diff --git a/feiertage.php b/feiertage.php
index e0c9b45..31004a7 100644
--- a/feiertage.php
+++ b/feiertage.php
@@ -1,5 +1,7 @@
 <?php
 
+require 'season.php';
+
 abstract class Bundesland {
 	private static $Namen = array(array('Baden-Württemberg', 'BW'), array('Bayern', 'BY'), array('Berlin', 'BE'), array('Brandenburg', 'BB'),
 					array('Bremen', 'HB'), array('Hamburg', 'HH'), array('Hessen', 'HE'), array('Mecklenburg-Vorpommern', 'MV'),
@@ -140,6 +142,8 @@ class FeiertagKalender {
 				Bundesland::Schleswig_Holstein, Bundesland::Thueringen);
 		$ostersonntag = $this->calcOstersonntag($jahr);
 		$busstag = mktime(0, 0, 0, 11, 22 - ($jahr - 1 + $jahr / 4) % 7, $jahr);
+		$jahreszeiten = new Season();
+		$jahreszeiten->calc($jahr);
 		array_push($this->feiertage, new Feiertag(mktime(0, 0, 0, 1, 1, $jahr), 'Neujahr', $alle));
 		array_push($this->feiertage, new Feiertag(mktime(0, 0, 0, 1, 6, $jahr), 'Heilige Drei Könige',
 					array(Bundesland::Baden_Wuerttemberg, Bundesland::Bayern, Bundesland::Sachsen_Anhalt)));
@@ -197,6 +201,10 @@ class FeiertagKalender {
 		array_push($this->feiertage, new Feiertag(mktime(0, 0, 0, 3, 31 - ($jahr + 4 + $jahr / 4) % 7, $jahr), 'Sommerzeit (+1h)'));
 		array_push($this->feiertage, new Feiertag(mktime(0, 0, 0, 10, 31 - ($jahr + 1 + $jahr / 4) % 7, $jahr), 'Winterzeit (-1h)'));
 		array_push($this->feiertage, new Feiertag(mktime(0, 0, 0, 7, 31 - ($jahr + 2 + $jahr / 4) % 7, $jahr), 'System Administrator Appreciation Day'));
+		array_push($this->feiertage, new Feiertag($jahreszeiten->get(Season::Spring), 'Frühlingsanfang'));
+		array_push($this->feiertage, new Feiertag($jahreszeiten->get(Season::Summer), 'Sommeranfang'));
+		array_push($this->feiertage, new Feiertag($jahreszeiten->get(Season::Autumn), 'Herbstanfang'));
+		array_push($this->feiertage, new Feiertag($jahreszeiten->get(Season::Winter), 'Winteranfang'));
 		sort($this->feiertage);
 	}
 
diff --git a/season.php b/season.php
new file mode 100644
index 0000000..3c624c8
--- /dev/null
+++ b/season.php
@@ -0,0 +1,158 @@
+<?php
+
+/**
+ * Dates of seasons for any year
+ * Credit: P. Rocher/G. Satre/IMCCE/CNRS
+ * https://www.imcce.fr/en/grandpublic/temps/saisons.php
+ * https://promenade.imcce.fr/en/pages4/439.html
+ */
+
+class Season {
+	const Spring = 0;
+	const Summer = 1;
+	const Autumn = 2;
+	const Winter = 3;
+
+	private $JJD;
+	private $Year;
+	private $Month;
+	private $Day;
+	private $Dates = array();
+
+	public function get($n) {
+		return $this->Dates[$n];
+	}
+
+	private function trunc($x) {
+		if ($x > 0.0)
+			return floor($x);
+		else
+			return ceil($x);
+	}
+
+	private function JJDATEJ() {
+		$z1 = $this->JJD + 0.5;
