From ce599e4f9f94b4eb00c1b5edb85bce5431ab3df2 Mon Sep 17 00:00:00 2001 From: toma Date: Wed, 25 Nov 2009 17:56:58 +0000 Subject: Copy the KDE 3.5 branch to branches/trinity for new KDE 3.5 features. BUG:215923 git-svn-id: svn://anonsvn.kde.org/home/kde/branches/trinity/kdeedu@1054174 283d02a7-25f6-0310-bc7c-ecb5cbfe19da --- doc/kstars/flux.docbook | 69 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 69 insertions(+) create mode 100644 doc/kstars/flux.docbook (limited to 'doc/kstars/flux.docbook') 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 @@ + + + + + +Jasem +Mutlaq +
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 + + + +Flux +Flux +Luminosity + + + +The flux is the amount of energy that passes through a unit area each second. + + + +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. + + + +The flux measures the rate of flow 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 spread away from each. Consequently, the number of dots (or energy) enclosed in one cm^2 has decreased as illustrated in Figure 1. + + + + + + + +Figure 1 + + + + +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 luminosity per unit area: + + + + + + + + + +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: + + + + + + + + + + -- cgit v1.2.1