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Extended moon phase utils
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Moon.swift
/** Extended moon phase utils
Ported from https://github.com/solarissmoke/php-moon-phase/blob/master/Solaris/MoonPhase.php
Maksym Huk 2017
*/
import Foundation
import SwiftMoment
class Moon {
enum Phase : Int {
case newMoon
case firstQuarter
case fullMoon
case lastQuarter
case nextNewMoon
case nextFirstQuarter
case nextFullMoon
case nextLastQuarter
}
var timestamp: Double = 0
var currentPhase: Double = 0 // Phase (0 to 1)
var illumination: Double = 0 // Illuminated fraction (0 to 1)
var age: Double = 0 // Age of moon (days)
var distance: Double = 0 // Distance (kilometres)
var angularDiameter: Double = 0 // Angular diameter (degrees)
var sunAngularDiameter: Double = 0 // Sun angular diameter (degrees)
var sunDistance: Double = 0 // Distance to Sun (kilometres)
var synodicMonth: Double = 0 // Synodic month (new Moon to new Moon)
private var quarters: [Date] = []
init(_ date: Date) {
var pdate = date.timeIntervalSince1970
self.timestamp = pdate
/* Astronomical constants */
let epoch = 2444238.5 // 1980 January 0.0
/* Constants defining the Sun's apparent orbit */
let elonge = 278.833540 // Ecliptic longitude of the Sun at epoch 1980.0
let elongp = 282.596403 // Ecliptic longitude of the Sun at perigee
let eccent = 0.016718 // Eccentricity of Earth's orbit
let sunsmax = 1.495985e8 // Semi-major axis of Earth's orbit, km
let sunangsiz = 0.533128 // Sun's angular size, degrees, at semi-major axis distance
/* Elements of the Moon's orbit, epoch 1980.0 */
let mmlong = 64.975464 // Moon's mean longitude at the epoch
let mmlongp = 349.383063 // Mean longitude of the perigee at the epoch
let mecc = 0.054900 // Eccentricity of the Moon's orbit
let mangsiz = 0.5181 // Moon's angular size at distance a from Earth
let msmax = 384401.0 // Semi-major axis of Moon's orbit in km
let synmonth = 29.53058868 // Synodic month (new Moon to new Moon)
// pdate is coming in as a UNIX timstamp, so convert it to Julian
pdate = pdate / 86400 + 2440587.5
/* Calculation of the Sun's position */
let Day = pdate - epoch // Date within epoch
let N = fixangle((360 / 365.2422) * Day) // Mean anomaly of the Sun
let M = fixangle(N + elonge - elongp) // Convert from perigee co-ordinates to epoch 1980.0
var Ec = kepler(M, eccent) // Solve equation of Kepler
Ec = sqrt((1 + eccent) / (1 - eccent)) * tan(Ec / 2)
Ec = 2 * radToDeg(atan(Ec)) // True anomaly
let Lambdasun = fixangle(Ec + elongp) // Sun's geocentric ecliptic longitude
let F = ((1 + eccent * cos(degToRad(Ec))) / (1 - eccent * eccent)); // Orbital distance factor
let SunDist = sunsmax / F // Distance to Sun in km
let SunAng = F * sunangsiz // Sun's angular size in degrees
/* Calculation of the Moon's position */
let ml = fixangle(13.1763966 * Day + mmlong) // Moon's mean longitude
let MM = fixangle(ml - 0.1114041 * Day - mmlongp) // Moon's mean anomaly
let Ev = 1.2739 * sin(degToRad(2 * (ml - Lambdasun) - MM)) // Evection
let Ae = 0.1858 * sin(degToRad(M)) // Annual equation
let A3 = 0.37 * sin(degToRad(M)) // Correction term
let MmP = MM + Ev - Ae - A3 // Corrected anomaly
let mEc = 6.2886 * sin(degToRad(MmP)) // Correction for the equation of the centre
let A4 = 0.214 * sin(degToRad(2 * MmP)) // Another correction term
let lP = ml + Ev + mEc - Ae + A4 // Corrected longitude
let V = 0.6583 * sin(degToRad(2 * (lP - Lambdasun))) // Variation
let lPP = lP + V // True longitude
/* Calculation of the phase of the Moon */
let MoonAge = lPP - Lambdasun // Age of the Moon in degrees
let MoonPhase = (1 - cos(degToRad(MoonAge))) / 2 // Phase of the Moon
// Distance of moon from the centre of the Earth
let MoonDistPart1 = (msmax * (1 - mecc * mecc))
let MoonDistPart2 = (1 + mecc * cos(degToRad(MmP + mEc)))
let MoonDist = MoonDistPart1 / MoonDistPart2
let MoonDFrac = MoonDist / msmax
let MoonAng = mangsiz / MoonDFrac // Moon's angular diameter
// store results
self.synodicMonth = synmonth
self.currentPhase = fixangle(MoonAge) / 360 // Phase (0 to 1)
self.illumination = MoonPhase // Illuminated fraction (0 to 1)
self.age = synmonth * currentPhase // Age of moon (days)
self.distance = MoonDist // Distance (kilometres)
self.angularDiameter = MoonAng // Angular diameter (degrees)
self.sunDistance = SunDist // Distance to Sun (kilometres)
self.sunAngularDiameter = SunAng // Sun's angular diameter (degrees)
}
private func degToRad(_ x: Double) -> Double {
return x * M_PI / 180.0
}
private func radToDeg(_ x: Double) -> Double {
return x * 180 / M_PI
}
private func fixangle(_ a: Double) -> Double {
return ( a - 360 * floor(a / 360) )
}
private func kepler(_ m: Double, _ ecc: Double) -> Double { // Solve the equation of Kepler.
