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https://github.com/jwodder/julian-rs
Convert between Julian day numbers and Julian & Gregorian calendars
https://github.com/jwodder/julian-rs
available-on-crates-io calendar gregorian-calendar julian-calendar julian-day rust
Last synced: 2 months ago
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Convert between Julian day numbers and Julian & Gregorian calendars
- Host: GitHub
- URL: https://github.com/jwodder/julian-rs
- Owner: jwodder
- License: mit
- Created: 2023-04-23T17:59:54.000Z (over 1 year ago)
- Default Branch: master
- Last Pushed: 2024-05-27T14:13:59.000Z (7 months ago)
- Last Synced: 2024-05-30T17:57:22.608Z (7 months ago)
- Topics: available-on-crates-io, calendar, gregorian-calendar, julian-calendar, julian-day, rust
- Language: Rust
- Homepage:
- Size: 429 KB
- Stars: 3
- Watchers: 2
- Forks: 1
- Open Issues: 2
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- License: LICENSE
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[GitHub](https://github.com/jwodder/julian-rs) | [crates.io](https://crates.io/crates/julian) | [Documentation](https://docs.rs/julian) | [Issues](https://github.com/jwodder/julian-rs/issues) | [Changelog](https://github.com/jwodder/julian-rs/blob/master/CHANGELOG.md)
`julian` is a Rust library for converting between [Julian day numbers][] and
dates in the [Gregorian calendar][] (either proleptic or with the Reformation
occurring at a given date) and/or the proleptic [Julian calendar][]. There are
also features for querying details about years & months in a "reforming"
Gregorian calendar and how they are affected by the calendar reformation date
of your choice.
[Julian day numbers]: https://en.wikipedia.org/wiki/Julian_day
[Gregorian calendar]: https://en.wikipedia.org/wiki/Gregorian_calendar
[Julian calendar]: https://en.wikipedia.org/wiki/Julian_calendar
Examples
========
Before you construct a date, you must first choose a calendar in which to
reckon dates. `Calendar::GREGORIAN` is the proleptic Gregorian calendar, which
should be both simple and useful enough for most basic purposes.
To convert a Julian day number to a date in a calendar, use the
`Calendar::at_jdn()` method, like so:
```rust
use julian::{Calendar, Month};
let cal = Calendar::GREGORIAN;
let date = cal.at_jdn(2460065);
assert_eq!(date.year(), 2023);
assert_eq!(date.month(), Month::April);
assert_eq!(date.day(), 30);
```
So JDN 2460065 is April 30, 2023, in the proleptic Gregorian calendar.
To convert a date to a Julian day number, use `Calendar::at_ymd()` to construct
the date, and then call its `julian_day_number()` method:
```rust
use julian::{Calendar, Month};
let cal = Calendar::GREGORIAN;
let date = cal.at_ymd(2023, Month::April, 30).unwrap();
assert_eq!(date.julian_day_number(), 2460065);
```
See [the documentation](https://docs.rs/julian) for more things you can do!
Command
=======
`julian` also provides a command of the same name for converting between Julian
day numbers and dates in Julian-style calendars. To install this command on
your system, run:
cargo install julian
Usage
-----
```text
julian [] [ ...]
```
When invoked without arguments, the `julian` command displays the current date
in the proleptic Gregorian calendar & UTC timezone along with the corresponding
Julian day number.
When `julian` is invoked with one or more arguments, any calendar date
arguments (in the form "YYYY-MM-DD" or "YYYY-JJJ") are converted to Julian day
numbers, and any integer arguments are treated as Julian day numbers and
converted to calendar dates. By default, dates are read & written using the
proleptic Gregorian calendar, but this can be changed with the `--julian` or
`--reformation` option.
`julian` uses [astronomical year numbering][yzero], where 1 BC (the year
immediately before AD 1) is denoted on input & output as year 0 (displayed as
"0000"), and the year before that (normally called 2 BC) is denoted -1
(displayed as "-0001"). In addition, the start of the year is always taken as
being on January 1, even though [not all users of the Julian calendar
throughout history have followed this convention][NYD].
Options
-------
- `-c`, `--countries` — List the country codes recognized by the
`-r`/`--reformation` option. The output is a table with the following
columns:
- "Code" — the two-letter country code accepted by `--reformation`
- "Country" — the country's English name (or a common variation thereof)
- "Reformation" — the Julian day number of the date on which the country
first observed the Gregorian calendar
- "Last Julian" — the Old Style calendar date of the day before the
reformation
- "First Gregorian" — the New Style calendar date of the day of the
reformation
The database of country reformations dates is drawn from [the Debian
version of `ncal.c` as of 2023-04-26][src], so blame Debian for any
historical inaccuracies.
- `-h`, `--help` — Display a summary of the command-line options and exit
- `-j`, `--julian` — Read & write dates using the proleptic Julian calendar
- `-J`, `--json` — Output JSON. See [JSON Output](#json-output) below for more
information.
- `-o`, `--ordinal` — Output calendar dates in the form "YYYY-JJJ", where the
part after the hyphen is the day of the year from 001 to 366 (the ordinal
date)
- `-q`, `--quiet` — Do not print the input value before each output value. Do
not print "JDN" before Julian day numbers.
- `-r `, `--reformation ` — Read & write dates using a reforming
calendar in which the Gregorian calendar is first observed on the date with
the given Julian day number
A two-letter country code (case insensitive) may be given in place of a JDN
in order to use the calendar reformation as it was observed in that
country. Run `julian --countries` to get a list of recognized country
codes and their corresponding dates.
- `-s`, `--style` — Mark dates in reforming calendars as "O.S." (Old Style) or
"N.S." (New Style)". Has no effect when `-r`/`--reformation` is not given or
when `-o`/`--ordinal` is given.
- `-V`, `--version` — Show the program version and exit
[yzero]: https://en.wikipedia.org/wiki/Astronomical_year_numbering
[NYD]: https://en.wikipedia.org/wiki/Julian_calendar#New_Year's_Day
[src]: https://salsa.debian.org/meskes/bsdmainutils/-/blob/70ff77b0f084de4a14d79bed935e1958020f43dc/usr.bin/ncal/ncal.c
JSON Output
-----------
When `julian` is invoked with the `-J`/`--json` option, it outputs a JSON
breakdown of the chosen calendar and input & output values. The output
structure is an object with two keys, `"calendar"` and `"dates"`.
- `"calendar"` — Denotes the type of calendar selected for the `julian`
invocation. This is an object that always contains at least one key,
`"type"`, the value of which is `"gregorian"` (for the default proleptic
Gregorian calendar), `"julian"` (for the proleptic Julian calendar), or
`"reforming"` (for a reforming calendar). When `"type"` is `"reforming"`,
there will be an additional field, `"reformation"`, whose value is the Julian
day number of the date on which the calendar first follows the Gregorian
calendar.
- `"dates"` — A list of objects, one per argument (or, if no arguments were
given, one object for the current date). Each object contains the following
fields describing the date indicated by the argument, regardless of whether
the argument was a calendar date or a Julian day number:
- `"julian_day_number"` — the date's Julian day number
- `"year"` — the date's year
- `"month"` — the number (1-12) of the date's month
- `"day"` — the date's day-of-month (1-31)
- `"ordinal"` — the date's one-based day-of-year ordinal (1-366)
- `"display"` — the date in "YYYY-MM-DD" form
- `"ordinal_display"` — the date in "YYYY-JJJ" form
- `"old_style"` — This field is only present if the calendar in use is a
reforming calendar. It is `true` if the date occurs before the calendar
reformation, `false` otherwise.