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@jg-l
Last active Dec 23, 2020
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Get the moon phase for a given DateTime in dart! Demo: https://dartpad.dev/d2c9cc4e700694d4e997bdb1f202b4d1
void main() {
var today = DateTime.now();
var aWeekAgo = today.subtract(Duration(days: 7));
print('The moon phase today is: ${Moon.phase(today)}');
print('The moon phase last week was: ${Moon.phase(aWeekAgo)}');
}
/// JulianDate extension on DateTime provides thee DateTime object a `julianDate` property which useful for plently astronomy algorithms.
/// Calculations were all adapted and based on the following book:
/// "Practical Astronomy with your Calculator or Spreadsheet Fourth Edition" by Peter Duffett-Smith and Jonathan Zwart
extension JulianDate on DateTime {
/// isLeapYear determines if the given DateTime is a leap year
/// `DateTime.now().isLeapYear`
bool get isLeapYear {
if (year % 400 == 0) {
return true;
} else if (year % 100 == 0) {
return false;
} else if (year % 4 == 0) {
return true;
}
return false;
}
// Section 3. Converting Date to Day Number
/// This converts the date of the month to day number
/// e.g. What is the day number of June 19 (not a leap year?) 170
int get dayNumber {
var month = this.month;
if (month > 2) {
month += 1;
month = (month.toDouble() * 30.6).toInt();
month = isLeapYear ? month -= 62 : month -= 63;
} else {
month -= 1;
month = isLeapYear ? month * 62 : month * 63;
month = month ~/ 2;
}
month += day;
return month;
}
// dayAsFraction returns the day with the time as fraction
// e.g. Midday of January 3 is, 3.5 (dayNumber 3 at 12:00PM)
double get dayAsFraction {
return day.toDouble() + (hour / 24.0);
}
// from Section 4. Julian Dates
/// get the Julian Date of a DateTime object
/// `DateTime.now().julianDate`
double get julianDate {
var utcnow = toUtc();
var yPrime;
var mPrime;
if (utcnow.month == 1 || utcnow.month == 2) {
yPrime = year - 1;
mPrime = month + 12;
} else {
yPrime = year;
mPrime = month;
}
var compare = DateTime(1582, 10, 15).toUtc();
int A;
int B;
int C;
int D;
if (utcnow.isAfter(compare)) {
A = yPrime ~/ 100;
B = 2 - A + (A ~/ 4);
} else {
B = 0;
}
if (yPrime < 0) {
C = ((365.25 * yPrime) - 0.75).floor();
} else {
C = (365.25 * yPrime).floor();
}
D = (30.6001 * (mPrime + 1)).floor();
return B.toDouble() +
C.toDouble() +
D.toDouble() +
dayAsFraction +
1720994.5;
}
}
enum MoonPhase {
NewMoon,
WaningCrescent,
LastQuarter,
WaningGibbous,
Full,
WaxingGibbous,
FirstQuarter,
WaxingCrescent,
}
/// Moon class has a convinience function `phase(DateTime)` which returns the moonPhase for a given time.
/// This Class relies on the JulianDate extension
class Moon {
static MoonPhase phase(DateTime input) {
var D = ageOfMoon(input);
return getMoonPhase(D);
}
/// ageOfMoon returns the number of days since the latest New Moon
/// This calculation was adapted from https://www.subsystems.us/uploads/9/8/9/4/98948044/moonphase.pdf
static double ageOfMoon(DateTime input) {
const lunarCycle = 29.53;
final lastNewMoon = DateTime(2019, 1, 6, 1, 29);
final daysSinceLastNewMooon = input.julianDate - lastNewMoon.julianDate;
final newMoons = daysSinceLastNewMooon / lunarCycle;
return (newMoons - newMoons.floor()) * lunarCycle;
}
/// Returns a MoonPhase
// ignore: missing_return
static MoonPhase getMoonPhase(double daysSinceNewMoon) {
if (daysSinceNewMoon == 0 || daysSinceNewMoon == 29.5) {
return MoonPhase.NewMoon;
}
if (daysSinceNewMoon > 0 && daysSinceNewMoon < 3.5) {
return MoonPhase.NewMoon;
}
if (daysSinceNewMoon >= 3.5 && daysSinceNewMoon < 7) {
return MoonPhase.WaxingCrescent;
}
if (daysSinceNewMoon >= 7 && daysSinceNewMoon < 11) {
return MoonPhase.FirstQuarter;
}
if (daysSinceNewMoon >= 11 && daysSinceNewMoon < 15.0) {
return MoonPhase.WaxingGibbous;
}
if (daysSinceNewMoon >= 15.0 && daysSinceNewMoon < 18.5) {
return MoonPhase.Full;
}
if (daysSinceNewMoon >= 18.5 && daysSinceNewMoon < 22.0) {
return MoonPhase.WaningGibbous;
}
if (daysSinceNewMoon >= 22.0 && daysSinceNewMoon < 25.7) {
return MoonPhase.LastQuarter;
}
if (daysSinceNewMoon >= 25.7 && daysSinceNewMoon < 29.5) {
return MoonPhase.WaningCrescent;
}
}
}
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