NAME

Date::Vruceleto - Compute year's vruceleto and solar cycle as used in old Russian calendar

SYNOPSIS

  use Date::Vruceleto;
  $letter = vruceleto(2016); # NB: means year 2016 since March 1, 5508 BCE
  $letter = vruceleto(2016, 'AD'); # Anno Domini, valid for March 2016 - February 2017
  $letter = vruceleto(2016, 1); # the same
  $letter = vrutseleto(2016, 1); # the same

  # can also get the solar cycle (old Russian style)

  $cycle = solarcycle($year);

DESCRIPTION

Vruceletos (or vrutseletos) are similar to European Sunday letters (see Date::SundayLetter) with a few differences:

- Letters are Cyrillic

- A January-based year has always 2 letters, not just a leap one. That's because March-based style is used.

Vruceleto (or vrutseleto) letters are Cyrillic letters А, В, Г, Д, Е, Ѕ, З (pronounced Az, Vedi, Glagol', Dobro, Yest', Zelo, Zemlya), assigned sequentially to the days of the year in reverse order, starting from the 1st of March being Г. Thus within a March-based year (common among East Slavs until 1492) each letter corresponds to the same day of the week, the letter corresponding to Sunday being called "the vruceleto of the year". The latter then could be used for Easter calculations and to refer to specific years in chronicles along with other dating techniques.

The cycle of correspondences between vruceletos and the days of the week is repeated every 28 years, a period also used in old Russian chronology as "solar cycle". The count of solar cycles in this calendar system starts from March 1, 5508 BCE (called Constantinople World Aera).

I.A.Klimishin in his book "Calendar and Chronology" (Moscow, Nauka, 1985, pp. 66-70) gives the following formulae to calculate solar cycles and vruceletos ([] meaning the integer part of the quotient and || the remainder):

- First get the solar cycle (Q) of the year of Constantinople aera (B):

    Q = |B/28|

or Christian aera (R):

    Q = |(R-8)/28|

- Then calculate the vruceleto number (W) of the year:

    W = [Q/4] + |Q/7|

А, В, Г, Д, Е, Ѕ, З corresponding to numbers 1-7 respectively.

In this module the same result is achieved with solarcycle and vruceleto functions, the latter calling the former internally. vrutseleto is an alias for vruceleto.

CAVEATS

Finding 2 vruceletos for a January-based year is not yet supported. One should find vruceleto of the previous year for dates in January and February.

This module does not use any external modules to get solar cycle. In fact we don't even know if they exist, hardly though, Eastern and Western solar cycles being different anyway. We haven't checked either if Date::SundayLetter is of any use for our goals.

The module is intended to find only "the vruceleto of the year" and not to be used as a Perpetual Calendar, though it may be helpful in building some tools that achieve that goal.

The module is intended for use in work with old Russian texts as well as ecclesiastical calculations, i.e. where Julian calendar is common. Usage with Gregorian calendar is generally senseless and thus untested.

EXPORT

None by default. solarcycle, vruceleto and vrutseleto can be exported on request.

SEE ALSO

Date::SundayLetter

AUTHOR

Roman Pavlov <rp@freeshell.org>

COPYRIGHT AND LICENSE

Copyright (C) 2016-2018 Roman Pavlov

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

cpanm Date::Vruceleto

perl -MCPAN -e shell
install Date::Vruceleto