let epsilon = 0.000001 // 1E-6
let m = degToRad(m)
var e = m
var delta: Double
repeat {
delta = e - ecc * sin(e) - m
e -= delta / ( 1 - ecc * cos(e) )
} while abs(delta) > epsilon
return e
}
/** Calculates time of the mean new Moon for a given
base date. This argument K to this func is the
precomputed synodic month index, given by:
K = (year - 1900) * 12.3685
where year is expressed as a year and fractional year.
*/
private func meanPhase(_ sdate: Double, _ k: Double) -> Double {
// Time in Julian centuries from 1900 January 0.5
let t = ( sdate - 2415020.0 ) / 36525
let t2 = t * t
let t3 = t2 * t
let nt1 = 2415020.75933 + synodicMonth * k
+ 0.0001178 * t2
- 0.000000155 * t3
+ 0.00033 * sin( degToRad( 166.56 + 132.87 * t - 0.009173 * t2 ) )
return nt1
}
/** Given a K value used to determine the mean phase of
the new moon, and a phase selector (0.0, 0.25, 0.5,
0.75), obtain the true, corrected phase time.
*/
private func truePhase(_ k: Double, _ phase: Double) -> Double {
var apcor = false
let k = k + phase // Add phase to new moon time
let t = k / 1236.85 // Time in Julian centuries from 1900 January 0.5
let t2 = t * t // Square for frequent use
let t3 = t2 * t // Cube for frequent use
var pt = 2415020.75933 // Mean time of phase
+ synodicMonth * k
+ 0.0001178 * t2
- 0.000000155 * t3
+ 0.00033 * sin( degToRad( 166.56 + 132.87 * t - 0.009173 * t2 ) )
let m = 359.2242 + 29.10535608 * k - 0.0000333 * t2 - 0.00000347 * t3 // Sun's mean anomaly
let mprime = 306.0253 + 385.81691806 * k + 0.0107306 * t2 + 0.00001236 * t3 // Moon's mean anomaly
let f = 21.2964 + 390.67050646 * k - 0.0016528 * t2 - 0.00000239 * t3 // Moon's argument of latitude
if ( phase < 0.01 || abs( phase - 0.5 ) < 0.01 ) {
// Corrections for New and Full Moon
pt += (0.1734 - 0.000393 * t) * sin( degToRad( m ) )
+ 0.0021 * sin( degToRad( 2 * m ) )
- 0.4068 * sin( degToRad( mprime ) )
+ 0.0161 * sin( degToRad( 2 * mprime) )
- 0.0004 * sin( degToRad( 3 * mprime ) )
+ 0.0104 * sin( degToRad( 2 * f ) )
- 0.0051 * sin( degToRad( m + mprime ) )
- 0.0074 * sin( degToRad( m - mprime ) )
+ 0.0004 * sin( degToRad( 2 * f + m ) )
- 0.0004 * sin( degToRad( 2 * f - m ) )
- 0.0006 * sin( degToRad( 2 * f + mprime ) )
+ 0.0010 * sin( degToRad( 2 * f - mprime ) )
+ 0.0005 * sin( degToRad( m + 2 * mprime ) )
apcor = true
} else if ( abs( phase - 0.25 ) < 0.01 || abs( phase - 0.75 ) < 0.01 ) {
pt += (0.1721 - 0.0004 * t) * sin( degToRad( m ) )
+ 0.0021 * sin( degToRad( 2 * m ) )
- 0.6280 * sin( degToRad( mprime ) )
+ 0.0089 * sin( degToRad( 2 * mprime) )
- 0.0004 * sin( degToRad( 3 * mprime ) )
+ 0.0079 * sin( degToRad( 2 * f ) )
- 0.0119 * sin( degToRad( m + mprime ) )
- 0.0047 * sin( degToRad ( m - mprime ) )
+ 0.0003 * sin( degToRad( 2 * f + m ) )
- 0.0004 * sin( degToRad( 2 * f - m ) )
- 0.0006 * sin( degToRad( 2 * f + mprime ) )
