sidereal.m

function stime = sidereal(y, m, d,h, min, sec,gam)
    %% Calculate the sidereal time from the given date and UT time
    %{
    Jeremy Penn
    21 October 2017
    
    Revision: 21/10/17
              09/11/17 - replaced while loops with mod to keep ang
                         between 0 and 360
               
    function stime = sidereal(y, m, d,h, min, sec)
    
    Purpose:  This function calculates the sidereal time.
     
    Inputs:    o y     - The year
               o m     - The month
               o d     - The day
               o h     - The hour
               o min   - The minutes
               o sec   - The seconds
               o gam   - The eastward longitude
    
    Outputs:  o stime - The sidereal time
    %}
    
    j0 = 367*y - fix(7*(y + fix((m + 9)/12))/4) + fix((275*m)/9) + d + 1721013.5;
    T0 = (j0 - 2451545) / 36525;
    
    thg0 = 100.4606184 + 36000.77004*T0 + 0.000387933*T0^2 - 2.583e-08*T0^3;

    thg0 = mod(thg0, 360);
    
    UT  = h + min/60 + sec/3600;
    thg = thg0 + 360.98564724*(UT/24);
    th  = thg + gam; 

    th = mod(th, 360);
    
    stime = th;
end