Physical world and mathematics

Planck (spacecraft)

Planck was a European Space Agency satellite that surveyed the whole sky from 2009 to 2013 to map the cosmic microwave background, the relic radiation of the Big Bang.

Planck constant

The Planck constant (Planck's quantum of action) is a fundamental physical constant relating a photon's energy to its frequency, which has defined the kilogram since 2019.

Planck energy

The Planck energy is a natural unit of energy, about 1.22 × 10¹⁹ GeV, the scale where quantum gravity becomes important and far beyond any accelerator.

Planck epoch

The Planck epoch is the earliest period of the Universe, lasting from the Big Bang to one Planck time, about 5.39 × 10⁻⁴⁴ seconds, when gravity was as strong as the other forces.

Planck length

The Planck length is a natural unit of length built from fundamental physical constants, about 1.616 × 10⁻³⁵ meters, where quantum mechanics and general relativity both apply.

Planck mass

The Planck mass is a natural unit of mass formed from the constants of gravity, quantum mechanics, and light, equal to about 20 micrograms, roughly a flea egg.

Planck Sunyaev-Zel'dovich cluster catalogue

The Planck Sunyaev-Zel'dovich cluster catalogue lists galaxy clusters found by the Planck satellite through the Sunyaev-Zel'dovich effect, growing from 189 clusters in 2011 to 1653 detections in 2015.

Planck units

Planck units, sometimes called God's units, are natural units built from fundamental physical constants, proposed by Max Planck in 1899 and used in quantum gravity.

Planck's law

Planck's law, also called Planck's law of black-body radiation, gives the spectral radiance of radiation emitted by a blackbody, derived by Max Planck in 1900 through energy quantization.

Planckian dissipation

Planckian dissipation is a pattern in condensed matter physics where a metal's scattering rate is set by the Planckian time, h-bar over k-B times T, with order-one coefficient.

Plane

In geometry, a plane is a two-dimensional flat surface, one of the basic undefined objects, with the point and line, on which geometry is built.

Plane mirror

A plane mirror, or flat mirror, is a flat reflective surface forming a virtual, upright, same-size image as far behind the mirror as the object is in front.

Plane partition

A plane partition is a partition of an integer n whose parts are arranged in a two-dimensional array, weakly decreasing across rows and down columns.

Plane stress

Plane stress is a two-dimensional stress state in which the out-of-plane stresses vanish, describing thin plates loaded in their plane and used as a simplification in elasticity and finite element analysis.

Plane wave

A plane wave is a wave whose value is constant over every plane perpendicular to its direction of travel, depending on only one coordinate and time.

Plane-wave basis set

A plane-wave basis set is a set of plane-wave functions built from a crystal's reciprocal lattice, used to expand one-electron wavefunctions in solid-state density-functional theory calculations.

Planet

A planet, sometimes called a major planet, is a body orbiting the Sun that is nearly round and has cleared its orbital neighborhood, a definition adopted in 2006.

Planet Hunters TESS

Planet Hunters TESS is a Zooniverse citizen science project launched in 2018 in which volunteers inspect NASA TESS light curves to find transiting planets pipelines missed.

Planet Nine

Planet Nine is a hypothetical planet of five to ten Earth masses proposed in 2016 to orbit the Sun far beyond Neptune and explain the clustering of distant Kuiper Belt object orbits.

Planet Nine hypothesis

The Planet Nine hypothesis, proposed by Caltech's Konstantin Batygin and Mike Brown in 2016, holds that an undiscovered planet of 5 to 10 Earth masses orbits far beyond Neptune.

Planetarium

A planetarium is a theater with a hemispherical dome on which the motions of stars, the sun, moon, and planets are projected, often for science education.

Planetary and Space Science (journal)

Planetary and Space Science (ISSN 0032-0633) is an Elsevier peer-reviewed planetary science journal founded in 1959 under Pergamon Press, edited by Maria Cristina De Sanctis, hybrid access with a USD 3,460 APC, SCIE/Scopus-indexed, JCR Q3.

Planetary boundary layer

The planetary boundary layer, or atmospheric boundary layer, is the turbulent layer of the atmosphere adjacent to Earth's surface, typically about 1 km deep, where friction affects wind and temperature.

Planetary core

A planetary core is the iron-rich central region of a differentiated planet, formed when dense metal sank from the silicate mantle during the body's earliest evolution.

Planetary differentiation

Planetary differentiation is the process by which gravity separates a planet's molten interior into layers of different density: a dense metal core, a silicate mantle, and a crust.

Planetary engulfment

Planetary engulfment is the consumption of a planet by its host star when the star expands or dynamics drive the planet inward, leaving chemical signatures.

Planetary habitability

Planetary habitability is the study of whether a planetary body can sustain life, extrapolated from Earth and centered on the habitable zone where liquid water can exist.

Planetary migration

Planetary migration is the drift of a forming planet's semi-major axis from tidal interaction with its protoplanetary disk; models like the Nice model explain the Solar System's giant planets.

Planetary mnemonic

A planetary mnemonic is a sentence whose word initials encode the planets in order from the Sun, such as "My Very Educated Mother Just Served Us Noodles."