+ 0.0021 * sin( degToRad( 2 * f - mprime ) )
+ 0.0003 * sin( degToRad( m + 2 * mprime ) )
+ 0.0004 * sin( degToRad( m - 2 * mprime ) )
- 0.0003 * sin( degToRad( 2 * m + mprime ) )
if phase < 0.5 { // First quarter correction
pt += 0.0028 - 0.0004 * cos( degToRad( m ) ) + 0.0003 * cos( degToRad( mprime ) )
} else { // Last quarter correction
pt += -0.0028 + 0.0004 * cos( degToRad( m ) ) - 0.0003 * cos( degToRad( mprime ) )
}
apcor = true
}
if !apcor { // func was called with an invalid phase selector
return 0
}
return pt
}
/** Find time of phases of the moon which surround the current date.
Five phases are found, starting and
ending with the new moons which bound the current lunation.
*/
private func phaseHunt() {
let sdate = utcToJulian( timestamp )
var adate = sdate - 45
let ats = timestamp - 86400 * 45
let atsMoment = moment(Date(timeIntervalSince1970: ats))
let yy = Double(atsMoment.year)
let mm = Double(atsMoment.month)
var k1 = floor( ( yy + ( ( mm - 1 ) * ( 1 / 12 ) ) - 1900 ) * 12.3685 )
var nt1 = meanPhase( adate, k1 )
adate = nt1
var k2: Double = 0
var nt2: Double = 0
while (true) {
adate += synodicMonth
k2 = k1 + 1
nt2 = meanPhase( adate, k2 )
// if nt2 is close to sdate, then mean phase isn't good enough, we have to be more accurate
if( abs( nt2 - sdate ) < 0.75 ) {
nt2 = truePhase( k2, 0.0 )
}
if ( nt1 <= sdate && nt2 > sdate ) {
break
}
nt1 = nt2
k1 = k2
}
// results in Julian dates
let data = [
truePhase( k1, 0.0 ),
truePhase( k1, 0.25 ),
truePhase( k1, 0.5 ),
truePhase( k1, 0.75 ),
truePhase( k2, 0.0 ),
truePhase( k2, 0.25 ),
truePhase( k2, 0.5 ),
truePhase( k2, 0.75 )
]
quarters = []
for v in data {
quarters.append(Date(timeIntervalSince1970:(v - 2440587.5) * 86400)) // convert to UNIX time
}
}
/* Convert UNIX timestamp to astronomical Julian time (i.e. Julian date plus day fraction). */
private func utcToJulian(_ ts: TimeInterval) -> Double {
return ts / 86400 + 2440587.5
}
func phase(_ phase: Phase) -> Date {
if quarters.isEmpty {
phaseHunt()
}
return quarters[phase.rawValue]
}
func nextMajorPhase(after date: Date) -> (Phase, Date) {
let phases: [(Phase, Date)] = [
(.newMoon, phase(.newMoon)),
(.nextNewMoon, phase(.nextNewMoon)),
(.fullMoon, phase(.fullMoon)),
(.nextFullMoon, phase(.nextFullMoon)),
]
var earliestPhaseIndex = 0
for (index, phase) in phases.enumerated() {
let date = phase.1
let earliestDate = phases[earliestPhaseIndex].1
if date.compare(earliestDate) == .orderedAscending {
earliestPhaseIndex = index
}
}
return phases[earliestPhaseIndex]
}
func currentPhaseName() -> String {
let names = [ "New Moon", "Waxing Crescent", "First Quarter", "Waxing Gibbous", "Full Moon", "Waning Gibbous", "Third Quarter", "Waning Crescent", "New Moon" ]
// There are eight phases, evenly split. A "New Moon" occupies the 1/16th phases either side of phase = 0, and the rest follow from that.
