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Ruby gem for calendar computations according to the Roman Catholic liturgical calendar as instituted by MP Mysterii Paschalis of Paul VI. (AAS 61 (1969), pp. 222-226), defined in General Norms for the Liturgical Year and the Calendar (English translation) and subsequent documents of liturgical legislation.

calendarium-romanum aspires to become the most complete and most accurate FOSS implementation of this calendar system (see list of implementations available).


calendarium-romanum is now a feature-complete implementation of the abovementioned calendar system, capable of generating a complete and (at least mostly) correct Roman Catholic liturgical calendar for any year according to the most recent calendar rules and data (i.e. today's state of the calendar is used also for years in the past - for historically accurate computations see a related project).

It is continuously kept up-to-date with latest developments of the liturgical legislation and newly introduced feasts.

Accuracy is highly valued. Therefore just a very limited set of calendar data is bundled in the library, but with a guarantee that a theologian continuously takes care of them being up-to-date and correct. Users of the library will usually want to prepare and maintain their own data files representing their local calendars. (For ready-to-use calendar data without guarantees of correctness see a related repository.)

The project's scope is strictly limited to computing liturgical calendar in a narrow sense. It doesn't provide functionality specific for individual liturgical books, unless it is dealt with in general liturgical norms regarding the calendar. (Liturgical colours being an exception from this rule, as it is very common to include them in all kinds of liturgical calendars.) But the library is designed with machine-readability in mind, so that additional layers of functionality, implementing book-specific calculations, can be built upon it.

Strings are localized (using the i18n Ruby gem). Translations to six languages (Latin, English, Spanish, French, Italian, Czech) are provided. The built-in translations can be both replaced and/or supplemented with translations to additional languages without having to modify the gem's code.


includes computation of the Easter date from the easter gem by James Robertson.

See also changelog for list of contributions and their authors.


dual licensed: freely choose between GNU/LGPL 3 and MIT

Project status

The library is currently considered feature-complete for release 1.0.0 and it's public API mostly stabilized. Development focuses on reaching higher degree of certainty regarding correctness by means of making the test suite more comprehensive and rigorous.

Backward compatibility

The gem's public interface has now been mostly stabilized, but until v1.0.0 release there is still no guaranteed backward compatibility between minor versions.

When using the gem in your projects, it is recommended to lock the dependency to a particular minor version.

In your app's Gemfile

gem 'calendarium-romanum', '~>0.8.0'

or in gemspec of your gem

spec.add_dependency 'calendarium-romanum', '~>0.8.0'


All the examples below expect that you first required the gem:

require 'calendarium-romanum'

1. Typical usage

The easiest way to obtain calendar entry of a liturgical day:

I18n.locale = :en # set locale

# build calendar
pcal =
  sanctorale: CalendariumRomanum::Data::GENERAL_ROMAN_ENGLISH.load

# query
day = pcal[, 1, 1)]

For explanation see the detailed steps below.

2. What liturgical day is it today?

PerpetualCalendar used in the example above is a high-level API. In order to understand what's happening under the hood, we will now take a lower-level approach and work on the level of a simple Calendar. Each Calendar instance describes a particular liturgical year. We may not know which liturgical year our day of interest belongs to, but fortunately there is "alternative constructor" Calendar.for_day() to rescue:

date =, 8, 19)
calendar = CalendariumRomanum::Calendar.for_day(date)
day = calendar[date]

day.season # => #<CalendariumRomanum::Season:0x00000001d4cfa0 @symbol=:ordinary, @colour=#<CalendariumRomanum::Colour:0x00000001d4d928 @symbol=:green, @i18n_key="">, @i18n_key="temporale.season.ordinary">
day.season.equal? CalendariumRomanum::Seasons::ORDINARY # => true

# => [#<CalendariumRomanum::Celebration:0x00000001c69cc8 @title="Friday, 20th week in Ordinary Time", @rank=#<CalendariumRomanum::Rank:0x00000001d4c708 @priority=3.13, @desc="rank.3_13", @short_desc="rank.short.ferial">, @colour=#<CalendariumRomanum::Colour:0x00000001d4d928 @symbol=:green, @i18n_key="">, @symbol=nil>]
c = day.celebrations.first
c.title # => "Friday, 20th week in Ordinary Time"
c.rank # => #<CalendariumRomanum::Rank:0x00000001d4c708 @priority=3.13, @desc="rank.3_13", @short_desc="rank.short.ferial">
c.rank.equal? CalendariumRomanum::Ranks::FERIAL # => true
c.rank < CalendariumRomanum::Ranks::MEMORIAL_PROPER # => true
# => #<CalendariumRomanum::Colour:0x00000001d4d928 @symbol=:green, @i18n_key="">

Calendar#[] returns a single Day, describing a liturgical day. Each day belongs to some #season; every day, we can choose from one or more #celebrations to celebrate. (The only case with multiple choices is combination of a ferial with one or more optional memorials; higher-ranking celebrations are always exclusive.)

