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- P-processProcesses in astrophysics
- P/2013 R3 (Catalina–PanSTARRS)Disintegrated active main-belt asteroid
- P/2019 LD2 (ATLAS)Jupiter-family comet
- Pair-instability supernovaType of high-energy supernova in very large stars
- Palermo Astronomical ObservatoryThe Giuseppe S. Vaiana Astronomical Observatory is an astronomical observatory located in
- Palermo scaleLogarithmic scale in astronomy
- Palomar ObservatoryAstronomical observatory in Southern California
- Palomar Transient FactoryAstronomical survey program
- Palomar–Leiden surveyAstronomical survey
- Palus PutredinisPalus Putredinis (Latin palūs pūtrēdinis "Marsh of Decay") is a small lunar mare in the ba
- Pan-STARRSMulti-telescope astronomical survey
- Pancake domeA pancake dome is an unusual type of lava dome found on the planet Venus. They are widely
- PanspermiaHypothesis on the interstellar spreading of primordial life
- Paolo FarinellaItalian astronomer
- Parabolic trajectoryType of orbit
- ParallaxDifference in apparent position with viewing angle
- Parallax in astronomyDistance measuring technique
- Paranal ObservatoryAstronomical observatory in Chile
- Paris ObservatoryForemost astronomical observatory of France
- Parker Solar ProbeNASA probe of the Sun's outer corona
- Parkes ObservatoryRadio telescope observatory in New South Wales, Australia
- Particle chauvinismParticle chauvinism is the term used by British astrophysicist Martin Rees to describe the
- Particle horizonDistance measurement used in cosmology
- Pascale EhrenfreundAustrian astrophysicist (born 1960)
- Paul HergetAmerican astronomer (1908–1981)
- Paul Oswald AhnertGerman astronomer (1897–1989)
- Paul W. HodgeAmerican astronomer (1934–2019)
- Paul WiegertCanadian astronomer
- Paul Wild (Swiss astronomer)Swiss astronomer
- Paulo R. HolvorcemBrazilian amateur astronomer and mathematician
- Pavo (constellation)Constellation in the southern celestial hemisphere
- Pavonis MonsMartian volcano
- PCPaintPCPaint was one of the first IBM PC-based mouse-driven GUI paint programs, released in 198
- Peak of eternal lightA peak of eternal light (PEL) is a hypothetical point on the surface of an astronomical bo
- Peculiar galaxyGalaxy of unusual size, shape, or composition
- Peculiar velocityPeculiar motion or peculiar velocity refers to the velocity of an object relative to a res
- Pegasus (constellation)Constellation in the northern celestial hemisphere
- Pegasus Dwarf Irregular GalaxyThe Pegasus Dwarf Irregular Galaxy (also known as Peg DIG or the Pegasus Dwarf) is a dwarf
- Peneus PateraPeneus Patera is a feature in the Noachis quadrangle of Mars. It is located at 58.1 S and
- Period-luminosity relationAstronomical principle
- PerseidsProlific meteor shower associated with the comet Swift-Tuttle
- Perseus (constellation)Constellation in the northern celestial hemisphere
- Perseus ArmOne of two major spiral arms of the Milky Way galaxy
- Perseus ClusterGalaxy cluster in the constellation Perseus
- Persian astrologyPersian astrology, particularly during the Sasanian era and earlier, is considered one of
- Perturbation (astronomy)Classical approach to the many-body problem of astronomy
- Pete FrankNASA engineer
- Peter Andreas HansenGerman astronomer (1795–1874)
- Peter GoldreichAmerican astrophysicist (born 1939)
- Peter GrinspoonPeter Grinspoon (born 1966) is an American physician. He is an internist and medical canna
- Péter MészárosPéter István Mészáros (born 15 July 1943) is a Hungarian-American theoretical astrophysici
- Peter T. GallagherIrish astrophysicist and observatory director, specialised in solar physics
- Phaeton (hypothetical planet)Hypothetical former Solar System planet
- Phases of VenusVariations of lighting of the planet's surface
- Phi GeminorumPhi Geminorum, Latinized from φ Geminorum, is a binary star in the constellation Gemini, t
- PhlegopsisPhlegopsis is a genus of insectivorous passerine birds in the antbird family, Thamnophilid
- Phobos (moon)Larger of the two moons of Mars
- Phoebe (moon)Moon of Saturn
- Phoenix (constellation)Minor constellation in the southern sky
- Phoenix DwarfThe Phoenix Dwarf is a dwarf irregular galaxy discovered in 1976 by Hans-Emil Schuster and
- PhootprintProposed sample-return mission to Phobos
