R/sunr.R

In insol: Solar Radiation

sunr <-
function(jd) {
    # Julian Centuries (Meeus, Astronomical Algorithms 1999. (24.1))
    T = (jd - 2451545)/36525.0
    # mean obliquity of the ecliptic (21.2)
    epsilon = (23+26/60.0+21.448/3600.0) - (46.8150/3600.0)*T - 
    			(0.00059/3600.0)*T^2 + (0.001813/3600.0)*T^3
    # mean anomaly of the Sun (24.3)
    M = 357.52910 + 35999.05030*T - 0.0001559*T^2 - 0.00000048*T^3
    # eccentricity of the Earth's orbit (24.4)
    e = 0.016708617 - 0.000042037*T - 0.0000001236*T^2
    # Sun's equation of center
    C = (1.914600 - 0.004817*T - 0.000014*T^2)*sin(radians(M)) + 
        (0.019993 - 0.000101*T)*sin(2*radians(M)) +
        0.000290*sin(3*radians(M))
    # Sun's true anomaly
    v = M + C
    # Sun's Radius Vector (24.5)
    R = (1.000001018*(1-e^2))/(1 + e*cos(radians(v)))
	return(R)
}