+		$z = $this->trunc($z1);
+		$a = $z;
+		$b = $a + 1524;
+		$c = $this->trunc(($b - 122.1) / 365.25);
+		$d = $this->trunc(365.25 * $c);
+		$e = $this->trunc(($b - $d) / 30.6001);
+		$this->Day = $this->trunc($b - $d - $this->trunc(30.6001 * $e));
+		if ($e < 13.5)
+			$this->Month = $this->trunc($e - 1);
+		else
+			$this->Month = $this->trunc($e - 13);
+		if ($this->Month >= 3)
+			$this->Year = $this->trunc($c - 4716);
+		else
+			$this->Year = $this->trunc($c - 4715);
+	}
+
+	private function JJDATE() {
+		$z1 = $this->JJD + 0.5;
+		$z = $this->trunc($z1);
+		if ($z < 2299161)
+			$a = $z;
+		else {
+			$alpha = $this->trunc(($z - 1867216.25) / 36524.25);
+			$a = $z + 1 + $alpha - $this->trunc($alpha / 4);
+		}
+		$b = $a + 1524;
+		$c = $this->trunc(($b - 122.1) / 365.25);
+		$d = $this->trunc(365.25 * $c);
+		$e = $this->trunc(($b - $d) / 30.6001);
+		$this->Day = $this->trunc($b - $d - $this->trunc(30.6001 * $e));
+		if ($e < 13.5)
+			$this->Month = $this->trunc($e - 1);
+		else
+			$this->Month = $this->trunc($e - 13);
+		if ($this->Month >= 3)
+			$this->Year = $this->trunc($c - 4716);
+		else
+			$this->Year = $this->trunc($c - 4715);
+	}
+
+	private function conv($n) {
+		$fdj = ($this->JJD + 0.5E0) - floor($this->JJD + 0.5E0);
+		$hh = floor($fdj * 24);
+		$fdj -= $hh / 24.0;
+		$mm = floor($fdj * 1440);
+		$tz = date_default_timezone_get();
+		date_default_timezone_set('UTC');
+		$this->Dates[$n] = mktime($hh, $mm, 0, $this->Month, $this->Day, $this->Year);
+		date_default_timezone_set($tz);
+	}
+
+	public function calc($yy) {
+		$code1 = $yy;
+		$nline = 1;
+		$k = $yy - 2000 - 1;
+		for ($n = 0; $n < 8; $n++) {
+			$nn = $n % 4;
+			$dk = $k + 0.25E0 * $n;
+			$t = 0.21451814e0 + 0.99997862442e0 * $dk
+				+ 0.00642125e0 * sin(1.580244e0 + 0.0001621008e0 * $dk)
+				+ 0.00310650e0 * sin(4.143931e0 + 6.2829005032e0 * $dk)
+				+ 0.00190024e0 * sin(5.604775e0 + 6.2829478479e0 * $dk)
+				+ 0.00178801e0 * sin(3.987335e0 + 6.2828291282e0 * $dk)
+				+ 0.00004981e0 * sin(1.507976e0 + 6.2831099520e0 * $dk)
+				+ 0.00006264e0 * sin(5.723365e0 + 6.2830626030e0 * $dk)
+				+ 0.00006262e0 * sin(5.702396e0 + 6.2827383999e0 * $dk)
+				+ 0.00003833e0 * sin(7.166906e0 + 6.2827857489e0 * $dk)
+				+ 0.00003616e0 * sin(5.581750e0 + 6.2829912245e0 * $dk)
+				+ 0.00003597e0 * sin(5.591081e0 + 6.2826670315e0 * $dk)
+				+ 0.00003744e0 * sin(4.3918e0 + 12.56578830e0 * $dk)
+				+ 0.00001827e0 * sin(8.3129e0 + 12.56582984e0 * $dk)
+				+ 0.00003482e0 * sin(8.1219e0 + 12.56572963e0 * $dk)
+				- 0.00001327e0 * sin(-2.1076e0 + 0.33756278e0 * $dk)
+				- 0.00000557e0 * sin(5.549e0 + 5.7532620e0 * $dk)
