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diff --git a/doc/kstars/flux.docbook b/doc/kstars/flux.docbook new file mode 100644 index 00000000..ba24ea31 --- /dev/null +++ b/doc/kstars/flux.docbook @@ -0,0 +1,69 @@ +<sect1 id="ai-flux"> + +<sect1info> + +<author> +<firstname>Jasem</firstname> +<surname>Mutlaq</surname> +<affiliation><address> +</address></affiliation> +</author> +</sect1info> + +<title>Flux</title> +<indexterm><primary>Flux</primary> +<seealso>Luminosity</seealso> +</indexterm> + +<para> +The <firstterm>flux</firstterm> is the amount of energy that passes through a unit area each second. +</para> + +<para> +Astronomers use flux to denote the apparent brightness of a celestial body. The apparent brightness is defined as the the amount of light received from a star +above the earth atmosphere passing through a unit area each second. Therefore, the apparent brightness is simply the flux we receive from a star. +</para> + +<para> +The flux measures the <emphasis>rate of flow</emphasis> of energy that passes through each cm^2 (or any unit area) of an object's surface each second. +The detected flux depends on the distance from the source that radiates the energy. This is because the energy has to spread over a volume of space before it reaches us. +Let us assume that we have an imaginary balloon that encloses a star. Each dot on the balloon represents a unit of energy emitted from the star. Initially, the dots in an area +of one cm^2 are in close proximity to each other and the flux (energy emitted per square centimeter per second) is high. After a distance d, the volume and surface area of the +balloon increased causing the dots to <emphasis>spread away</emphasis> from each. Consequently, the number of dots (or energy) enclosed in one cm^2 has decreased as illustrated in Figure 1. +</para> + +<para> +<mediaobject> +<imageobject> +<imagedata fileref="flux.png" format="PNG"/> +</imageobject> +<caption><para><phrase>Figure 1</phrase></para></caption> +</mediaobject> +</para> + +<para> +The flux is inversely proportional to distance by a simple r^2 relation. Therefore, if the distance is doubled, we receive 1/2^2 or 1/4th of the original flux. +From a fundamental standpoint, the flux is the <link linkend="ai-luminosity">luminosity</link> per unit area: + +<mediaobject> +<imageobject> +<imagedata fileref="flux1.png" format="PNG"/> +</imageobject> +</mediaobject> +</para> + +<para> +where (4 * PI * R^2) is the surface area of a sphere (or a balloon!) with a radius R. +Flux is measured in Watts/m^2/s or as commonly used by astronomers: Ergs/cm^2/s. +For example, the luminosity of the sun is L = 3.90 * 10^26 W. That is, in one second the sun radiates 3.90 * 10^26 joules of energy into space. Thus, the flux we receive +passing through one square centimeter from the sun at a distance of one AU (1.496 * 10^13 cm) is: +</para> + +<para> +<mediaobject> +<imageobject> +<imagedata fileref="flux2.png" format="PNG"/> +</imageobject> +</mediaobject> +</para> +</sect1> |