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A flow chart describing the relationship of various physical quantities, including radiant flux and exitance. 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 ...
Hence, units of electric flux are, in the MKS system, newtons per coulomb times meters squared, or N m 2 /C. (Electric flux density is the electric flux per unit area, and is a measure of strength of the normal component of the electric field averaged over the area of integration. Its units are N/C, the same as the electric field in MKS units.)
The most widely used is the AB magnitude system, [15] in which photometric zero points are based on a hypothetical reference spectrum having constant flux per unit frequency interval, rather than using a stellar spectrum or blackbody curve as the reference. The AB magnitude zero point is defined such that an object's AB and Vega-based ...
To calculate the flux density in janskys, the total power detected (in watts) is divided by the receiver collecting area (in square meters), and then divided by the detector bandwidth (in hertz). The flux density of astronomical sources is many orders of magnitude below 1 W·m −2 ·Hz −1 , so the result is multiplied by 10 26 to get a more ...
In physics and many other areas of science and engineering the intensity or flux of radiant energy is the power transferred per unit area, where the area is measured on the plane perpendicular to the direction of propagation of the energy. [a] In the SI system, it has units watts per square metre (W/m 2), or kg⋅s −3 in base units.
= where the flux has been multiplied by the surface area of the star. To find the incident stellar flux on the planet, I x {\displaystyle I_{x}} , at some orbital distance from the star, a {\displaystyle a} , one can divide by the surface area of a sphere with radius a {\displaystyle a} : [ 8 ]
The apparent magnitude, the magnitude as seen by the observer (an instrument called a bolometer is used), can be measured and used with the absolute magnitude to calculate the distance d to the object in parsecs [14] as follows: = + or = (+) / where m is the apparent magnitude, and M the absolute magnitude. For this to be accurate, both ...
The Cambridge Guide to Astronomical Discovery states that Practical Astronomy with your Calculator is a "must"-have book if one has no personal computer for astronomical calculations. [4] New Scientist magazine gave a favourable review of the book, although stating that there were small errors in some calculations. [5]