Function NCheckEclipseSolar

calc.cpp:2138–2195

// of distance overlap. Detects partial, annular, and total solar eclipses.

int NCheckEclipseSolar(int iEar, int iMoo, int iSun, real *prPct)
{
  PT3R pSun, pMoo, pEar, pNear, pUmb, vS2M, vS2E, vE2U, vS2Mu, vS2N;
  real radiS, radiE, radiM, radiU, radiP, lNear, lSM, lSU, lSE, lSN, lEU, dot;

  // Objects must be different.
  if (iEar == iSun || iEar == iMoo || iMoo == iSun)
    return etUndefined;

  // Calculate radius and coordinates of the objects in km.
  radiS = rObjDiam[iSun] / 2.0;
  radiE = rObjDiam[iEar] / 2.0;
  radiM = rObjDiam[iMoo] / 2.0;

  pSun = space[iSun]; pMoo = space[iMoo]; pEar = space[iEar];
  PtMul(pSun, rAUToKm);
  PtMul(pMoo, rAUToKm);
  PtMul(pEar, rAUToKm);

  // Determine point along Sun/Moon ray nearest the center of Earth.
  PtVec(vS2M, pSun, pMoo);
  PtVec(vS2E, pSun, pEar);
  dot = PtDot(vS2E, vS2M) / PtDot(vS2M, vS2M);
  vS2N = vS2M; PtMul(vS2N, dot);
  pNear = pSun; PtAdd2(pNear, vS2N);
  PtSub2(pNear, pEar); lNear = PtLen(pNear);

  // Determine point of maximum extent of Moon's umbra shadow.
  lSM = PtLen(vS2M);
  lSU = lSM * radiS / (radiS - radiM);
  vS2Mu = vS2M; PtDiv(vS2Mu, lSM);
  pUmb = vS2Mu; PtMul(pUmb, lSU); PtAdd2(pUmb, pSun);
  PtVec(vE2U, pEar, pUmb);
  lSE = PtLen(vS2E);
  lEU = PtLen(vE2U);
  lSN = PtLen(vS2N);
  radiU = radiS * (lSU - lSN) / lSU;
  if (radiU < 0.0)
    radiU = 0.0;

  // If Sun/Moon ray intersects Earth, must be an annular or total eclipse.
  if (lNear - radiU < radiE) {
    if (prPct != NULL)
      *prPct = 100.0;
    if (lSU < lSE && lEU > radiE)
      return etAnnular;
    return etTotal;
  }

  // Check if Earth intersects penumbra shadow, for a partial solar eclipse.
  radiP = (radiS + radiM) / lSM * lSN - radiS;
  if (lNear - radiE < radiP && radiM > 0.0) {
    if (prPct != NULL)
      *prPct = 100.0 - (lNear - radiE) / radiP * 100.0;
    return etPartial;
  }
  return etNone;
}