How to calculate sun position?

[admin]

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