Each Celebration is described by a #title, #rank and #colour.

3. But does it take feasts of saints in account?

Actually, no. Not yet. We need to load some calendar data first:

CR = CalendariumRomanum
loader =
sanctorale = loader.load_from_file 'data/universal-en.txt' # insert path to your data file
date =, 8, 19)
calendar = CR::Calendar.for_day(date, sanctorale)
day = calendar[date]
day.celebrations # => [#<CalendariumRomanum::Celebration:0x000000027d9590 @title="Friday, 20th week in Ordinary Time", @rank=#<CalendariumRomanum::Rank:0x000000029e1108 @priority=3.13, ... >, @colour=#<CalendariumRomanum::Colour:0x000000029e1f68 @symbol=:green>>, #<CalendariumRomanum::Celebration:0x000000029c96c0 @title="Saint John Eudes, priest", @rank=#<CalendariumRomanum::Rank:0x000000029e1180 @priority=3.12, ... >, @colour=#<CalendariumRomanum::Colour:0x000000029e1f18 @symbol=:white>>]

Unless a sanctorale is loaded, Calendar only counts with temporale feasts, Sundays and ferials.

Note how we saved some typing by defining new constant CR referencing the CalendariumRomanum module. In fact you can save even more typing by replacing require 'calendarium-romanum' by require 'calendarium-romanum/cr' which loads the gem and defines the CR shortcut for you. Following examples expect the CR constant to be defined and reference the CalendariumRomanum module.

Another possible way of saving some typing (if you don't care about possible name clashes or polluting current namespace) is including CalendariumRomanum module in the current module. Then CalendariumRomanum classes can be referenced unqualified:

include CalendariumRomanum

loader =
# etc.

4. Isn't there an easier way to get sanctorale data?

Yes! There are a few data files bundled in the gem. You can explore them by iterating over CalendariumRomanum::Data.all. Those of general interest are additionally identified by their proper constants, e.g. CalendariumRomanum::Data::GENERAL_ROMAN_ENGLISH. Bundled data files can be loaded by a handy shortcut method #load:

sanctorale = CR::Data::GENERAL_ROMAN_ENGLISH.load # easy loading
date =, 8, 19)
calendar = CR::Calendar.for_day(date, sanctorale)
day = calendar[date]

5. I don't want to care about (liturgical) years

Each Calendar instance is bound to a particular liturgical year. Calling Calendar#[] with a date out of the year's range results in a RangeError:

calendar =
  day = calendar[, 1, 1)]
rescue RangeError
  STDERR.puts 'ouch' # will happen

The example demonstrates the well known fact, that the civil and liturgical year don't match: 1st January 2000 does not belong to the liturgical year 2000-2001 (which will begin on the first Sunday of Advent, i.e. on 3rd December 2000), but to the year 1999-2000. For the sake of simplicity, calendarium-romanum denotes liturgical years by the starting year only, so you create a Calendar for liturgical year 1999-2000 by calling

We have already seen Calendar.for_day(), which takes care of finding the liturgical year a particular date belongs to and creating a Calendar for this year. But maybe you want to query a calendar without caring about liturgical years altogether, possibly picking days across multiple years. The best tool for such use cases is PerpetualCalendar.

pcal =

# get days
d1 = pcal[, 1, 1)]
d2 = pcal[, 1, 1)]
d3 = pcal[, 1, 1)]

# get Calendar instances if you need them
calendar = pcal.calendar_for_year(1987)

Just like Calendar with the default settings (no sanctorale data etc.) is usually of little use, so is a PerpetualCalendar creating such Calendars. Of course it is possible to specify configuration which is then applied on the Calendars being created:

pcal =
  # Sanctorale instance
  sanctorale: CR::Data::GENERAL_ROMAN_ENGLISH.load,
  # options that will be passed to
  temporale_options: {
    transfer_to_sunday: [:epiphany],
    extensions: [CR::Temporale::Extensions::ChristEternalPriest]
d = pcal[, 1, 1)]

# It is also possible to supply Temporale factory instead of options:
pcal =
  # Proc returning a Temporale instance for the specified year
  temporale_factory: lambda do |year|, transfer_to_sunday: [:ascension])
pcal[, 1, 1)]

Memory management note: Internally, PerpetualCalendar builds Calendar instances as needed and by default caches them perpetually. This is OK in most cases, but it can lead to memory exhaustion if you traverse an excessive amount of liturgical years. In such cases you can supply your own cache (a Hash or anything with hash-like interface) and implement some kind of cache size limiting.

my_cache = {}
pcal = my_cache)

Sanctorale Data

Use prepared data or create your own

The gem expects data files following a custom format - see README in the data directory for it's description. The same directory contains a bunch of example data files. (All of them are also bundled in the gem and accessible via CalendariumRomanum::Data, as described above.)

universal-en.txt and universal-la.txt are data of the General Roman Calendar in English and Latin.

