamics of gas, plasma, i.e., compressible fluids
- gauss: measurement of magnetic field β
- general relativity: formula relating gravity, space, time, and mass
- Godunov scheme: computational fluid dynamics method
- gravitational collapse: shrinking of an object from gravitational force
- gravitational constant: indicates how much pull between two masses
- gravitational field: gravitational force as distributed over a space
- gravitational potential: conceptual field indicating the strength of gravity at each point
- gravitational potential energy: energy implied by some mass being some distance from another
- gravitational potential model: mathematical model of an astronomical body's gravitational field
- gravitational potential well: a dip in the gravitational-potential field
- gravitational singularity: point where density and gravity reach infinity
- gravitational wave: ripples in the curvature of spacetime propagating as a wave
- gravitational wave background: combination of weak gravitational waves such as from distant sources
- gravitational wave spectrum: various frequencies of gravitational waves
- gravitational wave strain: a measure of the magnitude of a gravitational wave
- gravitational-wave memory: a gravitational wave that does not return
- gravitationally bound: description of objects kept together by gravity
- gravitomagnetic field: magnetic-like-field produced by gravitation
- gravity: theory that mass attracts
- gravity wave: wave in fluid where restoring force is gravity
- gray body: ideal object that reflects the same fraction of light at any wavelength
- greenhouse effect: mechanism that boosts temperature through selective blocking of EMR
- ground state: lowest energy level
- Hall effect: voltage generated by interacting current and magnetic field
- Hanle effect: effect of magnetic field on the polarization of emitted photons
- Hartle-Thorne metric: metric approximating GR effects of slow neutron star rotation
- Hawking radiation: EMR theorized to be emitted by black holes, powered by their mass
- heating: increasing the velocity of particles
- Heisenberg uncertainty principle: limit on observable position and momentum of an object
- HERMIT: code to carry out N-body simulations
- holographic duality: notion that all the physics of three dimensions can be described in two
- homologous collapse: collapse such that the increasing density remains uniform
- hydrodynamics: study of fluids in motion
- hydrostatic equilibrium: state of a fluid body when forces are such that the fluid is at rest
- hyperon: exotic type of baryon
- ice: solid state of water
- ideal gas law: relates pressure, temperature, and volume
- Immirzi parameter: theoretical value relating black hole to its entropy
- intensity: power reaching a surface from a specific source
- interference: result of interaction of waves
- interferometer: device detecting EMR properties using interference between waves
- internal gravity wave: ripples in a change in density in a fluid
- inverse square law: a value's dependency upon reciprocal of the square of the distance from something
- ion: non-neutral atom or molecule, with missing or extra electrons
- ionization potential: energy needed to ionize an atom
- isothermal core: core region of a body of all the same temperature
- isotope: subclass of an element with a specific number of nucleons
- jansky: unit of measurement of spectral flux density
- jet: stream of matter from an astronomical body
- Johannsen-Psaltis metric: metric template allowing metrics to be written as a general expansion
- joule: SI unit of energy
- kappa distribution: one distribution of velocities of particles out of equilibrium
- kappa mechanism: stellar instability caused by opacity increasing with temperature
- KATRIN: experiment to measure neutrino mass
- Kelvin-Helmholtz mechanism: release of energy from gravitational collapse
- Kerr-NUT spacetime: Kerr spacetime defined in terms of Taub-NUT spacetime
- kinetic energy: an object's energy due to its motion
- Kirchhoff's law of thermal radiation: for an object in thermodynamic equilibrium, emissivity equals absorptance
- Kirchhoff's laws: laws regarding the source of spectral lines
- Klein-Nishina formula: formula for the effects of electrons scattering photons
- Kramers opacity law: opacity's relation to density and temperature
- kugelblitz: theoretical black hole arising from a high radiation density
- Landau damping: type of damping of waves that occurs in thin plasma
- lattice Boltzmann method: computational fluid dynamics method treating the fluid as particles
- Lense-Thirring effect: effect on precession from frame dragging
- lepton: elementary particle with 1/2 integer spin such as electron
- Lorentz force: force on a point charge due to magnetic fields
- Lorentz transformation: equations describing the effect of relative motion on length and velocity
- Lorentzian distribution: probability distribution applicable to some physics phenomena
- Love number: measures of rigidity of a body
- Lovelock gravity: generalization of general relativity
- Lyapunov time: timescale beyond which a dynamical system is chaotic
- Mach number: ratio of flow-speed to sound-speed
- Mach's principle: the notion that rotation is relative to all the mass of the universe
- magnetic energy spectrum: spatial spectral density of the energy associated with magnetic fields
- magnetic field: magnetic force as distributed over a space
- magnetic field strength: a field associated with magnetism
- magnetic flux: measure of magnetism passing through a surface
- magnetic flux density: vector field describing magnetism in relation to the Lorentz force
- magnetic induction: voltage across a conductor induced by changing magnetic field
- magnetic reconnection: change in magnetic topology within a fluid
- magnetohydrodynamics: dynamics of electrically conducting fluids
- magnetorotational instability: instability in the fluid of a disk from MHD effects
- magnetosonic wave: a type of sonic wave in a plasma
- Majorana particle: theoretical particle that is its own antiparticle
- mass: object's quality that determines the effects of forces and gravity
- mass number: number of nucleons in an atomic nucleus
- mass ratio: ratio of masses of two objects such as a binary star
- mass spectrometer: device to determine the mass of molecules in a mixture
- Maxwell's equations: four equations describing electricity and magnetism
- Maxwell-Boltzmann distribution: distribution of velocities of gas particles
- mean free path: average length that a particle travels before interaction
- mechanics: the science of forces and motions
- membrane paradigm: simplified black-hole model enabling calculation of some effects
- MERCURY: code to carry out N-body simulations
- metallic hydrogen: a high-pressure state of hydrogen that is conductive
- metric: mathematical generalization of the concept of distance
- Michelson interferometer: device to measure small changes in distance or light speed
- Mikheyev-Smirnov-Wolfenstein effect: effect of matter on neutrino oscillation
- modified Newtonian dynamics: alternative theory to "dark matter"
- moment of inertia factor: characterization of mass distribution within a planet
- nanohertz gravitational waves: size of GWs that pulsar-timing observations might catch
- NBODY: code to carry out N-body simulations
- neutrino: light, electrically neutral elementary particle
- neutrino oscillation: neutrinos regularly morph into another flavor
- neutrinoless double beta decay: possible type of rare beta decay
- neutron: type of baryon that is stable and has no electric charge
- neutron capture: combination of an atomic nucleus and a neutron
- neutron degenerate matter: matter made up primarily of neutrons
- neutron scattering: scattering of neutrons by atomic nuclei
- neutron spectrometer: device determining the energy of received free neutrons
- Newton's laws: physical laws of dynamics and gravitation
- no-hair theorem: proposition that a black hole only has mass, rotation, and charge
- non-thermal emission: EMR not due to a body's heat
- nuclear energy generation rate: fusion power per unit mass
