节气通用算法

    /*
     * 节气通用算法
     */
    function get_term($_year,$month,$day)
    {
        $year = substr($_year,-2)+0;
        $coefficient = array(
            array(5.4055,2019,-1),//小寒
            array(20.12,2082,1),//大寒
            array(3.87),//立春
            array(18.74,2026,-1),//雨水
            array(5.63),//惊蛰
            array(20.646,2084,1),//春分
            array(4.81),//清明
            array(20.1),//谷雨
            array(5.52,1911,1),//立夏
            array(21.04,2008,1),//小满
            array(5.678,1902,1),//芒种
            array(21.37,1928,1),//夏至
            array(7.108,2016,1),//小暑
            array(22.83,1922,1),//大暑
            array(7.5,2002,1),//立秋
            array(23.13),//处暑
            array(7.646,1927,1),//白露
            array(23.042,1942,1),//秋分
            array(8.318),//寒露
            array(23.438,2089,1),//霜降
            array(7.438,2089,1),//立冬
            array(22.36,1978,1),//小雪
            array(7.18,1954,1),//大雪
            array(21.94,2021,-1)//冬至
        );
        $term_name = array(
            "小寒","大寒","立春","雨水","惊蛰","春分","清明","谷雨",
            "立夏","小满","芒种","夏至","小暑","大暑","立秋","处暑",
            "白露","秋分","寒露","霜降","立冬","小雪","大雪","冬至");

        $idx1 = ($month-1)*2;
        $_leap_value = floor(($year-1)/4);

        $day1 = floor($year*0.2422+$coefficient[$idx1][0])-$_leap_value;
        if(isset($coefficient[$idx1][1])&&$coefficient[$idx1][1]==$_year) $day1 += $coefficient[$idx1][2];
        $day2 = floor($year*0.2422+$coefficient[$idx1+1][0])-$_leap_value;
        if(isset($coefficient[$idx1+1][1])&&$coefficient[$idx1+1][1]==$_year) $day1 += $coefficient[$idx1+1][2];

        if($day==$day1) return $term_name[$idx1];
        if($day==$day2) return $term_name[$idx1+1];
        return '';
    }