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The zero point is used to calibrate a system to the standard magnitude system, as the flux detected from stars will vary from detector to detector. [2] Traditionally, Vega is used as the calibration star for the zero point magnitude in specific pass bands (U, B, and V), although often, an average of multiple stars is used for higher accuracy. [3]
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 shown below).
Therefore, the magnitude m, in the spectral band x, would be given by = (,), which is more commonly expressed in terms of common (base-10) logarithms as = (,), where F x is the observed irradiance using spectral filter x, and F x,0 is the reference flux (zero-point) for that photometric filter.
Mathematically, mass flux is defined as the limit =, where = = is the mass current (flow of mass m per unit time t) and A is the area through which the mass flows.. For mass flux as a vector j m, the surface integral of it over a surface S, followed by an integral over the time duration t 1 to t 2, gives the total amount of mass flowing through the surface in that time (t 2 − t 1): = ^.
Continuous charge distribution. The volume charge density ρ is the amount of charge per unit volume (cube), surface charge density σ is amount per unit surface area (circle) with outward unit normal n̂, d is the dipole moment between two point charges, the volume density of these is the polarization density P.
Faraday showed that the magnitude of the electromotive force (EMF) generated in a conductor forming a closed loop is proportional to the rate of change of the total magnetic flux passing through the loop (Faraday's law of induction). Thus, for a typical inductance (a coil of conducting wire), the flux linkage is equivalent to magnetic flux ...
To convert intensity [W/sr/m 2] to flux [W/m 2], calculations usually invoke the "two-stream" and "plane parallel" approximations. [13] [18] The radiative flux is decomposed into three components, upward (+z), downward (-z), and parallel to the surface. This third component contributes nothing to heating or cooling the planet.
The condition of zero divergence is satisfied whenever a vector field v has only a vector potential component, because the definition of the vector potential A as: = automatically results in the identity (as can be shown, for example, using Cartesian coordinates): = =