JulianDayNumber

Julian day number and Julian date calculations supporting the following calendars:

Calendar	Epoch ¹	Era
Armenian	0552-07-11 CE	Armenian
Astronomical	0001-01-01 CE	CE
Baháʼí	1844-03-21 CE	Baháʼí
Coptic	0284-08-29 CE	Diocletian
Egyptian	0747-02-26 BCE	Nabonassar
Ethiopian	0008-08-29 CE	Incarnation
French Republican	1792-09-22 CE	Republican
Gregorian	0001-01-01 CE	CE
Hebrew	3761-10-07 BCE	AM
Islamic	0622-07-16 CE	AH
ISO
Julian	0001-01-01 CE	CE
Khwarizmian	0632-06-21 CE	Yazdegerd
Macedonian	0312-09-01 BCE	Alexander
Maya	3114-09-06 BCE
Persian	0632-06-16 CE	Yazdegerd
Śaka	0079-03-24 CE	Śaka
Syrian	0312-10-01 BCE	Alexander

¹ Epoch in Julian calendar

The Julian day number interconverting algorithms use integer math to avoid rounding errors and the implementations have been round-trip tested for all valid Julian day numbers in the years -999,999 to +999,999.

Installation

Swift Package Manager

Add a package dependency to https://github.com/sbooth/JulianDayNumber in Xcode.

Manual or Custom Build

Clone the JulianDayNumber repository.
swift build.

Examples

Calculate the Julian date for the total solar eclipse on 1919-05-29.

let jd = AstronomicalCalendar.julianDateFrom(year: 1919, month: 5, day: 29)
// 2422107.5

Note

The astronomical calendar is a hybrid calendar using the Julian calendar for dates before October 15, 1582 and the Gregorian calendar for later dates.

Convert the Julian date 2422107.5 to a Date instance.

let d = Date(julianDate: 2422107.5)
// Foundation.Date	1919-05-29 00:00:00 UTC

Convert the Gregorian calendar date 2013-10-31 to a date in the Julian calendar.

let j = GregorianCalendar.julianDayNumberFrom(year: 2013, month: 10, day: 31)
let julianYMD = JulianCalendar.dateFromJulianDayNumber(j)
// (year: 2013, month: 10, day: 18)

Documentation

The latest documentation is hosted by Swift Package Index.

Limits

The following table summarizes the arithmetic limits for Julian day number calculations.

Calendar	Minimum JDN	Maximum JDN
Armenian	`Int.min` + 341	`Int.max` - 317
Baháʼí	`Int.min` + 56457	2305795661307959248
Coptic	`Int.min` + 384	(`Int.max` - 3) / 4 - 124
Egyptian	`Int.min` + 611	`Int.max` - 47
Ethiopian	`Int.min` + 384	(`Int.max` - 3) / 4 - 124
French Republican	`Int.min` + 56759	2305795661307960548
Gregorian	`Int.min` + 56457	2305795661307959247
Hebrew	`Int.min` + 106960181	355839970905570
Islamic	`Int.min` + 325	(`Int.max` - 15) / 30 - 7664
Julian	`Int.min` + 144	(`Int.max` - 3) / 4 - 1401
Khwarizmian	`Int.min` + 341	`Int.max` - 317
Macedonian	`Int.min` + 144	(`Int.max` - 3) / 4 - 1401
Maya Long Count	`Int.min` + 584291	`Int.max`
Persian	`Int.min` + 336	`Int.max` - 77
Śaka	`Int.min` + 56457	2305795661307959298
Syrian	`Int.min` + 144	(`Int.max` - 3) / 4 - 1401

License

JulianDayNumber is released under the MIT License.