+				+ 0.00000537e0 * sin(1.255e0 + 0.0033930e0 * $dk)
+				+ 0.00000486e0 * sin(19.268e0 + 77.7121103e0 * $dk)
+				- 0.00000426e0 * sin(7.675e0 + 7.8602511e0 * $dk)
+				- 0.00000385e0 * sin(2.911e0 + 0.0005412e0 * $dk)
+				- 0.00000372e0 * sin(2.266e0 + 3.9301258e0 * $dk)
+				- 0.00000210e0 * sin(4.785e0 + 11.5065238e0 * $dk)
+				+ 0.00000190e0 * sin(6.158e0 + 1.5774000e0 * $dk)
+				+ 0.00000204e0 * sin(0.582e0 + 0.5296557e0 * $dk)
+				- 0.00000157e0 * sin(1.782e0 + 5.8848012e0 * $dk)
+				+ 0.00000137e0 * sin(-4.265e0 + 0.3980615e0 * $dk)
+				- 0.00000124e0 * sin(3.871e0 + 5.2236573e0 * $dk)
+				+ 0.00000119e0 * sin(2.145e0 + 5.5075293e0 * $dk)
+				+ 0.00000144e0 * sin(0.476e0 + 0.0261074e0 * $dk)
+				+ 0.00000038e0 * sin(6.45e0 + 18.848689e0 * $dk)
+				+ 0.00000078e0 * sin(2.80e0 + 0.775638e0 * $dk)
+				- 0.00000051e0 * sin(3.67e0 + 11.790375e0 * $dk)
+				+ 0.00000045e0 * sin(-5.79e0 + 0.796122e0 * $dk)
+				+ 0.00000024e0 * sin(5.61e0 + 0.213214e0 * $dk)
+				+ 0.00000043e0 * sin(7.39e0 + 10.976868e0 * $dk)
+				- 0.00000038e0 * sin(3.10e0 + 5.486739e0 * $dk)
+				- 0.00000033e0 * sin(0.64e0 + 2.544339e0 * $dk)
+				+ 0.00000033e0 * sin(-4.78e0 + 5.573024e0 * $dk)
+				- 0.00000032e0 * sin(5.33e0 + 6.069644e0 * $dk)
+				- 0.00000021e0 * sin(2.65e0 + 0.020781e0 * $dk)
+				- 0.00000021e0 * sin(5.61e0 + 2.942400e0 * $dk)
+				+ 0.00000019e0 * sin(-0.93e0 + 0.000799e0 * $dk)
+				- 0.00000016e0 * sin(3.22e0 + 4.694014e0 * $dk)
+				+ 0.00000016e0 * sin(-3.59e0 + 0.006829e0 * $dk)
+				- 0.00000016e0 * sin(1.96e0 + 2.146279e0 * $dk)
+				- 0.00000016e0 * sin(5.92e0 + 15.720504e0 * $dk)
+				+ 0.00000115e0 * sin(23.671e0 + 83.9950108e0 * $dk)
+				+ 0.00000115e0 * sin(17.845e0 + 71.4292098e0 * $dk);
+			$jjd = 2451545 + $t * 365.25e0;
+			$jjd += 0.0003472222e0; // add 30s for rounding to nearest minute
+			$d = $code1 / 100.0;
+			$tetuj = (32.23e0 * ($d - 18.30e0) * ($d - 18.30e0) - 15) / 86400.e0;
+			$jjd -= $tetuj; // minus TE-TU before conversion to date
+			$this->JJD = $jjd;
+			if ($jjd < 2299160.5e0)
+				$this->JJDATEJ();
+			else
+				$this->JJDATE();
+			if ($this->Year == $code1)
+				$this->conv($nn);
+		}
+	}
+}
+
+?>
\ No newline at end of file
diff --git a/season_test.php b/season_test.php
new file mode 100644
index 0000000..6e8a450
--- /dev/null
+++ b/season_test.php
@@ -0,0 +1,14 @@
+<?php
+
+require 'season.php';
+
+$jz = new Season();
+for ($j = 2000; $j < 2100; $j++) {
+	$jz->calc($j);
+	echo date('d.m.Y', $jz->get(Season::Spring)) . "\t";
+	echo date('d.m.Y', $jz->get(Season::Summer)) . "\t";
+	echo date('d.m.Y', $jz->get(Season::Autumn)) . "\t";
+	echo date('d.m.Y', $jz->get(Season::Winter)) . "\n";
+}
+
+?>