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      CoffeeScript 计算月球的相位

      计算月球的相位

      问题

      你想找出月球的相位。

      解决方案

      以下代码提供了一种计算给出日期的月球相位计算方案:

      # 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 )
      

      讨论

      此代码显示一个月球相位计算器对象的方法有两种。计算器 ->getmoonphase 将返回一用个文本表示的日期的月球相位。

      这可以用在浏览器和 Node.js 中。

      $ 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'
      
      目录
      目录