GREENWICHSRT Compute greenwich sidereal time from Julian date

compute greenwich sidereal time from D. Vallado 4th edition

Contents

Inputs
Outputs

Inputs

Jdate: Julian days from Jan 1, 4713 BCE from juliantime(utc) or juliandate(utc)

Outputs

gst: greenwich sidereal time    [0, 2pi)

function gst = greenwichsrt(Jdate)

% Vallado Eq. 3-42 p. 184, Seidelmann 3.311-1
tUT1 = (Jdate - 2451545) / 36525;
% Eqn. 3-47 p. 188
gmst_sec = 67310.54841 + (876600 * 3600 + 8640184.812866) * tUT1 + 0.093104 * tUT1 .^ 2 - 6.2e-6 * tUT1 .^ 3;
% 1/86400 and 2*pi implied by units of radians
tau = 2*pi;
gst = mod(gmst_sec * tau / 86400.0, tau);

end