- PhotodissociationChemical reaction in which a compound is broken down by light
- PhotoevaporationPhotoevaporation is the process where energetic radiation ionises gas and causes it to dis
- PhotoionizationIon formation via a photon interacting with a molecule or atom
- Photometric systemFilters for an optical system
- Photometry (astronomy)Determination of light intensities of astronomical bodies
- Photon epochPeriod in the evolution of the early universe
- PhotosphereStar's outer shell from which light is radiated
- Physical cosmologyBranch of physics that studies mathematical models of the universe
- PictorConstellation in the southern celestial hemisphere
- Pictor APictor A, around 485 million light-years away in the constellation Pictor, is a double-lob
- Pierre EncrenazFrench astronomer (born 1945)
- Piet HutDutch astrophysicist (born 1952)
- Pieter Dirkszoon KeyserPieter Dirkszoon Keyser (occasionally Petrus Theodorus; c. 1540 – 11 September 1596) was a
- Pinwheel GalaxyGalaxy in the constellation Ursa Major
- Pisces (astrology)Twelfth astrological sign of the zodiac
- Pisces (constellation)Zodiac constellation straddling the celestial equator
- Pisces DwarfThe Pisces Dwarf, also known as Pisces I, is an irregular dwarf galaxy that is part of the
- Pisces–Cetus Supercluster ComplexGalaxy supercluster complex containing the Virgo Supercluster
- Piscis AustrinusConstellation in the southern celestial hemisphere
- PKS 2155-304PKS 2155-304 is a BL Lac object, a galaxy hosting a type of blazar. It is a strong emitter
- PlanetLarge, round non-stellar astronomical object
- Planet NineHypothetical Solar System planet
- Planetary coreInnermost layer(s) of a planet
- Planetary differentiationAstrogeological concept
- Planetary equilibrium temperatureTemperature of a planet when approximated as radiating as a black body
- Planetary flybySending a space probe past a planet or dwarf planet
- Planetary geologyGeological study of planets
- Planetary habitabilityKnown extent to which a planet is suitable for life
- Planetary habitability in the Solar SystemHabitability of the celestial bodies of the Solar System
- Planetary massMeasure of the mass of a planet-like astronomical body
- Planetary migrationAstronomical phenomenon
- Planetary nebulaType of emission nebula created by dying red giants
- Planetary nebula luminosity functionAstronomical function
- Planetary Observer programCancelled NASA space exploration program
- Planetary oceanographyStudy of extraterrestrial oceans
- Planetary protectionPrevention of interplanetary biological contamination
- Planetary scienceScience of planets and planetary systems
- Planetary Science Decadal SurveyPublication of the United States National Research Council
- Planetary surfaceA planetary surface is where the solid or liquid material of certain types of astronomical
- Planetary symbolsGraphical symbols used in astrology and astronomy
- Planetary systemSet of non-stellar objects in orbit around a star
- Planetary-mass moonPlanetary-mass bodies that are also natural satellites
- Planetary-mass objectSize-based definition of celestial objects
- PlanetesimalSolid objects in protoplanetary disks and debris disks
- Planets beyond NeptuneHypothetical planets further than Neptune
- Planets in astrologyInterpretations of the planets of the Solar System
- Planum BoreumPlanum Boreum (Latin: "the northern plain") is the northern polar plain on Mars. It extend
- Plasma betaThe beta of a plasma, symbolized by β, is the ratio of the plasma pressure (p = nkBT) to t
- Plasma Instrument for Magnetic SoundingFaraday cup instrument for Europa Clipper
- Plasma stabilityDegree to which disturbing a plasma system at equilibrium will destabilize it
- PlasmasphereRegion of Earth's magnetosphere consisting of cool plasma
- Plataforma Solar de AlmeríaThe Solar Platform of Almería (PSA) is the largest concentrating solar technology research
- PleiadesStar cluster in the constellation of Taurus
- PlutinoDynamical group of trans-Neptunian objects
- PlutoLargest dwarf planet in the Solar System
- Po Ya (crater)Po Ya is a crater on Mercury. Its name was adopted by the IAU in 1976, after Bo Ya, a Chin
- Polar circleCircle of latitude
- Polar motionMotion of Earth's rotational axis relative to its crust