- nucleon: proton or neutron
- nucleosynthesis: creation of atomic nuclei
- nuclide: atomic nucleus associated with a specific isotope
- observable: any physical phenomenon that you can detect
- Ohmic heating: heating resulting from an electric current through a material
- opacity: a measure of opaqueness of a material
- optical depth: a measure of opaqueness of a path of light
- oscillator strength: fraction expressing QM's contribution to the probability of absorption
- partial differential equation: equation constructed as if the variables differentiated are independent
- particle: very small thing
- particle physics: physics such as carried out in accelerators
- particle spectrometer: device to determine the characteristics of incoming particles
- partition function: scale factor for Boltzmann factors
- Pauli exclusion principle: fermions in a quantum system cannot have identical quantum numbers
- Penrose Compton scattering: type of Compton scattering within a black hole's ergosphere
- phase space: space of all possible states of a system
- phase transition: transformation from one state of matter to another
- photoevaporation: dispersal of a gas from UV radiation
- photoionization: photon striking neutral atom expelling an electron
- photon: quantum of light, i.e., light as a particle
- physical field: physical property of some volume of space
- PICO experiment: a search for a candidate dark matter particle
- pion: first type of meson discovered
- Planck constant: quantum of action in quantum mechanics
- Planck function: yields black-body spectrum curve
- Planck units: a set of units based on Planck constant and other fundamental constants
- plasma: state of matter in which atoms are separate and ionized
- plasma frequency: frequency of electron plasma oscillation
- plasma wave: wave incorporating the EM forces within plasma
- Poisson's equation: relates one function's Laplacian to another function
- polarization: property of waves that oscillate in a particular direction
- polarization modes: curl- and divergent-like components of CMB polarization patterns
- positron: electron-like antimatter particle with electric charge of +1
- potential energy: an object's energy that can be released
- Poynting vector: measures directional energy flux density
- primordial black hole: black holes forming at the most dense volumes when inflation ceased
- primordial gravitational waves: gravitational waves formed in the early universe
- Project 8: experiment in development to measure neutrino mass
- proton: type of baryon that is stable and has an electric charge of +1
- Q factor: measure of oscillator's damping
- quadratic field strength: a measure of a star's varying magnetic field
- quantum: minimal amount of something that triggers a reaction
- quantum field theory: reworking of quantum mechanics incorporating fields
- quantum mechanics: modern mechanical theory of small things, on the scale of atoms
- quantum mixing: means by which one particle spontaneously changes to another
- quantum number: number representing a conserved quantity
- quantum system: situation in which quantum theory applies
- quantum tunneling: quantum mechanical effect of particles passing through a barrier
- quark: type of elementary particle incorporated in protons and neutrons
- quark matter: matter not made of protons and neutrons but of quarks
- quark-gluon plasma: extreme-temperature state of matter
- quasiparticle: disturbance that acts like a particle
- radiation hydrodynamics: hydrodynamics plus the effects of EMR
- radiative transfer: energy transfer in the form of electromagnetic radiation
- radioactive dating: determining the age of a substance that has a radioactive component
- radioactive decay: changes in atomic nuclei that happen over time
- radioactive heating: a source of heat of some planets and moons
- radioactivity: an unstable nucleus's tendency to change through emission of particles
- radiometer equation: shows how long to observe a radio source
- ram pressure: pressure on a body moving through a fluid
- Rayleigh-Jeans law: yields approximation of black-body curve useful at low frequencies
- REBOUND: code to carry out N-body simulations
- reduced mass: the reciprocal of the sum of the reciprocals of the masses of two objects
- refractory material: material with high condensation temperature
- relativistic effect: a substantial fraction of the speed of light
- relativistic energy: energy of an object including relativistic effects
- relativistic invariance: quantity that remains the same regardless of frame of reference
- relativistic momentum: momentum of an object including relativistic effects
- relativistic speed: a substantial fraction of the speed of light
- relativity: physics models accommodating the constancy of the speed of light
- relaxation time: time associated with exponential falloff
- rest wavelength: normal wavelength observed when not moving in relation to the source
- runaway process: a process with positive feedback so progress speeds progress
- Sagnac effect: an effect of the movement of light beams regarding their interference
- Saha equation: equation relating ionization to temperature
- Salpeter timescale: timescale for black hole growth
- scalar-tensor gravity: GR-like gravity that incorporates a scalar field
- scattering: changing the direction of a particle's movement
- Schrödinger equation: quantum-mechanical wave-equation-like equation
- Schrödinger-Poisson equation: Schrödinger equation including a term for gravity
- Schuster-Schwarzschild model: simplified model of a star's production of absorption lines
- sedimentation: settling of heavier material to the bottom
- self-absorption: EMR absorption by the same substance that emitted it
- self-gravitation: gravitational force holding a body together
- Shapiro delay: EMR delay due to passing near massive object
- shock wave: abrupt propagating disturbance in a fluid
- siderophile: material that dissolves in molten iron
- siemens: SI unit of electrical conductance
- solar constant: flux from the Sun at 1 AU
- sound speed: speed at which compression waves traverse a gas
- source function: measure indicating the effect of a material on EMR passing through
- spacetime: four dimensions: time and the three space dimensions
- Special Breakthrough Prize: Breakthrough Prize award in addition to the year's annual awards
- special relativity: physics explaining how the speed of light can be constant
- specific heat: ratio of added temperature to added heat for a material
- specific intensity: intensity per unit wavelength or frequency
- specific volume: ratio of volume to mass
- spectral energy distribution: function or plot of brightness at each wavelength in the spectrum
- spectral line energy distribution: function or plot of brightness of lines in a spectrum
- speed of light: fundamental constant measured as the speed at which light travels
- spin: an angular-momentum quantum number
- spiral density wave: spiral structure that can form in disks
- standard model: model of elementary particles including quarks
- Stark effect: electric field influence on spectral lines
- state of excitation: energy level of something above the minimum
- state of ionization: difference in an ion's electron count versus proton count
- statistical mechanics: mechanical behavior based upon probability
- Stefan-Boltzmann constant: relates radiation power to temperature and surface area
- stellar-mass black hole: black hole that is a stellar remnant
- stimulated emission: emission triggered by received photons
- string theory: type of physics theory bringing together current models
- strong force: force that holds quarks and nuclei together
- strong-field gravity: gravity much stronger than in the solar system such as near a black hole
- sublimation: single material phase transition from solid to gas
- supercooling: cooling water below freezing point without it freezing
- supercritical fluid: state of matter at sufficient pressure and temperature
- supergravity: combination of general relativity and supersymmetry
- superluminal motion: faster-than-light movement
