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Spectral index. In astronomy, the spectral index of a source is a measure of the dependence of radiative flux density (that is, radiative flux per unit of frequency) on frequency. Given frequency in Hz and radiative flux density in Jy, the spectral index is given implicitly by Note that if flux does not follow a power law in frequency, the ...
Radiant flux: Φ e [nb 2] watt: W = J/s M⋅L 2 ⋅T −3: Radiant energy emitted, reflected, transmitted or received, per unit time. This is sometimes also called "radiant power", and called luminosity in Astronomy. Spectral flux: Φ e,ν [nb 3] watt per hertz: W/Hz: M⋅L 2 ⋅T −2: Radiant flux per unit frequency or wavelength. The latter ...
An illustration of light sources from magnitude 1 to 3.5, in 0.5 increments. In astronomy, magnitude is a measure of the brightness of an object, usually in a defined passband. An imprecise but systematic determination of the magnitude of objects was introduced in ancient times by Hipparchus. Magnitude values do not have a unit.
In radiometry, radiance is the radiant flux emitted, reflected, transmitted or received by a given surface, per unit solid angle per unit projected area. Radiance is used to characterize diffuse emission and reflection of electromagnetic radiation, and to quantify emission of neutrinos and other particles. The SI unit of radiance is the watt ...
The jansky (symbol Jy, plural janskys) is a non- SI unit of spectral flux density, [1] or spectral irradiance, used especially in radio astronomy. It is equivalent to 10 −26 watts per square metre per hertz. The spectral flux density or monochromatic flux, S, of a source is the integral of the spectral radiance, B, over the source solid angle:
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 (or, equivalently, per unit frequency). It is a radiometric rather than a photometric measure.
Irradiance. In radiometry, irradiance is the radiant flux received by a surface per unit area. The SI unit of irradiance is the watt per square metre (W⋅m −2). The CGS unit erg per square centimetre per second (erg⋅cm −2 ⋅s −1) is often used in astronomy. Irradiance is often called intensity, but this term is avoided in radiometry ...
The monochromatic AB magnitude is defined as the logarithm of a spectral flux density with the usual scaling of astronomical magnitudes and a zero-point of about 3 631 janskys (symbol Jy), [1] where 1 Jy = 10−26 W Hz−1 m−2 = 10−23 erg s−1 Hz−1 cm−2 ("about" because the true definition of the zero point is based on magnitudes as ...