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P Cygni profile
P wave
Pace, Norman
pacemaker
Pacioli, Luca (1445–1517)
packed cell volume
packetizing
packing
paddlewheel satellite
Paedocypris
PAET (Planetary Atmospheric Entry Test)
Pageos (Passive GEOS)
Paget, James (1814–1899)
Paget's disease
pahoehoe
PAHs
pain
Paine, Thomas (1737–1809)
Paine, Thomas O. (1921–1992)
pair production
Pal, George (1908–1980)
Palade, George Emil (1912–2008)
Palapa
palate
paleobotany
Paleocene
paleoclimatology
paleocontact hypothesis
paleomagnetism
paleontology
PALEONTOLOGY
Paleozoic era
palimpsest
palindrome
palindromic number
Palisa, Johann (1848–1925)
palisade parenchyma
palladium
Pallas (minor planet 2)
pallasite
Palmachim
Palmer, Raymond (Arthur) (1910–1977)
palmitic acid
Palomar Observatory
Palomar Observatory Sky Survey (POSS)
Palomar Testbed Interferometer
palpitations
Pan
pancreas
pancreatic cancer
pancreatic cancer treatment
pancreatic polypeptide
pandigital number
Pandora
Panel on Extraterrestrial Life
Panel 2 on Extraterrestrial Life
Pangea
pangram
panspermia
pantograph
pantothenic acid
paper
paper cheomatography
Paperclip, Operation
Papin, Denis (1647-1712)
Pappus of Alexandria (lived c. AD 300)
parabola
parabolic flight
parabolic orbit
parabolic velocity
paraboloid
Paracelsus, Philippus Aureolus (1493–1541)
paracetamol
parachute
paradox
PARADOXES
parallactic angle
parallactic displacement
parallax
parallel circuit
parallel postulate
parallel universe
parallelepiped
parallelogram
parallelogram of forces
parallelogram of velocities
paralysis
paramagnetism
parameter
Paranal Observatory
paranasal sinus
parapsychology
parasite
parasitic disease
PARASOL (CNES satellite)
parasympathetic nervous system
parathyroid gland
parathyroid hormone
paratyphoid fever
Paré, Ambroise (c.1510–1590)
parenchyma
paresis
percentage
parietal bone
Paris Gun
Paris Observatory (Observatoire de Paris)
parity
Parkes Observatory
Parkes Radio Telescope
parking orbit
Parkinson's disease
Parmenides (fl. c.475 BC)
Parrondo's Paradox
parsec (pc)
parthenogenesis
partial derivative
partial differential equation
partial eclipse
PARTICLE PHYSICS
partition number
Parus
pascal (Pa)
Pascal, Blaise (1623–1662)
Pascal's law
Pascal's mystic hexagon
Pascal's triangle
Paschen, Friedrich (1865–1947)
Paschen-Back effect
Pasiphaë
Pasteur, Louis (1822–1895)
pasteurization
patella
patent ductus arteriosus
Pathfinder
pathogen
pathological curve
pathology
Patrick Air Force Base
Patroclus (minor planet 617)
Paul Wild Observatory
Paulet, Pedro E. (1874–1945)
Pauli, Wolfgang (1900–1958)
Pauli exclusion principle
Pauling, Linus Carl (1901–1994)
Pavlov, Ivan Petrovich (1849–1936)
Payload Assist Module (PAM)
Payne-Gaposchkin, Cecilia Helena (1900–1979)
Peano, Giuseppe (1858–1932)
Peano curve
Pearce, Joseph Algernon (1893–1988)
pearl
Pearls of Sluze
Pearson, Keith (1857–1936)
Pease, Francis Gladheim (1881–1938)
pectin
pectoral
pectoralis major
pectoralis minor
peculiar galaxy
peculiar motion
peculiar star
pedal curve
pediatrics
pedicel
pedipalps
Peekskill meteorite
Peenemünde
Peewee-1 (nuclear reactor)
peg solitaire
51 Pegasi
51 Pegasi-type planets
Pegasus (launch vehicle)
Pegasus Dwarf Spheroidal (Peg dSph, DDO 216)
pegmatite
Peirce, Charles Sanders (1839–1914)
pelagic
Pele's hair
Pele's tears
Pelican Nebula (IC 5070)
Pell equation
Pell numbers
pellagra
Peltier effect
pelvis
pen
pencil
Pencil Nebula (NGC 2736)
Pendred syndrome
pendulum
peneplain
penetration probe
Penfield, Wilder Graves (1891–1976)
penicillin
penis
Penning Trap
Penrose, Roger (1931–)
Penrose diagram
Penrose stairway
Penrose tiling
Penrose triangle
penta-
pentadactyl limb
pentlandite
pentose
penumbra
Penzias, Arno Allan (1933–)
pepsin
peptic ulcer
peptide
peptide bond
peptide nucleic acid
peptidoglycan
perception
Peregrinus, Petrus (fl. 13th century)
