haversine formula in PHP

haversine.php

<?php

$radiusOfEarth = 3959; //miles

// Address 1
$latitudeOne = deg2rad(33.4151843);
$longitudeOne = deg2rad(-111.8314724);
// Address 2
$latitudeTwo = deg2rad(33.0581063);
$longitudeTwo = deg2rad(-112.0476423);

$distanceLongitude = $longitudeTwo - $longitudeOne;
$distanceLatitude = $latitudeTwo - $latitudeOne;

// This is the Haversine Formula expressed Mathematically
// a = sin²(Δφ/2) + cos φ1 ⋅ cos φ2 ⋅ sin²(Δλ/2)
// c = 2 ⋅ atan2( √a, √(1−a) )
// d = R ⋅ c

// This is the haversine Formula expressed in PHP
$a = sin($distanceLatitude/2) * sin($distanceLatitude/2) + cos($latitudeOne) * cos($latitudeTwo) * sin($distanceLongitude/2) * sin($distanceLongitude/2);
$c = 2 * asin(sqrt($a));
$distance = $radiusOfEarth * $c;

// This is the output of all the variable assignments, steps, and final calculation
echo "Radius of the Earth in miles: ".$radiusOfEarth." Miles";
echo "<br>";
echo "Latitude One in Radians: ".$latitudeOne;
echo "<br>";
echo "Longittude One in Radians: ".$longitudeOne;
echo "<br>";
echo "LatitudeTwo in Radians: ".$latitudeTwo;
echo "<br>";
echo "LongitudeTwo in Radians:".$longitudeTwo;
echo "<br>";
echo "DistanceLongitude Variable: ".$distanceLongitude;
echo "<br>";
echo "DistanceLatitude Variable: ".$distanceLatitude;
echo "<br>";
echo "a variable: ".$a;
echo "<br>";
echo "c variable: ".$c;
echo "<br>";
echo "Distance between Sedi and Steven is: ".$distance." miles";
?>