How to calculate sun position?

[Trond Hoyem]

Try this one instead:

Code:

function suncalc(lat, lng, time)  -- sun calculations are based on http://aa.quae.nl/en/reken/zonpositie.html formulas  local PI   = math.pi  local sin  = math.sin  local cos  = math.cos  local tan  = math.tan  local asin = math.asin  local atan = math.atan2  local acos = math.acos  local deg  = math.deg  local rad  = PI / 180  local e = rad * 23.4397 -- obliquity of the Earth  local daysec = 60 * 60 * 24  local J1970 = 2440588  local J2000 = 2451545  local function toDays(time)    return time / daysec - 0.5 + J1970 - J2000  end  local function rightAscension(l, b)    return atan(sin(l) * cos(e) - tan(b) * sin(e), cos(l))  end  local function declination(l, b)    return asin(sin(b) * cos(e) + cos(b) * sin(e) * sin(l))  end  local function azimuth(H, phi, dec)    return atan(sin(H), cos(H) * sin(phi) - tan(dec) * cos(phi))  end  local function altitude(H, phi, dec)    return asin(sin(phi) * sin(dec) + cos(phi) * cos(dec) * cos(H))  end  local function siderealTime(d, lw)    return rad * (280.16 + 360.9856235 * d) - lw  end  local function astroRefraction(h)    if h < 0 then -- the following formula works for positive altitudes only.      h = 0 -- if h = -0.08901179 a div/0 would occur.    end    -- formula 16.4 of "Astronomical Algorithms" 2nd edition by Jean Meeus (Willmann-Bell, Richmond) 1998.    -- 1.02 / tan(h + 10.26 / (h + 5.10)) h in degrees, result in arc minutes -> converted to rad:    return 0.0002967 / math.tan(h + 0.00312536 / (h + 0.08901179))  end  -- general sun calculations  local function solarMeanAnomaly(d)    return rad * (357.5291 + 0.98560028 * d)  end  local function eclipticLongitude(M)    local C = rad * (1.9148 * sin(M) + 0.02 * sin(2 * M) + 0.0003 * sin(3 * M)) -- equation of center    local P = rad * 102.9372 -- perihelion of the Earth    return M + C + P + PI  end  local function sunCoords(d)    local M = solarMeanAnomaly(d)    local L = eclipticLongitude(M)    return declination(L, 0), rightAscension(L, 0)  end  local lw      = rad * -lng  local phi     = rad * lat  local d       = toDays(time or os.time())  local dec, ra = sunCoords(d)  local H       = siderealTime(d, lw) - ra  local alt, az = altitude(H, phi, dec), azimuth(H, phi, dec)  return deg(alt), 180 + deg(az) end

Thanks. That one worked.

Trond