return names[ Int(floor( ( currentPhase + 0.0625 ) * 8 )) ]
}
}
var age: Double = 0 // Age of moon (days)
var distance: Double = 0 // Distance (kilometres)
var angularDiameter: Double = 0 // Angular diameter (degrees)
var sunAngularDiameter: Double = 0 // Sun angular diameter (degrees)
var sunDistance: Double = 0 // Distance to Sun (kilometres)
var synodicMonth: Double = 0 // Synodic month (new Moon to new Moon)
private var quarters: [Date] = []
init(_ date: Date) {
var pdate = date.timeIntervalSince1970
self.timestamp = pdate
/* Astronomical constants */
let epoch = 2444238.5 // 1980 January 0.0
/* Constants defining the Sun's apparent orbit */
let elonge = 278.833540 // Ecliptic longitude of the Sun at epoch 1980.0
let elongp = 282.596403 // Ecliptic longitude of the Sun at perigee
let eccent = 0.016718 // Eccentricity of Earth's orbit
let sunsmax = 1.495985e8 // Semi-major axis of Earth's orbit, km
let sunangsiz = 0.533128 // Sun's angular size, degrees, at semi-major axis distance
/* Elements of the Moon's orbit, epoch 1980.0 */
let mmlong = 64.975464 // Moon's mean longitude at the epoch
let mmlongp = 349.383063 // Mean longitude of the perigee at the epoch
let mecc = 0.054900 // Eccentricity of the Moon's orbit
let mangsiz = 0.5181 // Moon's angular size at distance a from Earth
let msmax = 384401.0 // Semi-major axis of Moon's orbit in km
let synmonth = 29.53058868 // Synodic month (new Moon to new Moon)
// pdate is coming in as a UNIX timstamp, so convert it to Julian
pdate = pdate / 86400 + 2440587.5
/* Calculation of the Sun's position */
let Day = pdate - epoch // Date within epoch
let N = fixangle((360 / 365.2422) * Day) // Mean anomaly of the Sun
let M = fixangle(N + elonge - elongp) // Convert from perigee co-ordinates to epoch 1980.0
var Ec = kepler(M, eccent) // Solve equation of Kepler
Ec = sqrt((1 + eccent) / (1 - eccent)) * tan(Ec / 2)
Ec = 2 * radToDeg(atan(Ec)) // True anomaly
let Lambdasun = fixangle(Ec + elongp) // Sun's geocentric ecliptic longitude
let F = ((1 + eccent * cos(degToRad(Ec))) / (1 - eccent * eccent)); // Orbital distance factor
let SunDist = sunsmax / F // Distance to Sun in km
let SunAng = F * sunangsiz // Sun's angular size in degrees
/* Calculation of the Moon's position */
let ml = fixangle(13.1763966 * Day + mmlong) // Moon's mean longitude
let MM = fixangle(ml - 0.1114041 * Day - mmlongp) // Moon's mean anomaly
let Ev = 1.2739 * sin(degToRad(2 * (ml - Lambdasun) - MM)) // Evection
let Ae = 0.1858 * sin(degToRad(M)) // Annual equation
let A3 = 0.37 * sin(degToRad(M)) // Correction term
let MmP = MM + Ev - Ae - A3 // Corrected anomaly
let mEc = 6.2886 * sin(degToRad(MmP)) // Correction for the equation of the centre
let A4 = 0.214 * sin(degToRad(2 * MmP)) // Another correction term
let lP = ml + Ev + mEc - Ae + A4 // Corrected longitude
let V = 0.6583 * sin(degToRad(2 * (lP - Lambdasun))) // Variation
let lPP = lP + V // True longitude
/* Calculation of the phase of the Moon */
let MoonAge = lPP - Lambdasun // Age of the Moon in degrees
let MoonPhase = (1 - cos(degToRad(MoonAge))) / 2 // Phase of the Moon
// Distance of moon from the centre of the Earth
let MoonDistPart1 = (msmax * (1 - mecc * mecc))
let MoonDistPart2 = (1 + mecc * cos(degToRad(MmP + mEc)))
let MoonDist = MoonDistPart1 / MoonDistPart2
let MoonDFrac = MoonDist / msmax
let MoonAng = mangsiz / MoonDFrac // Moon's angular diameter
// store results
self.synodicMonth = synmonth
self.currentPhase = fixangle(MoonAge) / 360 // Phase (0 to 1)
self.illumination = MoonPhase // Illuminated fraction (0 to 1)
self.age = synmonth * currentPhase // Age of moon (days)
self.distance = MoonDist // Distance (kilometres)
self.angularDiameter = MoonAng // Angular diameter (degrees)
self.sunDistance = SunDist // Distance to Sun (kilometres)
self.sunAngularDiameter = SunAng // Sun's angular diameter (degrees)
}
private func degToRad(_ x: Double) -> Double {
return x * M_PI / 180.0
}
private func radToDeg(_ x: Double) -> Double {
return x * 180 / M_PI
}
private func fixangle(_ a: Double) -> Double {
return ( a - 360 * floor(a / 360) )
}
private func kepler(_ m: Double, _ ecc: Double) -> Double { // Solve the equation of Kepler.