Perelman, Yakov Isidorovitch (1882–1942)
perennial
perfect cube
perfect number
perfect power
perfect square
perfume
perianth
periapsis
pericardial cavity
pericarditis
pericardium
perichondrium
pericycle
periderm
peridot
peridotite
perigee
perihelion
perimeter
period
period, of a decimal expansion
period-age relation
periodic attractor
periodic table
periodic tiling
period-luminosity relation
period-mass relation
period-spectra relation
peripheral arterial disease
peripheral nervous system
periscope
Perissodactyla
peristalsis
peritoneal cavity
peritoneum
peritonitis
perivisceral cavity
Perkin, William Henry (1838–1907)
permafrost
permalloy
permeability
Permian period
permittivity
permutation
pernicious anemia
peroxides
peroxisome
perpendicular
perpetual motion
Perrin, Jean Baptiste (1870–1942)
Perrin sequence
Perrotin, Henri (1845–1904)
Perseids
Perseus Arm
Perseus Cluster (Abell 426)
Perseus-Pisces Supercluster
Persinger, Michael
persistent train
perspective
Perspex
perspiration
perturbation
Perutz, Max Ferdinand (1914–2002)
PET (positron emission tomography) scanning
petal
petiole
Petit, Alexis Thérèse (1791–1820)
Petit-Prince
Petri dish
petrochemical
petrification
petrochemical
petroleum
pewter
PFS (Particles and Fields Subsatellite)
PG 1159 star
pH
Phaethon (minor planet 3200)
phage
phagocytosis
Phair, Venetia (1919–2009)
phalange
Phanerozoic
pharmacology
pharmacy
pharyngitis
pharynx
phase
phase angle
phase change
phase diagram
phase equilibria
phase space
phase transition
phase-contrast microscope
phaser
phenacite
phenol
phenolphthalein
phenotype
phenylalanine
phenylketonuria
pheromone
Philae
PHILOSOPHY
Phillips, Hubert (1891–1964)
Phillips, Samuel C. (1921–1990)
phillipsite
phlebitis
phloem
phlogiston
phlogopite
Phobos
Phocaea group
Phoebe
Phoebus (nuclear reactor series)
Phoenix, Project
Phoenix Cluster
Phoenix Dwarf
Phoenix Lander
Pholus
phon
phoneme
phonetics
phonon
Phoronida
phosgene
phosphate
phosphine
phospholipid
phosphorescence
phosphoric acid
phosphor
phosphorus
phosphorus-based life
phosphorylation
PHOTINT
photoautotrophs
photochemical
photochemistry
photochromic glass
Photocorynus spiniceps
photodiode
photodissociation
photoelectric cell
photoelectric effect
photoelectric effect and Einstein
photographic magnitude
photography, analog
photoionization
photoluminescence
photolysis
photometer
photometry
photomultiplier
photon
photon propulsion
photopolarimeter
photoperiodism
photoreceptor cell
photosphere
photosynthesis
photosynthetic
photosynthetic gas exchanger
photosynthetic pigments
phototropism
phreatic eruption
Phutball
phycobilin
phyllite
phyllotaxis
phylogenetics
phylum
PHYSICAL CHEMISTRY
physical chemistry
physical map
physical units
PHYSICIANS, SURGEONS, AND ANATOMISTS
PHYSICISTS
physics
physiology
phytoplankton
pi
pia mater
Piazzi, Guiseppe (1746–1826)
Piccard, Auguste (1884–1962) and Jean Félix (1884–1963)
Pic-du-Midi Observatory
Pickering, Edward Charles (1846–1919)
Pickering, William Henry (1858–1938)
Pickering, William H. (1910–2004)
picket ship
Pick's theorem
picosat
picric acid
piedmont
Pierce, John R. (1910–2002)
piezoelectric effect
piezoelectricity and pyroelectricity
pig iron
piggyback search
pigment
Pigott, Edward (1753?–1825)
Pilâtre de Rozier, Jean François (1756–85)
pillow lava
pilus
pinch effect
pinchbeck
pineal gland
pingo
pinna
pinocytosis
pint
Pinwheel Galaxy
pion
Pioneer 6
Pioneer 7
Pioneer 8
Pioneer 9
Pioneer 10
Pioneer 11
Pioneer anomaly
Pioneer plaque
Pioneer series
Pipe Nebula
piranha
Pirs Docking Compartment (ISS)
Pisces Cloud (NGC 379, 380, 382-5)
Pisces Dwarf (LGS-3)
pistil
Pistol Star
pit
pit crater
pitch (chemical)
pitch (movement)
pitch (musical)
pitch drop experiment
pitchblende
pith
pitot tube
pituitary gland
pivot joint
placenta
placental mammal
placer deposits
place-value system
plage
plagioclase
plague
plain
planarian
