R/Julian2Date.R

In helixcn/ephem: Creating figures for astronomical almanac

Julian2Date <-
function(jd) {
  int2 <-
    function(v) {
      return(floor(v));
    }
  r = list();
  D = int2(jd + 0.5);
  F = jd + 0.5 - D
  if (D >= 2299161) {
    c = int2((D - 1867216.25) / 36524.25);
    D = D + 1 + c - int2(c / 4);
  }
  D = D + 1524;
  r$Y = int2((D - 122.1) / 365.25);

  D = D - int2(365.25 * r$Y);
  r$M = int2(D / 30.601);
  D = D - int2(30.601 * r$M);
  r$D = D;
  if (r$M > 13) {
    r$M = r$M - 13;
    r$Y = r$Y - 4715;
  } else {
    r$M = r$M - 1;
    r$Y = r$Y - 4716;
  }
  F = F * 24;
  r$h = int2(F);
  F = F - r$h;
  F = F * 60;
  r$m = int2(F);
  F = F - r$m;
  F = F * 60;
  r$s = F;
  return(r);
}