let epsilon = 0.000001 // 1E-6
let m = degToRad(m)
var e = m
var delta: Double
repeat {
delta = e - ecc * sin(e) - m
e -= delta / ( 1 - ecc * cos(e) )
} while abs(delta) > epsilon
return e
}
/** Calculates time of the mean new Moon for a given
base date. This argument K to this func is the
precomputed synodic month index, given by:
K = (year - 1900) * 12.3685
where year is expressed as a year and fractional year.
*/
func meanPhase(_ sdate: Double, _ k: Double) -> Double {
// Time in Julian centuries from 1900 January 0.5
let t = ( sdate - 2415020.0 ) / 36525
let t2 = t * t
let t3 = t2 * t
let nt1 = 2415020.75933 + synodicMonth * k
+ 0.0001178 * t2
- 0.000000155 * t3
+ 0.00033 * sin( degToRad( 166.56 + 132.87 * t - 0.009173 * t2 ) )
return nt1
}
/** Given a K value used to determine the mean phase of
the new moon, and a phase selector (0.0, 0.25, 0.5,
0.75), obtain the true, corrected phase time.
*/
func truePhase(_ k: Double, _ phase: Double) -> Double {
var apcor = false
let k = k + phase // Add phase to new moon time
let t = k / 1236.85 // Time in Julian centuries from 1900 January 0.5
let t2 = t * t // Square for frequent use
let t3 = t2 * t // Cube for frequent use
var pt = 2415020.75933 // Mean time of phase
+ synodicMonth * k
+ 0.0001178 * t2
- 0.000000155 * t3
+ 0.00033 * sin( degToRad( 166.56 + 132.87 * t - 0.009173 * t2 ) )
let m = 359.2242 + 29.10535608 * k - 0.0000333 * t2 - 0.00000347 * t3 // Sun's mean anomaly
let mprime = 306.0253 + 385.81691806 * k + 0.0107306 * t2 + 0.00001236 * t3 // Moon's mean anomaly
let f = 21.2964 + 390.67050646 * k - 0.0016528 * t2 - 0.00000239 * t3 // Moon's argument of latitude
if ( phase < 0.01 || abs( phase - 0.5 ) < 0.01 ) {
// Corrections for New and Full Moon
pt += (0.1734 - 0.000393 * t) * sin( degToRad( m ) )
+ 0.0021 * sin( degToRad( 2 * m ) )
- 0.4068 * sin( degToRad( mprime ) )
+ 0.0161 * sin( degToRad( 2 * mprime) )
- 0.0004 * sin( degToRad( 3 * mprime ) )
+ 0.0104 * sin( degToRad( 2 * f ) )
- 0.0051 * sin( degToRad( m + mprime ) )
- 0.0074 * sin( degToRad( m - mprime ) )
+ 0.0004 * sin( degToRad( 2 * f + m ) )
- 0.0004 * sin( degToRad( 2 * f - m ) )
- 0.0006 * sin( degToRad( 2 * f + mprime ) )
+ 0.0010 * sin( degToRad( 2 * f - mprime ) )
+ 0.0005 * sin( degToRad( m + 2 * mprime ) )
apcor = true
} else if ( abs( phase - 0.25 ) < 0.01 || abs( phase - 0.75 ) < 0.01 ) {
pt += (0.1721 - 0.0004 * t) * sin( degToRad( m ) )
+ 0.0021 * sin( degToRad( 2 * m ) )
- 0.6280 * sin( degToRad( mprime ) )
+ 0.0089 * sin( degToRad( 2 * mprime) )
- 0.0004 * sin( degToRad( 3 * mprime ) )
+ 0.0079 * sin( degToRad( 2 * f ) )
- 0.0119 * sin( degToRad( m + mprime ) )
- 0.0047 * sin( degToRad ( m - mprime ) )
+ 0.0003 * sin( degToRad( 2 * f + m ) )
- 0.0004 * sin( degToRad( 2 * f - m ) )
- 0.0006 * sin( degToRad( 2 * f + mprime ) )
+ 0.0021 * sin( degToRad( 2 * f - mprime ) )
+ 0.0003 * sin( degToRad( m + 2 * mprime ) )
