Sunset returns false for some locations

ext/date/tests/date_sunrise_variation10.phpt

@@ -0,0 +1,18 @@
+--TEST--
+Test date_sunrise() function : function returns false when the sun don't rise
+--FILE--
+<?php
+
+echo "*** The sun is all day up at 26 Jul 2017 at the North Pole ***\n";
+var_dump(date_sunrise(mktime(0, 0, 0, 7, 26, 2017), SUNFUNCS_RET_STRING, 84.430519, 4.218750));
+
+echo "*** The sun don't rise at 26 Jul 2017 at the South Pole ***\n";
+var_dump(date_sunrise(mktime(0, 0, 0, 7, 26, 2017), SUNFUNCS_RET_STRING, -80.605880, -1.757813));
+
+echo "===DONE===";
+--EXPECTF--
+*** The sun is all day up at 26 Jul 2017 at the North Pole ***
+bool(false)
+*** The sun don't rise at 26 Jul 2017 at the South Pole ***
+bool(false)
+===DONE===

ext/date/tests/date_sunset_variation10.phpt

@@ -0,0 +1,19 @@
+--TEST--
+Test date_sunset() function : function returns false when the sun don't set
+--FILE--
+<?php
+date_default_timezone_set('UTC');
+
+echo "*** The sun don't rise at 24 Dec 2017 at the North Pole ***\n";
+var_dump(date_sunset(mktime(0, 0, 0, 12, 24, 2017), SUNFUNCS_RET_STRING, 84.430519, 4.218750));
+
+echo "*** The sun is all day up at 24 Dec 2017 at the South Pole ***\n";
+var_dump(date_sunset(mktime(0, 0, 0, 12, 24, 2017), SUNFUNCS_RET_STRING, -80.605880, -1.757813));
+
+echo "===DONE===";
+--EXPECTF--
+*** The sun don't rise at 24 Dec 2017 at the North Pole ***
+bool(false)
+*** The sun is all day up at 24 Dec 2017 at the South Pole ***
+bool(false)
+===DONE===