Plancius, Petrus (1552–1622)
Planck
Planck, Max Karl Ernst Ludwig (1858–1947)
Planck and the origins of quantum theory
Planck constant
Planck length
Planck time
Planck's quantum principle
plane
PLANE CURVES
plane joint
plane partition
planet
PLANET (Probing Lensing Anomalies Network)
Planet- (Japanese spacecraft)
Planet Imager
planet migration
planet swallowing
Planet X
planetarium
planetary features
planetary nebula
planetary protection
planetary protection test
Planetary Society
planetary system
planetary systems, formation
planetesimals
planetocentric coordinates
planets, as living beings
PLANETS AND MOONS
planisphere
plankton
plano-concave lens
plano-convex lens
plant
plant cell
plant diseases
plant root
plant stem
Plaskett, John Stanley (1865–1941)
Plaskett's Star (V640 Mon)
plasma (blood)
plasma (physics)
plasma frequency
plasma membrane
plasma sheath
plasma-based life
plasmasphere
plasmid
plasmodesmata
plastic
plastic number
plastid
plate tectonics
Plateau, Joseph Antoine Ferdinand (1801–1883)
Plateau curves
Plateau's problem
platelet
platinum
platinum group
Plato
Platonic solid
Platonic year
Platonism
playa
pleated surface
Pleiades (M45)
Pleione (28 Tauri)
Pleistocene epoch
plenitude, principle of
Plesetsk Cosmodrome
plesiosaur
pleura
pleural cavity
pleural effusion
pleurisy
plexus
plinean eruption
Pliocene epoch
plug-hole vortex
Plum Brook Research Station
Plumbing Mars: Macro-engineering an Arid Terraformed Planet
plumule
pluralism
plurality of worlds
Plutarch (c.46–120 AD)
Pluto
Pluto, moons of
plutoid
pluton
plutonium
PMG (Plasma Motor/Generator)
p-n junction
PNA
pneumonia
pneumoconiosis
pneumothorax
Poe, Edgar Allan (1809–1849)
POES (Polar Operational Environmental Satellite)
Poggendorff illusion
pogo effect
Pogue, William R. (1930–)
poikilotherm
Poincaré, (Jules) Henri (1854–1912)
Poincaré conjecture
Poincaré disk
Poinsot, Louis (1777–1859)
point
Point Mugu
point source
point-set topology
Poisson, Siméon Denis (1781–1840)
Polar
Polar BEAR (Polar Beacon Experiment and Auroral Research)
polar body
polar coordinates
polar distance
polar molecule
polar orbit
polar ring galaxy (PRG)
polar solvent
polar wandering
polarimeter
polarimetry
Polaris (Alpha Ursae Minoris)
Polarissima Borealis (NGC 3172)
polarization
polarized light
polarography
pole
pole star
poliomyelitis
pollen
pollen tube
pollination
Pollux (Beta Geminorum)
polonium
Polyakov, Valery Vladimirovich (1942–)
Pólya's conjecture
polychoron
polycube
polycyclic aromatic hydrocarbons (PAHs)
polycythemia vera
polyextremophile
polygon
polygonal number
POLYGONS
polyhedron
polyiamond
polymerase
polymerization
polymers
polymorphism
polynomial
Polyot
polyoxometalate-based life
polyp
Polypterus
polypeptide
Polyplacophora (chitons)
polysaccharide
polystyrene
polythene
polytope
polywater
pome
Poncelet, Jean Victor (1788–1867)
Poncelet's theorem
Pond, John (1767–1836)
Ponnamperuma, Cyril (1923–1995)
pons
Pons, Jean Louis (1761–1831)
Pony Puzzle
Pope, Gustavus W. (1828–1902)
popliteal artery
popliteal vein
Popper, Karl Raimund (1902–1994)
population
Population I
Population II
Population III
population types
pore
porosity
porphin
porphyria
porphyrins
porphyry
portal vein
Porter, George (1920–2002)
Portia
posigrade rocket
position vector
positional angle
positive g
positivism
positron
positron emission tomography (PET) scanning
positronium
Post, Wiley Hardeman (1898–1935)
postage stamp problems
posterior
posterior auricular artery
posterior triangle (of the neck)
potash
potassium
potential difference
potential energy
potential theory
potentially hazardous asteroid
potentiometer
Potok
pottery and porcelain
pound
Powell, Cecil Frank (1903–1969)
power (mathematics)
power (physics)
power law
power series
power tower
powerful number
Poynting-Robertson effect
p-process
practical number
Praesepe (M44, NGC 2632)
pragmatism
