Schelly's post on her Tracing the Tribe: The Jewish Genealogy Blog about Steve Morse's NYC April lecture about the Jewish calendar was an impetus to remind me to post about a great resource that has been on the virtual shelf of the Hungarian Electronic Library since Nov 2007.

Although originally published in 1912 (and revised in 1940), Prof. Szentpétery's Chronologia and Calendar of Diplomatics most of the knowledge and tools they provide still prove to be useful for those digging deep into the history of Hungary or that of families. Mind you, these handbooks are written in Hungarian.

Two of the most common situations a genealogist doing research in Christian sources may want to consult an authority on chronology: 1) to resolve what all those dates referring to church holidays are, 2) the obscurity in the use of the Gregorian (New) calendar and the Julian (Old) calendar.

For 1) you might want to look up the date in the list of Christian feast day starting on page 39. This is a multi-lingual collection, including names in Latin, Hungarian and German. Starting on page 51 there is a collection of special holy days named in old documents in Hungary going through the church year cycle starting in January.

Old documents, charters written in Latin in Hungary often provide the dates in their relation to the closest Sunday (Dominica in Latin), like feria secunda post Dominicam Palmarum - it translates to the second day (Monday that is) of the week after Palm Sunday in English. Then the question comes, given that Palm Sunday is calculated in its relation to the moving day of Easter, what day Palm Sunday was that year. To answer this you could use any of the perpetual calendars available on the web or use the charts in Szentpétery's work covering years 750 through 2059, A.D. For this latter look up the year you are interested in on pages 86-93 of the pdf file, then go the chart number (pages 16-85) found next to the year.

If you are into Islamic or Jewish dates, there are guides for you, too in Szentpétery's Handbook of chronology. The introduction to the Islamic calendar starts on page 33 of the pdf file, and that of the Jewish calendar can be found on pages 35-39.