## Problem You want to find the current phase of the moon. ## Solution The following code provides a method to calcualate the phase of the moon for a given date. ~~~ # moonPhase.coffee # Moon-phase calculator # Roger W. Sinnott, Sky & Telescope, June 16, 2006 # http://www.skyandtelescope.com/observing/objects/javascript/moon_phases # # Translated to CoffeeScript by Mike Hatfield @WebCoding4Fun proper_ang = (big) -> tmp = 0 if big > 0 tmp = big / 360.0 tmp = (tmp - (~~tmp)) * 360.0 else tmp = Math.ceil(Math.abs(big / 360.0)) tmp = big + tmp * 360.0 tmp jdn = (date) -> month = date.getMonth() day = date.getDate() year = date.getFullYear() zone = date.getTimezoneOffset() / 1440 mm = month dd = day yy = year yyy = yy mmm = mm if mm < 3 yyy = yyy - 1 mmm = mm + 12 day = dd + zone + 0.5 a = ~~( yyy / 100 ) b = 2 - a + ~~( a / 4 ) jd = ~~( 365.25 * yyy ) + ~~( 30.6001 * ( mmm+ 1 ) ) + day + 1720994.5 jd + b if jd > 2299160.4999999 moonElong = (jd) -> dr = Math.PI / 180 rd = 1 / dr meeDT = Math.pow((jd - 2382148), 2) / (41048480 * 86400) meeT = (jd + meeDT - 2451545.0) / 36525 meeT2 = Math.pow(meeT, 2) meeT3 = Math.pow(meeT, 3) meeD = 297.85 + (445267.1115 * meeT) - (0.0016300 * meeT2) + (meeT3 / 545868) meeD = (proper_ang meeD) * dr meeM1 = 134.96 + (477198.8676 * meeT) + (0.0089970 * meeT2) + (meeT3 / 69699) meeM1 = (proper_ang meeM1) * dr meeM = 357.53 + (35999.0503 * meeT) meeM = (proper_ang meeM) * dr elong = meeD * rd + 6.29 * Math.sin( meeM1 ) elong = elong - 2.10 * Math.sin( meeM ) elong = elong + 1.27 * Math.sin( 2*meeD - meeM1 ) elong = elong + 0.66 * Math.sin( 2*meeD ) elong = proper_ang elong elong = Math.round elong moonNum = ( ( elong + 6.43 ) / 360 ) * 28 moonNum = ~~( moonNum ) if moonNum is 28 then 0 else moonNum getMoonPhase = (age) -> moonPhase = "new Moon" moonPhase = "first quarter" if age > 3 and age < 11 moonPhase = "full Moon" if age > 10 and age < 18 moonPhase = "last quarter" if age > 17 and age < 25 if ((age is 1) or (age is 8) or (age is 15) or (age is 22)) moonPhase = "1 day past " + moonPhase if ((age is 2) or (age is 9) or (age is 16) or (age is 23)) moonPhase = "2 days past " + moonPhase if ((age is 3) or (age is 1) or (age is 17) or (age is 24)) moonPhase = "3 days past " + moonPhase if ((age is 4) or (age is 11) or (age is 18) or (age is 25)) moonPhase = "3 days before " + moonPhase if ((age is 5) or (age is 12) or (age is 19) or (age is 26)) moonPhase = "2 days before " + moonPhase if ((age is 6) or (age is 13) or (age is 20) or (age is 27)) moonPhase = "1 day before " + moonPhase moonPhase MoonPhase = exports? and exports or @MoonPhase = {} class MoonPhase.Calculator getMoonDays: (date) -> jd = jdn date moonElong jd getMoonPhase: (date) -> jd = jdn date getMoonPhase( moonElong jd ) ~~~ ## Discussion This code exposes a MoonPhase Calculator object with two methods. Calculator -> getMoonPhase will return a text representation of the lunar phase for the date provided. This can be used in both the browser and Node.js. ~~~ $ node > var MoonPhase = require('./moonPhase.js'); undefined > var calc = new MoonPhase.Calculator(); undefined > calc.getMoonPhase(new Date()); 'full moon' > calc.getMoonPhase(new Date(1972, 6, 30)); '3 days before last quarter' ~~~