- superstring theory: version of string theory including supersymmetry
- supersymmetry: extension to standard model of particle physics
- suprathermal: having more energy than would be created by thermal excitation
- symmetry breaking: loss of symmetry, such as due to loss of stability in a regime change
- synchrotron radiation: radiation emitted when high-speed charged particles are accelerated
- synchrotron self-Compton: charged particle cloud scattering its own synchrotron-produced photons
- tau neutrino: neutrino flavor that becomes a tau particle during interactions
- Taub spacetime: early 1950s model for a rotating-black-hole spacetime
- Taub-NUT spacetime: early mathematics for a rotating black hole spacetime
- telegrapher's equations: two equations describing a transmission line
- temperature: measure of hotness/coldness of matter
- tesla: unit of magnetic flux density
- theoretical modified GR metric: metric devised to define modifications to GR
- Theory of Everything: single law explaining the four forces of nature
- theory of figures: type of model relating a planet's shape to its rotation
- thermal emission: EMR due to a body's heat
- thermal equilibrium: state of a system with no net heat flows
- thermal inertia: a measure of a material's ability to absorb heat through conduction
- thermal runaway: situation where heat triggers more heat production
- thermodynamic equilibrium: state of a system with no net heat flows
- thermodynamics: physics of heat and energy
- Thomson optical depth: a measure of effects of Thomson scattering
- Thomson scattering: elastic scattering of photons by a charged particle
- tidal force: effect of a third body on the gravitational force between two bodies
- tidal heating: heating due to friction from motions caused by tidal force
- time dilation: relativity's ability to make time differ for different objects
- time standard: method of designating points in time and quantifying time periods
- tomography: observation of sections of a 3D object
- torr: unit of pressure approximating a millimeter of mercury on Earth
- turbulence: irregular flow of a fluid
- turbulent pressure: pressure component due to the presence of turbulence
- twinkling: blinking, apparent movement and color changes of observed stars
- two-stream approximation: approximation of a star's internal EMR's divergence from isotropic
- valley of beta stability: set of isotopes not prone to beta decay
- VHE: 100 GeV or more
- virial parameter: calculated quantity showing whether a cloud is gravitationally bound
- virial theorem: average kinetic energy equals half the average negative potential energy
- viscous dissipation: fluid KE converted to heat due to viscosity
- Vlasov-Poisson equation: equation describing plasma ignoring the magnetic field
- volatile material: material with low condensation temperature
- vortensity: ratio of vorticity to surface mass-density
- vortex: fluid region where the flow is spinning
- water: compound of oxygen atom and two hydrogen atoms
- wave-particle duality: at atomic scale, things act like both particles and waves
- weak interaction: interaction of weak bosons with other atomic particles
- white hole: the inverse of a black hole, into which matter cannot enter
- Wien approximation: yields approximation of black body curve useful at short wavelengths
- Wien's displacement law: relates temperature to wavelength of maximum emission
- Wigner crystal: crystalline phase of matter formed without specific bonds
- worldline: path of an object through space and time
- wormhole: connection between two regions in a curved space
- ZAMO frame: a frame of reference that is not rotating
- Zeeman effect: magnetic field influence on spectral lines
- Physics At High Angular Resolution of Nearby Galaxies (PHANGS): set of surveys of nearby galaxies
- physisorption: see adsorption
- ice: solid state of water
- PI (principal investigator): lead researcher in a scientific endeavor
- pi meson (pion): first type of meson discovered
- Pi of the Sky: survey aimed at finding gamma-ray-burst visual counterparts
- Pi3 Orionis
- F-type star: spectral class of star a bit hotter than then Sun
- PIA: see Giotto
- PIC simulation: method used in simulating plasma
- PICASO: rt code specifically for exoplanet transmission spectroscopy
- PICASSO: see PICO experiment
- PICO (PICO experiment): a search for a candidate dark matter particle
- Pico dos Dias Observatory
- Pico dos Dias Survey: survey aimed to find T-Tauri stars
- PICO experiment: a search for a candidate dark matter particle
- PICO-2L: see PICO experiment
- PICO-40L: see PICO experiment
- PICO-500: see PICO experiment
- PICO-60: see PICO experiment
- PICS: see Mauna Loa Solar Observatory
- PICsIT: see INTEGRAL
- Pierre Auger Observatory: cosmic-ray observatory in Argentina
- piggyback
- commensal mode: telescope usage that accomplishes multiple observations simultaneously
- PILS (ALMA-PILS Survey): millimeter survey of a protostar
- PIMS: see Europa Clipper
- pin-wheel nebula: see WR 104
- pincushion distortion: distortion such that a square shows with concave edges
- pingo: hill formed of ice
- pink noise: see red noise
- Pinwheel Galaxy: easily-observed spiral galaxy
- pion: first type of meson discovered
- pion condensate: see pion
- Pioneer
- Callisto: well-known Jupiter moon
- Europa: well-known Jupiter moon
- Ganymede: well-known Jupiter moon
- gravity sounding: measuring a planet's gravitation field by study of nearby probe flights
- Io: well-known Jupiter moon
- Saturn: second largest planet in the solar system
- Pioneer 12 (Pioneer Venus Orbiter): NASA Venus probe launched 1978
- Pioneer Venus 1 (Pioneer Venus Orbiter): NASA Venus probe launched 1978
- Pioneer Venus Orbiter: NASA Venus probe launched 1978
- PIONIER: see European Southern Observatory Very Large Telescope
- pipeline: set series of tasks to perform on something
- Pis: see rare designator prefixes
- PISCES: see MMT
- PISCeS (Panoramic Imaging Survey of Centaurus and Sculptor): survey of extended halos of two nearby galaxies
- Pisces II
- Pisces Overdensity
- Pisces-Cetus Supercluster: see Pisces-Cetus Supercluster Complex
- Pisces-Cetus Supercluster Complex: large scale structure containing Milky Way
- Pisces-Pegasus Filament: see galaxy filament
- Pisces-Perseus Supercluster
- PISN (pair-instability supernova): type of large supernova
- pixel
- data cube: three-dimensional array of numerical data
- Pixel-lensing Observations with the Isaac Newton Telescope-Andromeda Galaxy Amplified Pixels Experiment (POINT-AGAPE): survey of M31 for microlensing
- PIXIE: satellite-concept to to survey CMB polarization
- PIXL: see Mars 2020
- PK (Catalogue of Galactic Planetary Nebulae): 1967 catalog
- PK67 (Catalogue of Galactic Planetary Nebulae): 1967 catalog
- PKS (Parkes Catalog): catalog of from 1960s-1990 of radio sources in southern hemisphere
- PKS 1302-102 (PG 1302-102): galaxy possibly with binary SMBH
- plage: see chromosphere
- plan
- Planck: microwave telescope in space
- CSA: includes astronomical research
- Planck constant: quantum of action in quantum mechanics
- Planck energy: see Planck units
- Planck function: yields black-body spectrum curve
- Planck hole: see black hole
- Planck length: see Planck units
- Planck mass: see Planck units
- Planck mass: see mass
- Planck relation: see Planck constant
- Planck temperature: see Planck units
- Planck time: see Planck units
- Planck units: a set of units based on Planck constant and other fundamental constants
- Planck units: see Planck units
- Planck's constant (Planck constant): quantum of action in quantum mechanics
- Planck's law (Planck function): yields black-body spectrum curve
- Planckian: see thermal emission
- plane of reference: see orbital element
- plane of the sky: plane tangent to the celestial sphere
- plane parallel wave (plane wave): simplified wave concept useful for modeling
- plane wave: simplified wave concept useful for modeling
- plane-parallel atmosphere: simplified atmosphere model ignoring its curvature around the body
- planemo (planetary mass object): has the mass of a planet
