<?php   /* Earth's Average Internal Temperature Code © Charles Chandler http://qdl.scs-inc.us/?top=19195 */   // Given some temperatures at specific depths, // we assign those temps to specific radii. $gradientPts = array( $solSys->earth->radius_mean_km - 6370 => 7000, $solSys->earth->radius_mean_km - 5150 => 5000, $solSys->earth->radius_mean_km - 2900 => 3500, $solSys->earth->radius_mean_km - 2800 => 3000, $solSys->earth->radius_mean_km - 200 => 1300, $solSys->earth->radius_mean_km - 0 => 300, );   // Now we're going to divide the Earth into 100 equal-volume // concentric shells, and we'll assign temperatures to those // volumes, by interpolating between the temps at known radii. $volumeIncrement = VolumeOfSphere($solSys->earth->radius_mean_km) / 100; $thisVolume = 0; $temperatures = array(); for ($i = 1; $i <= 100; $i++) { $thisVolume += $volumeIncrement; $thisRadius = RadiusOfSphere($thisVolume); $lastRad = 0; $lastTmp = 7000; foreach($gradientPts as $rad => $tmp) { if (($thisRadius <= $rad) and ($thisRadius >= $lastRad)) { $diffRad = $rad - $lastRad; $diffTmp = $lastTmp - $tmp; $diffRadPartial = $thisRadius - $lastRad; $diffTmpPartial = $lastTmp - ($diffTmp * ($diffRadPartial / $diffRad)); break; } $lastRad = $rad; $lastTmp = $tmp; } $temperatures[] = $diffTmpPartial; }   // Now just average the temperature array, to get // the average temperature inside the Earth. echo (array_sum($temperatures) / 100).'<br >'; // 2220.7930090397   ?>