+ 0.0004 * sin( degToRad( m - 2 * mprime ) )
- 0.0003 * sin( degToRad( 2 * m + mprime ) )
if phase < 0.5 { // First quarter correction
pt += 0.0028 - 0.0004 * cos( degToRad( m ) ) + 0.0003 * cos( degToRad( mprime ) )
} else { // Last quarter correction
pt += -0.0028 + 0.0004 * cos( degToRad( m ) ) - 0.0003 * cos( degToRad( mprime ) )
}
apcor = true
}
if !apcor { // func was called with an invalid phase selector
return 0
}
return pt
}
/** Find time of phases of the moon which surround the current date.
Five phases are found, starting and
ending with the new moons which bound the current lunation.
*/
func phaseHunt() {
let sdate = utcToJulian( timestamp )
var adate = sdate - 45
let ats = timestamp - 86400 * 45
let atsMoment = moment(Date(timeIntervalSince1970: ats))
let yy = Double(atsMoment.year)
let mm = Double(atsMoment.month)
var k1 = floor( ( yy + ( ( mm - 1 ) * ( 1 / 12 ) ) - 1900 ) * 12.3685 )
var nt1 = meanPhase( adate, k1 )
adate = nt1
var k2: Double = 0
var nt2: Double = 0
while (true) {
adate += synodicMonth
k2 = k1 + 1
nt2 = meanPhase( adate, k2 )
// if nt2 is close to sdate, then mean phase isn't good enough, we have to be more accurate
if( abs( nt2 - sdate ) < 0.75 ) {
nt2 = truePhase( k2, 0.0 )
}
if ( nt1 <= sdate && nt2 > sdate ) {
break
}
nt1 = nt2
k1 = k2
}
// results in Julian dates
let data = [
truePhase( k1, 0.0 ),
truePhase( k1, 0.25 ),
truePhase( k1, 0.5 ),
truePhase( k1, 0.75 ),
truePhase( k2, 0.0 ),
truePhase( k2, 0.25 ),
truePhase( k2, 0.5 ),
truePhase( k2, 0.75 )
]
quarters = []
for v in data {
quarters.append(Date(timeIntervalSince1970:(v - 2440587.5) * 86400)) // convert to UNIX time
}
}
/* Convert UNIX timestamp to astronomical Julian time (i.e. Julian date plus day fraction). */
func utcToJulian(_ ts: TimeInterval) -> Double {
return ts / 86400 + 2440587.5
}
func phase(_ phase: Phase) -> Date {
if quarters.isEmpty {
phaseHunt()
}
return quarters[phase.rawValue]
}
func nextMajorPhase(after date: Date) -> (Phase, Date) {
let phases: [(Phase, Date)] = [
(.newMoon, phase(.newMoon)),
(.nextNewMoon, phase(.nextNewMoon)),
(.fullMoon, phase(.fullMoon)),
(.nextFullMoon, phase(.nextFullMoon)),
]
var earliestPhaseIndex = 0
for (index, phase) in phases.enumerated() {
let date = phase.1
let earliestDate = phases[earliestPhaseIndex].1
if date.compare(earliestDate) == .orderedAscending {
earliestPhaseIndex = index
}
}
return phases[earliestPhaseIndex]
}
func currentPhaseName() -> String {
let names = [ "New Moon", "Waxing Crescent", "First Quarter", "Waxing Gibbous", "Full Moon", "Waning Gibbous", "Third Quarter", "Waning Crescent", "New Moon" ]
// There are eight phases, evenly split. A "New Moon" occupies the 1/16th phases either side of phase = 0, and the rest follow from that.
return names[ Int(floor( ( currentPhase + 0.0625 ) * 8 )) ]
}
}
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