- planes of satellite galaxies problem (satellite plane problem): satellite galaxies inexplicably tend to fall in a plane
- PLANET (Probing Lensing Anomalies Network): survey that recorded microlensing event lightcurves
- MicroFUN: observers following up on microlensing events in the galactic bulge
- planet: round object orbiting a star that clears out its own orbital path
- Earth: third solar system planet from the Sun
- Jupiter: largest planet in the solar system
- Mars: well-explored planet in the solar system
- Mercury: inner-most and smallest planet in the solar system
- Neptune: outer-most solar system planet
- Saturn: second largest planet in the solar system
- Uranus: second outer-most solar system planet
- Venus: second inner-most planet in the solar system
- Planet 10
- Planet 9 (Planet Nine): theoretical planet beyond Neptune
- Planet Crossing Asteroid Survey: search for NEOs using small Palomar Schmidt Camera
- planet demographics: statistics regarding the number of planets
- planet emission: see transit spectroscopy
- planet formation: process by which planets form
- planet formation barrier (barrier): challenging issue regarding planet formation
- Planet Hunters: crowdsourcing website to identify galaxy types from surveys
- Planet Hunters TESS: see Planet Hunters
- planet multiplicity: see planetary system
- Planet Nine: theoretical planet beyond Neptune
- planet occurrence rate (planet demographics): statistics regarding the number of planets
- planet rotation: see rotation period
- planet structure: internal structure of planets
- planet type: classification of a planet regarding some criteria
- Planet X
- planet-disk interaction: see planetary migration
- planet-hosting wide binary: see wide binaries
- planet-planet scattering: see planetary migration
- planetar: see brown dwarf
- planetary boundary layer: low level of atmosphere affected by ground
- planetary differentiation: stratification of the materials making up a planet
- planetary disk (protoplanetary disk): disk of dust and gas around a young star or protostar
- planetary embryo: object that may grow into a future planet
- planetary engulfment: see giant star
- planetary equilibrium temperature (equilibrium temperature): temperature a planet would have if it were an externally-heated black body
- planetary habitability (habitability): ability of a planet to support life
- Planetary Intensity Code for Atmospheric Scattering Observations (PICASO): rt code specifically for exoplanet transmission spectroscopy
- planetary mass object: has the mass of a planet
- planetary migration: change in planet's orbit
- planetary nebula: glowing gas shell ejected by a red giant
- planetary nebula luminosity function: model used in distance estimation
- planetary nebula nucleus: see planetary nebula
- planetary nebula nucleus variable: see planetary nebula
- planetary nebulae
- planetary precession: see precession of the equinoxes
- planetary protection: the principle of avoiding the contamination of planets with Earth life forms
- planetary ring system (ring system): disk or set of rings orbiting a planet
- planetary rotation: see rotation period
- planetary science: study of planet characteristics
- decadal survey: periodic NASA effort to plan for future astrophysical research
- Planetary Science Institute: US research institution
- planetary system: all the planets orbiting a star
- star system: a gravitationally bound set of a few stars
- Planetary Transits and Oscillations of stars (PLATO): planned observatory-satellite aimed at finding exoplanets
- planetesimal: object held together by gravity that combines with others to form planets
- isolation mass: mass of an oligarch after accreting all nearby planetesimals
- planetoid: an asteroid or physically similar body
- PlanetQuest: NASA publicity name for efforts to find exoplanets and life
- PLANETS: see Colossus Telescope
- planets
- Planets Around Low-mass Stars (PALMS): survey to find exoplanets for direct imaging
- planetshine: see earthshine
- planetWRF: see MarsWRF
- plasma: state of matter in which atoms are separate and ionized
- plasma astrophysics: includes cosmology, IGM, ISM, HI regions
- plasma beta (beta): ratio of plasma pressure to magnetic pressure
- plasma filament
- filament: linear volume of high molecular gas density within a galaxy
- plasma frequency: frequency of electron plasma oscillation
- plasma parameters
- plasma wave: wave incorporating the EM forces within plasma
- PlasMag: see DISCOVR
- plasmon: quasiparticle that is quantum of plasma vibration
- plasmon decay: see plasmon
- PLASTIC: see STEREO
- PLAsTiCC
- Platais: see rare designator prefixes
- plate: product of astronomical photography
- comparator: device to compare the position of objects on plates
- plate measuring machine: machine to measure position of images on photographic plates
- plate scale: relation between angle and distance across an image
- plate tectonics: see crustal plates
- dynamo: mechanism for generating magnetic fields around astronomical bodies
- Earth: third solar system planet from the Sun
- very-long-baseline interferometry: interferometry based upon storing timing data at each telescope
- plateau: see supernova light curve
- supernova: stellar explosion larger than a nova
- Plateau de Bure
- Plateau de Bure High-z Blue Sequence Survey (PHIBSS): survey of CO in distant galaxies
- Plateau de Bure Interferometer: 6-dish interferometer in French Alps
- PHIBSS: survey of CO in distant galaxies
- Plateau Observatory for Ridge A: see High Elevation Antarctic Terahertz Telescope
- platinum
- r-process: synthesis of elements through neutron capture faster than beta decay
- PLATO: planned observatory-satellite aimed at finding exoplanets
- PLATO 2.0 (PLATO): planned observatory-satellite aimed at finding exoplanets
- PLATO-R: see High Elevation Antarctic Terahertz Telescope
- Pleiades: visible open cluster with seven B-stars
- plerion (pulsar wind nebula): type of nebula generated by a young pulsar
- PLQ: see double star designation
- PLS (Palomar-Leiden Survey): 1960s survey to identify distant asteroids
- PLS: see Galileo
- PLS: see Voyager
- plug plate: see Sloan Digital Sky Survey
- plutino: see plutoid
- PLUTO (PLUTO Code): fluid-dynamic simulation code
- Pluto: dwarf planet formerly listed as one of the nine planets
- PLUTO Code: fluid-dynamic simulation code
- Pluto Discovery Telescope: see Lowell Observatory
- Pluto Telescope: see Lowell Observatory
- plutoid: Pluto-like dwarf planet
- plutonium-238 dioxide: see MMRTG
- PLX: see General Catalogue of Trigonometric Parallaxes
- PM (proper motion): apparent motion in relation to the position of the Sun
- PM: see rare designator prefixes
- PMAS/PPak
- CALIFA: spectroscopic map of 600 galaxies
- PMC: see Tokyo Photoelectric Meridian Circle
- PMC Catalog: see Tokyo Photoelectric Meridian Circle
- PMF (probability mass function): shows probability of taking one of a number of discrete values
- PMF: see probability density function
- PMIRR: see Mars Observer
- PMMR: see rare designator prefixes
- PMN (Parkes-MIT-NRAO Surveys): 1990 southern-hemisphere radio surveys
- CRATES: catalog of 8.4 GHz data on radio sources
- PMO (planetary mass object): has the mass of a planet
- PMPS (Parkes Multibeam Pulsar Survey): late 1990s radio survey in search of pulsars
- PMS (pre-main-sequence star): star not yet with a nuclear reaction
- Herbig AeBe star: type of pre-main-sequence star more massive than a T-Tauri star
- PMS object (pre-main-sequence star): star not yet with a nuclear reaction
- PMS star
- AB Aurigae: YSO with disk apparently forming planets
- DM Tau: nearby T-Tauri star
- DQ Tau: young binary star system
- Elias 2-27: much-studied YSO
- GG Tau: much-studied quadruple star system
- HD 163296: YSO with gaps in its protoplanetary disk
- HD 169142: protostar with planet
- HL Tau: much-studied T-Tauri star
- PDS 70: T-Tauri star with protoplanetary disk and protoplanet
- RXJ1615: protostar with transition disk showing rings
- TW Hydrae: nearest T-Tauri star
- PMT (photomultiplier tube): electronic device to detect light
- PN (planetary nebula): glowing gas shell ejected by a red giant
