// make two arrays
var img_left = new Array();
var img_right = new Array();

// pair 1
img_left[0] = '/images/skyterra-today_01.jpg';
img_right[0] = '/images/skyterra-tomorrow_01.jpg';

// pair 2
img_left[1] = '/images/skyterra-today_02.jpg';
img_right[1] = '/images/skyterra-tomorrow_02.jpg';

// pair 3
img_left[2] = '/images/skyterra-today_03.jpg';
img_right[2] = '/images/skyterra-tomorrow_03.jpg';

// pair 4
img_left[3] = '/images/skyterra-today_04.jpg';
img_right[3] = '/images/skyterra-tomorrow_04.jpg';

// pair 5
img_left[4] = '/images/skyterra-today_05.jpg';
img_right[4] = '/images/skyterra-tomorrow_05.jpg';

// generate a random number limited by the number of options available.
var n=Math.floor(Math.random() * img_left.length);