Calculate Phase of the Moon for a Date
最后更新于：2022-04-01 10:50:19
## 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'
~~~