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## Albedo

Albedo (albedo, meaning "whiteness") is the measure of the diffuse reflection of solar radiation out of the total solar radiation received by an astronomical body (e.g. a planet like Earth).

## Astronomy

Astronomy (from ἀστρονομία) is a natural science that studies celestial objects and phenomena.

## Centimetre–gram–second system of units

The centimetre–gram–second system of units (abbreviated CGS or cgs) is a variant of the metric system based on the centimetre as the unit of length, the gram as the unit of mass, and the second as the unit of time.

## Dimensional analysis

In engineering and science, dimensional analysis is the analysis of the relationships between different physical quantities by identifying their base quantities (such as length, mass, time, and electric charge) and units of measure (such as miles vs. kilometers, or pounds vs. kilograms) and tracking these dimensions as calculations or comparisons are performed.

## Erg

The erg is a unit of energy and work equal to 10−7 joules.

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## Frequency

Frequency is the number of occurrences of a repeating event per unit of time.

## Hertz

The hertz (symbol: Hz) is the derived unit of frequency in the International System of Units (SI) and is defined as one cycle per second.

## Illuminance

In photometry, illuminance is the total luminous flux incident on a surface, per unit area.

## Integral

In mathematics, an integral assigns numbers to functions in a way that can describe displacement, area, volume, and other concepts that arise by combining infinitesimal data.

## Intensity (physics)

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 energy.

## International Organization for Standardization

The International Organization for Standardization (ISO) is an international standard-setting body composed of representatives from various national standards organizations.

## International System of Units

The International System of Units (SI, abbreviated from the French Système international (d'unités)) is the modern form of the metric system, and is the most widely used system of measurement.

## Linear polarization

In electrodynamics, linear polarization or plane polarization of electromagnetic radiation is a confinement of the electric field vector or magnetic field vector to a given plane along the direction of propagation.

## Magnetic susceptibility

In electromagnetism, the magnetic susceptibility (Latin: susceptibilis, "receptive"; denoted) is one measure of the magnetic properties of a material.

## Noon

Noon (also midday or noon time) is 12 o'clock in the daytime, as opposed to midnight.

## Normal (geometry)

In geometry, a normal is an object such as a line or vector that is perpendicular to a given object.

## Partial derivative

In mathematics, a partial derivative of a function of several variables is its derivative with respect to one of those variables, with the others held constant (as opposed to the total derivative, in which all variables are allowed to vary).

## Permeability (electromagnetism)

In electromagnetism, permeability is the measure of the ability of a material to support the formation of a magnetic field within itself.

## Photometry (optics)

Photometry is the science of the measurement of light, in terms of its perceived brightness to the human eye.

## Photon diffusion

Photon diffusion is a situation where photons travel through a material without being absorbed, but rather undergoing repeated scattering events which change the direction of their path.

## PI curve

The PI (photosynthesis-irradiance) curve is a graphical representation of the empirical relationship between solar irradiance and photosynthesis.

## Plane wave

In the physics of wave propagation, a plane wave (also spelled planewave) is a wave whose wavefronts (surfaces of constant phase) are infinite parallel planes.

## Power (physics)

In physics, power is the rate of doing work, the amount of energy transferred per unit time.

## Poynting vector

In physics, the Poynting vector represents the directional energy flux (the energy transfer per unit area per unit time) of an electromagnetic field.

## Prentice Hall

Prentice Hall is a major educational publisher owned by Pearson plc.

In radiometry, radiant exitance or radiant emittance is the radiant flux emitted by a surface per unit area, whereas spectral exitance or spectral emittance is the radiant exitance of a surface per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength.

In radiometry, radiant exposure or fluence is the radiant energy received by a surface per unit area, or equivalently the irradiance of a surface, integrated over time of irradiation, and spectral exposure or is the radiant exposure per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength.

In radiometry, radiant flux or radiant power is the radiant energy emitted, reflected, transmitted or received, per unit time, and spectral flux or spectral power is the radiant flux per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength.

In radiometry, radiant intensity is the radiant flux emitted, reflected, transmitted or received, per unit solid angle, and spectral intensity is the radiant intensity per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength.

Radiometry is a set of techniques for measuring electromagnetic radiation, including visible light.

## Refractive index

In optics, the refractive index or index of refraction of a material is a dimensionless number that describes how light propagates through that medium.

## Solar azimuth angle

The solar azimuth angle is the azimuth angle of the Sun's position.

Solar irradiance is the power per unit area received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.

## Spectral flux density

In spectroscopy, spectral flux density is the quantity that describes the rate at which energy is transferred by electromagnetic radiation through a real or virtual surface, per unit surface area and per unit wavelength.

## Speed of light

The speed of light in vacuum, commonly denoted, is a universal physical constant important in many areas of physics.

## Stefan–Boltzmann law

The Stefan–Boltzmann law describes the power radiated from a black body in terms of its temperature.

## Vacuum

Vacuum is space devoid of matter.

## Vacuum permeability

The physical constant μ0, (pronounced "mu naught" or "mu zero"), commonly called the vacuum permeability, permeability of free space, permeability of vacuum, or magnetic constant, is an ideal, (baseline) physical constant, which is the value of magnetic permeability in a classical vacuum.

## Vacuum permittivity

The physical constant (pronounced as "epsilon nought"), commonly called the vacuum permittivity, permittivity of free space or electric constant, is an ideal, (baseline) physical constant, which is the value of the absolute dielectric permittivity of classical vacuum.

## Visible spectrum

The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye.

## Watt

The watt (symbol: W) is a unit of power.

## Wavelength

In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.

## References

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