- Polar nightPhenomenon where the Sun remains below the horizon for more than 24 hours
- Polar orbitSatellite orbit with high inclination
- Polarimeter to Unify the Corona and HeliosphereNASA satellite of the Explorer program
- PolarimetryMeasurement and interpretation of the polarization of transverse waves
- PolarisNorthern pole-star; brightest star in Ursa Minor
- POlarization Emission of Millimeter Activity at the SunPair of radio telescopes
- Polarization in astronomyPolarization of electromagnetic radiation is a useful tool for detecting various astronomi
- Pole starVisible star that is nearly aligned with Earth's axis of rotation
- Pollux (star)Star in the constellation Gemini
- Polydeuces (moon)Polydeuces , also designated Saturn XXXIV, is a small trojan moon of Saturn occupying the
- Portia (moon)Portia is an inner satellite of Uranus. It was discovered from the images taken by Voyager
- Position angleConvention for measuring angles on the sky
- Position of the SunCalculating the Sun's location in the sky at a given time and place
- Potentially hazardous objectHazardous near-Earth asteroid or comet
- Pre-main-sequence starStar in the stage when it has not yet reached the main sequence
- Pre-stellar corePhase in the formation of low-mass stars
- PrecoveryProcess of finding the image of an object in images predating its discovery
- President of the Royal Astronomical SocietyThe president of the Royal Astronomical Society (prior to 1831 known as President of the A
- Primary life support systemA primary (or portable or personal) life support system (or subsystem) (PLSS), is a device
- Primordial fluctuationsEarliest theoretical cosmological structures
- Priscilla Fairfield BokAmerican astronomer (1896–1975)
- Prix Jules JanssenAward
- Prix Paul Doistau–Émile BlutetThe Prix Paul Doistau–Émile Blutet is a biennial prize awarded by the French Academy of Sc
- ProcyonStar in the constellation Canis Minor
- Project Phoenix (SETI)Project Phoenix was a SETI project to search for extraterrestrial intelligence by analyzin
- Proleptic Gregorian calendarExtension of the Gregorian calendar before its introduction
- Proleptic Julian calendarThe proleptic Julian calendar is produced by extending the Julian calendar backwards to da
- Propellant mass fractionConcept in aerospace engineering
- Proper lengthLength of an object in the object's rest frame
- Proper motionMeasure of observed changes in the apparent locations of stars
- ProplydDust ring surrounding large stars thousands of solar radii wide
- Proton–proton chainNuclear fusion reaction
- ProtoplanetLarge planetary embryo
- Protoplanetary diskGas and dust surrounding a newly formed star
- Protoplanetary nebulaNebula surrounding a dying star
- ProtostarEarly stage in the process of star formation
- Provisional designation in astronomyDesignation of an astronomical body after its discovery and before its official name
- Provost (civil)Provost is a title held by the civic heads of local governments in Scotland. It is similar
- Proxima CentauriNearest star to the Solar System
- Proxima Centauri bTerrestrial planet orbiting the star Proxima Centauri
- PSR B1257+12Millisecond pulsar in the constellation Virgo
- PSR B1257+12 BPSR B1257+12 c, alternatively designated PSR B1257+12 B, also named Poltergeist, is an ext
- PSR B1937+21Pulsar in the constellation Vulpecula
- PSR J2144−3933PSR J2144−3933 is a pulsar about 180 parsecs (587 light-years) from Earth. It is the colde
- Psyche (spacecraft)Reconnaissance NASA mission of the main belt asteroid 16 Psyche
- Psychological astrologyAstrology based on psychology
- Public health observatoryA public health observatory is an organization or program that monitors and reports on the
- Puck (moon)Moon of Uranus
- PulsarType of neutron star with beams of radiation
- Pulsar wind nebulaA pulsar wind nebula (PWN, plural PWNe), sometimes called a plerion (derived from the Gree
- PuppisConstellation in the southern celestial hemisphere
- Pushkin (crater)Pushkin is a crater on Mercury. Its name was adopted by the International Astronomical Uni
- PyxisConstellation in the southern celestial hemisphere
- Pyxis globular clusterThe Pyxis globular cluster is a globular cluster in the constellation Pyxis. It lies aroun
