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The Stefan–Boltzmann law, also known as Stefan’s law, describes the power radiated from a black body in terms of its temperature. Specifically, the ... more

Reflectance of the surface of a material is its effectiveness in reflecting radiant energy. It is the fraction of incident electromagnetic power that is ... more

Luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the ... more

In photography, exposure is the amount of light per unit area (the image plane illuminance times the exposure time) reaching a photographic film, as ... more

Attenuation coefficient or narrow beam attenuation coefficient of the volume of a material characterizes how easily it can be penetrated by a beam of ... more

In astronomy, luminosity is the total amount of energy emitted by a star, galaxy, or other astronomical object per unit time. It is related to the ... more

The spectral exitance of a real surface around a given frequency or wavelength, according to the Lambert’s cosine law and the Planck’s law, is ... more

In physics, optical depth or optical thickness, is the natural logarithm of the ratio of incident to transmitted radiant power through a material, and ... more

Black-body radiation is the thermal electromagnetic radiation within or surrounding a body in thermodynamic equilibrium with its environment, or emitted by ... more

is a unit of radiant flux (power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars. It is defined in ... more

In astronomy, luminosity is the total amount of energy emitted by a star, galaxy, or other astronomical object per unit time. It is related to brightness, ... more

Temperature difference – I-nodes model of an Earth spacecraft

In physics, intensity is the power transferred per unit area, where the area is measured on the plane perpendicular to the direction of propagation of the ... more

In chemistry, a closely related quantity called “absorbance” or “decadic absorbance” is used instead of optical depth: the common ... more

Thermionic emission is the thermally induced flow of charge carriers from a surface or over a potential-energy barrier. This occurs because the thermal ... more

The speed of sound is the distance travelled per unit time by a sound wave propagating through an elastic medium. The SI unit of the speed of sound is the ... more

In astronomy, luminosity is the total amount of energy emitted by a star, galaxy, or other astronomical object per unit time. It is related to the ... more

Eb/N0 (the energy per bit to noise power spectral density ratio) is an important parameter in digital communication or data transmission. It is a ... more

Infiltration is the process by which water on the ground surface enters the soil. Infiltration rate in soil science is a measure of the rate at which soil ... more

A rocket engine nozzle is a propelling nozzle (usually of the de Laval type) used in a rocket engine to expand and accelerate the combustion gases produced ... more

Planck’s law describes the electromagnetic radiation emitted from a black body at a certain temperature. Radiance and spectral radiance are measures ... more

Pressure (symbol: p or P) is the ratio of force to the area over which that force is distributed.

Pressure is force per unit area applied in a ... more

Every single thermodynamic system exists in a particular state. When a system is taken through a series of different states and finally returned to its ... more

A rocket engine, or simply “rocket”, is a jet engine that uses only stored propellant mass for forming its high speed propulsive jet. Rocket ... more

Black-body radiation is the thermal electromagnetic radiation within or surrounding a body in thermodynamic equilibrium with its environment, or emitted by ... more

Planck’s law describes the electromagnetic radiation emitted from a black body at a certain temperature. Radiance and spectral radiance are measures ... more

The gravity of Earth, which is denoted by g, refers to the acceleration that the Earth imparts to objects on or near its surface due to gravity. In SI ... more

In physics, jounce or snap is the fourth derivative of the position vector with respect to time, with the first, second, and third derivatives being ... more

Gravitational waves are disturbances in the curvature (fabric) of spacetime, generated by accelerated masses, that propagate as waves outward from their ... more

Wien’s displacement law states that the black body radiation curve for different temperature peaks at a wavelength that is inversely proportional to ... more