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Dither/moon_phase.js

Created September 17, 2016 10:07
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  1. Dither created this gist Sep 17, 2016.
    32 changes: 32 additions & 0 deletions moon_phase.js
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    function moon_phase(date) { // ported from http://www.voidware.com/moon_phase.htm
    var year = date.getYear(),
    month = date.getMonth(),
    day = date.getDay();

    if (month < 3) {
    year--;
    month += 12;
    }

    ++month;

    jd = 365.25 * year + 30.6 * month + day - 694039.09; // jd is total days elapsed
    jd /= 29.53; // divide by the moon cycle (29.53 days)
    phase = parseInt(jd, 10); // int(jd) -> phase, take integer part of jd
    jd -= phase; // subtract integer part to leave fractional part of original jd
    phase = Math.ceil(jd * 8); // scale fraction from 0-8 and round by adding 0.5
    phase = phase & 7; // 0 and 8 are the same so turn 8 into 0

    switch (phase) {
    case 0: phase = "New Moon"; break;
    case 1: phase = "Waxing Crescent Moon"; break;
    case 2: phase = "Quarter Moon"; break;
    case 3: phase = "Waxing Gibbous Moon"; break;
    case 4: phase = "Full Moon"; break;
    case 5: phase = "Waning Gibbous Moon"; break;
    case 6: phase = "Last Quarter Moon";
    case 7: phase = "Waning Crescent Moon"; break;
    }
    return phase;
    }
    //document.write(moon_phase(new Date(Date.now())))