The czech-*.txt files, when layered properly, can be used to assemble proper calendar of any diocese in the Czech Republic.

Implement custom loading strategy

In case you already have sanctorale data in another format, it might be better suited for you to implement your own loading routine instead of transforming them to our custom format. SanctoraleLoader is the class to look into for inspiration.

The important bit is that for each celebration you build a Celebration instance and push it in a Sanctorale instance by a call to Sanctorale#add, which receives a month, a day (as integers) and a Celebration:

sanctorale =
celebration ='Saint John Eudes, priest', CR::Ranks::MEMORIAL_OPTIONAL, CR::Colours::WHITE)
sanctorale.add 8, 19, celebration

date =, 8, 19)
calendar = CR::Calendar.for_day(date, sanctorale)

day = calendar[date]
day.celebrations # => [#<CalendariumRomanum::Celebration:0x000000010deea8 @title="", @rank=#<struct CalendariumRomanum::Rank priority=3.13, desc="Unprivileged ferials", short_desc="ferial">, @colour=:green>, #<CalendariumRomanum::Celebration:0x000000010fec08 @title="Saint John Eudes, priest", @rank=#<struct CalendariumRomanum::Rank priority=3.12, desc="Optional memorials", short_desc="optional memorial">, @colour=:white>]

Proper calendar of a church

One common case of preparing custom sanctorale data is implementing proper calendar of a church (cf. General Norms for the Liturgical Year and the Calendar par. 52 c). Proper calendar of a church is built by adding to the calendar of the diocese (or religious institute) the church'es proper celebration, which are usually just two solemnities: anniversary of dedication and titular solemnity.

Let's say you have calendar of your diocese in sanctorale data file my-diocese.txt. You could copy the file to a new location and add the two proper solemnities, but your programmer better self won't allow you to do that. What options are left? You can create a new sanctorale file with the two proper celebrations and then load it over the calendar of the diocese, as explained in data. Or, if you need the calendar just for that single little script and don't care about creating data files, you can build the two proper solemnities in code:

# here you would load your 'diocese.txt' instead
diocese = 'data/universal-en.txt'

dedication ='Anniversary of Dedication of the Parish Church', CR::Ranks::SOLEMNITY_PROPER, CR::Colours::WHITE)
titular ='Saint Nicholas, Bishop, Titular Solemnity of the Parish Church', CR::Ranks::SOLEMNITY_PROPER, CR::Colours::WHITE)

# solution 1 - directly modify the loaded Sanctorale

diocese.replace(10, 25, [dedication])
diocese.replace(12, 6, [titular])

# solution 2 - create a new Sanctorale with just the two solemnities,
# then create a third instance merging contents of the two without modifying them

proper_solemnities =
proper_solemnities.replace(10, 25, [dedication])
proper_solemnities.replace(12, 6, [titular])

complete_proper_calendar = CR::SanctoraleFactory.create_layered(diocese, proper_solemnities)

I18n, or, how to fix names of temporale feasts

One drawback of the current implementation is that names of temporale feasts are totally independent of sanctorale feast names. They are hardcoded in the gem, as i18n translation strings.

When you load sanctorale data in your favourite language, the Calendar will by default still produce temporale feasts with names in English. This can be fixed by changing locale to match your sanctorale data.

I18n.locale = :la # or :en, :fr, :it, :cs

The gem ships with English, Latin, Italian, Spanish, French and Czech translation. Contributed translations to other languages are most welcome.

Transfer of solemnities to a Sunday

As specified in General Norms for the Liturgical Year and the Calendar 7, the solemnities of Epiphany, Ascension and Corpus Christi can be transferred to a Sunday. Temporale by default preserves the regular dates of these solemnities, but it has an option to enable the transfer:

# transfer all three to Sunday
temporale =, transfer_to_sunday: [:epiphany, :ascension, :corpus_christi])

Usually you don't want to work with Temporale alone, but with a Calendar. In order to create a Calendar with non-default Temporale settings, it is necessary to provide a Temporale as third argument to the constructor.

year = 2000
sanctorale = CR::Data::GENERAL_ROMAN_ENGLISH.load
temporale =, transfer_to_sunday: [:epiphany])

calendar =, sanctorale, temporale)

Custom movable feasts

Some local calendars may include proper movable feasts. In Czech Republic this has recently been the case with the newly introduced feast of Christ the Priest (celebrated on Thursday after Pentecost). Support for this feast, celebrated in several other dioceses and religious institutes, is included in the gem as Temporale extension.