praseodymium
prebiotic
prebiotic evolution
Precambrian
preceding
precessing orbit
precession
precipitation
precision
prednisone
pregnancy
pre-main-sequence object
presbyopia
pre-Socratic philosophy
presolar grains
pressure
pressure broadening
pressure ionization
pressure limit
pressure ridges
pressure suit
pressurized-water reactor
prevailing westerlies
Príbram meteorite
Priestley, Joseph (1733–1804)
Prigogine, Ilya (1917–2003)
primary
primary endosperm nucleus
primary growth
primary immunodeficiency
primary mirror
primate
PRIME (Precision Recovery Including Maneuvering Entry)
Prime Directive
prime focus
prime meridian
prime number
PRIME NUMBERS
primer
primitive material
primitive root
primitive root of unity
primitive streak
primorial
primordial atmosphere
Prince Rupert's problem
principal quantum number
principle of equivalence
prisoner's dilemma
Private (rocket)
probability
PROBABILITY AND STATISTICS
probability theory
Probing Lensing Anomalies Network (PLANET)
Proboscidea
proboscis
procaine
procambium
process philosophy
Proclus Diadochus (c. AD 410–485)
Proctor, Richard Anthony (1837–1888)
Procyon (Alpha Canis Minoris)
producer gas
product
progesterone
prograde
Progress
progressive burning
Project 1640
Project Apollo
Project Argus
Project BETA
Project Blue Book
Project Cyclops
Project Daedalus
Project Gemini
Project Grudge
Project Longshot
Project Manhigh
Project Mercury
Project META
Project Mogul
Project Orion
Project Ozma
Project Phoenix
Project Prometheus
Project Rover
Project Sentinel
Project Sign
Project Skyhook
Project Stargazer
Project Twinkle
projectile
projection
projective geometry
projective plane
prokaryote
prokaryotic
prokaryotic cell
prolactin
prolate
prolate spheroid
Prometheus
Prometheus, Project
promethium
prominence
promoter
prompt neutron
prone g
pronic number
pronotum
pronucleus
propane
propanol
propellant
propellant storage
PROPELLANTS
propeller
proper motion
PROPERTIES OF MATTER
prophase
proportion
proportional
proportional counter
proprioception
propulsion
Propulsive Small Expendable Deployer System (ProSEDS)
prosimian
prospecting
Prospector
Prospero (moon of Uranus)
Prospero (UK artificial satellite)
prostaglandin
prostate cancer
prostate cancer treatment
prostate gland
prosthetic group
prosthetics
protactinium
protease
protective coloration
proteins
Proteus
prothorax
protists
protocells
Proton (rocket)
proton (particle)
proton-proton chain
protoplanet
protoplanetary disk
protoplanetary nebula
protoplasm
protostar
protostellar core
protozoan
protractor
Proust, Joseph Louis (1754–1826)
Proxima Centauri (Gliese 551)
proximal
Prussian Blue
Przybylski's Star (HD 101065)
pseudogene
pseudohalogens
pseudopodium
pseudoprime
pseudosphere
psittacosis
psoriasis
PSLV (Polar Satellite Launch Vehicle)
PSR 1257+12
PSR B1620-26
psychiatry
psychic teleportation
psychology
psychotherapy
psychrophiles
pterodactyl
pterosaur
PTI
Ptolemaic system
Ptolemy (c.100–168)
Ptolemy's Cluster (M7, NGC 6475)
Ptolemy's theorem
P-type asteroid
p-type semiconductor
puberty
Puck
puerperal fever
pulley
pulmonary arterial hypertension
pulmonary artery
pulmonary embolism
pulmonary trunk
pulmonary valve
pulsar
pulsar planets
pulsar timing noise
pulsar wind nebula
pulsating variable
pulse (medicine)
pulse (botany)
pulse detonation engine
pulse oximetry
pulsed plasma thruster (PPT)
pulse-jet
pumice
pump
punctuated equilibrium
pupa
pupil
Puppis A
Purcell, Edward M. (1912–1997)
pure mathematics
purines
Purkinje, Johannes Evangelista (1787–1869)
Purkinje effect
pursuit curve
pus
putrefaction
puzzle jug
puzzle rings
PV Telescopii star
pyloric sphincter
pylorus
pyramid
pyramidal number
pyridine
pyridoxine
pyrimidine
pyrite
pyroclastic
pyroclastic flow
pyrolusite
pyrolysis
pyrometer
pyroxene
pyrrhotite
pyrrole
pyruvic acid
Pythagoras (c.569–c.500 BC)
Pythagoras's theorem
Pythagorean triplet