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	0001-01-03 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

1. Clone the JulianDayNumber repository.
2. swift build.

Examples

1. 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 on or before October 4, 1582 and the Gregorian calendar for dates on or after October 15, 1582.

2. 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

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

let julianYMD = GregorianCalendar.convert(year: 2013, month: 10, day:31, to: JulianCalendar.self)
// (year: 2013, month: 10, day: 18)

Documentation

The latest documentation is hosted by Swift Package Index.

All public classes, structs, and functions should be documented. If you notice a documentation shortcoming please open a new issue.

Limits

The following table summarizes the arithmetic limits for Julian day number calculations on platforms where Int is 64 bits.

Calendar	Minimum JDN	Maximum JDN
Armenian	Int.min + 341	Int.max
Baháʼí	Int.min	Int.max
Coptic	Int.min	Int.max
Egyptian	Int.min + 611	Int.max
Ethiopian	Int.min	Int.max
French Republican	Int.min	Int.max
Gregorian	Int.min	Int.max
Hebrew	Int.min + 106960181	355839970905664
Islamic	Int.min	Int.max
Julian	Int.min	Int.max
Khwarizmian	Int.min + 341	Int.max
Macedonian	Int.min	Int.max
Maya Long Count	Int.min	Int.max
Persian	Int.min + 336	Int.max
Śaka	Int.min	Int.max
Syrian	Int.min	Int.max

License

JulianDayNumber is released under the MIT License.