/**
* Calculates the nutations in longitude (Δψ) and latitude (Δε) for a date
*
* @param AstroDate $date
* @return static
*
* @see Meeus, Jean. Astronomical Algorithms. Richmond, Virg.: Willmann-Bell,
* 2009. 143-147. Print.
*/
public static function find(AstroDate $date)
{
// Time factor
$t = ($date->copy()->toUTC()->jd - 2451545.0) / 36525;
/*
* Required terms
* ----------------
* D = mean elongation of the Moon from the Sun
* M = mean anomaly of the Earth
* M´ = mean anomaly of the Moon
* F = argument of latitude for Moon
* Ω = long. of asc. node for Moon's mean ecl. orbit (mean equi. of date)
*/
$coeffD = [297.85036, 445267.1148, -0.0019142, 1 / 189474];
$coeffM = [357.52772, 35999.05034, -0.0001603, -1 / 300000];
$coeffM´ = [134.96298, 477198.867398, 0.0086972, 1 / 5620];
$coeffF = [93.27191000000001, 483202.017538, -0.0036825, 1 / 327270];
$coeffΩ = [125.04452, -1934.136261, 0.0020708, 1.0 / 450000];
// Calculate the terms
$D = Angle::deg(static::Horner($t, $coeffD))->norm();
$M = Angle::deg(static::Horner($t, $coeffM))->norm();
$M´ = Angle::deg(static::Horner($t, $coeffM´))->norm();
$F = Angle::deg(static::Horner($t, $coeffF))->norm();
$Ω = Angle::deg(static::Horner($t, $coeffΩ))->norm();
// Nutation coefficient terms
$nutationTerms = static::NutationTerms();
// Evaluate the nutation terms
$Δψ = 0;
$Δε = 0;
for ($i = 0; $i < count($nutationTerms); $i++) {
$row = $nutationTerms[$i];
$arg = 0 + $row[0] * $D->rad + $row[1] * $M->rad + $row[2] * $M´->rad + $row[3] * $F->rad + $row[4] * $Ω->rad;
$Δψ += ($row[5] + $row[6] * $t) * sin($arg) / 10000.0 / Time::SEC_IN_HOUR;
$Δε += ($row[7] + $row[8] * $t) * cos($arg) / 10000.0 / Time::SEC_IN_HOUR;
}
// Store as angles
$Δψ = Angle::deg($Δψ);
$Δε = Angle::deg($Δε);
// Return the nutation
return new Nutation($Δψ, $Δε);
}
/**
* @covers Marando\AstroDate\AstroDate::sub
*/
public function testSub()
{
$tests = [[Time::min(10), 2015, 11, 1, 12, 40, 10], [Time::sec(33), 2015, 11, 1, 12, 49, 37], [Time::days(3), 2015, 10, 29, 12, 50, 10], [Time::days(15), 2015, 10, 17, 12, 50, 10], [Time::days(365), 2014, 11, 1, 12, 50, 10], [Time::hours(13), 2015, 10, 31, 23, 50, 10]];
foreach ($tests as $t) {
$time = $t[0];
$y = $t[1];
$m = $t[2];
$d = $t[3];
$h = $t[4];
$i = $t[5];
$s = $t[6];
$dt0 = new AstroDate(2015, 11, 1, 12, 50, 10);
$dt = $dt0->copy()->sub($time);
$this->assertEquals($y, $dt->year, $t[0] . ' y');
$this->assertEquals($m, $dt->month, $t[0] . ' m');
$this->assertEquals($d, $dt->day, $t[0] . ' d');
$this->assertEquals($h, $dt->hour, $t[0] . ' h');
$this->assertEquals($i, $dt->min, $t[0] . ' i');
$this->assertEquals($s, $dt->sec, $t[0] . ' s');
}
}
