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Calculating the suns path in sky

  1. Apr 24, 2015 #1


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    I've searched the internet and found a few sites, of varying depth, that contain some of the equations to calculating the solar path. At the moment, I'm not particularly concerned with precision. I am trying to discern the equations in order to implement them into a java program I am writing.

    Some of the equations use degrees multiplied by time constants and so I'm trying to decide if I need to change the degree value to time values? The reason I ask is that my result is not a value I expected. The link provided has the series of equations I would like to use.

    The equation of time uses trig functions, but says the result represents minutes. Does that mean I need to convert the degree value to minutes, or the result is already in minutes? No units are used in this case and so its a little confusing to discern.

    http://www.pveducation.org/pvcdrom/properties-of-sunlight/solar-time [Broken]
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Apr 25, 2015 #2

    Simon Bridge

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    You should start by saying what you mean by "the Sun's path in the sky".
    Usually I would think of you tracking right-ascention and declination from a particular lat/long position on the Earth... but you may just be interested in tracking the spherical-polar coordinates from the center of the earth.

    The web page you cite uses "minutes" for time but not for angles - it's pretty good at explaining which bit has what units.
    The EoT formual gives the EoT in minutes ... but the angle B, as the following text explains, is in degrees.

    In general a description "the equation gives X (in y)" tells you that the equation for X is formulated so that it comes out in units of y.
    You can usually tell from the units in the body of the equation.
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