- post-AGB star: stellar-evolution phase between AGB and white dwarf
- PN approximation: see post-Newtonian formalism
- PN correction term: see post-Newtonian formalism
- PN formalism (post-Newtonian formalism): method of approximating GR-based mechanics from Newtonian mechanics
- PNe
- PNG (Strasbourg-ESO Catalog of Galactic Planetary Nebulae): 1992 catalog of 1820 objects
- PNLF (planetary nebula luminosity function): model used in distance estimation
- PNN: see planetary nebula
- PNNV: see planetary nebula
- PNS: see neutron star
- PNV: see rare designator prefixes
- POEMMA: planned space cosmic-ray neutrino observatory
- POETS: see Lowell Discovery Telescope
- Poincaré map
- Poincaré section: pattern formed by a the locations an orbiting body passes through a plane
- Poincaré section: pattern formed by a the locations an orbiting body passes through a plane
- point mass: see mass
- point source: celestial object that focuses to a point or single Airy disk
- extended source: term for astronomical object covering some area of the sky
- flux density: measure of the strength of a radio signal
- radio source: astronomical object producing observable radio
- source: astronomical object producing some observed signal
- point source sensitivity: determination of how readily an instrument detects a point source
- point spread function
- PSF fitting: untangling airy disks to gain effective resolution
- point spread function fitting (PSF fitting): untangling airy disks to gain effective resolution
- point spread function subtraction: see point-spread function
- POINT-AGAPE: survey of M31 for microlensing
- point-spread function: function describing an optical system's response to a point of light
- pointed observation: observation of a specific target
- slew survey: survey conducted by imaging during a telescope's repointings
- pointing: the directing of a telescope at a point in the celestial sphere
- pointing error: discrepancy in telescope's aim
- Poisson distribution: statistics on count of events happening within a given interval
- Poisson equation (Poisson's equation): relates one function's Laplacian to another function
- Poisson level: see photon noise
- Poisson noise (photon noise): variation in light measurement due to its quantum nature
- Poisson's equation: relates one function's Laplacian to another function
- POL: see double star designation
- POL-2: see James Clerk Maxwell Telescope
- polar: see variable star
- polar alignment: see circumstellar disk
- polar cell
- Hadley cell: circulation pattern of up at the equator, poleward, down, and back
- polar cyclone: storm centered on the pole
- polar disk: see circumstellar disk
- polar jet (jet): stream of matter from an astronomical body
- polar moment of inertia: see moment of inertia factor
- precession: periodic change in a body's rotation or orbit
- polar moment of inertia factor: see moment of inertia factor
- polar vortex
- Hadley cell: circulation pattern of up at the equator, poleward, down, and back
- Polar-ring Catalog: 1990 catalog of polar-ring galaxies
- polar-ring galaxy: galaxy encircled by a ring of stars
- POLARBEAR: instrument to map CMB polarization
- POLARBEAR-1 (POLARBEAR): instrument to map CMB polarization
- POLARBEAR-2: see POLARBEAR
- POLARBEAR-2: see Simons Array
- polarimeter: see polarimetry
- Mimir: multi-function near-infrared instrument on Perkins Telescope
- POLARBEAR: instrument to map CMB polarization
- QUaD: survey to measure the polarization of the CMB
- QUBIC: survey measuring the polarization of the CMB
- QUIET: survey to measure the polarization of the CMB
- Simons Array: telescope array to map CMB polarization
- SPIDER: 2015 balloon-borne observatory to observe CMB polarization
- SPIRou: CFHT spectropolarimeter for exoplanet research
- Taurus: balloon-borne polarimeter to study the CMB
- Polarimeter to Unify the Corona and Heliosphere (PUNCH): 4 microsatellites to observe the Sun
- polarimetry: measurement of polarization of EMR
- polarization: property of waves that oscillate in a particular direction
- polarization modes: curl- and divergent-like components of CMB polarization patterns
- PIXIE: satellite-concept to to survey CMB polarization
- Polarization Sky Survey of the Universe's Magnetism: see Australian Square Kilometre Array Pathfinder
- Polarized Light from Atmospheres of Nearby Extraterrestrial Systems: see Colossus Telescope
- pole: see dipole
- pole star: star aligned with a planet's axis of rotation
- Polish
- All Sky Automated Survey: Polish survey of 20 million objects brighter than 14 magnitude
- OGLE: survey searching for microlensing transients
- Pi of the Sky: survey aimed at finding gamma-ray-burst visual counterparts
- POLISH2: see Gemini Observatory
- poloidal: see torus coordinates
- polycyclic aromatic hydrocarbon: hydrocarbons consisting of meshes of benzene rings
- polycyclic aromatic hydrocarbon emissions (PAH emissions): infrared emission from polycyclic aromatic hydrocarbons in gas clouds
- polygonal ground: crack pattern in ground forming polygons due to freezing
- polygonal patterned ground (polygonal ground): crack pattern in ground forming polygons due to freezing
- polytrope: see Lane-Emden equation
- specific heat: ratio of added temperature to added heat for a material
- polytropic: see Lane-Emden equation
- POM: see Mauna Loa Solar Observatory
- Pop I (Population I): stars with substantial metallicity
- Pop I star: see Population I
- Pop II (Population II): stars with lower metallicity
- Pop II star: see Population II
- Pop III (Population III): stars with no metallicity
- Pop III star: see Population III
- Population I: stars with substantial metallicity
- Population I star: see Population I
- Population II: stars with lower metallicity
- Population II star: see Population II
- Population III: stars with no metallicity
- Population III star: see Population III
- Population III stars
- population inversion: see atomic excitation
- maser: electromagnetic radiation amplified by stimulated emission
- stimulated emission: emission triggered by received photons
- population statistics (demographics): statistics of characteristics within a group
- population synthesis simulation: see stellar population synthesis
- porosity: fraction of the volume of solid material that is open or void
- POS (plane of the sky): plane tangent to the celestial sphere
- position angle: indication of a direction across the celestial sphere
- position vector (displacement): vector quantity showing the position of one point in relation to another
- position-position space: see position-position-velocity space
- position-position-position space: see position-position-velocity space
- position-position-velocity space: 3D space concept using velocity as one of the three dimensions
- data cube: three-dimensional array of numerical data
- position-velocity space: see position-position-velocity space
- positional astronomy: calculation methods for relating sky position to position in space
- astrometry: precise measurement of the position and movement of stars
- Positions and Proper Motions Star Catalog (PPM Star Catalogue): 1991 astrometric catalog with proper motions
- positive feedback: see runaway process
- positive gravity anomaly: see gravity anomaly
- positron: electron-like antimatter particle with electric charge of +1
- antimatter: similar to normal matter but with opposite electrical charge
- beta decay: radioactivity such that an electron or positron is emitted
- electron: type of lepton that is stable and has an electric charge of -1
- plasma frequency: frequency of electron plasma oscillation
- radioactive decay: changes in atomic nuclei that happen over time
- spark chamber: type of ion detector
- positron capture: see beta decay
- POSS (Palomar Observatory Sky Survey): 1950s photographic plates from Palomar 48 inch telescope
- POSS plate: see plate
- POSS Plates: see Palomar Observatory Sky Survey
- POSS-I (Palomar Observatory Sky Survey): 1950s photographic plates from Palomar 48 inch telescope
- POSS-II: see Palomar Observatory Sky Survey