In order to build a complete Czech Calendar with proper sanctorale feasts and the additional temporale feast of Christ the Priest, it is necessary, apart of loading the sanctorale data, to provide a Temporale instance with the extension applied:

year = 2016
sanctorale = CR::Data::CZECH.load
temporale =
    # the important bit: apply the Temporale extension
    extensions: [CR::Temporale::Extensions::ChristEternalPriest]

calendar =, sanctorale, temporale)

The feast of Christ the Priest, by it's nature, extends the cycle of Feasts of the Lord in the Ordinary Time and thus clearly belongs to the temporale. Even if your proper movable feast is by it's nature a sanctorale feast, just having a movable date, the only way to handle it using this gem is to write a temporale extension. There is no support for movable feasts in the Sanctorale class. Even the single movable sanctorale feast of the General Roman Calendar, the memorial of Immaculate Heart of Mary, is, by a little cheat, currently implemented in the Temporale.

Any object defining method each_celebration, which yields pairs of "date computer" and Celebration, can be used as temporale extension. Unless you have a good reason to do otherwise, a class or module defining each_celebration as class/module method is a convenient choice.

module MyExtension
  # yields celebrations defined by the extension
  def self.each_celebration
      :my_feast_date, # name of a method computing date of the feast
        'My Feast', # feast title
        CR::Ranks::FEAST_PROPER, # rank
        CR::Colours::WHITE # colour

      # Proc can be used for date computation instead of a method
      # referenced by name
      lambda {|year| CR::Temporale::Dates.easter_sunday(year) + 9 },
        # It is possible to use a Proc as feast title if you want it
        # to be determined at runtime - e.g. because you want to
        # have the feast title translated and follow changes of `I18n.locale`
        proc { I18n.t('my_feasts.another_feast') },

  # computes date of the feast;
  # the year passed as argument is year when the liturgical
  # year in question _began_
  def self.my_feast_date(year)
    # the day before Christ the King
    CR::Temporale::Dates.christ_king(year) - 1

temporale =, extensions: [MyExtension])

# the feast is there!
temporale[, 11, 25)] # => #<CalendariumRomanum::Celebration:0x0000000246fd78 @title="My Feast", @rank=#<CalendariumRomanum::Rank:0x000000019c27e0 @priority=2.8, ... >, @colour=#<CalendariumRomanum::Colour:0x000000019c31e0 @symbol=:white>>

Internationalization internals

It was already mentioned earlier in this document that for internationalization of temporale feast names and other "built-in strings" calendarium-romanum relies upon the i18n gem. Some internal details may be worth a mention:

On require 'calendarium-romanum', paths of a few translation files bundled in the gem are added to I18n.config.load_path. While otherwise we avoid polluting or modifying the environment outside the gem's own scope, in this case we exceptionally modify global configuration in order to make the internationalization easily and conveniently work. If your application requires calendarium-romanum to handle languages not bundled in the gem, or if you don't like the default translations, just prepare a translation file, put it anywhere in your project's tree and add it's path to I18n.config.load_path. If, on the other hand, even the officially supported languages don't work for you, check if paths to the gem's translation files are present in I18n.config.load_path and possibly search your application (and it's other dependencies) for code which kicked them out.


This gem provides an executable, calendariumrom. It's handful of subcommands can be used to query liturgical calendar from the command line and to check validity of sanctorale data files.

1. Query liturgical calendar from the command line

  • calendariumrom query prints calendar entries for today or a specified day, month or year. See calendariumrom help query for available options and arguments.
  • calendariumrom calendars lists data files bundled in calendarium-romanum.

Tip: calendariumrom query is a rather bare-bones calendar querying tool. Check out the calrom gem for a more feature-rich liturgical calendar for your command line.

2. Check sanctorale data files

  • calendariumrom cmp FILE1 FILE2 loads two data files and prints any differences between them (excepting differences in celebration titles)
  • calendariumrom errors FILE1, ... attempts loading a data file (or several of them), reports eventual errors

3. Help

  • calendariumrom lists available subcommands
  • calendariumrom help [COMMAND] outputs a short help for all available subcommands
  • calendariumrom version prints installed version of the gem

For Developers

Get the sources and install development depencencies:

  1. git clone [email protected]:igneus/calendarium-romanum.git
  2. cd calendarium-romanum
  3. bundle install or bundle install --path vendor/bundle

Run from CLI

bundle exec ruby -Ilib bin/calendariumrom

Run Tests

bundle exec rake spec

See also .travis.yml for comprehensive tests run on the CI.