function moon_cycle($time) {
    // calcuates where a day is in moon's cycle
    //     
    // input:    time in seconds since epoch
    // ouput:    0 to <2 where:
    //           new moon = 0, waxing moon = .5, 
    //           full moon = 1, waining moon = 1.5
    // requires: none
    // based on: http://www.voidware.com/moon_phase.htm
    // and also: http://mikesmith.com/blog.html

    $year = date('Y', $time);
    $month = date('m', $time);
    $day = date('d', $time);

    $c = $e = $jd = $b = 0;
    if ($month < 3) {
        $year--;
        $month += 12;
    }
    ++$month;
    $c = 365.25 * $year;     // avg days per year
    $e = 30.6 * $month;     // avg days per month
    $jd = $c + $e + $day - 694039.09;  // jd is total days elapsed
    $jd /= 29.5305882;      // divide by the moon cycle
    $b = (int) $jd;      // int(jd) -> b, take integer part of jd
    $jd -= $b;        // subtract integer part to leave 

    return $jd * 2;
}