- POSSUM: see Australian Square Kilometre Array Pathfinder
- post AGB star
- post-AGB star: stellar-evolution phase between AGB and white dwarf
- post-common envelope binary
- post-common-envelope binary: binary star system showing unusual stellar evolution
- post-main-sequence star: star evolved beyond its main sequence phase
- post-Newtonian approximation: see post-Newtonian formalism
- post-Newtonian correction term: see post-Newtonian formalism
- post-Newtonian formalism: method of approximating GR-based mechanics from Newtonian mechanics
- post-starburst galaxy: galaxy indicating star formation some time back
- posterior: see Bayesian statistics
- posterior density: see Bayesian statistics
- posterior distribution: see Bayesian statistics
- posterior mass: see Bayesian statistics
- posterior probability: see Bayesian statistics
- potassium
- potassium nitrite: see nitrite
- potassium/thorium ratio: indication of thermal history
- potential
- gradient: vector indicating the slope at a point within a field
- Poisson's equation: relates one function's Laplacian to another function
- potential energy: an object's energy that can be released
- potential field
- potential vorticity: see vortensity
- potential well: see gravitational potential well
- potentially hazardous asteroid: see near-Earth object
- potentially hazardous object: see near-Earth object
- POTS (Pre-OmegaTranS): transit search using MPG/ESO Telescope
- POU: see double star designation
- pounds-force
- Powderday: see Turtlebeach
- power: see energy
- power: see watt
- focal length: length from optical element to focal plane
- plate scale: relation between angle and distance across an image
- power law: relationship between a quantity and a power of another
- power law spectrum: see power law
- cosmic rays: very-high-energy particles from beyond the solar system
- power recycling mirror: see LIGO
- power spectral density: see spectral density
- power spectrum (angular power spectrum): method of characterizing the CMB
- power spectrum: see spectral density
- powerful radio galaxy: see radio galaxy
- POX: see rare designator prefixes
- Poynting flux: see Poynting vector
- Poynting flux jet: see Poynting vector
- Poynting flux vector: see Poynting vector
- Poynting vector: measures directional energy flux density
- Poynting-Robertson drag (Poynting-Robertson effect): force that slows dust grains orbiting a star
- Poynting-Robertson effect: force that slows dust grains orbiting a star
- PP: see rare designator prefixes
- PP chain (proton-proton chain): type of fusion reaction chain turning hydrogen into helium
- PP disk (protoplanetary disk): disk of dust and gas around a young star or protostar
- PP space: see position-position-velocity space
- PP-chain (proton-proton chain): type of fusion reaction chain turning hydrogen into helium
- PPARC (Particle Physics and Astronomy Research Council): former UK science agency
- PPD (protoplanetary disk): disk of dust and gas around a young star or protostar
- PPL: see rare designator prefixes
- PPM (parts per million): method of expressing a small ratio
- PPM: see PPM Star Catalogue
- PPM Star Catalogue: 1991 astrometric catalog with proper motions
- PPN (protoplanetary nebula): short AGB phase before planetary nebula
- post-AGB star: stellar-evolution phase between AGB and white dwarf
- PPN expansion: see parameterized post-Newtonian formalism
- PPN formalism (parameterized post-Newtonian formalism): method of approximating GR-based gravity from Newtonian gravity
- PPP: see Penrose Compton scattering
- PPP space: see position-position-velocity space
- PPR: see Galileo
- PPS: see Voyager
- PPTA (Parkes Pulsar Timing Array): group of pulsars timed by Parkes Observatory
- PPTA4: see Parkes Pulsar Timing Array
- PPV (position-position-velocity space): 3D space concept using velocity as one of the three dimensions
- PQ: see Palomar 48 Inch Telescope
- PQT: see Palomar 48 Inch Telescope
- Pr: see rare designator prefixes
- PRA: see Voyager
- Prandtl-Meyer expansion fan (expansion fan): the "sound" of a supersonic flow flowing around a convex corner
- praseodymium
- PRC (Polar-ring Catalog): 1990 catalog of polar-ring galaxies
- PRE: see X-ray burster
- pre-degenerate (PG 1159 star): star in transition between planetary nebula and white dwarf
- Pre-HEAT: see High Elevation Antarctic Terahertz Telescope
- pre-main-sequence star: star not yet with a nuclear reaction
- Herbig AeBe star: type of pre-main-sequence star more massive than a T-Tauri star
- pre-MS (pre-main-sequence star): star not yet with a nuclear reaction
- Pre-OmegaTranS: transit search using MPG/ESO Telescope
- pre-white dwarf (PG 1159 star): star in transition between planetary nebula and white dwarf
- pre-white dwarf: see white dwarf
- post-AGB star: stellar-evolution phase between AGB and white dwarf
- precession: periodic change in a body's rotation or orbit
- precession constant: see precession of the equinoxes
- precession of the ecliptic: see precession of the equinoxes
- precession of the equator: see precession of the equinoxes
- precession of the equinoxes: Earth axial precession with a 26000-year cycle
- celestial pole: point within the celestial sphere aligned with Earth's rotation axis
- nutation: precession of a body's axis of rotation
- precession: periodic change in a body's rotation or orbit
- precipitable water (precipitable water vapor): depth of liquid water equivalent to the atmosphere's water vapor
- precipitable water vapor: depth of liquid water equivalent to the atmosphere's water vapor
- Precision Array for Probing the Epoch of Reionization (PAPER): radio interferometer for 21-cm measurement
- precision photometry: see photometry
- preheating: see reheating
- preliminary design review (PDR): review checking initial design with requirements
- preon star: see exotic star
- preplanetary disk (protoplanetary disk): disk of dust and gas around a young star or protostar
- preplanetary nebula (protoplanetary nebula): short AGB phase before planetary nebula
- presolar grain: grains of dust within meteorites predating the solar system
- Press-Schechter formalism: cosmological model of how structures form from fluctuations
- Press-Schechter theory (Press-Schechter formalism): cosmological model of how structures form from fluctuations
- pressure
- atm: unit of pressure
- radiation pressure: the pressure exerted by electromagnetic radiation
- ram pressure: pressure on a body moving through a fluid
- torr: unit of pressure approximating a millimeter of mercury on Earth
- turbulent pressure: pressure component due to the presence of turbulence
- pressure broadening (collisional broadening): line broadening due to nearby particles
- pressure broadening: see line broadening
- pressure integral: integral relating pressure to a gas's characteristics
- pressure scale height: see scale height
- PRESTO
- prevailing winds: see zonal flow
- PRG: see radio galaxy
- PRIDE: see JUICE
- PRIMA: plan for 2030s NASA 1.8-m FIR space telescope
- PRIMA: see European Southern Observatory Very Large Telescope
- PRIMAger: see PRIMA
- primary: central body of a system such as the Sun within the solar system
- primary (primary mirror): main mirror in a reflector telescope
- primary anisotropies: see CMB anisotropies
- primary beam: see beam
- primary body (primary): central body of a system such as the Sun within the solar system
- primary eclipse: see secondary eclipse
- primary eclipse: see transit
- primary mirror: main mirror in a reflector telescope
- primary mission: the minimum operation expected of a scientific space mission
- primary modes: see CMB polarization
- prime focus: reflector telescope with no secondary mirror
- Prime Focus Spectrograph (Subaru PFS): multi-object spectrograph in development for the Subaru telescope
- Prime Focus Spectrograph: see Subaru Telescope
- prime meridian: see meridian
- Prime-Cam: see Fred Young Submillimeter Telescope
- primordial (relic): particles left over from the events of the early universe
- primordial abundance: see Big Bang nucleosynthesis
- helium: non-metallic element, He, atomic number 2
- primordial abundances: see abundances
- primordial atmosphere
- primordial B-modes: see CMB polarization
- SPIDER: 2015 balloon-borne observatory to observe CMB polarization
- Taurus: balloon-borne polarimeter to study the CMB
- primordial BHMF: see black hole mass function
- primordial binary: see binary star
- primordial black hole: black holes forming at the most dense volumes when inflation ceased
- black hole: region of such high mass that light cannot escape
- primordial black hole mass function: see black hole mass function
- primordial fireball (radiation era): early-universe era when radiation pressure dominated
- primordial fluctuations (initial fluctuations): early universe density variations leading to current universe
- primordial gravitational wave: see gravitational wave spectrum
- primordial gravitational waves: gravitational waves formed in the early universe
- POLARBEAR: instrument to map CMB polarization
- primordial GW: see gravitational wave spectrum
- primordial GWs (primordial gravitational waves): gravitational waves formed in the early universe
- Primordial Inflation Explorer (PIXIE): satellite-concept to to survey CMB polarization
- primordial lithium problem: see lithium
- primordial non-Gaussianity.: see non-Gaussian
- primordial nucleosynthesis (Big Bang nucleosynthesis): creation of atomic nuclei in the very early universe
- PRIMUS: spectrographic survey of galaxies out to redshift 1
- principal component: see principal component analysis
- principal component analysis: statistical strategy of devising independent variables
- PCA analysis: an automatable method of determining galaxy morphology
- telluric line: absorption line in ground observation due to Earth atmosphere
- principal curve: see PCA analysis
- Principal Galaxies Catalog: modern catalog of more than 70k galaxies
- LEDA: galaxy database with observation data
- principal investigator: lead researcher in a scientific endeavor
- principal quantum number: see electron orbital
- electron shell: radius-level around an atomic nucleus at which electrons can orbit
- spin: an angular-momentum quantum number
- principle component
- PCA analysis: an automatable method of determining galaxy morphology
- prior: see Bayesian statistics
- prior density: see Bayesian statistics
- prior distribution: see Bayesian statistics
- prior mass: see Bayesian statistics
- prior probability: see Bayesian statistics
- PRISM: see NIRSpec
- prism
- disperser: prism, grating, or grism within a spectrometer
- grating: spectrometer component
- grism: combination of a grating and a prism
- Prism Multi-object Survey (PRIMUS): spectrographic survey of galaxies out to redshift 1
- probability
- probability density function: shows probability of taking a particular value from a continuous range
- probability distribution
- probability distribution function
- probability mass function: shows probability of taking one of a number of discrete values
- probability mass function: see probability density function
- probe
- Hope Probe: UAE Mars orbiter currently studying Mars
- InSight: NASA Mars mission to study its interior
- Mars 2020: Mars rover mission currently on Mars after 2021 landing
- Mars Express: Mars probe launched by ESA in 2003
- Mars Global Surveyor: Mars probe launched by NASA in 1996
- Mars Odyssey: Mars orbiter launched by NASA in 2001
- Mars Reconnaissance Orbiter: Mars probe launched by NASA in 2005
- MESSENGER: Mercury probe launched by NASA in 2004
- MMX: Japanese probe to bring back a sample of a Martian moon
- Phoenix: Mars polar-region probe launched by NASA in 2007 with lander
- radar: probe based on reflecting radio waves
- Rosalind Franklin: Mars rover in development for 2028 launch
- Tianwen-1: active Chinese Mars rover/orbiter mission
- Trace Gas Orbiter: ESA and Russian Mars orbiter-probe launched in 2016
- Venus Express: Venus probe launched by ESA in 2005
- Voyager: space probes to observe planets and the edge of the solar system
- Probe Far-infrared Mission for Astrophysics (PRIMA): plan for 2030s NASA 1.8-m FIR space telescope
- Probe of Extreme Multi-Messenger Astrophysics (POEMMA): planned space cosmic-ray neutrino observatory
- Probe of Inflation and Cosmic Origins
- Probing Lensing Anomalies Network: survey that recorded microlensing event lightcurves
- problem
- Procyon: brightest star in Canis Minor
- Procyon A
- F-type star: spectral class of star a bit hotter than then Sun
- progenitor (supernova progenitor): the star or star system that produces a supernova
- Prognoz 9: see RELIKT-1
- prograde orbit: see retrograde orbit
- prograde rotation: see rotation period
- prograde wind (superrotating wind): wind traveling in the same direction as the planet is rotating
- program
- project
- Project 1640: see Hale Telescope
- Project 8: experiment in development to measure neutrino mass
- Project In Canada to Search for Supersymmetric Objects: see PICO experiment
- projected distance: see angular distance
- projected distance: see projected separation
- projected semi-major axis: semi-major axis projected onto line-of-sight or plane of the sky
- projected separation: lower limit on distance between two objects in same part of the sky
- projection of the semi-major axis (projected semi-major axis): semi-major axis projected onto line-of-sight or plane of the sky
- prolate spheroid: see spheroid
- Prometheus: see shepherd moon
- PROMETHEUS/VERTEX: hydrodynamic simulation system
- prominence eruption: see solar eruption
- propellant
- proper distance: see relativity
- proper length: see relativity
- proper motion: apparent motion in relation to the position of the Sun
- proper time: see relativity
- proplyd: see protoplanetary disk
- proportional counter: type of ionizing-radiation sensor that senses photon energy
- IXPE: space observatory with X-ray polarimeters
- protected region: an area around a body where an orbit can be stable
- protium (1H): hydrogen isotope with no neutrons
- proto galaxy cluster: see proto-cluster
- proto stellar cluster: see proto-cluster
- proto-cluster: newly-formed galaxy cluster
- proto-cluster candidate: see proto-cluster
- proto-neutron star: see neutron star
- proto-planetary disk (protoplanetary disk): disk of dust and gas around a young star or protostar
- protogalaxy: gas cloud forming a galaxy
- proton: type of baryon that is stable and has an electric charge of +1
- baryon: protons, neutrons, and other three-quark particles
- nucleon: proton or neutron
- quark: type of elementary particle incorporated in protons and neutrons
- quark matter: matter not made of protons and neutrons but of quarks
- standard model: model of elementary particles including quarks
- valley of beta stability: set of isotopes not prone to beta decay
- proton aurora: see aurora
- proton capture: see p-process
- rp-process: synthesis of elements through repeated proton capture
- proton decay
- proton number (atomic number): number of protons in an atomic nucleus
- proton rich: see neutron rich
- proton synchrotron radiation: see synchrotron radiation
- proton-capture process (p-process): synthesis of elements through proton capture
- proton-proton chain: type of fusion reaction chain turning hydrogen into helium
- proton-rich: see p-process
- protoplanet: simplest, least-developed object classified as a planet
- protoplanetary disk: disk of dust and gas around a young star or protostar
- circumstellar disk: disk or ring shaped accumulation of matter around a star
- disk gap: empty radius-range within a disk separating it into rings
- protoplanetary disks
- Disk Detective: Zooniverse effort to find planets within protoplanetary disks
- MAPS: ALMA survey researching planet-formation
- radial drift: inward drift of objects within a protoplanetary disk
- protoplanetary nebula: short AGB phase before planetary nebula
- post-AGB star: stellar-evolution phase between AGB and white dwarf
- protostar: contracted mass of gas that will become a star
- L483: protostar of interest
- MWC 758: protostar with spiral disk
- T Tauri: variable star taken as example of young star
- protostars
- protostellar object (protostar): contracted mass of gas that will become a star
- provisional designation: way to designate newly discovered solar system objects
- minor planet: lesser solar system body without comet characteristics
- Proxima b: exoplanet orbiting Proxima Centauri
- Proxima Centauri: see Alpha Centauri
- M-type star: spectral class of star with a temperature in the vicinity of 2500 K
- Proxima b: exoplanet orbiting Proxima Centauri
- Proxima Centauri b (Proxima b): exoplanet orbiting Proxima Centauri
- proximity effect: Ly-α forest characteristics revealing quasar history
- proximity effect: see Lyman-alpha forest
- proximity zone: see Lyman-alpha forest
- proximity zone: see proximity effect
- PRY: see double star designation
- PRZ: see double star designation
- PS: see rare designator prefixes
- PS sensitivity (point source sensitivity): determination of how readily an instrument detects a point source
- PS1: see Pan-STARRS
- PS2: see Pan-STARRS
- PS4: see Pan-STARRS
- PSB galaxy (post-starburst galaxy): galaxy indicating star formation some time back
- PSC: see IRAS
- pSCT: see Cherenkov Telescope Array
- PSD: see spectral density
- pseudobulge: like a galaxy bulge only flatter
- PSF (point-spread function): function describing an optical system's response to a point of light
- PSF fitting: untangling airy disks to gain effective resolution
- PSF subtraction: see point-spread function
- PSGS: see Palomar high-redshift quasar surveys
- PSI (Planetary Science Institute): US research institution
- PSN: see rare designator prefixes
- PSO: see Pan-STARRS
- PSO J246.4222+15.4698
- PSP (Parker Solar Probe): space probe investigating solar corona
- PSPC: see ROSAT
- PSPT: see Mauna Loa Solar Observatory
- PSR (pulsar): type of astronomical body with EMR in regular cycles of seconds or less
- PSR 1257+12: pulsar with first discovered planet system
- PSR 1257+12 A: see PSR 1257+12
- PSR 1257+12 B: see PSR 1257+12
- PSR 1257+12 C: see PSR 1257+12
- PSR 1913+16 (Hulse-Taylor Binary): binary system consisting of a pulsar and neutron star
- PSR B0531+21: see Crab Nebula
- PSR B0950+08: young pulsar
- PSR B1257+12 (PSR 1257+12): pulsar with first discovered planet system
- PSR B1259-63: pulsar part of an eclipsing binary
- PSR B1913+16 (Hulse-Taylor Binary): binary system consisting of a pulsar and neutron star
- PSR B1957+20 (Black Widow Pulsar): binary system consisting of a pulsar and small companion
- PSR B2145-07.8 (PSR J2145-0750): binary system consisting of a pulsar and white dwarf
- PSR J1300+1240 (PSR 1257+12): pulsar with first discovered planet system
- PSR J1301+0833: see Black Widow Pulsar
- PSR J1713+0447: see J1713+0747
- PSR J1745-2900 (SGR J1745-2900): magnetar orbiting the Milky Way SMBH
- PSR J1915+1606 (Hulse-Taylor Binary): binary system consisting of a pulsar and neutron star
- PSR J1959+2048 (Black Widow Pulsar): binary system consisting of a pulsar and small companion
- PSR J2145-07 (PSR J2145-0750): binary system consisting of a pulsar and white dwarf
- PSR J2145-0750: binary system consisting of a pulsar and white dwarf
- PSR J2146-07 (PSR J2145-0750): binary system consisting of a pulsar and white dwarf
- PSS: see rare designator prefixes
- Psyche: asteroid discovered in 1852
- Psyche: space mission on its way to asteroid Psyche
- PTA (pulsar timing array): cooperating set of pulsar timing observatories
- PTF (Palomar Transient Factory): survey designed to find transients
- PTF Orion Project: see Palomar Transient Factory
- PTFO: see Palomar Transient Factory
- PTGS: see Palomar high-redshift quasar surveys
- PTI (Palomar Testbed Interferometer): near-infrared interferometer experiment
- Ptolemy: see Rosetta
- PTT: see double star designation
- Public ESO Spectroscopic Survey of Transient Objects (PESSTO): NTT survey following up on transients
- publication
- Publications of the Astronomical Society of Japan: bimonthly journal
- Publications of the Astronomical Society of the Pacific: monthly journal
- PUEO/KIR: see Canada-France-Hawaii Telescope
- Puerto Rican Ultimate Pulsar Processing Instrument (PUPPI): Arecibo radio-telescope instrument aimed at observing pulsars
- Puerto Rico
- pulsar: type of astronomical body with EMR in regular cycles of seconds or less
- Pulsar ALFA
- Pulsar Array (Interplanetary Scintillation Array): UK radio telescope that first detected pulsars
- pulsar braking: see magnetic dipole braking
- pulsar braking index: see pulsar characteristic age
- pulsar characteristic age: approximate age determination of a pulsar based upon rotation rate
- pulsar characteristic magnetic field: see pulsar characteristic age
- pulsar dispersion measure (dispersion measure): to what degree an EMR signal's lower frequencies are delayed
- pulsar holography: see interstellar holography
- pulsar kick: see velocity kick
- pulsar planet: see PSR 1257+12
- pulsar term: see pulsar timing array
- pulsar timing array: cooperating set of pulsar timing observatories
- pulsar timing data: see pulsar timing array
- pulsar wind nebula: type of nebula generated by a young pulsar
- SN 1987A: supernova in February 1987 rare for being visible by the naked eye
- Pulsar X-1: see Kvant 1
- pulsars
- pulsating star: variable star that varies through energy pulses
- pulsar: type of astronomical body with EMR in regular cycles of seconds or less
- variable star: star that varies in magnitude
- pulsating stars
- pulsating variable star (pulsating star): variable star that varies through energy pulses
- pulsating white dwarf: see white dwarf
- pulsation modes: see asteroseismology
- pulsator (pulsating star): variable star that varies through energy pulses
- pumping: see maser
- pumping: see stimulated emission
- PUNCH: 4 microsatellites to observe the Sun
- Pup A (Puppis A): supernova remnant bright in X-ray
- pupil size: see exit pupil
- PUPPI: Arecibo radio-telescope instrument aimed at observing pulsars
- Puppis A: supernova remnant bright in X-ray
- purity: see completeness
- purity limit: see completeness
- PV: see vortensity
- PV space: see position-position-velocity space
- PV Telescopii variable: see variable star
- PVO (Pioneer Venus Orbiter): NASA Venus probe launched 1978
- PVTEL: see variable star
- PW (precipitable water vapor): depth of liquid water equivalent to the atmosphere's water vapor
- PWD: see white dwarf
- PWM: see rare designator prefixes
- PWN (pulsar wind nebula): type of nebula generated by a young pulsar
- SN 1987A: supernova in February 1987 rare for being visible by the naked eye
- PWS: see Galileo
- PWS: see Voyager
- PWV (precipitable water vapor): depth of liquid water equivalent to the atmosphere's water vapor
- PyDISORT
- DISORT: simulation of radiative transfer in an atmosphere
- PyMC: Python package for Bayesian statistical modeling
- PyMC3: see PyMC
- pyramid sensor
- pyroxene
- CAI: calcium/aluminum specs in chondrites
- PyTensor: see PyMC
- Python: programming language used for a lot of astrophysics research
- Astrocats: software to create and manage an astronomy catalog
- astropy: general Python package for astrophysical research
- batman: code to calculate model transit lightcurves
- CASA: software package for radio interferometry image generation
- corner.py: Python library for scatter plot matrices
- ExoCTK: collection of software for exoplanet observation and analysis
- Gala: galaxy-formation and evolution software package
- Glue: visualization software good for astrophysical data
- JWST ETC: Python-based exposure time calculator for JWST
- lightkurve: software to analyze time series data
- MaNGA Stellar Library: catalog of SEDs of representative stars
- Matplotlib: Python library for plotting
- NumPy: Python library for numerical programming with arrays
- orbitize: planet orbit-fitting software for direct image observations
- PICASO: rt code specifically for exoplanet transmission spectroscopy
- PyMC: Python package for Bayesian statistical modeling
- SciPy: Python library for scientific programming
- SIMSTACK: software to correlate intensity maps with sources
- yt: analysis and display software
- PZ: see double star designation
- PZT (photographic zenith tube): telescope permanently mounted to the zenith
Index